Distinct roles of CD4(+ )T cell subpopulations in retroviral immunity: lessons from the Friend virus mouse model

It is well established that CD4(+ )T cells play an important role in immunity to infections with retroviruses such as HIV. However, in recent years CD4(+ )T cells have been subdivided into several distinct populations that are differentially regulated and perform widely varying functions. Thus, it is important to delineate the separate roles of these subsets, which range from direct antiviral activities to potent immunosuppression. In this review, we discuss contributions from the major CD4(+ )T cell subpopulations to retroviral immunity. Fundamental concepts obtained from studies on numerous viral infections are presented along with a more detailed analysis of studies on murine Friend virus. The relevance of these studies to HIV immunology and immunotherapy is reviewed.