Direct visualization of endogenous Salmonella‐specific B cells reveals a marked delay in clonal expansion and germinal center development

Abstract

CD4+ T cells and B cells are both essential for acquired immunity to Salmonella infection. It is well established that Salmonella inhibit host CD4+ T-cell responses, but a corresponding inhibitory effect on B cells is less well defined. Here, we utilize an antigen tetramer and pull-down enrichment strategy to directly visualize OVA-specific B cells in mice, as they respond to infection with Salmonella-OVA. Surprisingly, OVA-specific B-cell expansion and germinal center formation was not detected until bacteria were cleared from the host. Furthermore, Salmonella infection also actively inhibited both B- and T-cell responses to the same coinjected antigen but this did not require the presence of iNOS. The SPI2 locus has been shown to be responsible for inhibition of Salmonella-specific CD4+ T-cell responses, and an examination of SPI2-deficient bacteria demonstrated a recovery in B-cell expansion in infected mice. Together, these data suggest that Salmonella can simultaneously inhibit host B- and T-cell responses using SPI2-dependent mechanisms.

Soluble flagellin coimmunization attenuates Th1 priming to Salmonella and clearance by modulating dendritic cell activation and cytokine production

“…Coimmunization with sFliC had a dramatic impact on the induction of Th1 cells, but it was also possible this may influence B‐cell responses too. In this model, the B‐cell response to STm is atypical since there is an extensive and rapid extrafollicular response that occurs in the absence of germinal centers and the generation of high‐affinity antibody to the bacterium . The induction of the B‐cell response is T‐independent but switching requires T cells.…”

Techniques to Study Antigen-Specific B Cell Responses

“…One weakness of the flow cytometric approach is the reliance on antigens that can be readily conjugated to a fluorochrome or biotinylated. In addition to recombinant proteins and synthesized peptides, labeled polysaccharides, lipids, haptens, virus-like particles, and pseudo viruses have also been used to identify antigen-specific cells by flow cytometry (33,(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59). Further, epitope-specific B cells have been identified by screening bacteriophage-displays or microarray peptide libraries with polyclonal antibodies targeting the native antigen to select conformational epitopes that can be fused to fluorescent proteins for use in flow cytometry (47,60).…”

Salmonella Infection Enhances Erythropoietin Production by the Kidney and Liver, Which Correlates with Elevated Bacterial Burdens

“…Salmonella enterica serovar Typhimurium strain SL1344 and a variety of mutants, including BRD509 (aroA mutant) (47), BRD509-SPI2 (aroA aroD spiB mutant) (29), and BRD509-Flagellin (aroA aroD fliC fljB mutant) (18), were grown overnight in LB broth without shaking before bacterial concentrations were estimated by using a spectrophotometer (optical density at 600 nm). All mice were infected intravenously (i.v.)…”

“…In order to survive within an immunocompetent host, Salmonella has evolved multiple mechanisms to combat innate and adaptive immune responses (23)(24)(25)(26). Some of these evasion strategies rely on the expression of Salmonella pathogenicity island (SPI) genes that encode a molecular syringe to deliver effector proteins to infected cells and disrupt cellular signaling or vesicle trafficking (27)(28)(29). Salmonella can also shut down the synthesis of flagellin soon after infecting host tissues (30), most likely because this antigen serves as a target for innate and adaptive immune responses (31,32).…”