IL-15 is a novel growth factor for murine γδ T cells induced by Salmonella infection

We have previously shown evidence for the early recruitment of γδ T cells during the disease course of primary infections with Listeria monocytogenes or Salmonella choleraesuis in mice. Since γδ T cells at this stage of the disease do not produce IL-2, the growth factor for the γδ T cells remains unknown. IL-15 is a novel cytokine that uses β- and γ-chain of IL-2R for signal transduction, and is produced by activated monocytes/macrophages. In this study, we investigated the proliferative activity of IL-15 for γδ T cells appearing after primary infection with S. choleraesuis 31N-1. The γδ T cells, which expressed β- and γ-chains of IL-2R, proliferated in the presence of rIL-15 and produced appreciable levels of γ-IFN and IL-4. Addition of anti-IL-2Rβ mAb significantly inhibited the IL-15-induced proliferation of the γδ T cells. Furthermore, the γδ T cells produced γ-IFN in response to monocyte/macrophage cell line, J774A.1 infected with S. choleraesuis, which expressed an abundant level of IL-15 mRNA. This cytokine production was inhibited significantly by anti-IL-15 Ab. Taken together, these results suggest that IL-15 derived from infected macrophages may contribute to the early activation of γδ T cells during salmonellosis.