Glossary of HIV-Related Terms
The Glossary of HIV-Related Terms was compiled to define words
that are commonly used to describe the HIV virus, its pathogenesis,
its associated treatments, and the medical management of related
conditions.
The glossary contains many up-to-date terms associated with this disease. Not every technical term has been included because of the enormity of such an undertaking. This glossary will help readers define the most common technical terms associated with HIV.
The six PHS agencies that co-sponsor the HIV/AIDS Treatment Information Service (ATIS) were instrumental in supporting this effort. ATIS, the newest component of the Centers for Disease Control and Prevention National AIDS Clearinghouse, is a free telephone reference service for health care providers and people with HIV infection. It provides the latest information about federally approved treatment guidelines. With the number of approved treatment guidelines increasing each year, it is essential for care providers and people living with HIV/AIDS to have one place to call for current treatment information.
AIDS Clinical Trials Information Service
AIDS Clinical Trials Information Service (ACTIS) provides up-to-date information on clinical trials that evaluate experimental drugs and other therapies for adults and children at all stages of HIV infection.
800-874-2572 (Voice)
800-243-7012 (Deaf Access/TDD)
301-738-6616 (Fax)
HIV/AIDS GLOSSARY
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ACQUIRED IMMUNODEFICIENCY SYNDROME (AIDS):
The most severe manifestation of infection with the human immunodeficiency
virus (HIV). The Centers for Disease Control and Prevention list numerous
opportunistic infections and neoplasms (cancers) which, in the presence of
HIV infection, constitute an AIDS diagnosis. In addition, a CD4+ T-cell count
below 200/mm3 in the presence of HIV infection constitutes an AIDS diagnosis.
The period between infection with HIV and the onset of AIDS averages 10 years
in the United States. People with AIDS often suffer infections of the lungs,
brain, eyes and other organs, and frequently suffer debilitating weight loss,
diarrhea and a type of cancer called Kaposi's sarcoma. Even with treatment,
most people with AIDS die within two years of developing infections or cancers
that take advantage of their weakened immune systems. See also CD4 (T4) or
CD4+ Cells; Diarrhea; HIV Disease; Kaposi's Sarcoma; Opportunistic Infection;
Wasting Syndrome.
ACTG:
See AIDS Clinical Trials Group.
ACUTE INFECTION:
An infection causing disease with a sudden onset, severity and (often) short
course. As related to HIV infection: Once the virus enters the body, HIV
infects a large number of CD4+ T cells and replicates rapidly. During this
acute or primary phase of infection, the blood contains many viral particles
that spread throughout the body, seeding themselves in various organs, particularly
the lymphoid tissues. See also Acute Retroviral Syndrome; CD4 (T4) or CD4+
Cells; Infection; Lymphoid Organs.
ACUTE RETROVIRAL SYNDROME:
The acute or primary HIV infection often passes unrecognized, but may be present
as a mononucleosis-like syndrome within three months of the infection. The
diagnosis is made by demonstrating HIV antibody seroconversion. See also
Seroconversion.
ACYCLOVIR:
(Acycloguanosine). A nucleoside analog antiviral drug used to treat the symptoms
of the genital form of herpes simplex virus infection. See also Herpes Simplex
Virus; Nucleoside Analog.
ADENOPATHY:
Any disease involving or causing enlargement of glandular tissues, especially
one involving the lymph nodes.
ADJUVANT:
An ingredient-as in a prescription or solution-that facilitates or modifies
the action of the principal ingredient. May be used in HIV therapies or for
HIV vaccines.
ADMINISTRATION:
(Route of Administration). A term used to refer to how a drug or therapy is
introduced into the body. Systemic administration means that the drug goes
throughout the body (usually carried in the bloodstream), and includes oral
administration (by mouth) and intravenous administration (injection into
the vein). Local administration means that the drug is applied or introduced
into the specific area affected by the disease, such as application directly
onto the affected skin surface (topical administration). The effects of most
therapies depend upon the ability of the drug to reach the affected area,
thus the route of administration and consequent distribution of a drug in
the body is an important determinant of its effectiveness.
ADVERSE EVENT:
In a clinical trial, an unwanted effect detected in participants. The term
is used whether or not the effect can be attributed to the intervention under
study.
ADVERSE REACTION:
See Side Effects.
AEROSOLIZED:
A form of administration in which a drug, such as pentamidine, is turned into
a fine spray or mist by a nebulizer and inhaled. See also Pentamidine.
AETC:
See AIDS Education and Training Centers.
AFFECTED COMMUNITY:
This includes HIV-positive people, persons living with AIDS and other individuals,
including their families, friends and advocates, directly impacted by HIV
infection and its physical, psychological and sociological ramifications.
AGAMMAGLOBULINEMIA:
A nearly total absence of immunoglobulins. See also Antibodies.
AIDS:
See Acquired Immunodeficiency Syndrome.
AIDS CLINICAL TRIALS GROUP (ACTG):
The ACTG is composed of a number of US medical centers that valuate treatment
for HIV and HIV-associated infections. ACTG studies are sponsored by the
National Institute of Allergy and Infectious Diseases.
AIDS DEMENTIA COMPLEX:
About half the people infected with HIV, the virus that causes AIDS, develop
infections or other problems involving the brain or spinal cord. These neurological
complications may include inflammation of the brain (encephalitis), or of
the membrane surrounding the brain (meningitis), infections of the brain,
brain or spinal cord tumors, nerve damage, difficulties in thinking and behavioral
changes (i.e., AIDS dementia complex) and stroke.
AIDSDRUGS:
An online database service administered by the National Library of Medicine,
with references to drugs undergoing testing against AIDS, AIDS-related complex
and related opportunistic infections.
AIDSLINE:
An online database service administered by the National Library of Medicine,
with citations and abstracts covering the published scientific and medical
literature on AIDS and related topics.
AIDS-RELATED CANCERS:
Several cancers are more common or more aggressive in people infected with
HIV, the virus that causes AIDS. These malignancies include certain types
of immune system cancers known as lymphomas, Kaposi's sarcoma and anogenital
cancers primarily affecting the cervix and the anus. HIV, or the immune suppression
it induces, appears to play a role in the development of these cancers. See
also Cervical Cancer; Kaposi's Sarcoma; Lymphoma.
AIDS-RELATED COMPLEX (ARC):
1. A term, not officially defined or recognized by the Centers for Disease
Control and Prevention, that has been used to describe a variety of symptoms
and signs found in some persons infected with HIV. These may include recurrent
fevers, unexplained weight loss, swollen lymph nodes, and/or fungus infection
of the mouth and throat. Also commonly described as symptomatic HIV infection.
2. Symptoms that appear to be related to infection by the HIV virus. They
include an unexplained, chronic deficiency of white blood cells (leukopenia)
or a poorly functioning lymphatic system with swelling of the lymph nodes
(lymphadenopathy) lasting for more than three months without the opportunistic
infections required for a diagnosis of AIDS. See also Wasting Syndrome.
AIDS SERVICE ORGANIZATION (ASO):
A health association, support agency or other service active in the prevention
and treatment of AIDS.
AIDSTRIALS:
An online database service administered by the National Library of Medicine,
with information about clinical trials of agents under evaluation against
HIV infection, AIDS and related opportunistic infections.
AIDS WASTING SYNDROME:
See Wasting Syndrome.
ALTERNATIVE THERAPY:
In Western countries, alternative therapy refers to any type of medicine that
supplements or is used in lieu of biomedicine (i.e., conventional medicine)
or allopathic medicine. In other parts of the world, where traditional medicine
predominates, the term may refer to biomedicine itself.
AMINO ACIDS:
Any of a class of organic compounds having a carboxyl group (COOH) and an amino
group (NH2). Some 22 amino acids are commonly found in animals, and more
than 100 less common forms are found in nature, chiefly in plants. When the
carboxyl carbon atom of one amino acid binds to the nitrogen of another with
the release of a water molecule, a linkage called a peptide bond is formed.
Chains of amino acids, joined head-to-tail in this manner, are synthesized
by living systems and are called polypeptides (up to about 50 amino acids)
and proteins (over 50 amino acids). See also Peptide; Proteins.
ANALOG:
In chemistry, a compound with a structure similar to that of another compound,
but differing from it in respect to certain components or structural makeup;
it may have a similar or opposite action metabolically.
ANEMIA:
A lower than normal number of red blood cells.
ANTIBIOTIC:
An antimicrobial agent, derived from cultures of a microorganism or produced
semisynthetically, used to treat infections.
ANTIBODIES:
Molecules in the blood or secretory fluids that tag, destroy or neutralize
bacteria, viruses or other harmful toxins. They are members of a class of
proteins known as immunoglobulins, which are produced and secreted by B lymphocytes
in response to stimulation by antigens. An antibody is specific to an antigen.
See also Antigen; Lymphocyte.
ANTIGEN:
A substance that, when introduced into the body, is capable of inducing the
production of a specific antibody. See also Antibodies.
ANTIRETROVIRAL AGENTS:
Substances used against retroviruses such as HIV. See also Retrovirus.
ANTITOXINS:
Antibodies that recognize and inactivate toxins produced by certain bacteria,
plants or animals. See also Antibodies.
ANTIVIRAL:
A substance or process that destroys a virus or suppresses its replication.
ARM:
A group of participants in a clinical trial, all of whom receive the same treatment
or placebo. See also Placebo.
ASO:
See AIDS Service Organization.
ASYMPTOMATIC:
Without symptoms. Usually used in AIDS literature to describe a person who
has a positive reaction to one of several tests for HIV antibodies, but who
shows no clinical symptoms of the disease.
ATTENUATED:
Weakened or decreased. For example, an attenuated virus can no longer produce
disease, but might be used to produce a vaccine.
AUTOANTIBODY:
1. An antibody that is active against some of the tissues of the organism that
produced it. 2. An antibody directed against the body's own tissue. See also
Antibodies.
AUTOIMMUNIZATION:
The induction in an individual of an immune response to its own cells (tissue).
See also Immune Response.
AZT:
Azidothymidine (also called zidovudine or ZDV; the Burroughs-Wellcome trade
name is Retrovir). One of the first drugs used against HIV infection, AZT
is a nucleoside analog that suppresses replication of HIV. See also Nucleoside
Analog.
BACTERICIDAL:
Capable of killing bacteria.
BASELINE:
1. Information gathered at the beginning of a study from which variations found
in the study are measured. 2. A known value or quantity with which an unknown
is compared when measured or assessed.
BASOPHIL:
A type of white blood cell, also called a granular leukocyte, filled with granules
of toxic chemicals that can digest microorganisms. Basophils, as well as
other types of white blood cells, are responsible for the symptoms of allergy.
