Survival analysis and microarray profiling identify Cd40 as a candidate for the Salmonella susceptibility locus, Ity5.

The outcome of infection with Salmonella Typhimurium in mouse models of human typhoid fever is dependent upon a coordinated complex immune response. A panel of recombinant congenic strains (RCS) derived from reciprocal backcross of A/J and C57BL/6J mice was screened for their susceptibility to Salmonella infection and two susceptibility loci, Ity4 (Immunity to Typhimurium locus 4) and Ity5, were identified. We validated Ity5 in a genetic environment free of the impact of Ity4 using a cross between A/J and 129S6. Using a time-series analysis of genome-wide transcription during infection, comparing A/J with AcB60 mice having a C57BL/6J-derived Ity5 interval, we have identified the differential expression of the positional candidate gene Cd40, Cd40-associated signaling pathways, and the differential expression of numerous genes expressed in neutrophils. CD40 is known to coordinate T cell-dependent B-cell responses and myeloid cell activation. In fact, CD40 signaling is altered in A/J mice as seen by impaired IgM upregulation during infection, decreased Ig class switching, neutropenia, reduced granulocyte recruitment in response to infection and inflammation, and decreased ERK1/2 activity. These results suggest that altered CD40 signaling and granulocyte recruitment in response to infection are responsible for the Ity5-associated Salmonella susceptibility of A/J mice.

Impact of Usp18 and IFN signaling in Salmonella-induced typhlitis.

In humans, Salmonella infection causes two major clinical diseases, typhoid fever and a self-limiting gastro-enteritidis. Salmonella transmission occurs by the fecal-oral route and the interactions between the bacteria and the digestive tract epithelium are central to the outcome of the infection. Using a mouse model of typhoid fever, we previously identified a mutation in USP18 affecting type I interferon (IFN) signaling resulting in increased susceptibility to systemic Salmonella infection. In this study, we demonstrate the effects of this mutation during the early response to Salmonella using a model of typhlitis. Mutant Usp18 mice showed a minimal inflammatory response early after Salmonella Typhimurium infection that was associated with low pathologic scores and low IFN-γ production. This resulted in an increased interaction of Salmonella with the cecal epithelium and earlier systemic dissemination of the bacteria. The global transcriptional signature in the cecum of mouse during Salmonella infection showed normal expression of tissue specific genes and upregulation of type I IFN pathway in mutant mice. In control mice, there was a significant over-representation of genes involved in cellular recruitment and antibacterial activity paralleling the histopathological features. These results show the impact of USP18 in the development of Salmonella-induced typhlitis.