This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The role of SIV-specific cellular immune responses in maintaining nonpathogenic SIV infection in sooty mangabeys is being investigated in SIV-infected sooty mangabeys using Elispot and intracellular cytokine staining assays as well as by in vivo CD8-positive T lymphocyte depletion studies.