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CACHEXIA:
General ill health and malnutrition, marked by weakness and emaciation, usually associated with serious disease. See AIDS Wasting Syndrome.

CANDIDA:
Yeast-like fungi commonly found in the normal flora of the mouth, skin, intestinal tract, and vagina, which can become clinically infectious in immune-compromised persons. See Candidiasis, Fungus; Thrush.

CANDIDIASIS:
An infection with a yeast-like fungus of the Candida family, generally Candida albicans. It most commonly involves the skin (dermatocandidiasis), oral mucosa (thrush), respiratory tract (bronchocandidiasis), and vagina (vaginal candidiasis, formerly called monilia). Candidiasis of the esophagus, trachea, bronchi, or lungs is an indicator disease for AIDS. Oral or recurrent vaginal candida infection is an early sign of immune system deterioration. See Opportunistic Infections; Thrush.

CARCINOGEN:
Any cancer-producing substance.

CATHETER:
A tubular medical device for insertion into canals, vessels, passageways, or body cavities, usually to permit injection (e.g., through an intravenous catheter into a vein), withdrawal of fluids, or to keep a passage open.

CBCT:
See Community-Based Clinical Trial.

CBO:
See Community-Based Organization.

CCR5:
Cell surface molecule, which is needed along with the primary receptor, the CD4 molecule, in order to fuse with the membranes of the immune system cells. Researchers have found that the strains of HIV most often transmitted from person to person require the CCR5 molecule and CD4 molecule in order for HIV to enter the cell. In addition to its role in fusion, CCR5 is a receptor for certain immune-signaling molecules called chemokines that are known to suppress HIV infection of cells. See Chemokines, CXCR4.

CDC:
See Centers for Disease Control and Prevention.

CD4 (T4) or CD4+ CELLS:
1. A type of T cell involved in protecting against viral, fungal, and protozoal infections. 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 for developing opportunistic infections. 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 CD8 (T8) Cells; Immunodeficiency.

CD8 (T8) CELLS:
A protein embedded in the cell surface of suppressor T lymphocytes. Also called cytotoxic T cells. Some CD8 cells recognize and kill cancerous cells and those infected by intracellular pathogens (some bacteria, viruses, and mycoplasma). These cells are called cytotoxic T lymphocytes.

CDC NATIONAL AIDS HOTLINE:
Provides education, information, and referrals for persons living with HIV, their families and friends, health professionals, and the general public on HIV/AIDS issues, including transmission, prevention, and testing. The Hotline number is 1-800-342-AIDS.

CDC NATIONAL PREVENTION INFORMATION NETWORK:
The National Prevention Information Network (NPIN) is a national reference, referral and distribution service for information on HIV/AIDS, STDs and TB, sponsored by the Centers for Disease Control and Prevention (CDC). All of the NPIN's services are designed to facilitate sharing of information and resources among people working in HIV, STD, and TB prevention, treatment, and support services. NPIN staff serve a diverse network of people who work in international, national, state, and local settings. Internet address: http://www.cdcnpin.org/.

CELL LINES:
Specific cell types artificially maintained in the laboratory (i.e., in vitro) for scientific purposes.

CELL-MEDIATED IMMUNITY (CMI):
This branch of the immune system exists primarily to deal with viruses that are more insidious than bacteria because they invade the host (e.g., human) cells where they can hide from the antibody-making cells of the immune system. With this system, the reaction to foreign material is performed by specific defense cells, such as killer T cells, macrophages, and other white blood cells rather than by antibodies.

CELLULAR IMMUNITY:
See Cell-Mediated Immunity.

CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC):
The U.S. Department of Health and Human Services agency with the mission to promote health and quality of life by preventing and controlling disease, injury, and disability. CDC operates 11 Centers including the National Center for HIV, STD, and TB Prevention. CDC assesses the status and characteristics of the HIV epidemic and conducts epidemiologic, laboratory, and surveillance investigations. Internet address: http://www.cdc.gov/.

CENTRAL NERVOUS SYSTEM (CNS) DAMAGE:
(By HIV infection). The central nervous system is composed of the brain, spinal cord, and the meninges (protective membranes surrounding them). 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. Persons living 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 by-products of these cells may be to blame for the neurological manifestations of HIV disease.

