Citrobacter rodentium Induces Tissue-Resident Memory CD4 T Cells.

Tissue-resident memory T cells (T cells) are a novel population of tissue-restricted antigen-specific T cells. T cells are induced by pathogens and promote host defense against secondary infections. Although T cells cannot be detected in circulation, they are the major memory CD4 and CD8 T-cell population in tissues in mice and humans. Murine models of CD8 T cells have shown that CD8 T cells maintain tissue residency via CD69 and though tumor growth factor β-dependent induction of CD103. In contrast to CD8 T cells, there are few models of CD4 T cells. Thus, much less is known about the factors regulating the induction, maintenance, and host defense functions of CD4 T cells. is known to induce IL-17 and IL-22 CD4 T cells (T17 and T22 cells, respectively). Moreover, data from IL-22 reporter mice show that most IL-22 cells in the colon 3 months after infection are CD4 T cells. This collectively suggests that may induce CD4 T cells. Here, we demonstrate that induces a population of IL-17A CD4 T cells that are tissue restricted and antigen specific, thus meeting the criteria of CD4 T cells. These cells expand and are a major source of IL-22 during secondary infection, even before the T-cell phase of the host response in primary infection. Finally, using FTY 720, which depletes circulating naive and effector T cells but not tissue-restricted T cells, we show that these CD4 T cells can promote host defense.