The granules stain blue when exposed to a basic dye for microscopic examination.
B CELLS:
See B Lymphocytes.
BINDING ANTIBODY:
As related to HIV infection: An antibody that attaches to some part of the
HIV virus. Binding antibodies may or may not adversely affect the virus.
BIOPSY:
The surgical removal of a piece of tissue from a living subject for microscopic
examination to make a diagnosis (for example, to determine whether abnormal
cells such as cancer cells are present).
BIOTECHNOLOGY:
1. The use of living organisms or their products to make or modify a substance.
These include recombinant DNA techniques (also referred to as genetic engineering)
and hybridoma technology. 2. The industrial application of the results of
biological research, particularly in fields such as recombinant DNA or gene
splicing, which permits the production of synthetic hormones or enzymes by
combining genetic material from different species.
BLINDED STUDY:
A clinical trial in which participants are unaware as to whether or not they
are in the experimental or control arm of the study.
BLOOD BRAIN BARRIER:
The barrier between brain blood vessels and brain tissues whose effect is to
restrict what may pass from the blood into the brain.
B LYMPHOCYTES (B CELLS):
One of the two major classes of lymphocytes. During infections, these cells
are transformed into plasma cells that produce large quantities of antibody
directed at specific pathogens. This transformation occurs through interactions
with various types of T cells and other components of the immune system.
In persons with AIDS, the functional ability of both the B and the T lymphocytes
is damaged, with the T lymphocytes being the principal site of infection
by the HIV virus. See also Lymphocyte; T Cells.
BODY FLUIDS:
Any fluid in the human body, such as blood, urine, saliva, sputum (spit), tears,
semen, mother's milk or vaginal secretions. Only blood, semen, mother's milk
and vaginal secretions have been linked directly to the transmission of the
HIV virus.
BONE MARROW:
Soft tissue located in the cavities of the bones where blood cells such as
erythrocytes, leukocytes and platelets are formed. See also Erythrocytes;
Leukocytes; Platelets.
BOOSTER:
A second or later dose of a vaccine given to increase the immune response to
the original dose. See also Vaccine.
CANDIDA:
Yeast-like fungi commonly found in the normal flora of the mouth, skin, intestinal
tract and vagina, but can become clinically infectious in immune compromised
people. See also Fungus.
CARCINOGEN:
Any cancer-producing substance.
CBCT:
See Community-Based Clinical Trial.
CBO:
See Community-Based Organization.
CDC:
See Centers for Disease Control and Prevention.
CD8 (T8) CELLS:
A protein embedded in the cell surface of suppressor T lymphocytes. Also called
cytotoxic T cells. See also CD Nomenclature; CD4 (T4) or CD4+ Cells; T Cells.
CD4 (T4) or CD4+ CELLS:
1. White blood cells killed or disabled during HIV infection. These cells normally
orchestrate the immune response, signaling other cells in the immune system
to perform their special functions. Also known as T helper cells. 2. HIV's
preferred targets are cells that have a docking molecule called cluster designation
4 (CD4) on their surfaces. Cells with this molecule are known as CD4-positive
(or CD4+) cells. Destruction of CD4+ lymphocytes is the major cause of the
immunodeficiency observed in AIDS, and decreasing CD4+ lymphocyte levels
appear to be the best indicator of morbidity in these patients. Although
CD4 counts fall, the total T-cell level remains fairly constant through the
course of HIV disease, due to a concomitant increase in the CD8+ cells. The
ratio of CD4+ to CD8+ cells is therefore an important measure of disease
progression. See also CD Nomenclature; CD8 (T8) Cells; Immunodeficiency.
CELL LINES:
Specific cell types artificially maintained in the laboratory (i.e., in vitro)
for scientific purposes.
CELL-MEDIATED IMMUNITY (CMI):
The branch of the immune system in which the reaction to foreign material is
performed by specific defense cells (i.e., killer cells, macrophage and other
white blood cells) rather than antibodies.
CELLULAR IMMUNITY:
See Cell-Mediated Immunity.
CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC):
A Public Health Service agency responsible (among others) for assessing the
status and characteristics of the AIDS epidemic and the prevalence of HIV
infections. CDC supports the design, implementation and evaluation of prevention
activities, and maintains various HIV/AIDS information services, such as
the CDC National AIDS Clearinghouse.
CENTRAL NERVOUS SYSTEM (CNS):
Composed of the brain, spinal cord and its coverings (meninges).
CENTRAL NERVOUS SYSTEM (CNS) DAMAGE:
(By HIV infection). Although monocytes and macrophages can be infected by HIV,
they appear to be relatively resistant to killing. However, these cells travel
throughout the body and carry HIV to various organs, especially the lungs
and the brain. People infected with HIV often experience abnormalities in
the central nervous system. Investigators have hypothesized that an accumulation
of HIV in brain and nerve cells or the inappropriate release of cytokines
or toxic byproducts by these cells may be to blame for the neurological manifestations
of HIV disease. See also Cytokines; Macrophage; Monocyte.
CEREBRAL:
Pertaining to the cerebrum, the main portion of the brain.
CERVICAL CANCER:
A neoplasm of the uterine cervix that can be detected in the early curable
stage by the Papanicolaou (Pap) test. See also Cervical Dysplasia; Cervix;
Pap Smear.
CERVIX:
The part of the uterus that protrudes into the cavity of the vagina. See also
Uterus.
CHALLENGE:
In vaccine experiments, the exposure of an immunized animal to the infectious
agent.
CHEMOTHERAPY:
The treatment, mostly of cancer, by the use of a series of cytotoxic drugs
that attack cancerous cells. This treatment commonly has adverse side effects
that may include the temporary loss of the body's natural immunity to infections,
loss of hair, digestive upset and a general feeling of illness. Although
unpleasant, the adverse effects of treatment are tolerated considering the
life-threatening nature of the cancers usually treated by chemotherapy. See
also Cytotoxic.
CLINICAL:
Pertaining to or founded on observation and treatment of patients, as distinguished
from theoretical or basic science.
CLINICAL ALERT:
A mechanism, adopted by the National Institutes of Health in onjunction with
the editors of several biomedical journals, for urgent cases in which timely
and broad dissemination of results of clinical trials could prevent morbidity
(sickness) and mortality (death). The Clinical Alert does not become a barrier
to subsequent publication of the full research paper. Clinical Alerts are
widely distributed electronically through the National Library of Medicine
and through standard mailings.
CLINICAL LATENCY:
The state or period of an infectious agent, such as a virus or bacterium, living
or developing in a host without producing clinical symptoms. As related to
HIV infection: Although infected individuals usually exhibit a period of
clinical latency with little evidence of disease, the virus is never truly
latent. Even early in the disease, HIV is active within lymphoid organs where
large amounts of virus become trapped in the FDC network. Surrounding germinal
centers are areas rich in CD4+ T cells. These cells increasingly become infected
and viral particles accumulate both in infected cells and as free virus.
See also CD4 (T4) or CD4+ Cells; Lymphoid Organs.
CLINICAL PRACTICE GUIDELINES:
Standards for physicians to adhere to in prescribing care for a given condition
or illness.
CLINICAL TRIAL:
A carefully designed and executed investigation of the effects of a drug (or
vaccine) administered to human subjects. The goal is to define the clinical
efficacy and pharmacological effects (toxicity, side effects, incompatibilities
or interactions) of the drug. The US government, through the Food and Drug
Administration, requires strict testing of all new drugs and vaccines prior
to their approval for use as therapeutic agents.
CMV:
See Cytomegalovirus.
COFACTORS:
1. Substances, microorganisms or characteristics of individuals that may influence
the progression of a disease or the likelihood of becoming ill. 2. A substance,
such as a metallic ion or coenzyme, that must be associated with an enzyme
for the enzyme to function. 3. A situation or activity that may increase
a person's susceptibility to AIDS. Examples of such cofactors are other infections,
drugs and alcohol use, poor nutrition, genetic factors and stress.
COHORT:
In epidemiology, a group of individuals with some characteristics in common.
COMMUNITY-BASED CLINICAL TRIAL (CBCT):
A clinical trial conducted primarily through primary-care physicians rather
than academic research facilities.
COMMUNITY-BASED ORGANIZATION (CBO):
A locally based service organization that provides social services at the community
level.
COMPASSIONATE USE:
A method of providing experimental drugs to very sick patients who have no
other treatment options. Often, case-by-case approval must be obtained from
the Food and Drug Administration for "compassionate use" of a drug.
CONCOMITANT DRUGS:
Drugs that are taken together. Certain concomitant medications may have adverse
interactions.
CONTAGIOUS:
Any infectious disease capable of being transmitted by casual contact from
one person to another. Casual contact can be defined as normal day-to-day
contact between people at home, school, work or in the community. A contagious
infection (e.g., a common cold) can be communicable by casual contact; an
infectious infection, on the other hand, is communicable by intimate contact
such as sex. AIDS is infectious, not contagious.
CONTRAINDICATION:
A specific circumstance when the use of certain treatments could be harmful.
CONTROL:
A standard against which experimental observations may be evaluated. In clinical
trials, one group of patients is given an experimental drug, while another
group (i.e., the control group) is given either a standard treatment for
the disease or a placebo. See also Placebo.
CRYPTOSPORIDIOSIS:
An opportunistic infection caused by the protozoan parasite Cryptosporidium
parvum.
CUTANEOUS:
Of, pertaining to or affecting the skin.
CYTOMEGALOVIRUS (CMV):
A herpes virus that is a common cause of opportunistic diseases in people with
AIDS and other people with immune suppression. While CMV can infect most
organs of the body, people with AIDS are most susceptible to CMV retinitis
(disease of the eye) and colitis (disease of the colon). See also Cytomegalovirus
(CMV) Retinitis.
CYTOMEGALOVIRUS (CMV) RETINITIS:
Most adults in the US have been infected by cytomegalovirus, although the virus
usually does not cause disease in healthy people. Because the virus remains
in the body for life, it can cause disease if the immune system becomes severely
damaged by disease or suppressed by drugs. CMV retinitis is an eye disease
common among people who are infected with HIV. Without treatment, people
with CMV retinitis can lose their vision. CMV infection can affect both eyes
and is the most common cause of blindness among people with AIDS.
DATABASE:
An organized compilation of information, usually maintained in a computer system.
DDC:
Dideoxycytidine (zalcitabine, HIVID), a nucleoside analog drug that inhibits
the replication of HIV. See also Nucleoside Analog.
DDI:
Dideoxyinosine (didanosine, Videx), a nucleoside analog drug that inhibits
the replication of HIV. See also Nucleoside Analog.
