Low levels of SIV infection in sooty mangabey central memory CD4 + T cells are associated with limited CCR5 expression

Understanding the resistance of natural hosts of simian immunodeficiency virus (SIV)—such as sooty mangabeys—to disease progression may yield insights applicable to HIV-1. In this issue, Paiardini et al. report that CD4+ central memory T (TCM) cells from sooty mangabeys do not strongly upregulate CCR5 upon activation and are more resistant to SIV infection than TCM cells from rhesus macaques, which may contribute to proper immune control and prevention of disease in these natural hosts.