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Abstract
Proliferation 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-2Rbeta on CD8+ cells than on CD4+ cells.