CEREBRAL:
Pertaining to the cerebrum, the main portion of the brain.

CEREBROSPINAL FLUID (CSF):
Fluid that bathes the brain and the spinal cord. A sample of this fluid is often removed from the body for diagnostic purposes by a lumbar puncture (spinal tap).

CERVICAL CANCER:
A neoplasm of the uterine cervix that can be detected in the early curable stage by the Papanicolaou (Pap) test. See Cervical Dysplasia; Cervix; Pap Smear.

CERVICAL DYSPLASIA:
Abnormality in the size, shape, and organization of adult cells of the cervix. Often a precursor lesion for cervical cancer. Studies indicate an increase in prevalence of cervical dysplasia among women living with HIV. Additional studies have documented that a higher prevalence is associated with greater immune suppression. HIV infection also may adversely affect the clinical course and treatment of cervical dysplasia and cancer.

CERVICAL INTRAEPITHELIAL NEOPLASIA (CIN1, CIN2, CIN3):
Dysplasia of the cervix epithelium, often premalignant (i.e., precancerous), characterized by various degrees of hyperplasia, abnormal keratinization (forming horny epidermal tissue), and condylomata. Considerable evidence implicates human papilloma virus (HPV) in the development of CIN. Immunosuppression may also play an important role in facilitating infection or persistence of HPV in the genital tract and progression of HPV-induced neoplasia. See Condyloma; Neoplasm.

CERVIX:
The lower, cylindrical terminus of the uterus that juts into the vagina and contains a narrow canal connecting the upper and lower parts of a woman's reproductive tract.

CHALLENGE:
In vaccine experiments, the exposure of an immunized animal to the infectious agent.

CHANCROID:
A highly contagious sexually transmitted disease caused by the Hemophilus ducreyi bacterium. It appears as a pimple, chancre, sore, or ulcer on the skin of the genitals. The lesion appears after an incubation period of 3 to 5 days and may help the transmission of HIV.

CHEMOKINES:
Also called beta chemokines. Studies of the relationship between HIV and these immune system chemicals have shown the complex exchanges that take place when HIV and white blood cells meet. Chemokines are intracellular messenger molecules secreted by CD8+ cells whose major function is to attract immune cells to sites of infection. Recent research has shown that HIV-1 needs access to chemokine receptors on the cell surface to infect the cell. Several chemokines -- called RANTES, MIP-1A, and MIP-1B -- interfere with HIV replication by occupying these receptors. Findings suggest that one mechanism these molecules use to suppress HIV infectivity is to block the process of fusion used by the virus to enter cells.

CHEMOTHERAPY:
The treatment, mostly of cancer, using 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.

CHLAMYDIA:
A sexually transmitted disease (see Sexually Transmitted Disease). The most common sexually transmitted bacterium (Chlamydia trachomatis) that infects the reproductive system. In fact, in a 1998 NIAID press release (fact sheet), chlamydia was reported to be the most common STD in the United States. The infection is frequently asymptomatic (i.e., shows no symptoms), but if left untreated, can cause sterility in women.

CHRONIC IDIOPATHIC DEMYELINATING POLYNEUROPATHY (CIPD):
Chronic, spontaneous loss or destruction of myelin. Myelin is a soft, white, somewhat fatty material that forms a thick sheath around the core of myelinated nerve fiber. Patients show progressive, usually symmetric weakness in the upper and lower extremities. Patients with clinical progression of the syndrome after 4 to 6 weeks by definition have CIPD. Treatment in most centers consists of giving IV-immune globulin for 4 to 5 days or plasmapheresis (5 to 6 exchanges over 2 weeks).

CIPD:
See Chronic Idiopathic Demyelinating Polyneuropathy.

CIRCULATING IMMUNE COMPLEXES:
See Immune Complex.

CIRCUMORAL PARESTHESIA:
An abnormal touch sensation, such as burning or prickling around the mouth, often in the absence of an external stimulus. See Paresthesia.

CLADE:
Also called a subtype. A clade is a group of related HIV isolates (see Isolate) classified according to their degree of genetic similarity (such as the percentage of identity within their envelope genes). There are currently three groups of HIV-1 isolates: M, N, and O. Isolate M (major strains) consists of at least ten clades, A through J. Group O (outer strains) may consist of a similar number of clades. French researchers reported the discovery of a new HIV-1 isolate that cannot be categorized in either group M or O. The new isolate was found in a Cameroonian woman with AIDS. They suggested that this new isolate be classified as group N (for new or for "non-M-non-O").

