Functional analyses of natural killer cells in macaques infected with neurovirulent simian immunodeciency virus

Clearance of HIV and SIV from the peripheral blood by the cellular immune system lessens the viral burden in infectedindividuals and may have an impact on virus infectionof the CNS and the development of CNS lesions. However, the role of immune responses in preventing or limiting CNS infection has not been clearlydeŽned.We investigatedthe role of natural killer cells in the outcome of SIV infection of macaques as a model for humans with AIDS and HIV encephalitis. In our study, six pig-tailed macaques were infected with the neurovirulent virus, SIV/17E-Fr, and the immunosuppressive virus, SIV/ DeltaB670, in a model system that causes rapid progression to AIDS and a high frequency of CNS lesions. NK lytic activity in each macaque was monitored longitudinally. In addition, we enumeratedNK cells and testedmacaque PBMC for the ability to lyse SIV-infected target cells. We found that there was a signiŽcant inverse correlation (P=0.02) between the robustness of NK response and the development of CNS lesions. Animals lacking strong NK cell responses developed more severe CNS lesions than those with robust NK responses did. Furthermore, pre-infection levels of NK activity were predictive of CNS lesion severity.Themacaque with themost robust pre-infectionNK activitydeveloped noCNS lesions.Intheseinfectedmacaques,NKactivitywasshown tobedirected against SIV-infected cells. We extended these in vivo Žndings to delineate precisely which cell type was mediating this SIV-directed lysis. We used both macaque and human cells to demonstrate that the population that mediated anti-SIV and anti-HIV cytolytic effects was NK cells. Furthermore, we showed that this anti-SIV and anti-HIV cytolytic effect was directed at the envelope protein and not gag proteins. Thus, NK cells have the capacity to recognizeand lysecellsexpressingSIVandHIVantigens.Thesedata support a role forNKcells in the modulation of CNS disease. Jo urna l o f NeuroViro logy (2001) 7, 11 ± 24.