Control mechanisms of virus replication in naturally SIVsmm infected mangabeys and experimentally infected macaques.

As a close cousin to Asian macaques, the African sooty mangabey monkey, a species naturally infected with SIV without ever developing disease, represents an intriguing and thought provoking model for the study of lentiviral infection and disease development. Pursuant to our previous findings that documented the presence of high frequencies of CD8+ T-cells capable of inhibiting lentiviral replication in vitro via a soluble factor, the potential contribution of beta-chemokines and their receptor was evaluated in samples from sooty mangabeys and disease susceptible macaques. Both mangabey and Rhesus macaque PBMC were found to secrete comparable levels of MIP-1alpha, MIP-1beta and RANTES after stimulation in vitro. Constitutive expression of CCR-5 appeared lower in mangabey PBMC but the vast majority of T-cells from mangabeys or macaques were found to express CCR-5 after in vitro activation. Sequence analysis of macaque and mangabey MIP-1alpha and RANTES showed complete homology to the human counterpart. MIP-1beta on the other hand while highly conserved among both monkey species, showed only 93% homology to human MIP-1beta. In addition, CCR-5, CCR-2b and CXCR-4 presented no consistent differences between rhesus and mangabey sequences. Thus, based on current data, differences in disease susceptibility between macaques and mangabeys do not appear to rely on differences in chemokine pathways. However, analyses of the ontogeny of CD8+ T-cell-mediated inhibition of SIV replication showed that macaque PBMC acquire this function shortly after infection, and show a progressive loss thereafter, correlated with progression towards disease. Mangabeys, on the other hand, appear to acquire the CD8+ T-cell inhibitory function long before any evidence of seroconversion to SIV and maintain this function for the lifetime of the animal. In vitro analyses of induction of the CD8+ inhibitory function showed that rhesus CD8+ T-cells have the potential to secrete the inhibitory factor(s) prior to SIV infection.