TCR alpha beta+ CD4- CD8- T cells differentiate extrathymically in an lck-independent manner and participate in early response against Listeria monocytogenes infection through interferon-gamma production.

T-cell receptor (TCR) alpha beta+ CD4- CD8- (double-negative; DN) T cells appear in the peritoneal cavity at an early stage of intraperitoneal (i.p.) infection with the intracellular pathogen Listeria monocytogenes. In the present report, we analysed the developmental pathway and functions of the TCR alpha beta+ DN T cells using the L. monocytogenes infection system. The TCR alpha beta+ DN T cells appeared in the peritoneal cavity after L. monocytogenes i.p. infection in adult-thymectomized lethally irradiated bone marrow chimeras and p56lck-deficient mice. The results demonstrated that the TCR alpha beta+ DN T cells can develop extrathymically in a p56lck-independent manner. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the TCR alpha beta+ DN T cells expressed genes for interferon-gamma (IFN-gamma), the macrophage chemotactic factors MCP-1 and Eta-1, and granulocyte-macrophage colony-stimulating factor (GM-CSF) but lacked expression of genes for interleukin-2 (IL-2), IL-4 and IL-10. As expected from the RT-PCR analysis, the TCR alpha beta+ DN T cells produced IFN-gamma in response to anti-TCR beta monoclonal antibody (mAb), anti-CD3 mAb and L. monocytogenes-infected macrophages but IL-4 was undetectable after the stimulation. Furthermore, the intracellular cytokine staining analysis demonstrated that approximately half of the TCR alpha beta+ DN T cells detectable at the early stage of L. monocytogenes infection were IFN-gamma-producing cells. All of the results suggest that the TCR alpha beta+ DN T cells develop through a unique extrathymic p56lck-independent pathway and participate in early protection against bacterial infection through activation and accumulation of macrophages.