Many strains of monkey become naturally infected with viruses that are related to HIV. These viruses are known collectively as SIV and naturally infected monkeys do not develop AIDS. It is hoped that understanding why monkeys naturally infected with SIV do not develop AIDS might teach researchers important lessons about the mechanisms underlying the development of AIDS in humans infected with HIV and identify ways to prevent this happening.

New insight into the mechanisms that control the number of virus particles in the blood of sooty mangabeys naturally infected with SIVsmm, the strain of SIV that naturally infects sooty mangabeys, has now been provided by a team of researchers from the University of Pennsylvania, Philadelphia, and Emory University, Atlanta.

HIV and SIV infect immune cells known as CD4+ T cells. So, the authors set out to determine how CD4+ T cells affected the number of virus particles in the blood of sooty mangabeys naturally infected with SIVsmm -- did they provide immune control of the number of virus particles or did they simply provide a place to live a replicate.

The number of SIVsmm particles in the blood of naturally infected sooty mangabeys decreased when the monkeys were depleted of CD4+ T cells and then increased again as the number of proliferating CD4+ T cells rebounded.

So, it was concluded that availability of proliferating CD4+ T cells is a key determinant of how many SIVsmm particles can be detected in the blood of naturally infected sooty mangabeys, rather than CD4+ T cells providing immune control of the virus.