Distinct Roles for IL-2 and IL-15 in the Differentiation and Survival of CD8+ Effector and Memory T Cells

IL-2 provides a memory differentiation signal to CD8(+) T cells during the primary response that impacts the ability of the subsequent memory pool to mount a successful recall response. In this study, we find that although primary effector CTL development is modestly decreased in the absence of IL-2, the persistence of short-term and long-term effector memory CD8(+) T cells on pathogen clearance is greatly diminished. Furthermore, secondary challenge of CD8(+) memory T cells lacking the highavidity IL-2R results in a failure to repopulate the effector pool. The role of IL-2 in promoting effector differentiation is not shared with the highly related cytokine, IL-15. Although IL-15 supports the survival of effector CD8(+) T cells after pathogen clearance, its absence does not impair either primary or secondary effector CTL differentiation, nor does it impact the differentiation of long-term effector memory CD8(+) T cells. These findings indicate a unique role for IL-2, but not IL-15, in promoting the differentiation not only of primary effector CD8(+) T cells, but also of CD8(+) memory T cells capable of secondary effector differentiation. The Journal of Immunology, 2010, 184: 6719-6730.