Relationship between immune system and gram-negative bacteria, binding of Salmonella pullorum-gallinarum to chicken lymphocytes

FimH alleles direct preferential binding of Salmonella to distinct mammalian cells or to avian cells

This study aimed to determine whether allelic variants of the FimH adhesin from Salmonella enterica confer differential bacterial binding to different types of mammalian cells [murine bone marrow-derived dendritic cells (DCs) and HEp-2 cells] and chicken leukocytes. Although the type 1 fimbriated S. enterica serovar Typhimurium strains AJB3 (SR-11 derivative) and SL1344 both aggregated yeast cells, only the former bound efficiently to DCs and HEp-2 cells. Type 1 fimbriae-mediated binding to DCs having previously been shown to require the FimH adhesin and to be inhibited by mannose, FimH sequences from strains SL1344 and AJB3 were compared and found to differ by only one residue, asparagine 158 in SL1344 being replaced by a tyrosine in AJB3. The importance of residue 158 for FimH-mediated binding was further confirmed in recombinant Escherichia coli expressing S. enterica type 1 fimbriae with a variety of substitutions engineered at this position. Additional studies with the 'non-adhesive' FimH of a type 2 fimbriated S. enterica serovar Gallinarum showed that this FimH did not mediate bacterial binding to murine DCs or HEp-2 cells. However, the type 2 FimH significantly improved bacterial adhesion to chicken leukocytes, in comparison to the type 1 FimH of strain AJB3, attributing for the first time a function to the type 2 fimbriae of S. enterica. Consequently, our data show that allelic variation of the S. enterica FimH adhesin directs not only host-cell-specific recognition, but also distinctive binding to mammalian or avian receptors. It is most relevant that this allele-specific binding profile parallels the host specificity of the respective FimH-expressing pathogen.