DEMENTIA:
Chronic intellectual impairment (i.e., loss of mental capacity) with organic
origins that affects a person's ability to function in a social or occupational
setting. See also AIDS Dementia Complex.
DENDRITIC CELLS:
Patrolling immune system cells that may begin the HIV disease process by carrying
the virus from the site of the infection to the lymph nodes, where other
immune cells become infected. Dendritic cells travel through the body and
bind to foreign invaders-such as HIV-especially in external tissues, such
as the skin and the membranes of the gut, lungs and reproductive tract. They
then ferry the foreign substance to the lymph nodes to stimulate T cells
and initiate an immune response. In laboratory experiments, the dendritic
cells that carry HIV also bind to CD4+ T cells, thereby allowing HIV to infect
the CD4+ T cells. CD4+ T cells are the critical immune system cells targeted
by HIV and depleted during HIV infection. See also CD4 (T4) or CD4+ Cells;
Lymph Nodes; T Cells.
D4T:
(Also known as Stavudine and Zerit). d4T is a dideoxynucleoside pyrimidine
analog (2'3'-didehydro-3'-deoxythymidine). Like other nucleoside analogs,
d4T inhibits HIV replication by inducing premature viral DNA chain termination.
d4T has been approved for patients with advanced HIV infection intolerant
to or failing other antiretroviral drugs. See also Nucleoside Analog.
DIAGNOSIS:
The determination of the presence of a specific disease or infection, usually
accomplished by evaluating clinical symptoms and laboratory tests.
DIARRHEA:
Uncontrolled, loose and frequent bowel movements. In the United States, almost
all people with AIDS develop diarrhea at some time in the course of their
disease. Severe or prolonged diarrhea can lead to weight loss and malnutrition.
The excessive loss of fluid that may occur with AIDS-related diarrhea can
be life-threatening. There are many possible causes of diarrhea in people
who have AIDS. The most common infectious organism causing AIDS-related diarrhea
include cytomegalovirus (CMV); the parasites Cryptosporidium, Microsporidia
and Giardia lamblia; and the bacterium Mycobacterium avium-inracellulare
(MAC). Other bacteria and parasites that cause diarrheal symptoms in otherwise
healthy people may cause more severe, prolonged or recurrent diarrhea in
people with HIV or AIDS. See also Cytomegalovirus; Giardiasis; Microsporidiosis;
Mycobacterium Avium Complex.
DNA:
(Deoxyribonucleic Acid). 1. The molecular chain found in genes within the nucleus
of each cell, which carries the genetic information that enables cells to
reproduce. 2. DNA is the principal constituent of chromosomes, the structures
that transmit hereditary characteristics. The amount of DNA is constant for
all typical cells of any given species of plant or animal (including humans),
regardless of the size or function of that cell. Each DNA molecule is a long,
two-stranded chain made up of subunits, called nucleotides, containing a
sugar (deoxyribose), a phosphate group and one of four nitrogenous bases:
adenine (A), guanine (G), thymine (T) and cytosine (C). In 1953 J.D. Watson
and F.H. Crick proposed that the strands, connected by hydrogen bonds between
the bases, were coiled in a double helix. Adenine bonds only with thymine
(A-T or T-A) and guanine only with cytosine (G-C or C-G). The complementarity
of this bonding ensures that DNA can be replicated (i.e., that identical
copies can be made in order to transmit genetic information to the next generation).
DORMANCY:
See Latency.
DOSE-RANGING STUDY:
A clinical trial in which two or more doses of an agent (such as a drug) are
tested against each other to determine which dose works best and is least
harmful. See also Clinical Trial.
DOUBLE-BLIND STUDY:
A clinical trial design in which neither the participating individuals nor
the study staff know which patients are receiving the experimental drug and
which are receiving placebo or another therapy. Double-blind trials are thought
to produce objective results, since the doctor's and patient's expectations
about the experimental drug do not affect the outcome. See also Clinical
Trial; Placebo.
DRUG-DRUG INTERACTION:
A modification of the effect of a drug when administered with another drug.
The effect may be an increase or a decrease in the action of either substance,
or it may be an adverse effect that is not normally associated with either
drug.
EFFICACY:
(Of a drug or treatment). The maximum ability of a drug or treatment to produce
a result regardless of dosage. A drug passes efficacy trials if it is effective
at the dose tested and against the illness for which it is prescribed. In
the procedure mandated by the Food and Drug Administration, phase II clinical
trials gauge efficacy, phase III trials confirm it.
ELISA:
(Enzyme-Linked Immunosorbent Assay). A laboratory test to determine the presence
of antibodies to HIV in the blood. A positive ELISA test generally is confirmed
by the Western Blot test. See also Antibodies; Western Blot.
END-STAGE DISEASE:
Final period or phase in the course of a disease leading to a person's death.
ENVELOPE:
In virology, a protein covering that packages the virus's genetic information.
The outer coat, or envelope, of HIV is composed of two layers of fat-like
molecules called lipids taken from the membranes of human cells. Embedded
in the envelope are numerous cellular protein, as well as mushroom-shaped
HIV proteins that protrude from the surface. Each mushroom is thought to
consist of a cap made of four glycoprotein molecules called gp120 and a stem
consisting of four gp41 molecules embedded in the envelope. The virus uses
these proteins to attach to and infect cells. See also Glycoprotein; gp41;
gp120; Lipid.
ENZYME:
A protein that accelerates a specific chemical reaction without altering itself
(i.e., a catalyst).
EPIDEMIC:
A disease that spreads rapidly through a demographic segment of the human population,
such as everyone in a given geographic area, a military base, or similar
population unit, or everyone of a certain age or sex, such as the children
or women of a region. Epidemic diseases can be spread from person to person
or from a contaminated source such as food or water.
EPIDEMIOLOGY:
The branch of medical science that deals with the incidence, distribution and
control of a disease in a population.
EXCLUSION/INCLUSION CRITERIA:
The medical or social standards determining whether a person may or may not
be allowed to enter a clinical trial. For example, some trials may not include
people with chronic liver disease, or may exclude people with certain drug
allergies; others may exclude men or women or only include people with a
lowered T-cell count.
EXPANDED ACCESS:
A general term for methods of distributing experimental drugs to patients who
are unable to participate in ongoing clinical trials and have no other treatment
options. Specific types of expanded access mechanisms include parallel track,
Treatment IND, and compassionate use. See also Investigational New Drug.
EXPRESSION SYSTEM:
In HIV vaccine production, cells into which an HIV gene has been inserted to
produce desired HIV proteins.
FOOD AND DRUG ADMINISTRATION (FDA):
The Public Health Service agency responsible for (among others) ensuring the
safety and effectiveness of drugs, biologics, vaccines and medical devices
used in the diagnosis, treatment and prevention of HIV infection, AIDS and
AIDS-related opportunistic infections. The FDA also works with the blood
banking industry to safeguard the nation's blood supply. See also Public
Health Service.
FUNCTIONAL ANTIBODY:
An antibody that binds to an antigen and has an effect. For example, neutralizing
antibodies inactivate HIV or prevent it from infecting other cells. See also
Antibodies; Antigen.
FUNGUS:
1. A general term used to denote a class of microbes including mushrooms, yeasts
and molds. 2. Fungi, which were once classified as plants, have since been
reclassified as unmoving organisms that lack chlorophyll. Mycologists (scientists
working with fungi) estimate that there are 100,000 species of fungi, ranging
from baker's yeast to dermatophytes (fungi that cause ringworm and athlete's
foot) to potentially invasive species such as Candida albicans and Aspergillus.
As many as 150 of these organisms have now been linked to animal or human
diseases.
GAMMA INTERFERON:
A T cell-derived stimulating substance that suppresses virus reproduction,
stimulates other T cells and activates macrophage cells. See also Macrophage;
T Cells.
GANGLION:
A mass of nervous tissue, composed principally of nerve-cell bodies, usually
lying outside the central nervous system.
GASTROINTESTINAL:
Relating to the stomach and intestines.
GENE:
1. A unit of DNA that carries information for the biosynthesis of a specific
product (in the cell). 2. Ultimate unit by which inheritable characteristics
are transmitted to succeeding generations in all living organisms. Genes
are contained by, and arranged along the length of, the chromosome. The gene
is composed of deoxyribonucleic acid (DNA). Each chromosome of each species
has a definite number and arrangement of genes, which govern both the structure
and metabolic functions of the cells and thus of the entire organism. They
provide information for the synthesis of enzymes and other proteins and specify
when these substances are to be made. Alteration of either gene number or
arrangement can result in mutation (a change in the inheritable traits).
See also DNA.
GENETIC ENGINEERING:
Group of new research techniques that manipulate the DNA (genetic material)
of cells. The gene-splicing technique, which produces recombinant DNA, is
a method of transporting selected genes from one species to another. For
example, in this technique, the genes, which are actually portions of molecules
of DNA, are removed from the donor (insect, plant, mammal or other organism)
and spliced into the genetic material of a virus; then the virus is allowed
to infect recipient bacteria. In this way the bacteria become recipients
of both viral and foreign genetic material. When the virus replicates within
the bacteria, large quantities of the foreign as well as viral material are
made.
GENOME:
The complete set of genes in the chromosomes of each cell of a particular organism.
See also Gene.
GP41:
Glycoprotein 41, a protein embedded in the outer envelope of HIV. Plays a key
role in HIV's infection of CD4+ T cells by facilitating the fusion of the
viral and the cell membranes. See also CD4 (T4) or CD4+ Cells; Envelope.
GP120:
Glycoprotein 120, a protein that protrudes from the surface of HIV and binds
to CD4+ T cells. See also CD4 (T4) or CD4+ Cells.
GP160:
Glycoprotein 160, a precursor of HIV envelope proteins gp41 and gp120.
HAIRY LEUKOPLAKIA:
A whitish, slightly raised lesion that appears on the side of the tongue. Thought
to be related to Epstein-Barr virus infection, it was not observed before
the HIV epidemic. See also Epstein-Barr Virus.
HALF-LIFE:
The time required for half the amount of a drug to be eliminated from the body.
HELPER/SUPPRESSOR RATIO:
(Of T cells). T cells are lymphocytes (white blood cells) that are formed in
the thymus and are part of the immune system; they have been found to be
abnormal in people with AIDS. The normal ratio of helper T cells (CD4+ cells)
to suppressor T cells (CD8+ cells) is approximately 2:1. This becomes inverted
in people with AIDS, but may be abnormal for a host of other temporary reasons.
