Cytokine-induced survival of activated T cellsin vitroandin vivo

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Abstract
Many antigen-specific T cells die after exposure to antigen in animals. These cells also die if they are isolated from animals shortly after activation and cultured. Various cytokines were tested for their ability to interfere with thisin vitrodeath. Surprisingly, tumor necrosis factor α and other inflammatory cytokines did not prevent thein vitrodeath of activated T cells, even though these cytokines do prevent activated T cell death in animals. Therefore, the inflammatory cytokines probably act on T cellsin vivovia an intermediary factor. Four cytokines, interleukin (IL)-2, IL-4, IL-7, and IL-15, did prevent activated T cell deathin vitro, with IL-4 and IL-15 more effective than IL-2 or IL-7. These cytokines share a component of their receptors, the common γ chain, γc. Therefore, their collective ability to protect activated T cells from death may be mediated by signals involving γc. To assess their activityin vivo, two of the cytokines, IL-2 and IL-4, were expressed in animals at local sites of superantigen responses. Both cytokines increased the numbers of T cells found at the local sites 14 days later. Interleukin 4 was more effective than IL-2, even though IL-2 stimulates T cell proliferation better than IL-4. This result suggested that IL-4 and related cytokines can promote T cell survivalin vivoas well asin vitro. The ability of these cytokines to prevent the death of activated T cells may be important at certain stages of immune responses in animals.

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