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Subject: l
Date: Thu, 12 Oct 95 23:34 PDT (188 lines of text)

LAI:

A group of closely related HIV isolates that includes the LAV, IIIB and BRU strains of HIV. Used in HIV vaccine development. See also Isolate.

LAK CELLS:

Lymphocytes transformed in the laboratory into lymphokine activated killer cells, which attack tumor cells. See also Lymphocyte; Lymphokines.

LANGERHANS CELLS:

Dendritic cells in the skin that pick up an antigen and transport it to the lymph nodes. See also Antigen; Dendritic Cells; Lymph Nodes.

LAS:

See Lymphadenopathy Syndrome.

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.

LAV:

Lymphadenopathy Associated Virus (see Human Immunodeficiency Virus Type I).

LENTIVIRUS:

"Slow" virus characterized by a long interval between infection and the onset of symptoms. HIV is a lentivirus as is the simian immunodeficiency virus (SIV), which infects nonhuman primates. See also Simian Immunodeficiency Virus.

LESION:

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

LEUKOCYTES:

All white blood cells.

LEUKOPENIA:

A decrease in the number of white blood cells. The threshold value for leukopenia is usually taken as less than 5000 white blood cells per cubic millimeter of blood.

LIP:

See Lymphoid Interstitial Pneumonitis.

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 TERMINAL REPEAT SEQUENCE (LTR):

A component of the AIDS genome. See also Genome.

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.

LTR:

See Long Terminal Repeat Sequence.

LUMBAR:

Of, relating to or constituting the loins or the vertebrae between the thoracic vertebrae and the sacrum region. The sacrum is the triangular bone made up of five fused vertebrae and forming the posterior section of the pelvis. The thorax is the part of the human body between the neck and the diaphragm, partially encased by the ribs and containing the heart and lungs; the chest.

LUMBAR PUNCTURE:

A procedure in which fluid from the subarachnoid space in the lumbar region is tapped for examination. Also known as spinal tap. See also Lumbar; Subarachnoid Space.

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.

LYMPHADENOPATHY SYNDROME (LAS):

Swollen, firm and possibly tender lymph nodes. The cause may range from an infection such as HIV, the flu, mononucleosis or lymphoma (cancer of the lymph nodes). See also Lymph Nodes.

LYMPHATIC VESSELS:

A bodywide network of channels, similar to the blood vessels, that transport lymph to the immune organs and into the bloodstream. See also Lymph.

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.

LYMPHOID INTERSTITIAL PNEUMONITIS (LIP):

A form of pneumonia that involves the lower lobes (of the lungs) with extensive alveolar infiltration by mature lymphocytes, plasma cells and histiocytes. LIP is associated with AIDS, dysproteinemia and other conditions. See also Alveolar; Lymphocyte; Macrophage.

LYMPHOID ORGANS:

Include tonsils, adenoids, lymph nodes, spleen and other tissues. Act as the body's filtering system, trapping invaders(i.e., foreign particles from bacteria, viruses, etc.) and presenting them to squadrons of immune cells that congregate there. Within these lymphoid tissues, immune activity is concentrated in regions called germinal centers, where the thread-like tentacles of follicular dendritic cells (FDCs) form networks that trap invaders. See also Follicular Dendritic Cells; Lymph Nodes.

LYMPHOKINES:

1. Products of the lymphatic cells that stimulate the production of disease-fighting agents and the activities of other lymphatic cells. Among the lymphokines are gamma interferon and interleukin-2. See also Gamma Interferon; Interleukin-2. 2. Nonanti-body mediators of immune responses, released by activated lymphocytes. See also Immune Response; Lymphocyte.

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.

LYSIS:

Rupture and destruction of a cell.