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 (T CM ) cells from sooty mangabeys do not strongly upregulate CCR5 upon activation and are more resistant to SIV infection than T CM cells from rhesus macaques, which may contribute to proper immune control and prevention of disease in these natural hosts.