Methods: Luminex screening of cytokine levels was used to identify cytokines regulated by S. enterica in immortalized B cell lines. To identify and characterize S. enterica genetic regions important in regulating the production of these cytokines, we used comparative genomics of S. enterica serovars, gene knockout mutants, and functional testing in cultured cells. Furthermore, C57BL/6 mice were used as a model for infection to test the effects of the putative factors in vivo.
Results: Salmonella enterica serovar Typhimurium induced the anti-inflammatory cytokines interleukin-10 (IL-10) and interleukin-1 receptor antagonist (IL-1RA) in immortalized cultured B cells. A previously uncharacterized gene, designated sara (Salmonella anti-inflammatory response activator) was determined to only be present in IL-10 inducing serovars of S. enterica. When this gene was deleted, S. Typhimurium was unable to induce IL-10, demonstrating that the protein is required for the IL-10 inducing phenotype. In addition, sara mutants showed altered intracellular survival and replication. These intracellular phenotypes were not restored upon addition of IL-10 to the media of Dsara-infected cells, indicating additional unidentified effects of SARA beyond cytokine regulation. To see the effect of SARA during a full host infection, I compared the amount of colony forming units (CFUs) in the spleen after infection with either wildtype Salmonella or Dsara. The Dsara S. Typhimurium showed consistently higher spleen CFU counts.
Conclusion: Together, these data suggest that SARA contributes to Salmonella-driven manipulation of the delicate balance of pro- and anti-inflammatory host immune responses. These findings are likely relevant to the ability of people to respond and clear Salmonella infections, and may have longer term consequences for the host immune response.
D. Ko, None