Early phenotypic and functional alterations in lymphocytes from simian immunodeficiency virus infected macaques

Phenotypic and functional changes in lymphocytes from rhesus monkeys (Macaca mulatta) were investigated during the first 6 months after infection with SIV mac 32H. Animals preimmunized with keyhole limpet hemocyanin (KLH) were sacrificed 1, 3, 6, 12, and 24 weeks post infection. Subset composition and function of lymphocytes from blood, spleen, lymph node and thymus were analysed. In addition to a rapid decline in CD4/CD8 ratios, a massive reduction in CD29+ CD4+ cells was seen in the periphery. Although depletion of this subset was observed throughout the course of this experiment, the loss of proliferative T cell responses was most pronounced very early after infection and partially recovered after Month 3. Polyclonal cytotoxic responses were only slightly affected. In the thymus, a gradual, but moderate loss of CD4+CD8+ immature thymocytes, and a relative increase in both CD4+ and CD8+ mature subsets was observed. Infectious virus was readily recovered from homogenates of lymph node and spleen, but not of thymus tissue. Interestingly, however, virus was detected in thymocytes from all infected animals by cocultivation with a simian immunodeficiency virus (SIV) susceptible cell line.