CLINICAL:
Pertaining to or founded on observation and treatment of patients, as distinguished from theoretical or basic science.

CLINICAL ALERT:
The National Institutes of Health in conjunction with the editors of several biomedical journals publish those bulletins on 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 ENDPOINT:
See Endpoint.

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. Pertaining to HIV infection, infected individuals usually exhibit a period of clinical latency with little evidence of disease, but viral load studies show that the virus is never truly latent (dormant). Even early in the disease, HIV is active within lymphoid organs where large amounts of virus become trapped in the FDC (see Follicular Dendritic Cells) network. Surrounding tissues are areas rich in CD4+ T cells. These cells increasingly become infected and viral particles accumulate both in infected cells and as free virus.

CLINICAL PRACTICE GUIDELINES:
Standards for physicians to adhere to in prescribing care for a given condition or illness.

CLINICAL TRIAL:
A scientifically designed and executed investigation of the effects of a drug (or vaccine) administered to human subjects. The goal is to define the safety, clinical efficacy, and pharmacological effects (including toxicity, side effects, incompatibilities, or interactions) of the drug. The U.S. government, through the FDA, requires strict testing of all new drugs and vaccines prior to their approval for use as therapeutic agents. See entries for Phase I, II, III, and IV Trials.

CLONE:
1. A group of genetically identical cells or organisms descended from a common ancestor. 2. To produce genetically identical copies. 3. A genetically identical replication of a living cell that is valuable for the investigation and reproduction of test cultures.

CMV:
See Cytomegalovirus.

CMV RETINITIS:
See Cytomegalovirus Retinitis.

CNS:
See Central Nervous System Damage.

COCCIDIOIDOMYCOSIS:
An infectious fungal disease caused by the inhalation of spores of Coccidioides immitis, which are carried on windblown dust particles. The disease is endemic in hot, dry regions of the Southwestern United States and Central and South America, and is an opportunistic disease associated with AIDS. Also called desert fever, San Joaquin fever, or Valley fever. See Fungus; Opportunistic Infections.

CODON:
A sequence of three nucleotides of messenger RNA that specifies addition of a particular amino acid to, or termination of, a polypeptide chain during protein synthesis. See Ribonucleic Acid.

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 cofactors are: other infections, drug and alcohol use, poor nutrition, genetic factors, and stress. In HIV immunology, the concept of cofactors is being expanded and new cofactors have been identified. A recent example is the discovery of the interaction of CXCR4 (fusin) and CD4 to facilitate entry of HIV into cells.

COGNITIVE IMPAIRMENT:
Loss of the ability to process, learn, and remember information.

COHORT:
In epidemiology, a group of individuals with some characteristics in common.

COLITIS:
Inflammation of the colon.

COMBINATION THERAPY:
(For HIV infection or AIDS). Two or more drugs or treatments used together to achieve optimum results against HIV infection and/or AIDS. Combination therapy may offer advantages over single-drug therapies by being more effective in decreasing viral load. An example of combination therapy would be the use of two nucleoside analog drugs (such as Lamivudine and Zidovudine; see entries for these drugs) plus either a protease inhibitor or a non-nucleoside reverse transcription inhibitor. See Synergism.

COMBIVIR:
A combined pill containing Zidovudine and Lamivudine that is FDA approved (09/26/97) for the treatment of HIV infection in adults and adolescents 12 years of age or older.

COMMUNITY-BASED CLINICAL TRIAL (CBCT):
A clinical trial conducted primarily through primary-care physicians rather than academic research facilities.

COMMUNITY-BASED ORGANIZATION (CBO):
A service organization that provides social services at the local level.

COMMUNITY PLANNING:
Community planning groups are responsible for developing comprehensive HIV prevention plans that are directly responsive to the epidemics in their jurisdictions. The goal of HIV Prevention Community Planning is to improve the effectiveness of HIV prevention programs. Together in partnership, representatives of affected populations, epidemiologists, behavioral scientists, HIV/AIDS prevention service providers, health department staff, and others analyze the course of the epidemic in their jurisdiction, determine their priority intervention needs, and identify interventions to meet those needs. CDC supports implementation of an effective planning process.