See also CD4 (T4) or CD4+ Cells; CD8 (T8) Cells; Lymphocyte; Thymus.
HELPER T CELLS:
See CD4 (T4) or CD4+ Cells.
HEMATOCRIT:
A laboratory measurement that determines the percentage of packed red blood
cells in a given volume of blood.
HEMATOTOXIC:
Poisonous to the blood or bone marrow.
HEMOGLOBIN:
The component of red blood cells that carries oxygen.
HEMOPHILIA:
An inherited disease that prevents the normal clotting of blood.
HEPATITIS:
An inflammation of the liver caused by certain viruses and other factors such
as alcohol abuse, some medications and trauma. Although many cases of hepatitis
are not a serious threat to health, the disease can become chronic and can
sometimes lead to liver failure and death. There are four major types of
viral hepatitis: (a) hepatitis A, caused by infection with the hepatitis
A virus; (b) hepatitis B, caused by infection with the hepatitis B virus
(HBV), which is most commonly passed on to a partner during intercourse,
especially during anal sex, as well as through sharing drug needles; (c)
non-A, non-B hepatitis, caused by the hepatitis C virus, which appears to
be spread through sexual contact as well as through sharing drug needles
(another type of non-A, non-B hepatitis is caused by the hepatitis E virus,
principally spread through contaminated water) (d) delta hepatitis occurs
only in people who are already infected with HBV and is caused by the HDV
virus; most cases of delta hepatitis occur among people who are frequently
exposed to blood and blood products such as people with hemophilia. See also
Hemophilia.
HERPES SIMPLEX VIRUS I (HSV-I):
A virus that causes cold sores or fever blisters on the mouth or around the
eyes, and can be transmitted to the genital region. The latent virus can
be reactivated by stress, trauma, other infections or suppression of the
immune system.
HERPES SIMPLEX VIRUS II (HSV-II):
A virus causing painful sores of the anus or genitals that may lie dormant
in nerve tissue. It can be reactivated to produce the symptoms. HSV-II may
be transmitted to a neonate (newborn child) during birth from an infected
mother, causing retardation and/or other serious complications. HSV-II is
a precursor of cervical cancer. See also Cervical Cancer.
HERPES VARICELLA ZOSTER VIRUS:
The varicella virus causes chicken pox in children and may reappear in adults
as herpes zoster. Also called shingles, herpes zoster consists of very painful
blisters on the skin that follow nerve pathways.
HIV-1:
See Human Immunodeficiency Virus Type 1.
HIV-2:
See Human Immunodeficiency Virus Type 2.
HIV DISEASE:
Characterized by a gradual deterioration of immune function. During the course
of infection, crucial immune cells called CD4+ T cells are disabled and killed,
and their numbers progressively decline. CD4+ T cells play a crucial role
in the immune response, signaling other cells in the immune system to perform
their special functions. See also Acquired Immunodeficiency Syndrome; CD4
(T4) or CD4+ Cells; Human Immunodeficiency Virus Type 1.
HIV-RELATED TUBERCULOSIS:
See Tuberculosis.
HOST:
A plant or animal harboring another organism.
HOST FACTORS:
The body's potent mechanisms for containing HIV, including immune system cells
called CD8+ T cells, which may prove more effective than any antiretro-viral
drug in controlling HIV infection. See also Antiretroviral Agents; CD8 (T8)
Cells.
HUMAN IMMUNODEFICIENCY VIRUS TYPE 1 (HIV-1):
1. The retrovirus isolated and recognized as the etiologic (i.e., causing or
contributing to the cause of a disease) agent of AIDS. HIV-1 is classified
as a lentivirus in a subgroup of retroviruses. See also Lentivirus; Retrovirus.
2. Most viruses and all bacteria, plants and animals have genetic codes made
up of DNA, which uses RNA to build specific proteins. The genetic material
of a retrovirus such as HIV is the RNA itself. HIV inserts its own RNA into
the host cell's DNA, preventing the host cell from carrying out its natural
functions and turning it into an HIV virus factory. See also DNA; Ribonucleic
Acid.
HUMAN IMMUNODEFICIENCY VIRUS TYPE 2 (HIV-2):
A virus closely related to HIV-1 that has been found to cause immune suppression.
Most commonin Africa.
HUMAN PAPILLOMA VIRUS (HPV):
A virus that is the cause of warts of the hands and feet, as well as lesions
of the mucous membranes of the oral, anal and genital cavities. More than
50 types of HPV have been identified, some of which are associated with cancerous
and precancerous conditions. The virus can be transmitted through sexual
contact and is a precursor to cancer of the cervix. There is no specific
cure for an HPV infection, but the virus often can be controlled by podophyllin
(medicine derived from the roots of the plant Podophyllum peltatum) or interferon,
and the warts can be removed by cryosurgery, laser treatment or conventional
surgery. See also Cervical Cancer; Condyloma.
HYPOTHESIS:
A tentative statement or supposition that may then be tested through research.
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IMMUNE COMPLEX:
Clusters formed when antigens and antibodies bind together.
IMMUNE DEFICIENCY:
A breakdown or inability of certain parts of the immune system to function,
thus making a person susceptible to certain diseases that they would not
ordinarily develop.
IMMUNE RESPONSE:
The activity of the immune system against foreign substances.
IMMUNE SYSTEM:
The complex functions of the body that recognize foreign agents or substances,
neutralize them and recall the response later when confronted with the same
challenge.
IMMUNE THROMBOCYTOPENIC PURPURA (ITP):
Also Idiopathic Immune Thrombocytopenic Purpura. A condition in which the body
produces antibodies against the platelets in the blood, which are cells responsible
for blood clotting. ITP is very common in HIV-infected people. See also Antibodies;
Platelets.
IMMUNITY:
A natural or acquired resistance to a specific disease. Im-munity may be partial
or complete, long-lasting or temporary.
IMMUNODEFICIENCY:
A deficiency of immune response or a disorder characterized by deficient immune
response; classified as antibody (B cell), cellular (T cell), combined deficiency
or phagocytic dysfunction disorders.
IMMUNOGEN:
A substance, also called an antigen, capable of provoking an immune response.
See also Antigen.
IMMUNOGENICITY:
The ability of an antigen or vaccine to stimulate an immune response. See also
Antigen.
IMMUNOGLOBULIN:
See Antibodies.
IMMUNOLOGICAL SURVEILLANCE or IMMUNOSURVEILLANCE:
See Surveillance.
IMMUNOMODULATOR:
Any substance that influences the immune system.
IMMUNOSTIMULANT:
Any agent or substance that triggers or enhances the body's defense; also called
immunopotentiators.
IMMUNOSUPPRESSION:
A state of the body in which the immune system is damaged and does not perform
its normal functions. Immunosuppression may be induced by drugs or result
from certain disease processes, such as HIV infection. See also Immune System.
IMMUNOTHERAPY:
Treatment aimed at reconstituting an impaired immune system. See also Immune
System.
IMMUNOTOXIN:
A plant or animal toxin (i.e., poison) that is attached to a monoclonal antibody
and used to destroy a specific target cell. See also Antibiotic; Monoclonal
Antibody.
INCIDENCE:
The number of new cases occurring in a given population over a certain period
of time.
INCLUSION/EXCLUSION CRITERIA:
The medical or social standards determining whether a person may or may not
be allowed to enter a clinical trial. For example, some trials may not allow
people with chronic liver disease or with certain drug allergies; others
may exclude men or women, or only include people with a lowered T-cell count.
INCUBATION PERIOD:
The time interval between the initial exposure to infection and appearance
of the first symptom or sign of disease.
IND:
See Investigational New Drug.
INFECTION:
The state or condition in which the body (or part of the body) is invaded by
an infectious agent (e.g., a bacterium, fungus or virus), which multiplies
and produces an injurious effect (active infection). As related to HIV: Infection
typically begins when HIV encounters a CD4+ cell. The HIV surface protein
gp120 binds tightly to the CD4 molecule on the cell's surface. The membranes
of the virus and the cell fuse, a process governed by gp41, another surface
protein. The viral core, containing HIV's RNA, proteins and enzymes, is released
into the cell. See CD4 (T4) or CD4+ Cells; gp41; gp120.
INFECTIOUS:
Capable of being transmitted by infection, with or without actual contact.
See also Infection.
INFORMED CONSENT:
Type of protection available to people considering entering a drug trial. Before
entering the trial, participants must sign a consent form that contains an
explanation of: (a) why the research is being done, (b) what researchers
want to accomplish, (c) what will be done during the trial and for how long,
(d) what risks are in the trial, (e) what benefits can be expected from the
trial, (f) what other treatments are available, and (g) the participant's
right to leave the trial at any time. See also Clinical Trial.
INOCULATION:
The introduction of a substance (inoculum; e.g., a vaccine, serum or virus)
into the body to produce or to increase immunity to the disease or condition
associated with the substance. See also Vaccine.
INSTITUTIONAL REVIEW BOARD (IRB):
1. A committee of physicians, statisticians, community advocates and others
that ensures that a clinical trial is ethical and that the rights of study
participants are protected. All clinical trials in the United States must
be approved by an IRB before they begin. See also Clinical Trial. 2. Every
institution that conducts or supports biomedical or behavioral research involving
human subjects must, by federal regulation, have an IRB that initially approves
and periodically reviews the research so as to protect the rights of human
subjects.
INTEGRASE:
An HIV enzyme used by the virus to integrate its genetic material into the
host cell's DNA. See also DNA; Enzyme.
INTEGRATION:
The process by which the different parts of an organism are made a functional
and structural whole, especially through the activity of the nervous system
and of hormones. As related to HIV: The process by which the viral DNA migrates
to the cell's nucleus, where it is spliced into the host's DNA with the help
of viral integrase. Once incorporated, HIV DNA is called the provirus and
is duplicated together with the cell's genes every time the cell divides.
Recent reports suggest that HIV's DNA also can integrate into the DNA of
nondividing cells such as macro-phages and brain and nerve cells. See also
Integrase; Macrophage.
INTENT TO TREAT:
Analysis of clinical trial results that includes all data from patients in
the groups to which they were randomized (i.e., assigned through random distribution)
even if they never received the treatment. See also Clinical Trial.
INTERFERON:
A general term used to describe a family of 20-25 proteins that cause a cell
to become resistant to a wide variety of viruses. They are produced by cells
infected by almost any virus.
