in vitro generation of IFN-γ-producing Listeria-specific T cells is dependent on IFN-γ production by non-NK cells

In vitro 5-day cultures of naive spleen cells with viable Listeria monocytogenes (VLM), but not heat-killed L. monocytogenes, induced CD4+ T cells that produced IFN-gamma upon secondary antigen stimulation. The VLM-induced Listeria-specific T cells produced IFN-gamma but lacked expression of IL-2 and IL-4. To study the role of IFN-gamma in the induction of the IFN-gamma-producing T cells, we added anti-IFN-gamma mAb to the primary culture and analyzed IFN-gamma production upon secondary antigen stimulation. Addition of anti-IFN-gamma mAb to the culture suppressed generation of IFN-gamma-producing CD4+ T cells, suggesting that IFN-gamma is important in the induction of IFN-gamma-producing CD4+ T cells. Furthermore, our results showed that depletion of NK cells from spleen cells by anti-asialo GM1 antibody plus complement before culture enhanced induction of IFN-gamma-producing CD4+ T cells. Although NK cells are known to produce IFN-gamma, the results indicate that NK cell-derived IFN-gamma may not be important in induction of the Listeria-specific IFN-gamma-producing CD4+ T cells in the culture system. In addition, we demonstrated that IFN-gamma expression was high in CD4+ T cells from cultures of spleen cells with VLM at the primary culture level. These results suggest that IFN-gamma derived from T cells may enhance production of IFN-gamma by CD4+ T cells, while NK cells rather suppress the induction of IFN-gamma producing CD4+ T cells.