Effect of the mouse Nramp1 genotype on the expression of IFN-gamma gene in early response to Salmonella infection.

The early interferon-gamma (IFN-gamma) response after Salmonella infection was compared in resistant and susceptible congenic mice strains differing by the allele of Nramp1. IFN-gamma gene expression in vivo was studied by quantitative reverse transcription-PCR performed from the spleen of mice challenged by Salmonella either in multiplication or in resting phase. The spleen colonisation by Salmonella in vivo was investigated and was shown to be identical in a genetically defined host, whatever the initial phase of the bacteria. However, the bacterial load of the spleen was significantly reduced in Nramp1(r) (resistant) mice compared to Nramp1(s) (susceptible) mice. The background level of IFN-gamma mRNA was higher in the spleen of resistant mice than in the susceptible mice, before infection. Interestingly, the early upregulation of IFN-gamma gene transcription, which was observed after infection with Salmonella, was reproducibly delayed in susceptible mice compared to resistant mice. Finally, the kinetics of the host IFN-gamma response seems to be Nramp1 dependent. Resistant mice present the advantage of being more prompt to express this anti-infectious cytokine gene than susceptible mice in response to Salmonella infection.