INTERLEUKIN-2 (IL-2):
One of a family of molecules that control the growth and function of many types
of lymphocytes. Interleukin-2 is an immune system protein produced in the
body by T cells. It has potent effects on the proliferation, differentiation
and activity of a number of immune system cells, including T cells, B cells
and natural killer cells. Commercially, IL-2 is produced by recombinant DNA
technology and is approved by the Food and Drug Administration for the treatment
of metastatic renal (i.e., kidney) cell cancer. Studies have shown that in
the test tube, addition of IL-2 can improve some of the immunologic functions
that are abnormal in HIV-infected patients. In addition, IL-2 is a growth
factor for T cells, causing them to increase in number. In a clinical study
with IL-2, it was found that in a small number of HIV-infected patients,
IL-2 boosted levels of CD4+ T cells (i.e., the infection-fighting white blood
cells normally destroyed during HIV infection) for more than two years, a
far longer time than typically seen with currently available anti-HIV drugs.
See also Biotechnology; B Lymphocytes; Genetic Engineering; Killer T Cells;
Lymphocyte; T Cells.
INTRAVENOUS (IV):
Of or pertaining to the inside of a vein, as of a thrombus, or an injection,
infusion or catheter.
INVESTIGATIONAL NEW DRUG (IND):
The status of an experimental drug after the Food and Drug Administration agrees
that it can be tested in people.
IN VITRO:
("In glass"). An artificial environment created outside a living
organism (e.g., a test tube or culture plate) used in experimental research
to study a disease or process.
IN VIVO:
("In life"). Studies conducted within a living organism (e.g., animal
or human studies).
IRB:
See Institutional Review Board.
KAPOSI'S SARCOMA:
1. A previously uncommon form of cancer that attacks the connective tissue,
bones, cartilage and muscles of the body. The cancer may spread and also
attack the eyes. If the cancerous area is near the surface of the skin, lesions
inches in length may develop. This disease was initially seen only in elderly
men and natives of Central Africa. Experimental work has shown that the AIDS-related
Kaposi's sarcoma and the Central African variety respond differently to some
types of medications. Radiotherapy and chemotherapy are usually recommended.
2. A type of cancer characterized by abnormal growths of blood vessels that
develop into purplish or brown lesions. It is suspected that the cause of
Kaposi's sarcoma is a newly found herpes virus.
KILLER T CELLS:
Killer cells infected with HIV or other viruses or transformed by cancer. Also
known as cytotoxic T cells (or cytotoxic T lymphocytes). See also Null Cell;
T Cells.
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LATENCY:
The period when an organism (i.e., a virus or a bacterium) is in the body and
not producing any ill effects. See also Clinical Latency.
LESION:
A general term to describe an area of altered tissue (e.g., the infected patch
or sore in a skin disease).
LIPID:
Any of a group of fats and fat-like compounds, including sterols, fatty acids
and many other substances.
LIPOSOMES:
A spherical particle in an aqueous (watery) medium (e.g., inside a cell) formed
by a lipid bilayer enclosing an aqueous compartment. See also Lipid.
LONG-TERM NON-PROGRESSORS:
Individuals who are HIV-infected for seven or more years, have stable CD4+
T cell counts of 600 or more cells per cubic millimeter of blood, no HIV-related
diseases and no previous antiretroviral therapy. Data suggest that this phenomenon
is associated with the maintenance of the integrity of the lymphoid tissues
and with less virus-trapping in the lymph nodes than seen in other HIV-infected
individuals.
LYMPH:
A transparent, slightly yellow fluid that carries lymphocytes. Lymph is derived
from tissue fluids collected from all parts of the body and is returned to
the blood via lymphatic vessels. See also Lymphatic Vessels; Lymphocyte.
LYMPH NODES:
Small, bean-sized organs of the immune system, distributed widely throughout
the body. Lymph fluid is filtered through the lymph nodes in which all types
of lymphocytes take up temporary residence. Antigens that enter the body
find their way into lymph or blood and are filtered out by the lymph nodes
or spleen respectively, for attack by the immune system. See also Antigen;
Lymphocyte.
LYMPHOCYTE:
A white blood cell. Present in the blood, lymph and lymphoid tissue. See also
B Lymphocytes; Lymph; T Cells.
LYMPHOMA:
Cancer of the lymphoid tissues. Lymphomas are often described as being large
or small cell types, cleaved or noncleaved, diffuse or nodular. The different
types often have different prognoses (i.e., prospect of survival or recovery).
Some of these lymphomas are named after the physicians who first described
them (e.g., Burkitt's lymphoma, Hodgkin's disease). Lymphomas can also be
referred to by the organ where they are active such as CNS lymphomas, which
are in the central nervous system, and GI lymphomas, which are in the gastrointestinal
tract. The types of lymphomas most commonly associated with HIV infection
are called non-Hodgkin's lymphomas or B cell lymphomas. In these types of
cancers, certain cells of the lymphatic system grow abnormally. They divide
rapidly, growing into tumors.
MACROPHAGE:
A large immune cell that devours invading pathogens and other intruders. Stimulates
other immune cells by presenting them with small pieces of the invader. Macrophages
can harbor large quantities of HIV without being killed, acting as reservoirs
of the virus.
MAGNETIC RESONANCE IMAGING (MRI):
Medical imaging that uses radiofrequency radiation as its source. MRI is a
noninvasive diagnostic technique that can provide information on the form
and function of internal tissues and organs of the body.
MAST CELL:
A granulocyte found in tissue. The contents of the mast cells, along with those
of basophils, are responsible for the symptoms of allergy. See also Basophil;
Granulocyte.
MEAN:
The arithmetic average, or the sum of all the values divided by the number
of values.
MEDIAN:
The middle number in a sequence of numbers, taken as the average of the two
middle numbers when the sequence has an even number of numbers (e.g., 4 is
the median of 1, 3, 4, 8, 9).
MEMORY CELLS:
A subset of T lymphocytes that have been exposed to specific antigens and can
then proliferate (i.e., reproduce) on subsequent immune system encounters
with the same antigen. See also Antigen; T Cells.
MESSENGER RNA:
Also referred to as mRNA. An RNA (ribonucleic acid) that carries the genetic
code for a particular protein from the nuclear DNA (i.e., the DNA in the
cell's nucleus) to a ribosome in the cytoplasm and acts as a template, or
pattern, for the formation of that protein. See also Cytoplasm; Ribosome.
METABOLISM:
The sum of the processes by which a particular substance is handled (as by
assimilation and incorporation, or by detoxification and excretion) in the
living body.
METABOLITE:
Any substance produced by metabolism or by a metabolic process. See also Metabolism.
METASTASIS:
Transfer of a disease-producing agent (e.g., cancer cells or bacteria) from
an original site of disease to another part of the body with development
of a similar lesion in the new location (e.g., spread of cancer from an original
site to other sites in the body).
MICROBES:
Microscopic living organisms, including bacteria, protozoa and fungi.
MICROBICIDE:
An agent (e.g., a chemical or antibiotic) that destroys microbes. See also
Microbes.
MOLECULE:
The smallest particle of a compound that has all the chemical properties of
that compound. Molecules are made up of two or more atoms, either of the
same element or of two or more different elements. Ionic compounds, such
as common salt, are made up not of molecules, but of ions arranged in a crystalline
structure. Unlike ions, molecules carry no electrical charge. Molecules differ
in size and molecular weight as well as in structure.
MONOCLONAL ANTIBODIES:
Antibodies produced by a hybridoma or antibody-producing cell source for a
specific antigen. Monoclonal antibodies are useful as a tool for identifying
specific protein molecules. See also Antibodies; Antigen; Hybridoma.
MRI:
See Magnetic Resonance Imaging.
MUCOCUTANEOUS:
Anything that concerns or pertains to mucous membranes and the skin (e.g.,
mouth, vagina, lips, anal area). See also Mucous Membrane.
MUCOSA:
See Mucous Membrane.
MUCOSAL IMMUNITY:
Resistance to infection across the mucous membranes. Dependent on immune cells
and antibodies present in the lining of the urogenital tract, gastrointestinal
tract and other parts of the body exposed to the outside world. See also
Antibodies; Genitourinary Tract; Mucous Membrane.
MUCOUS MEMBRANE:
A moist layer of tissue that lines body cavities or passages that have an opening
to the external world (e.g., the lining of the mouth, nostrils or vagina).
MUTATION:
In biology, a sudden change in a gene or unit of hereditary material that results
in a new inheritable characteristic. In higher animals and many higher plants,
a mutation may be transmitted to future generations only if it occurs in
germ-or sex cell-tissue; body cell mutations cannot be inherited. Changes
within the chemical structure of single genes may be induced by exposure
to radiation, temperature extremes and certain chemicals. The term mutation
may also be used to include losses or rearrangements of segments of chromosomes,
the long strands of genes. Drugs such as colchicine double the normal number
of chromosomes in a cell by interfering with cell division. Mutation, which
can establish new traits in a population, is important in evolution. As related
to HIV: HIV mutates rapidly. During the course of HIV disease, viral strains
may emerge in an infected individual that differ widely in their ability
to infect and kill different cell types, as well as in their rate of replication.
Strains of HIV from patients with advanced disease appear to be more virulent
and infect more cell types than strains obtained earlier from the same individual.
See also Gene.
NATIONAL CANCER INSTITUTE (NCI):
An NIH institute with the overall mission of conducting and supporting research,
training and disseminating health information with respect to the causes,
diagnosis and treatment of cancer. NCI also performs these functions for
HIV infections and associated diseases. See also National Institutes of Health.
NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES
(NIAID):
An NIH institute that conducts and supports research to study the causes of
allergic, immunologic and infectious diseases, and to develop better means
of preventing, diagnosing and treating illnesses. NIAID is responsible for
the federally funded, national basic research program in AIDS. See also National
Institutes of Health.
NATIONAL INSTITUTES OF HEALTH (NIH):
A multi-institute agency of the Public Health Service, NIH is the federal focal
point for health research. It conducts research in its own laboratories and
supports research in universities, medical schools, hospitals and research
institutions throughout this country and abroad. See also Public Health Service.
NATURAL KILLER CELLS:
(NK cells). A type of lymphocyte that does not carry the markers to be B cells
or T cells. Like cytotoxic T cells, they attack and kill tumor cells and
protect against a wide variety of infectious microbes. They are "natural" killers
because they do not need additional stimulation or need to recognize a specific
antigen in order to attack and kill. Persons with immunodeficiences such
as those caused by HIV infection have a decrease in "natural" killer
cell activity. See also Antigen; B Lymphocytes; Cytotoxic; Lymphocyte; Null
Cell; T Cells.
NCI:
See National Cancer Institute.
NEURALGIA:
A sharp, shooting pain along a nerve pathway.
NEUROLOGICAL COMPLICATIONS OF AIDS:
See Central Nervous System (CNS) Damage.
