Salmonella SopB suppresses post-transcriptionally regulated cytokine release to reduce early tissue inflammation and delay disease progression.

Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) manipulates cellular processes through the translocation of effector molecules into the host cell cytosol. Using a recently established neonatal S. Typhimurium infection model, we provide functional insights into how Salmonella outer protein B (SopB) suppresses early mucosal tissue inflammation and prolongs host survival. Mechanistically, SopB prevents a disintegrin and metalloprotease 17 (ADAM17) activation, plasma membrane translocation and the release of membrane-bound TNFα from enterocytes and reduces epithelial secretion of IL-18 via mTOR-controlled secretory autophagy. This abolishes the early epithelial transcriptional response and reduces immune cell recruitment and programmed cell death-mediated mucosal barrier disruption delaying disease progression. The immunosuppressive effect of SopB is independent of the C-terminally encoded phosphatidylinositol phosphatase and phosphotransferase activity but requires an intact N-terminal domain. Also, it is restricted to the neonatal mouse model characterised by Salmonella pathogenicity island (SPI)1 type 3 secretion system (T3SS)-dependent enterocyte invasion-driven mucosal translocation. Thus, here we demonstrate that SopB suppresses the early, post-transcriptional regulation of epithelial cytokine release in an inositol phosphatase-independent manner likely promoting pathogen transmission.