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Glossary of HIV/AIDS Terms

for Health Care Providers

Glossary of HIV/AIDS Terms


Yellow pigmentation of the skin, mucous membranes, whites of the eyes, and body fluids caused by elevated blood levels of bilirubin. The condition is associated with either liver or gallbladder disease or excessive destruction of red blood cells.

Kaposi sarcoma (KS)

An AIDS-defining illness consisting of individual cancerous sores caused by an overgrowth of blood vessels. KS typically appears as pink or purple painless spots or nodules on the surface of the skin or mouth. KS also can occur internally, especially in the intestines, lymph nodes, and lungs, and in such cases, is life threatening. A species of herpes virus — also referred to as Kaposi sarcoma herpes virus (KSHV) or HHV-8 — similar to the Epstein-Barr virus is the probable cause.

Karnofsky score

A score from 0 to 100 assigned by a physician based on observations of a patient's ability to perform common tasks. Thus, 100 signifies normal physical abilities with no evidence of disease. Decreasing numbers indicate a reduced ability to perform activities of daily living.

Killer T cells

Because viruses lurk inside host (e.g., human) cells where antibodies cannot reach them, the only way to eliminate them is by killing the infected host cell. To do this, the immune system uses a kind of white blood cell, called the killer T cell. Also known as cytotoxic T cells (or cytotoxic T lymphocytes).

See Natural killer (NK) cells; T cells.


Kaposi sarcoma herpes virus.

See Kaposi sarcoma (KS).

Lactic acidosis

A buildup of lactic acid in the blood, accompanied by low blood pH. This is a potentially fatal condition characterized by nausea, abdominal pain, fatigue, muscle weakness, and shortness of breath. Also referred to as lactic acidemia.


The period when an infecting organism is in the body but is not producing any clinically noticeable ill effects or symptoms. In HIV disease, clinical latency is an asymptomatic period in the early years of HIV infection. The period of latency is characterized by near-normal CD4+ T-cell counts. Recent research indicates that HIV remains quite active in the lymph nodes during this period.


See Latency.


"Slow" virus characterized by a long time frame between infection and the onset of symptoms. HIV is a lentivirus, as is the simian immunodeficiency virus (SIV) that infects nonhuman primates.


A general term to describe an area of altered tissue (e.g., the infected patch or sore in a skin disease).


Any of the various white blood cells that together make up the immune system. Neutrophils, lymphocytes, and monocytes are all leukocytes.


An abnormally high number of leukocytes in the blood. This condition can occur during many types of infection and inflammation.


A decrease in the number of white blood cells. The threshold value for leukopenia usually is taken as <5,000 white blood cells per cubic millimeter of blood.


Any of a group of fats and fatlike compounds, including sterols, fatty acids, and many other substances.


Abnormal body fat distribution, either loss of subcutaneous fat (lipoatrophy) or accumulation of visceral fat (lipohypertrophy); both may occur in the same person. In HIV, lipodystrophy may be related to advanced disease, with older antiretroviral medications, or other factors. It has become much less common in recent years.

Live vector vaccine

As pertaining to HIV, a vaccine that uses an attenuated (i.e., weakened) virus or bacterium to carry pieces of HIV into the body to directly stimulate a cell-mediated immune response.

Liver function test (LFT)

A test that measures the blood serum level of any of several enzymes (e.g., AST and ALT) produced by the liver. An elevated liver function test result is a sign of possible liver damage.

Long-term nonprogressors

Individuals who have been living with HIV for at least 7 to 12 years (different authors use different time spans) and have stable CD4+ T-cell counts of 500 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 is seen in other individuals living with HIV.

Lumbar puncture

A procedure in which cerebrospinal fluid from the subarachnoid space in the lumbar region is removed for examination. Also known as spinal tap.


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.

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. Lymph nodes contain T cells, B cells, as well as other cells of the immune system.


Swollen or enlarged lymph nodes.


A white blood cell. Present in the blood, lymph, and lymphoid tissue.

See B lymphocytes (B cells); T cells.

Lymphoid interstitial pneumonitis (LIP)

A type of pneumonia that affects 35% to 40% of children with AIDS, and which causes hardening of the lung membranes involved in absorbing oxygen. LIP is an AIDS-defining illness in children. The cause of LIP is not clear. There is no established treatment for LIP, but the use of corticosteroids for progressive LIP has been advocated.

Lymphoid organs

Include tonsils, adenoids, lymph nodes, spleen, thymus, and other tissues. These organs act as the body's filtering system, trapping any invading foreign particles (e.g., bacteria and viruses) and presenting them to squadrons of immune cells that congregate there.

Lymphoid tissue

See Lymphoid organs.


Cancer of the lymphoid tissues. Lymphomas are often described as being large-cell or small-cell types, cleaved or noncleaved, or diffuse or nodular. The different types often have different prognoses (i.e., prospect of survival or recovery). Lymphomas can be referred to by the organs in which 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 lymphomas or B-cell lymphomas. In these types of cancers, certain cells of the lymphatic system grow abnormally. They divide rapidly, growing into tumors.


A relative or absolute reduction in the number of lymphocytes in the circulating blood.

Lymphoproliferative Response

A specific immune response that results in a rapid T-cell replication.


Rupture and destruction of a cell.