Potent and Selective Stimulation of Memory-Phenotype CD8+ T Cells In Vivo by IL-15

AbstractProliferation of memory-phenotype (CD44hi) CD8+ cells induced by infectious agents can be mimicked by injection of type I interferon (IFN I) and by IFN I–inducing agents such as lipopolysaccharide and Poly I:C; such proliferation does not affect naive T cells and appears to be TCR independent. Since IFN I inhibits proliferation in vitro, IFN I–induced proliferation of CD8+ cells in vivo presumably occurs indirectly through production of secondary cytokines, e.g., interleukin-2 (IL-2) or IL-15. We show here that, unlike IL-2, IL-15 closely mimics the effects of IFN I in causing strong and selective stimulation of memory-phenotype CD44hi CD8+ (but not CD4+) cells in vivo; similar specificity applies to purified T cells in vitro and correlates with much higher expression of IL-2Rβ on CD8+ cells than on CD4+ cells