Acquired Immunity
The body's ability to fight or prevent a specific infection. This ability can be acquired either actively (by having and recovering from an infection or by being vaccinated against an infection) or passively (by receiving antibodies from an outside source, such as from breast milk or donated blood components).

Acquired Immunodeficiency Syndrome (AIDS)
A disease of the body's immune system caused by the human immunodeficiency virus (HIV). AIDS is characterized by the death of CD4 cells (an important part of the body's immune system), which leaves the body vulnerable to life-threatening conditions such as infections and cancers.
See Also:   AIDS-Defining Condition
                   Human Immunodeficiency Virus
                   Opportunistic Infections
                   AIDS-Related Cancer

Active Immunity
Protection from a specific infection that develops after having and recovering from the infection or being vaccinated against the infection.
See Also:   Acquired Immunity

Acute HIV Infection
Also known as primary HIV infection or acute retroviral syndrome (ARS). The period of rapid HIV replication that occurs 2 to 4 weeks after infection by HIV. Acute HIV infection is characterized by a drop in CD4 cell counts and an increase in HIV levels in the blood. Some, but not all, individuals experience flu-like symptoms during this period of infection. These symptoms can include fever, inflamed lymph nodes, sore throat, and rash. These symptoms may last from a few days to 4 weeks and then go away.

Acute HIV Infection and Early Diseases Research Program (AIEDRP)
A program funded by the National Institute of Allergy and Infectious Diseases (NIAID) to conduct research with people who have been recently infected with HIV. This research is aimed at understanding how HIV infects humans and how the disease progresses to AIDS. Scientists believe that events that occur during acute and early infection may determine the ultimate course of the disease.

Acute Retroviral Syndrome (ARS)
See:    Acute HIV Infection

ADAPs
See: AIDS Drug Assistance Programs

ADC
See: AIDS Dementia Complex

Adherence
Closely following (adhering to) a prescribed treatment regimen. This includes taking the correct dose of a drug at the correct time, exactly as prescribed. Failure to adhere to an anti-HIV treatment regimen can lead to virological failure and drug resistance.
See Also:   Virologic Failure
                   Drug Resistance

Adjuvant
Substance added to a drug that enhances or modifies the original drug. Also refers to a substance added to a vaccine to improve the body's immune response to that vaccine.

ADR
See: Adverse Drug Reaction

Adult AIDS Clinical Trials Group (AACTG)
A large clinical trial organization that conducts clinical research to test treatment and prevention strategies for adult HIV infection and AIDS. The AACTG is funded by the National Institute of Allergy and Infectious Diseases (NIAID).
See Also:   Clinical Trial

Adverse Drug Reaction (ADR)
Any drug effect that is unwanted, unpleasant, or potentially harmful. These effects may be mild and may disappear when the drug is stopped or subside as the body adjusts to the drug. Other ADRs, such as skin rashes, anemia, or organ damage, are more serious.

AETCs
See: AIDS Education and Training Centers

Agammaglobulinemia
Absence or low levels of antibodies in the blood. This condition leaves a person vulnerable to infections.
See Also:   Antibody

Agency for Healthcare Research and Quality (AHRQ)
An agency of the Department of Health and Human Services (DHHS) that sponsors and conducts research on health care results, quality, cost, use, and access.

AHRQ
See: Agency for Healthcare Research and Quality

AIDS
See: Acquired Immunodeficiency Syndrome

AIDS Case Definition
See:    AIDS-Defining Condition

AIDS-Defining Condition
Any of a list of illnesses that, when occurring in an HIV-infected person, leads to a diagnosis of AIDS, the most serious stage of HIV infection. AIDS is also diagnosed if an HIV-infected person has a CD4 count below 200 cells/mm3, whether or not that person has an AIDS-defining condition. The Centers for Disease Control and Prevention (CDC) published a list of AIDS-defining conditions in 1993. The 26 conditions include candidiasis, cytomegalovirus disease, Kaposi's sarcoma, mycobacterium avium complex, pneumocystis carinii pneumonia, recurrent pneumonia, progressive multifocal leukoencephalopathy, pulmonary tuberculosis, invasive cervical cancer, and wasting syndrome.
See Also:   Acquired Immunodeficiency Syndrome

AIDS Dementia Complex (ADC)
Also called HIV-associated dementia. A progressive mental disorder with different nervous system and mental symptoms. Mental symptoms may be memory loss, speech problems, inabilty to concentrate, or poor judgment. There may be behavior changes, such as not being able to perform daily tasks. There may also be mood changes, such as depression. Motor difficulties may include loss of control of the legs or moving slowly or stiffly. ADC is considered an AIDS-defining condition in people with HIV.

