Interleukin-17A Promotes CD8+ T cell Cytotoxicity to Facilitate West Nile Virus Clearance

CD8(+) T cells are crucial components of immunity and play a vital role in recovery from West Nile virus (WNV) infection. Here, we identify a previously unrecognized function of interleukin-17A (IL-17A) in inducing cytotoxic-mediator gene expression and promoting CD8(+) T cell cytotoxicity against WNV infection in mice. We find that IL-17A-deficient (Il17a(-/-)) mice are more susceptible to WNV infection and develop a higher viral burden than wild-type (WT) mice. Interestingly, the CD8(+) T cells isolated from Il17a(-/-) mice are less cytotoxic and express lower levels of cytotoxic-mediator genes, which can be restored by supplying recombinant IL-17A in vitro and in vivo Importantly, treatment of WNV-infected mice with recombinant IL-17A, as late as day 6 postinfection, significantly reduces the viral burden and increases survival, suggesting a therapeutic potential for IL-17A. In conclusion, we report a novel function of IL-17A in promoting CD8(+) T cell cytotoxicity, which may have broad implications in other microbial infections and cancers. IMPORTANCE: Interleukin-17A (IL-17A) and CD8(+) T cells regulate diverse immune functions in microbial infections, malignancies, and autoimmune diseases. IL-17A is a proinflammatory cytokine produced by diverse cell types, while CD8(+) T cells (known as cytotoxic T cells) are major cells that provide immunity against intracellular pathogens. Previous studies have demonstrated a crucial role of CD8(+) T cells in recovery from West Nile virus (WNV) infection. However, the role of IL-17A during WNV infection remains unclear. Here, we demonstrate that IL-17A protects mice from lethal WNV infection by promoting CD8(+) T cell-mediated clearance of WNV. In addition, treatment of WNV-infected mice with recombinant IL-17A reduces the viral burden and increases survival of mice, suggesting a potential therapeutic. This novel IL-17A-CD8(+) T cell axis may also have broad implications for immunity to other microbial infections and cancers, where CD8(+) T cell functions are crucial