Helper T lymphocytes. The relentless progression of HIV infection is now recognized as a continuum that extends from an initial asymptomatic state to the immune depletion that characterizes patients with overt AIDS. The fundamental lesion is infection of CD4+ (helper) T lymphocytes, which leads to the depletion of this cell population and impaired immune function. As a result, patients with AIDS usually die of opportunistic infections. HIV does infect the monocyte/macrophage lineage (choice D), but infected cells exhibit little if any cytotoxicity. NK cell activity (choice E) is also decreased in AIDS. This defect may contribute to the appearance of malignant tumors and the viral infections that plague these patients. The suppression of NK cell activity has been related to a decrease in the number of NK cells and to a reduction in IL-2 levels due to the loss of CD4+ cells.Diagnosis: AIDS