A salmonella typhimurium-typhi genomic chimera: A model to study vi polysaccharide capsule function in vivo

The vi capsular polysaccharide is a virulence-associated factor expressed by salmonella enterica serotype typhi but absent from virtually all other salmonella serotypes. in order to study this determinant in vivo,we characterised a vi-positive s. typhimurium (c5.507 vi +),harbouring the salmonella pathogenicity island (spi)-7,which encodes the vi locus. s. typhimurium c5.507 vi + colonised and persisted in mice at similar levels compared to the parent strain,s. typhimurium c5. however,the innate immune response to infection with c5.507 vi + and sgb1,an isogenic derivative not expressing vi,differed markedly. infection with c5.507 vi + resulted in a significant reduction in cellular trafficking of innate immune cells,including pmn and nk cells,compared to sgb1 vi - infected animals. c5.507 vi + infection stimulated reduced numbers of tnf-α,mip-2 and perforin producing cells compared to sgb1 vi -. the modulating effect associated with vi was not observed in myd88 -/- and was reduced in tlr4 -/- mice. the presence of the vi capsule also correlated with induction of the anti-inflammatory cytokine il-10 in vivo,a factor that impacted on chemotaxis and the activation of immune cells in vitro. © 2011 jansen et al.