AIDS Drug Assistance Programs (ADAPs)
Programs authorized under Title II of the Ryan White Comprehensive AIDS Resources Emergency (CARE) Act that operate in all 50 states, the District of Columbia, Guam, Northern Mariana Islands, Puerto Rico, and the Virgin Islands. These programs provide HIV-related prescription drugs to underinsured and uninsured individuals living with HIV/AIDS.

AIDS Education and Training Centers (AETCs)
A network of 15 regional centers that conduct targeted, multidisciplinary HIV education and training programs for health care providers. The mission of these centers is to increase the number of health care providers who are educated and motivated to counsel, diagnose, treat, and manage individuals with HIV infection and to assist in the prevention of high-risk behaviors that may lead to infection. AETCs are administered by the Health Resources and Services Administration (HRSA).

AIDS-Related Cancer
Several cancers are more common or more aggressive in people with HIV. These cancers include certain types of immune system cancers (lymphomas), Kaposi's sarcoma, cancers that affect the anus and the cervix, and others. Having HIV appears to play a role in the development and progression of these cancers, although people without HIV can also have them.

AIDS-Related Complex (ARC)
A group of complications that commonly occur in the early stage of HIV infection. These may include recurrent fever, unexplained weight loss, swollen lymph nodes, diarrhea, herpes, or fungus infection of the mouth and throat.

AIDS Service Organization (ASO)
A health association, support agency, or other service actively involved in the prevention and treatment of HIV/AIDS.

AIDSinfo
A Department of Health and Human Services (DHHS) project that offers the latest federally approved information on HIV/AIDS clinical research, treatment and prevention, and medical practice guidelines for people living with HIV/AIDS, their families and friends, health care providers, scientists, and researchers. The service includes a Web site with "Live Help," a toll-free hotline (1-800-448-0440), responses to e-mail inquiries, and a variety of publications. http://www.aidsinfo.nih.gov

AIEDRP
See: Acute HIV Infection and Early Diseases Research Program

Alanine Transaminase (ALT)
See:    Liver Function Tests

Alkaline Phosphatase
An enzyme normally present in certain cells within the liver, bone, kidney, intestine, and placenta. When cells are destroyed in those tissues, the enzyme leaks into the blood, and levels rise in proportion to the severity of the condition. Measurement of this enzyme is one way to evaluate the health of the liver.

ALT
See: Alanine Transaminase

Amino Acids
The building blocks the body uses to make proteins.
See Also:   Proteins

Anaphylaxis
Also called anaphylactic shock. A rare but life-threatening whole-body allergic reaction. Symptoms may appear quickly and include difficulty breathing, swelling of the throat or other parts of the body, rapid drop in blood pressure, dizziness, or unconsciousness. Anaphylaxis can be triggered by foods, drugs, insect stings, or exertion.

Anemia
A lower than normal number of red blood cells. Symptoms may include fatigue, chest pain, or shortness of breath.

Anorexia
Lack or loss of appetite.

Antagonism
See:    Drug Antagonism

Antenatal
See:    Prenatal

Antepartum
The time period before childbirth (refers to the mother).

Antibiotic
A natural or man-made substance that can kill or stop the growth of micro-organisms such as bacteria or fungi.

Antibody
Also known as immunoglobulin. A protein produced by the body's immune system that recognizes and fights infectious organisms and other foreign substances that enter the body. Each antibody is specific to a particular piece of an infectious organism or other foreign substance.
See Also:   Antigen

Antifungal
A natural or man-made substance that can kill or stop the growth of a fungus.

Antigen
Any substance that can stimulate the body to produce antibodies against it. Antigens include bacteria, viruses, pollen, and other foreign materials.
See Also:   Antibody

Antigen-Presenting Cell (APC)
A type of cell that collects foreign materials (antigens), digests them into small pieces, and "displays" or "presents" the pieces on its surface. Other cells of the immune system recognize these pieces and become activated to fight the foreign invader. APCs include B lymphoctyes, macrophages, and dendritic cells.
See Also:   B Lymphocytes
                   Macrophage
                   Dendritic Cells
                   Antigen

Antineoplastic
A natural or man-made substance that can kill or stop the growth or spread of cancer cells.

Antiprotozoal
A natural or man-made substance that can kill or stop the growth of single-celled micro-organisms called protozoa.