COMMUNITY PROGRAMS FOR CLINICAL RESEARCH ON AIDS (CPCRA):
The CPCRA, founded in 1989, and called the Terry Beirn Community Programs for Clinical Research on AIDS since 1992, is a network of research units composed of community-based health care providers who offer their patients the opportunity to participate in research where they get their health care. The 15 CPCRA units comprise a variety of clinical settings, including private physicians practices, university, and veterans hospital clinics; drug treatment centers; and freestanding community clinics. Patients at these clinics are eligible for participation in CPCRA studies. The CPCRA, funded by the National Institute of Allergy and Infectious Disease (see NIAID), is targeted to serve populations underrepresented in previous clinical trials efforts. The research focus and scientific agenda of the CPCRA is identifying and improving treatment options in the day-to-day clinical care of people with HIV. Internet address: http://www.cpcra.org/.

COMPASSIONATE USE:
A method of providing experimental therapeutics (including experimental drugs) prior to final FDA approval for use in humans. This procedure is used with very sick individuals who have no other treatment options. Often, case-by-case approval must be obtained from the FDA for "compassionate use" of a drug or therapy.

COMPLEMENT:
A group of proteins in normal blood serum and plasma that, in combination with antibodies, causes the destruction of antigens, particularly bacteria and foreign blood cells.

COMPLEMENT CASCADE:
A precise sequence of events, usually triggered by an antigen-antibody complex, in which each component of the complement system is activated in turn. See Antibodies; Antigen.

COMPLEMENTARY THERAPY:
A whole range of services designed to complement traditional medical practice as part of a practitioner's primary care plan for an individual.

CONCOMITANT DRUGS:
Drugs that are taken together. Certain concomitant medications may have adverse interactions.

CONCORDE STUDY:
Joint French/British clinical trial of AZT in asymptomatic HIV- infected individuals. See Zidovudine.

CONDYLOMA:
(Condyloma acuminatum). A papilloma with a central core of connective tissue in a treelike structure covered with epithelium, usually occurring on the mucous membrane or skin of the external genitals or in the perianal (tissue surrounding the anus) region. Although the lesions are usually few in number, they may aggregate to form large cauliflower-like masses. Caused by the human papilloma virus (see HPV), it is infectious and autoinoculable (i.e., capable of being transmitted by inoculation from one part of the body to another). Also called genital warts, venereal warts, or verruca acuminata.

CONTAGIOUS:
In the context of HIV, has come to be more popularly known as any infectious disease capable of being transmitted by casual contact from person to another. Casual contact can be defined as normal day-to-day contact among people at home, school, or work or in the community. A contagious pathogen (e.g., chicken pox) can be transmitted by casual contact. An infectious pathogen, on the other hand, is transmitted by direct or intimate contact (e.g., sex). HIV is infectious, not contagious.

CONTRAINDICATION:
A specific circumstance when the use of certain treatments could be harmful.

CONTROLLED TRIALS:
Control is 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.

CO-RECEPTORS:
A group of proteins that have been found to block the entry of HIV into immune cells.

CORE:
The protein capsule surrounding a virus DNA or RNA. In HIV, p55, the precursor molecule to the core, is broken down into the smaller protein molecules p24, p17, p7, and p6. HIV's core is primarily composed of p24.

CORE PROTEIN:
See Core.

CORRELATES OF IMMUNITY/CORRELATES OF PROTECTION:
The immune responses that protect an individual from a certain disease. The precise identities of the correlates of immunity in HIV are unknown.

CPCRA:
See Community Programs for Clinical Research on AIDS.

CREATININE:
A protein found in muscles and blood, and excreted by the kidneys in the urine. The level of creatinine in the blood or urine provides a measure of kidney function.

CRIXIVAN:
See Indinavir.

CROSS-RESISTANCE:
The phenomenon in which a microbe that has acquired resistance to one drug through direct exposure, also turns out to have resistance to one or more other drugs to which it has not been exposed. Cross-resistance arises because the biological mechanism of resistance to several drugs is the same and arises through the identical genetic mutations.