NEUROPATHY:
The name given to a group of disorders involving nerves. Symptoms range from
a tingling sensation or numbness in the toes and fingers to paralysis. It
is estimated that 35 percent of people with HIV disease have some form of
neuropathy. A "peripheral neuropathy" refers to the peripheral
nerves outside the spinal cord.
NEUTRALIZATION:
The process by which an antibody binds to specific antigens, thereby "neutralizing" the
microorganism. See also Antibodies; Antigen.
NEUTRALIZING ANTIBODY:
An antibody that keeps a virus from infecting a cell, usually by blocking receptors
on the cell or the virus. See also Antibodies; Receptor.
NEUTRALIZING DOMAIN:
The section of the HIV envelope protein gp120 that elicits antibodies with
neutralizing activities. See also Antibodies; gp120.
NIAID:
See National Institute of Allergy and Infectious Diseases.
NIH:
See National Institutes of Health.
NUCLEIC ACID:
Organic substance, found in all living cells, in which the hereditary information
is stored and from which it can be transferred. Nucleic acid molecules are
long chains that generally occur in combination with proteins. The two chief
types are DNA (deoxyribonucleic acid), found mainly in cell nuclei, and RNA
(ribonucleic acid), found mostly in cytoplasm. Each nucleic acid chain is
composed of subunits called nucleotides, each containing a sugar, a phosphate
group, and one of four bases: adenine (symbolized A), guanine (G), cytosine
(C) and thymine (T). RNA contains the sugar ribose instead of deoxyribose
and the base uracil (U) instead of thymine. The specific sequences of nucleotides
constitute the cell's genetic information: Each three-nucleotide DNA sequence
specifies one particular amino acid. The long sequences of DNA nucleotides
thus correspond to the sequences of amino acids in the cell's proteins. In
order to be expressed as protein, the genetic information is carried to the
protein-synthesizing machinery of the cell, usually in the cell cytoplasm.
Forms of RNA mediate this process. DNA not only provides information, but
also specifies its own exact replication. The cell replicates its DNA by
making a complementary copy of its exact nucleotide sequence: T for every
A, C for every G, G for every C, A for every T. Although the triplet nucleotide
code seems to be universal, the actual sequences of the nucleotides vary
according to the species and individual. See also Gene; Genetic Engineering;
Mutation.
NUCLEOLI:
Bodies in the nucleus that become enlarged during protein synthesis and contain
the DNA template for ribosomal RNA. See also Ribonucleic Acid; Ribosome.
NUCLEOSIDE ANALOG:
Nucleosides are related to nucleotides, the subunits of nucleic acids; however,
they do not carry the phosphate groups of the nucleotides. Nucleoside analogs
generally are synthetic compounds similar to one of the components of DNA
or RNA; a general type of antiviral drug (e.g., acyclovir and AZT). See also
Acyclovir; AZT; Nucleic Acid.
NUCLEUS:
1. The central controlling body within a living cell, usually a spherical unit
enclosed in a membrane and containing genetic codes for maintaining the life
systems of the organism and for issuing commands for growth and reproduction.
2. The nucleus of a cell is an organelle (i.e., a cellular organ) that is
essential to such cell functions as reproduction and protein synthesis. It
is composed of nuclear sap and a nucleoprotein-rich network from which chromosomes
and nucleoli arise and is enclosed in a definite membrane. See also Nucleoli.
OPEN-LABEL TRIAL:
A clinical trial in which doctors and participants know which drug or vaccine
is being administered. See also Clinical Trial.
OPPORTUNISTIC INFECTION:
1. An illness caused by an organism that usually does not cause disease in
a person with a normal immune system. People with advanced HIV infection
suffer opportunistic infections of the lungs, brain, eyes and other organs.
2. Opportunistic infections common in AIDS patients include Pneumocystis
carinii pneumonia, Kaposi's sarcoma, shigellosis, histoplasmosis and other
parasitic, viral, and fungal infections, and some types of cancers. See also
Histoplasmosis; Kaposi's Sarcoma; Pneumocystis carinii Pneumonia.
p24:
1. Within the envelope of the HIV virus is a bullet-shaped core made of another
protein, p24, that surrounds the viral RNA. 2. The p24 antigen test looks
for the presence of this protein in a patient's blood. 3. A positive result
for the p24 antigen suggests active HIV replication. p24 found in the peripheral
blood is thought to also correlate with the amount of virus in the peripheral
blood. It is believed that there are measurable levels of p24 when first
infected with the virus after which there is a strong antibody response to
p24 in early disease. Low or unmeasurable levels of p24 may indicate that
the virus is in a dormant stage. Spikes in p24 levels may indicate that HIV
has begun active replication.
PALLIATIVE:
A treatment that provides symptomatic relief, but not a cure.
PANCREAS:
A gland situated near the stomach that secretes a digestive fluid into the
intestine through one or more ducts and also secretes the hormone insulin.
PANCREATITIS:
Inflammation of the pancreas that can produce severe pain and debilitating
illness. See also Pancreas.
PANDEMIC:
A disease prevalent throughout an entire country, continent or the whole world.
See also Epidemic.
PAP SMEAR:
A method for the early detection of cancer and other abnormalities of the female
genital tract, especially of the cervix and uterus, employing exfoliated
cells (cells that have been shed into vaginal fluid) and a special staining
technique for microscopic examination that differentiates diseased tissue.
Also known as Papanicolaou Smear after George Papanicolaou, the American
cytologist who developed this method and published it in 1943. See also Cervix;
Uterus.
PAPILLOMA:
1. A benign tumor (as a wart or condyloma) resulting from an overgrowth of
epithelial tissue on papillae of vascularized connective tissue (as of the
skin). 2. An epithelial tumor caused by a virus. See also Condyloma; Epithelium.
PARALLEL TRACK:
A system of distributing experimental drugs to patients who are unable to participate
in ongoing clinical efficacy trials and have no other treatment options.
See also Clinical Trial.
PARASITE:
A plant or animal that lives and feeds on or within another living organism;
does not necessarily cause disease.
PATHOGEN:
Any disease-producing microorganism or material.
PATHOGENESIS:
The origin and development of a disease.
PBMC:
See Peripheral Blood Mononuclear Cell.
PCP:
See Pneumocystis carinii Pneumonia.
PCR:
See Polymerase Chain Reaction.
PEER REVIEW:
The process by which new scientific or medical findings, announced by one researcher,
are reviewed by other scientists or physicians before these findings are
published.
PENTAMIDINE:
An approved antiprotozoal drug used for the treatment and prevention of Pneumocystis
carinii pneumonia (PCP) infection. It can be delivered intravenously or intramuscularly
or inhaled as an aerosol. Aerosolized pentamidine is approved for the prophylaxis
of PCP in HIV-positive individuals with CD4+ counts below 200 per cubic millimeter
or for those with prior episodes of PCP. The drug is also known under the
names Pentam and NebuPent. See also Pneumocystis carinii Pneumonia.
PEPTIDE:
(Also polypeptide). Biochemical formed by the linkage of up to about 50 amino
acids to form a chain. Longer chains are called proteins. The amino acids
are coupled by a peptide bond, a special linkage in which the nitrogen atom
of one amino acid binds to the carboxyl carbon atom of another. Many peptides,
such as the hormones vasopressin and ACTH, have physiological or antibacterial
activity. See also Amino Acids.
PERIANAL:
Around the anus.
PERIPHERAL BLOOD MONONUCLEAR CELL (PBMC):
Cells in the bloodstream with one nucleus. See also Nucleus.
PHAGOCYTE:
A cell that is able to ingest and destroy foreign matter, including bacteria.
PHAGOCYTOSIS:
The process of ingesting and destroying a virus or other foreign matter by
phagocyte. See also Macrophage; Monocyte.
PHARMACOKINETICS:
The processes (in a living organism) of absorption, distribution, metabolism
and excretion of a drug or vaccine.
PLACEBO:
An inactive substance against which investigational treatments are compared
for efficacy. See also Placebo Controlled Study.
PLACEBO CONTROLLED STUDY:
A method of investigation of drugs in which an inactive substance (the placebo)
is given to one group of patients, while the drug being tested is given to
another group. The results obtained in the two groups are then compared.
PLACEBO EFFECT:
A physical or emotional change occurring after a substance is taken or administered
that is not the result of any special property of the substance. The change
may be beneficial, reflecting the expectations of the patient and, often,
the expectations of the person giving the substance.
PLASMA:
That 10 percent of the blood that contains nutrients, electrolytes (dissolved
salts), gases, albumin, clotting factors, wastes and hormones.
PLASMA CELLS:
Large antibody-producing cells that develop from B cells. See also Antibodies;
B Lymphocytes.
PLATELETS:
Active agents of inflammation when damage occurs to a blood vessel. They are
not actually cells, but fragments released by megakaryocyte cells. Megakaryocyte
is a large cell in the bone marrow whose function is to produce platelets.
When vascular damage (i.e., damage to blood vessels) occurs, the platelets
stick to the vascular walls, forming clots to prevent the loss of blood.
Thus, it is important to have adequate numbers of normally functioning platelets
to maintain effective coagulation of the blood. There are drugs that can
potentially alter the platelet count, making it necessary to monitor the
count. Also, some people with HIV infection develop thrombocytopenia (a condition
characterized by a platelet count of less than 100,000 platelets per cubic
millimeter of blood). The normal value for men is 154,000-354,000 platelets
per cubic millimeter of blood. For women, it is 162,000-380,000 platelets
per cubic millimeter of blood.
PNEUMOCYSTIS CARINII PNEUMONIA (PCP):
1. A protozoal infection of the lungs. 2. A life-threatening lung infection
that can affect people with weakened immune systems, such as those infected
with HIV. More than three-quarters of all people with HIV disease will develop
PCP if they do not receive treatment to prevent it. The standard treatment
for people with PCP is either a combination of trimethoprim and sulfamethoxazole
(TMP/SMX, also called Bactrim or Septra) or pentamidine. See also Pentamidine;
Protozoa.
POLYMERASE:
Any of several enzymes that catalyze the formation of DNA or RNA from precursor
substances in the presence of preexisting DNA or RNA acting as templates
(i.e., patterns). See also DNA; Enzyme; Ribonucleic Acid.
POLYMERASE CHAIN REACTION (PCR):
1. A laboratory process that selects a DNA segment from a mixture of DNA chains
and rapidly replicates it; used to create a large, readily analyzed sample
of a piece of DNA. It is used in DNA fingerprinting and in medical tests
to identify diseases from the infectious agent's DNA. See also DNA. 2. As
related to HIV: A sensitive laboratory technique that can detect and quantify
HIV in a person's blood or lymph node.
