DECLINE IN THE CD4-INFECTED MACAQUES IS NOT REFLECTED IN LYMPH-NODES(LYMPHOCYTE POPULATION IN THE BLOOD OF SIV)

Although loss of CD4+ lymphocytes in peripheral blood is a standard cr iterion for evaluating the course of HIV disease, little is known abou t changes within lymphoid organs, which contain the bulk (>50%) of the body's lymphocytes. Because such studies are feasible only by using n on-human primates, we have examined lymph nodes (LNs), spleen, and blo od from monkeys infected with two isolates of simian immunodeficiency virus (SIV). During both the acute and chronic phases of these infecti ons, characteristic reductions in the blood CD4+ cell levels are not r eflected in LN, where the CD4+ pool remains within normal levels. Howe ver, when circulating CD4/CD8 ratios have consistently fallen to appro ximately 0.5, striking decreases in the percentage of CD4 cells (CD4%) and CD4/CD8 ratios in LN occur concomitantly with dramatic increases in viral antigen expression on follicular dendritic cells within LN ge rminal centers (GCs). The data suggest that loss from the total T cell pool in minimal until the final stages of SIV and HIV disease and tha t the immunological deterioration of LN is the event that precipitates the increased susceptibility to infections and progression to AIDS.