Detection of viral RNA in CD4(-) CD8(-) and CD4(-) CD8(-) lymphocytes in vivo in rhesus monkeys infected with simian immunodeficiency virus of macaques

A definition of the specific cell types that support HIV replication early in the course of infection will be important for understanding AIDS pathoge nesis and designing strategies for preventing infection. Observations have indicated that the population of lymphocytes susceptible to productive infe ction extends beyond activated CD4(+) T cells. To explore this issue, we ha ve employed laser scanning cytometry technology and the techniques of lymph ocyte surface immunophenotyping followed by fluorescent in situ hybridizati on to detect simian immunodeficiency virus of macaques (SIVmac) RNA in phen otypically defined rhesus monkey lymphocytes. The immunophenotype of produc tively infected cells in either a rhesus monkey T cell line or in PBMCs inf ected in vitro with SIVmac was remarkably similar to that observed in produ ctively infected PBMCs obtained from monkeys during primary infection. We o bserved low levels or no detectable expression of CD4 on cells infected in vitro or on PBMCs of infected monkeys. However, a substantial number of SIV mac-infected PBMCs both in cultured lymphocytes and sampled directly from i nfected monkeys expressed CD8 but not CD4. These observations are consisten t with the possibility that the CD4 molecule may be modulated off the surfa ce of CD4(+)CD8(-) or CD4(+)CD8(+) lymphocytes after infection or that infe ction occurred via a CD4-independent mechanism. Moreover, there was no pref erential expression of CD25 on cells positive for SIVmac RNA, which might h ave been predicted if replication of the virus was occurring selectively in activated lymphocytes. These results broaden the range of lymphocytes that support productive SIVmac infection to include CD4(-)CD8(-) and CD4(-)CD8( +) subsets, and are consistent with virus replication occurring in nonactiv ated cells.