PREVALENCE:
A measure of the proportion of people in a population affected with a particular
disease at a given time.
PROPHYLAXIS:
Treatment that helps to prevent a disease or condition before it occurs or
recurs.
PROTEASE:
An enzyme that hydrolyzes (i.e., breaks down) proteins to their component peptides.
See also Enzyme; Peptide; Proteins.
PROTEASE INHIBITORS:
HIV protease is an aspartyl enzyme essential to the replicative life cycle
of HIV. The three-dimensional molecular structure of the HIV protease has
been fully determined. Pharmaceutical developers are therefore able to rationally
design compounds to inhibit it and thus interfere with replication of the
virus. In the US, five peptide-based protease inhibitors (saquinavir, Roche;
A-80987, ABT-538, Abbott Laboratories; L735,524, Merck; KNI-272, NCI) are
in clinical development. All compounds inhibit HIV-1 in vitro in nanomolar
concentrations. In Europe, two peptide-based compounds (ABT-987, Abbott Laboratories;
AG-1343, Agouron Pharmaceuticals, Inc.) are currently in development. See
also In Vitro.
PROTEINS:
Any of the group of highly complex organic compounds found in all living cells.
Protein is the most abundant class of all biological molecules, comprising
about 50 percent of cellular dry weight. Classified by biological function,
proteins include the enzymes, which catalyze cellular reactions; collagen,
keratin and elastin, which are structural, or support, proteins; hemoglobin
and other transport proteins; casein, ovalbumin and other nutrient proteins;
antibodies, which are necessary for immunity; protein hormones, which regulate
metabolism; and proteins such as actin and myosin, the contractile muscle
proteins that perform mechanical work. Structurally, proteins are large molecules
composed of one or more chains of varying amounts of the same 22 amino acids,
which are linked by peptide bonds. Each protein is characterized by a unique
and invariant amino acid sequence. Protein chains may contain hundreds of
amino acids; some proteins also incorporate phosphorus or such metals as
iron, zinc and copper. The amino acid sequence also determines the molecule's
three-dimensional structure; this so-called native state is required for
proper biological function. The information for the syntheses of the specific
amino acid sequences from free amino acids is carried by the cell's nucleic
acid. See also Peptide; Ribonucleic Acid.
PROTOCOL:
The detailed plan for a clinical trial that states the trial's rationale, purpose,
drug or vaccine dosages, length of study, routes of administration, who may
participate and other aspects of trial design. See also Clinical Trial; Inclusion/Exclusion
Criteria.
PROTOPLASM:
Fundamental material composing all living things. Protoplasm, which exists
in all plants and animals in the small units called cells, is mainly (85-90
percent) water and also contains proteins, fatty substances and inorganic
salts. It is always enclosed by a thin surface membrane that controls the
passage of materials into and out of the cell. It displays the general properties
associated with life-the capacity to respond to stimuli and the ability to
perform the essential physiological functions.
RANDOMIZED TRIAL:
A study in which participants are randomly assigned to either a treatment arm
or placebo arm of a clinical trial. See also Clinical Trial; Placebo.
RECEPTOR:
A molecule on the surface of a cell that serves as a recognition or binding
site for antigens, antibodies or other cellular or immunological components.
See also Antibodies; Antigen.
RECOMBINANT:
An organism whose genome contains integrated genetic material from a different
organism. See also Genome.
RECOMBINANT DNA:
See Biotechnology; Genetic Engineering.
REGULATORY T CELLS:
T cells that direct other immune cells to perform special functions. The chief
regulatory cell, the CD4+ T cell or T helper cell, is HIV's chief target.
See also CD4 (T4) or CD4+ Cells; T Cells.
REMISSIONS:
The lessening of the severity or duration of outbreaks of a disease, or the
abatement (diminution in degree or intensity) of symptoms altogether over
a period of time.
RETROVIRUS:
HIV and other viruses that carry their genetic material in the form of RNA
and that have the enzyme reverse transcriptase. Like all viruses, HIV can
replicate only inside cells, commandeering the cell's machinery to reproduce.
Like other retroviruses, HIV uses the enzyme called reverse transcriptase
to convert its RNA into DNA, which is then integrated into the host cell
DNA. See also DNA; Reverse Transcriptase; Ribonucleic Acid.
REV:
One of the regulatory genes of the HIV virus. Three HIV regulatory genes-tat,
rev and nef-and three so-called auxiliary genes-vif, vpr and vpu-contain
information necessary for the production of proteins that control the virus's
ability to infect a cell, produce new copies of the virus or cause disease.
See also nef; tat.
REVERSE TRANSCRIPTASE:
This enzyme of the HIV virus (and other retroviruses) converts the single-stranded
viral RNA into DNA, the form in which the cell carries its genes. The antiviral
drugs approved in the US for the treatment of HIV infection-AZT, ddC and
ddI-all work by interfering with this stage of the viral life cycle. See
also AZT; ddC; ddI; DNA; Ribonucleic Acid.
RIBONUCLEIC ACID (RNA):
1. A nucleic acid, found mostly in the cytoplasm of cells, that is important
in the synthesis of proteins. The amount of RNA varies from cell to cell.
RNA, like the structurally similar DNA, is a chain made up of subunits called
nucleotides. In protein synthesis, messenger RNA (mRNA) replicates the DNA
code for a protein and moves to sites in the cell called ribosomes. There,
transfer RNA (tRNA) assembles amino acids to form the protein specified by
the messenger RNA. Most forms of RNA (including messenger and transfer RNA)
consist of a single nucleotide strand, but a few forms of viral RNA that
function as carriers of genetic information (instead of DNA) are double-stranded.
2. A nucleic acid associated with the control of chemical activities inside
a cell. One type of RNA transfers information from the cell's DNA to the
protein-forming system of a cell outside the nucleus. Some viruses (e.g.,
HIV) carry RNA instead of the more usual genetic material DNA. See also Cytoplasm;
DNA; Retrovirus.
RIBOSOME:
A cytoplasmic organelle composed of ribonucleic acid and protein that functions
in the synthesis of protein. Ribosomes interact with messenger RNA and transfer
RNA to join together amino acid units into a polypeptide chain according
to the sequence determined by the genetic code. See also Cytoplasm; Ribonucleic
Acid.
RNA:
See Ribonucleic Acid.
SEROCONVERSION:
The development of antibodies to a particular antigen. When people develop
antibodies to HIV or an experimental HIV vaccine, they "seroconvert" from
antibody-negative to antibody-positive. See also Antibodies; Antigen.
SEROPREVALENCE:
As related to HIV infection: The proportion of persons who have serologic (i.e.,
pertaining to serum) evidence of HIV infection at any given time. See also
Serum.
SEROSTATUS:
Results of a test for specific antibodies. See also Antibodies.
SERUM:
The clear, thin and sticky fluid portion of the blood that remains after coagulation.
Serum contains no blood cells, platelets or fibrinogen.
SEXUALLY TRANSMITTED DISEASE (STD):
Also called venereal disease. A contagious disease usually acquired by sexual
intercourse or genital contact. Historically, the five venereal diseases
were: gonorrhea, syphilis, chancroid, granuloma inguinale and lymphogranuloma
venereum. To these have been added scabies, herpes genitalis and anorectal
herpes and warts, pediculosis, trichomoniasis, genital candidiasis, molluscum
contagiosum, nonspecific urethritis, chlamydial infections, cytomegalovirus
and AIDS. See also Herpes Simplex Virus II; Molluscum Contagiosum.
SF-2:
A strain of HIV used in vaccine development.
SHINGLES:
See Herpes Varicella Zoster Virus.
SHIV:
Genetically engineered hybrid virus having an HIV envelope and an SIV core.
See also Genetic Engineering; Hybrid; Simian Immunodeficiency Virus.
SIDE EFFECTS:
The action or effect of a drug (or vaccine) other than that desired. The term
usually refers to undesired or negative effects, such as headache, skin irritation
or liver damage. Experimental drugs must be evaluated for both immediate
and long-term side effects.
SIMIAN IMMUNODEFICIENCY VIRUS (SIV):
An HIV-like virus that infects monkeys, chimpanzees and other nonhuman primates.
SIV:
See Simian Immunodeficiency Virus.
STANDARDS OF CARE:
Treatment regimen or medical management based on state-of-the-art patient care.
STATISTICAL SIGNIFICANCE:
A term based on statistical tests that is used to denote the probability that
the observed association could have occurred by chance alone. Does not refer
to medical or biological significance of an association. For example, a statistical
significance at the 1-percent level indicates a 1-in-100 chance that a result
can be ascribed to chance.
STD:
See Sexually Transmitted Disease.
STEM CELLS:
Cells from which all blood cells derive. Bone marrow is rich in stem cells.
STERILIZING IMMUNITY:
An immune response that completely eliminates an infection.
SUBCLINICAL INFECTION:
An infection, or phase of infection, without readily apparent symptoms or signs
of disease.
SUBCUTANEOUS:
Beneath or introduced beneath the skin (e.g., subcutaneous injections).
SUBUNIT HIV VACCINE:
A genetically engineered vaccine that is based on only part of the HIV molecule.
See also Genetic Engineering.
SUPERANTIGEN:
Investigators have proposed that a molecule known as a superantigen, either
made by HIV or an unrelated agent, may stimulate massive quantities of CD4+
T cells at once, rendering them highly susceptible to HIV infection and subsequent
cell death. See also Antigen; CD4 (T4) or CD4+ Cells.
SUPPRESSOR T CELLS:
(T8, CD8). Subset of T cells that halt antibody production and other immune
responses. See also Antibodies; T Cells.
SURROGATE MARKER:
A substitute; a person or thing that replaces another. In HIV disease, the
number of CD4+ T cells and CD8+ cells is a surrogate immunological marker
of disease progression. See also CD4 (T4) or CD4+ Cells; CD8 (T8) Cells.
SURVEILLANCE:
Close or continuous observation or testing (e.g., serosurveillance), used,
among others, in epidemiology. Immunological surveillance, or immunosurveillance,
is a monitoring process of the immune system that detects and destroys neoplastic
(e.g., cancerous) cells and that tends to break down in immunosuppressed
individuals. See also Epidemiologic Surveillance.
SYMPTOMS:
Any perceptible, subjective change in the body or its functions that indicates
disease or phases of disease, as reported by the patient.
SYNDROME:
A group of symptoms and diseases that together are characteristic of a specific
condition.
SYNERGISM/SYNERGISTIC:
An interaction between two or more agents (drugs) that produces or enhances
an effect that is greater than the sum of the effects produced by the individual
agents.
