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Interleukin-15 (IL-15) regulates the development and maintenance of memory CD8+ T cells. Paradoxically, we previously reported that IL-15 could enhance CD8+ T-cell responses to IL-12, a proinflammatory cytokine required for optimal priming of effector CD8+ T cells. To expand the physiological relevance of these findings, we tested IL-15 for its ability to enhance T-cell responses to bacterial CpG. Expectedly, CpG enhanced the production of IFN-γ by CD8+ T cells polyclonally activated with anti-CD3. However, addition of IL-15 to CpG-stimulated cultures led to a striking increase in IFN-γ production. The effect of CpG and IL-15 was also evident with CD8+ T cells recovered from mice infected with the parasite Trypanosoma cruzi (T. cruzi) and restimulated with antigen. The observed synergy between CpG and IL-15 occurred in an IL-12-dependent manner, and this effect could even be demonstrated in cocultures of activated CD8+ T cells and CD4+CD25+ regulatory T cells. Although IFN-γ was not essential for CpG-induced IL-12, the ability of CpG and IL-15 to act on CD8+ T cells required expression of the IFN-γ-inducible transcription factor T-bet. These data have important implications for development of vaccines and design of therapies to boost CD8+ T-cell responses to infectious agents and tumors.
Copyright © 2013 Dustin Cobb et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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VCU Microbiology and Immunology Publications