The importance of viral IL-10 in vivo is highlighted by a recent study showing that primary infection of rhesus (Rh) macaques with a variant of RhCMV lacking the RhCMVIL-10 gene led to (1) increased innate responses at the site of inoculation, and (2) increased long-term B and T cell responses to RhCMV antigens, compared to infection with the parental variant expressing RhCMVIL-10 [15]. Here, IL10 is linked to infection.