CRYOTHERAPY:
The use of liquid nitrogen to freeze and destroy a lesion or growth, sometimes used to induce scar formation and healing to prevent further spread of a condition (e.g., warts or molluscum contagiosum).

CRYPTOCOCCAL MENINGITIS:
A life-threatening infection of the membranes (meninges) that line the brain and the spinal cord. Cryptococcal disease is caused by a fungus (Cryptococcus neoformans). Most people have been exposed to this organism, which is found in soil contaminated by bird droppings, but it usually does not cause disease in healthy people. The majority of persons with cryptococcal meningitis have immune systems that are damaged by disease, such as AIDS, or suppressed by drugs. The organism can infect almost all organs of the body, although it most commonly causes disease of the meninges, skin, or lungs. See Cryptococcosis.

CRYPTOCOCCOSIS:
An infectious disease seen in HIV-infected patients due to the fungus Cryptococcus neoformans, which is acquired via the respiratory tract. It can spread from the lungs to the brain, the central nervous system, the skin, the skeletal system, and the urinary tract. See Cryptococcal Meningitis.

CRYPTOSPORIDIOSIS:
See Cryptosporidium.

CRYPTOSPORIDIUM:
The protozoan parasite, Cryptosporidium parvum, which causes cryptosporidiosis. The parasite is found in the intestines of animals, and may be transmitted to humans by direct contact with an infected animal, by eating contaminated food, or by drinking contaminated water. The parasite grows in the intestines and may cause severe chronic diarrhea (6-29 bowel movements per day) in people with HIV disease. Cryptosporidiosis usually occurs late in the course of HIV disease as immunological deterioration progresses.

CT SCAN (Computed Tomography Scan):
Radiography (using x-rays) in which a three-dimensional image of a body structure is constructed by computer from a series of cross-sectional images made along an axis. Also referred to as CAT scan. See Magnetic Resonance Imaging (MRI).

CTL:
See Cytotoxic T Lymphocyte.

CUTANEOUS:
Of, pertaining to, or affecting the skin.

CXCR4:
(Also known as Fusin). A cell molecule that acts as a cofactor or co-receptor for the entry of HIV into immune system cells. Early in the epidemic, CD4 molecules were found to be the primary receptor for HIV on immune system cells. Recent data indicate that a second molecule, CXCR4, is also required for fusion and entry of certain strains of HIV into cells. New studies indicate a multistage interplay between HIV and two receptors on white blood cells. After binding to the receptor CD4, the virus fuses with a second receptor, CXCR4, which normally binds to chemokines. This double clasp may then signal the receptors to move the virus into the cell.

CYTOKINES:
A soluble, hormone-like protein, produced by white blood cells, that acts as a messenger between cells. Cytokines can stimulate or inhibit the growth and activity of various immune cells. Cytokines are essential for a coordinated immune response and can also be used as immunologic adjuvants. HIV replication is regulated by a delicate balance among the body's own cytokines. By altering that balance one can influence the replication of the virus in the test tube and potentially even in the body. See also Interleukins, Tumor Necrosis Factor.

CYTOMEGALOVIRUS (CMV):
A herpes virus that is a common cause of opportunistic diseases in persons with AIDS and other persons with immune suppression. While CMV can infect most organs of the body, persons with AIDS are most susceptible to CMV retinitis (disease of the eye) and colitis (disease of the colon).

CYTOMEGALOVIRUS (CMV) RETINITIS:
Most adults in the U.S. 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 persons who are living with HIV. Without treatment, persons with CMV retinitis can lose their vision. CMV infection can affect both eyes and is the most common cause of blindness among persons with AIDS.

CYTOPENIA:
Deficiency in the cellular elements of the blood.

CYTOPLASM:
All of the substance of a cell other than the nucleus.

CYTOTOXIC:
An agent or process that is toxic to cells (i.e., it causes suppression of function or cell death).

CYTOTOXIC T LYMPHOCYTE (CTL):
A lymphocyte that is able to kill foreign cells marked for destruction by the cellular immune system. CTLs can destroy cancer cells and cells infected with viruses, fungi, or certain bacteria. CTLs are also known as killer T cells; they carry the CD8 marker. CTLs kill virus-infected cells, whereas antibodies generally target free-floating viruses in the blood. See also CD8 (T8) Cells.