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. Author manuscript; available in PMC: 2010 Feb 1.
Published in final edited form as: Nat Rev Immunol. 2009 Jul;9(7):480. doi: 10.1038/nri2580

Figure 2. Direct and indirect actions of γc cytokines and TSLP on T cell expansion, homeostasis, and differentiation.

Figure 2

γc cytokines can directly influence the survival, activation, proliferation, and differentiation of T cells (see top half of the figure), as well as indirectly affecting these processes via actions on DCs, macrophages, and Treg cells (bottom half of the figure). Although IL-15 is a critical factor for memory CD8+ T cell homeostasis, it also is responsible for the recovery of naïve CD8+ T cells in lymphopenic conditions. In the absence of IL-7, IL-15 has major effects on the homeostasis of memory CD4+ T cells. Both IL-7 and TSLP are important for the survival of naïve T cells, with IL-7 playing the greater role. The action of TSLP on memory T cells has not been evaluated. IL-2, IL-4 and IL-21 are produced by activated T cells and play essential role in T cell differentiation. In addition, IL-2 and IL-15 can augment expansion of T cells upon antigen-stimulation.