Amino acid substitutions in LcrV at putative sites of interaction with toll-like receptor 2 do not affect the virulence of Yersinia pestis

LcrV, a component of the type III secretion system (T3SS) translocon in Yersinia pestis, has been concerned in suppressing inflammation through Toll-like receptor 2 (TLR2) by inducing expression of the anti-inflammatory cytokine interleukin-10 (IL-10). Previous studies have reported that LcrV aa E33, E34, K42 and/or E204 and E205 were important for interactions with TLR2 in vitro. While, recently there have been conflicting reports doubting this interaction and its importance in vivo. To further investigate the role of these residues, we replaced the wild-type lcrV gene on the pCD1Ap virulence plasmid of Y. pestis with lcrV2345 gene, which encodes a mutant protein by substituting all five of the amino acid residues with glutamine. The characteristics of the wild-type LcrV and mutant LcrV2345 were evaluated in tissue culture and mice. When purified protein was incubated with HEK293 cells synthesizing human TLR2 with or without CD14, LcrV2345 induced higher levels of IL-8 than wild-type LcrV, indicating that the LcrV2345 was not impaired in its ability to interact with TLR2. LcrV2345 stimulated higher levels of tumor necrosis factor-alpha (TNF-α) production than LcrV in J774A.1 cells, while neither protein elicited significant levels of IL-10. We also found there was no statistically significant difference in virulence between strains with wild-type LcrV and with mutated LcrV2345 administered by either subcutaneous or intranasal route in mice. Additionally, there were no discernible differences in survival kinetics. Serum levels of cytokines, such as IL-10 and TNF-α, bacterial burden, and the extent of organ inflammation were also indistinguishable in both strains. Our data confirm that immunomodulation mediated by LcrV/TLR2 interactions does not play a significant role in the pathogenicity of Y. pestis.