Antiretroviral (ARV)
A medication that interferes with the ability of a retrovirus (such as HIV) to make more copies of itself.
See Also:   Antiretroviral Therapy
                   Highly Active Antiretroviral Therapy

Antiretroviral Pregnancy Registry
An ongoing project to collect observational, nonexperimental information about the use of antiretrovirals during pregnancy. Information from the registry is used to help health care providers and patients weigh the potential risks and benefits of treatment. The registry does not use patient names, and registry staff obtain information from the patients' physicians. http://www.APRegistry.com

Antiretroviral Therapy (ART)
Treatment with drugs that inhibit the ability of retroviruses (such as HIV) to multiply in the body. The antiretroviral therapy recommended for HIV infection is referred to as highly active antiretroviral therapy (HAART), which uses a combination of medications to attack HIV at different points in its life cycle.
See Also:   Highly Active Antiretroviral Therapy
                   Retrovirus

Antisense Drugs
A man-made segment of DNA or RNA that can lock onto a strand of DNA or RNA from a virus or other micro-organism. This marks the organism's genetic instructions for destruction and prevents the organism from making more copies of itself.
See Also:   Deoxyribonucleic Acid
                   Ribonucleic Acid

Antiviral
A natural or man-made substance that can kill or stop the growth of a virus.

APC
See: Antigen-Presenting Cell

Aphthous Ulcer
A painful shallow sore in the mouth. The sore is usually oval shaped, with a yellow-white center surrounded by a narrow red ring. Aphthous ulcers are 1/8 to 1/4 inch across and have no blisters. They occur on the soft surfaces of the mouth, such as the inner cheeks, inner lips, soft areas of the roof and floor of the mouth, tongue, gums, and throat.

Apoptosis
The deliberate, programmed death of a cell. Apoptosis occurs as a normal part of life and helps the body stay healthy. If cells are damaged (for example, cancerous cells or cells infected with HIV), the body orders those cells to die in order to contain the disease.

Approved Drugs
In the United States, the Food and Drug Administration (FDA) must approve a drug before it can be marketed and sold to the public. The approval process involves several steps, including laboratory and animal studies, clinical trials for safety and efficacy, filing of a New Drug Application (NDA) by the manufacturer of the drug, FDA review of the application, and FDA approval/rejection of the application.
See Also:   New Drug Application

ARC
See: AIDS-Related Complex

Area Under the Curve (AUC)
A measure of how much drug reaches a person's bloodstream in a given period of time (usually the time between each dose or within 24 hours). The AUC is calculated by plotting the drug's blood levels on a graph at different times during the set period to form a curve. The area under this curve reflects the total drug exposure in the set time period.

Arm
Any of the treatment groups in a clinical trial. Most clinical trials have two arms, but some have three or even more. Each arm receives a different treatment or placebo.
See Also:   Clinical Trial
                      Placebo

ARS
See: Acute Retroviral Syndrome

ART
See: Antiretroviral Therapy

Arthralgia
Joint pain with symptoms such as heat, redness, tenderness to touch, loss of motion, or swelling.

ARV
See: Antiretroviral

ASO
See: AIDS Service Organization

Aspartate Aminotransferase (AST)
See:    Liver Function Tests

Aspergillosis
An infection of the lungs caused by the fungus Aspergillus. The infection may also spread through the blood to other organs. Symptoms include fever, chills, difficulty in breathing, and coughing up blood. If the infection reaches the brain, it may cause dementia.

AST
See: Aspartate Aminotransferase

Asymptomatic
Having no obvious signs or symptoms of disease.

Ataxia
Partial or complete loss of coordination of voluntary muscular movements. This can interfere with a person's ability to walk, talk, eat, and perform other tasks of daily living.

Attenuated
A term used to describe a bacterium or virus that has been changed in the laboratory so that it is not harmful to people. Attenuated viruses are often used as vaccines because they can no longer cause disease, but can still stimulate a strong immune response. Examples include the vaccines against polio (Sabin oral vaccine), measles, mumps, and rubella.

AUC
See: Area Under the Curve

Autoantibody
An antibody directed against the body's own tissue.
See Also:   Antibody

Avascular Necrosis (AVN)
Death of bone (osteonecrosis) caused by a loss of blood supply to the bone tissue. AVN has occured in the hip bones of some people with HIV, but it is not clear if bone death occurs because of HIV infection itself or as a side effect of the medications used to treat HIV. Symptoms include pain in the affected area of the body, limited range of motion, joint stiffness, limping, and muscle spasms. If untreated, AVN can cause progressive bone damage leading to bone collapse.
See Also:   Osteonecrosis

AVN
See: Avascular Necrosis
See Also:   Active Immunity
                   Passive Immunity