Salmonella typhimurium induces IFN-γ production in murine splenocytes: Role of natural killer cells and macrophages

IFN-γ is a cytokine known to play an important role in host defense against Salmonella typhimurium. The lymphoid cells required for in vitro production of IFN-γ after S. typhimurium stimulation of mouse spleen cells was investigated. Spleen cells depleted of cells bearing NK1.1, asialo GM₁, Thy 1.2, or CD5 resulted in a significant reduction in IFN-γ production after stimulation with S. typhimurium. In contrast, Con A-induced IFN-γ production was only slightly reduced after depletion of NK1.1- or asialo GM₁-bearing cells. Spleen cells from SCID mice produced elevated levels of IFN-γ after stimulation with S. typhimurium. IFN-γ production by SCID spleen cells was dependent upon asialo GM₁₊ T cells, suggesting that NK cells were the cells producing IFN-γ in response to S. typhimurium. Splenic adherent cells were required for optimal IFN-γ production. However, direct contact between the adherent and nylon wool nonadherent (NWNA) cell populations was not essential. IFN-γ production was observed when the adherent and NWNA cell populations were physically separated or when supernatant from S. typhimurium-stimulated adherent cells was added to NWNA cells. Optimal IFN-γ production was dependent on the presence of TNF-α, inasmuch as addition of antibody to TNF-α to spleen cell or NWNA cell cultures significantly reduced IFN-γ production. However, addition of rTNF-α did not induce IFN-γ production by NWNA cells. These findings document the existence of a T-independent mechanism for early IFN-γ production in response to S. typhimurium, and show that TNF-α is necessary but not sufficient for the production of IFN-γ.