The roles of innate T cells in bacterial infection

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Innate T cells are defined as(1) cells that develop in the thymus under different signal pathways from conventional T cells,(2) cells that express an activated and/or memory T-cell phenotype and exhibit immediate effector functions.(3) cells that includd y6 T cells, memory phenotype(MP) CD44^<hlgh> CD62L^<low> CD4^+ and CD8^+ T cells. Innate y6 T cells already differentiate into interleukin(IL)-li-producing cells within the fetal thymus. HESl plays a role in regulating differentiation of IL-li producing y6 T cells in thymus and" naturally occurring y6 T cells" play a protective role in the lung at very early stage after systemic infection with Mycobacterium bovis BCG. We further found that IL-lsKo mice are highly susceptible to Listeria monocytogenes and bystander proliferation of the innate CD8^+ T cells induced by L. monocytogenes was impaired in the absence of IL-Is. These results suggested that IL-Is plays an important role in the maintenance and functions of innate CD8^+ T cells, which participate in innate host defense mechanisms. We also found that CDsoLKO mice are highly susceptible to L. monocytogenes infection accompanied by a marked decrease in innate MP IFN-y+ CD4+ T cells at an early stage after infection. These findings suggested that a potential role of CDsoL in activation of innate CD4^+ T cells at an early stage after bacterial in fection.