Effects of SIVmac Infection on Peripheral Blood CD4+CD8+T Lymphocytes in Cynomolgus Macaques

We have previously reported that CD4+CD8+double-positive (DP) T cells with a resting memory phenotype exist in a substantial proportion of peripheral blood lymphocytes of adult cynomolgus macaques. In this study, we examined the effects of simian immunodeficiency virus of macaque (SIVmac) infection on DP T cells.In vitro,SIVmac239nef-open (239) and itsnef-deletion mutant replicated well in both CD4+CD8−and DP T cells. However, when the macaques were infected with 239, DP, but not CD4+CD8−, T cells were transiently increased in parallel with cell activation and viral replication, followed by depletion within 1 month postinfection. Interestingly, thenefgene was required for depletion but not for the increase and activation of DP T cells. These data suggest that the pathogenic SIV infection may downmodulate production and/or blood circulation of DP T cells by a Nef function-related mechanism(s) different from that for the depletion of CD4+CD8−T cells.