TAT:
One of the regulatory genes of the HIV virus. Three HIV regulatory genes-tat,
rev and nef-and three so-called auxiliary genes-vif, vpr and vpu-contain
information necessary for the production of proteins that control the virus's
ability to infect a cell, produce new copies of the virus or cause disease.
The tat gene is thought to enhance virus replication. See also nef; rev.
TB:
See Tuberculosis.
T CELLS:
(T Lymphocytes). A thymus-derived white blood cell that participates in a variety
of cell-mediated immune reactions. Three fundamentally different types of
T cells are recognized: helper, killer and suppressor (each has many subdivisions).
T lymphocytes are CD3+ and can be separated into the CD4+ T helper cells
and the CD8+ cytotoxic/suppresssor cells. See also Thymus.
THERAPEUTIC HIV VACCINE:
A vaccine designed to boost the immune response to HIV in persons already infected
with the virus.
3TC:
Also known as Lamivudine, 3TC is composed of the (-) enantiomer of the racemic
mixture 2'-deoxy-3'-thiacytidine. Like other nucleoside analogs, 3TC inhibits
HIV replication through viral DNA chain termination. It has been used in
clinical trials in combination with AZT. See also AZT; Nucleoside Analog.
THRUSH:
Sore patches in the mouth caused by the fungus Candida albicans. Thrush is
one of the most frequent early symptoms of an immune disorder. The fungus
commonly lives in the mouth, but only causes problems when the body's resistance
is reduced either by antibiotics that have reduced the number of competitive
organisms in the mouth, or by an immune deficiency such as HIV disease. See
also Candida.
TISSUE:
A collection of similar cells acting together to perform a particular function.
There are four basic tissues in the body: epithelial, connective, muscle
and nerve.
T LYMPHOCYTES:
See T Cells.
TOXICITY:
The extent, quality or degree of being poisonous or harmful to the body.
TOXOPLASMOSIS:
Toxoplasmosis is an infection that is caused by the protozoan parasite Toxoplasma
gondii. The parasite is carried by cats, birds and other animals and is found
in soil contaminated by cat feces and in meat, particularly pork. The parasite
can infect the lungs, retina of the eye, heart, pancreas, liver, colon and
testes. Once T. gondii invades the body, it remains there, but the immune
system in a healthy person usually prevents the parasite from causing disease.
If the immune system becomes severely damaged, as in people with AIDS, or
is suppressed by drugs, T. gondii can begin to multiply and cause severe
disease. The most common site of toxoplasmosis is the brain. When T. gondii
invades the brain, causing inflammation, the condition is called toxoplasmic
encephalitis. While the disease can occur in persons with healthy immune
systems, it can normally be cured successfully. See also Protozoa.
TRANSCRIPTION:
The process of constructing a messenger RNA molecule using a DNA molecule as
a template with the resulting transfer of genetic information to the messenger
RNA. As related to HIV: The process by which the provirus produces new viruses.
RNA copies called messenger RNA must be made that can be read by the host
cell's protein-making machinery. Transcription is facilitated by cellular
enzymes, including RNA polymerase II. The viral genes may partly control
this process: tat, for example, encodes a protein that accelerates the transcription
process by binding to a section of the newly made viral RNA. See also Integration;
Messenger RNA; tat; Template.
TRANSFUSION:
1. The process of transfusing fluid (such as blood) into a vein. 2. The transfer
of whole blood or blood products from one individual to another.
TRANSLATION:
As related to HIV: The process by which HIV messenger RNA is processed in a
cell's nucleus and transported to the cytoplasm, the cellular material outside
the nucleus. In the cytoplasm, the cell's protein-making machinery translates
the messenger RNA into viral protein and enzymes. See also Cytoplasm; Enzyme;
Messenger RNA; Nucleus.
TRANSMISSION:
In the context of HIV disease: HIV is spread most commonly by sexual contact
with an infected partner. The virus can enter the body through the mucosal
lining of the vagina, vulva, penis, rectum or, very rarely, the mouth during
sex. The likelihood of transmission is increased by factors that may damage
these linings, especially other sexually transmitted diseases that cause
ulcers or inflammation. Studies of SIV infection of the genital membranes
of nonhuman primates suggest that the sentinel cells known as mucosal dendritic
cells may be the first cells infected. Infected dendritic cells may migrate
to lymph nodes and infect other cells. HIV also is spread through contact
with infected blood, most often by the sharing of drug needles or syringes
contaminated with minute quantities of blood containing the virus. Children
can contract HIV from their infected mothers either during pregnancy or birth,
or postnatally, via breastfeeding. Current research indicates that the AIDS
virus may be 100 to 1000 times more contagious during the first two months
of infection, when routine AIDS tests are unable to tell whether people are
infected. See also Lymph Nodes; Simian Immunodeficiency Virus.
TREATMENT IND:
A program to provide experimental treatments to a class of patients who lack
satisfactory alternative treatment. IND stands for Investigational New Drug
application, which is part of the process to get approval from the Food and
Drug Administration for marketing a new prescription drug in the US. See
also Investigational New Drug.
TUBERCULOSIS (TB):
A bacterial infection caused by Mycobacterium tuberculosis. TB bacteria are
spread by airborne droplets expelled from the lungs when a person with active
TB coughs, sneezes or speaks. Repeated exposure to these droplets can lead
to infection in the air sacs of the lungs. The immune defenses of healthy
people usually prevent TB infection from spreading beyond a very small area
of the lungs. If the body's immune system is impaired because of infection
with HIV, aging, malnutrition or other factors, the TB bacterium may begin
to spread more widely in the lungs or to other tissues.
UTERUS:
A hollow muscular organ located in the pelvic cavity of female mammals in which
the fertilized egg implants and develops. Also called womb.
Back to Thumb Index
V3 LOOP:
Section of the gp120 protein on the surface of HIV. Appears to be important
in stimulating neutralizing antibodies. See also Antibodies; gp120.
VACCINATION:
Inoculation of a substance (vaccine) into the body for the purpose of producing
active immunity against a disease. The vaccine is usually a weakened culture
of the agent causing the disease; the use of vaccines is a cornerstone of
preventive medicine. Vaccination was used in ancient times in China, India
and Persia, and was introduced to the West in the late 18th century by E.
Jenner. Vaccinations have eradicated smallpox and are used today to prevent
diphtheria, poliomyelitis, rabies and typhoid. Experimental vaccines for
certain cancers have been developed for laboratory mice. See also Inoculation.
VACCINE:
A substance that contains antigenic components from an infectious organism.
By stimulating an immune response (but not disease), it protects against
subsequent infection by that organism. See also Antigen; Vaccination.
VACCINIA:
A cowpox virus, formerly used in human smallpox vaccines. Employed as a vector
in HIV vaccine research to transport HIV genes into the body. See also Vaccination;
Vector.
VECTOR:
A nonpathogenic bacterium or virus used to transport an antigen into the body
to stimulate protective immunity (e.g., in a vaccine). See also Antigen.
VIRAL BURDEN:
(Viral Load). The amount of HIV virus in the circulating blood. Monitoring
a person's viral burden is important because of the apparent correlation
between the amount of virus in the blood and the severity of the disease:
sicker patients generally have more virus than those with less advanced disease.
A new, sensitive, rapid test-called the branched DNA assay for HIV-1 infection-can
be used to monitor the HIV viral burden. In the future, this procedure may
help clinicians to decide when to give anti-HIV therapy. It may also help
investigators determine more quickly if experimental HIV therapies are effective.
VIRAL CORE:
1. Typically a virus contains an RNA (ribonucleic acid) or DNA (deoxyribonucleic
acid) core of genetic material surrounded by a protein coat. See also DNA;
Ribonucleic Acid. 2. As related to HIV: Within HIV's envelope is a bullet-shaped
core made of another protein, p24, that surrounds the viral RNA. Each strand
of HIV RNA contains the virus' nine genes. Three of these-gag, pol and env-are
structural genes that contain information needed to make structural proteins.
The env gene, for example, codes for gp160, a protein that is later broken
down to gp120 and gp41. See also env; gp41; gp120; gp160; p24.
VIRAL CULTURE:
A laboratory method for growing viruses.
VIRAL ENVELOPE:
As related to HIV: HIV is spherical in shape with a diameter of 1/10,000 of
a millimeter. The outer coat, or envelope, is composed of two layers of fat-like
molecules called lipids, taken from the membranes of human cells. Embedded
in the envelope are numerous cellular proteins, as well as mushroom-shaped
HIV proteins that protrude from the surface. Each mushroom is thought toconsist
of a cap made of four glycoprotein molecules called gp120, and a stem consisting
of four gp41 molecules embedded in the envelope. The virus uses these proteins
to attach to and infect cells.
VIRAL LOAD:
See Viral Burden.
VIREMIA:
The presence of virus in the bloodstream.
VIRION:
A virus particle existing freely outside a host cell. A mature virus.
VIROLOGY:
The study of viruses and viral disease.
VIRUCIDE:
Any agent that destroys or inactivates a virus.
VIRUS:
Organism composed mainly of nucleic acid within a protein coat, ranging in
size from 100 to 2000 angstroms (unit of length; 1 angstrom is equal to 10-10
meters); they can be seen only with an electron microscope. During the stage
of their life cycle when they are free and infectious, viruses do not carry
out the usual functions of living cells, such as respiration and growth;
however, when they enter a living plant, animal or bacterial cell, they make
use of the host cell's chemical energy and protein- and nucleic acid-synthesizing
ability to replicate themselves. Viral nucleic acids are single- or double-stranded
and may be DNA (deoxyribonucleic acid) or RNA (ribonucleic acid). After viral
components are made by the infected host cell, virus particles are released;
the host cell is often dissolved. Some viruses do not kill cells but transform
them into a cancerous state; some cause illness and then seem to disappear,
while remaining latent and later causing another, sometimes much more severe,
form of disease. Viruses, known to cause cancer in animals, are suspected
of causing cancer in humans. Viruses also cause measles, mumps, yellow fever,
poliomyelitis, influenza and the common cold. Some viral infections can be
treated with drugs. See also DNA; Nucleic Acid; Ribonucleic Acid.
WASTING SYNDROME:
The HIV wasting syndrome involves involuntary weight loss of 10 percent of
baseline body weight plus either chronic diarrhea (two loose stools per day
for more than 30 days) or chronic weakness and documented fever (for 30 days
or more, intermittent or constant) in the absence of a concurrent illness
or condition other than HIV infection that would explain the findings.
WESTERN BLOT:
A laboratory test for the presence of specific antibodies, more accurate than
the ELISA test. See also Antibodies; ELISA.
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