Interferon gamma (IFN-γ) production by gut-associated lymphoid tissue and spleen following oral Salmonella typhimurium challenge

Although IFN-γ has been shown to play an important role in protection against a systemic S. typhimurium challenge, the in vivo and in vitro production of this cytokine following S. typhimurium infection of the gastrointestinal tract has not been investigated. In this study, IFN-γ production by gut-associated lymphoid tissue and spleen was investigated in mice following oral challenge with S. typhimurium. Cells obtained from the Peyer's patches (PP), mesenteric lymph nodes (MLN) and spleen (Sp) of mice orally challenged with S. typhimurium were assessed for levels of IFN-γ mRNA after varying times following in vivo infection. RNA obtained from the above tissues was subjected to reverse transcription followed by PCR amplification using primers specific for murine IFN-γ. Elevated levels of IFN-γ mRNA were first detected in the PP at 6 h post-challenge. Elevated levels of IFN-γ mRNA were then detected in the MLN at 24 h and in the spleen at 4 days post-challenge. These in vivo results were in agreement with the ability of these lymphoid tissues to produce IFN-γ upon in vitro stimulation with killed S. typhimurium. Neutralization of endogenously produced IFN-γ by administration of mAb to IFN-γ completely abrogated resistance to an oral challenge of S. typhimurium. A significant difference in the percent mortality was observed between the antibody-treated and control groups. Evaluation of bacterial spread in the antibody treated group versus the control group at 4 days following oral challenge revealed higher numbers of bacteria in the spleen and liver of antibody treated mice. These results clearly show that IFN-γ is rapidly produced by gut-associated lymphoid tissue and spleen following oral S. typhimurium infection, and that endogenous production of IFN-γ is essential in host resistance to S. typhimurium.