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.