IMMUNOBIOLOGY The AIDS resistance of naturally SIV-infected sooty mangabeys is independent of cellular immunity to the virus

In contrast to human immunodeficiency virus (HIV)–infected humans, natural hosts for simian immunodeficiency virus (SIV) very rarely progress to acquired immunodeficiency syndrome (AIDS). While the mechanisms underlying this disease resistance are still poorly under-stood, a consistent feature of natural SIV infection is the absence of the general-ized immune activation associated with HIV infection. To investigate the immuno-logic mechanisms underlying the ab-sence of AIDS in SIV-infected sooty mangabeys (SMs), a natural host species, we performed a detailed analysis of the SIV-specific cellular immune responses in 110 SIV-infected SMs. We found that while SIV-specific T-cell responses are detectable in the majority of animals, their magnitude and breadth are, in fact, lower than what has been described in HIV-infected humans, both in terms of cyto