V antigen of Yersinia pestis inhibits neutrophil chemotaxis

V antigen (V), a secreted protein encoded by the 70 kb low-calcium response plasmid of Yersinia pestis, is an essential virulence factor. In animal models, it inhibits the early host inflammatory response to infection which is associated with decreased blood and tissue levels of proinflammatory cytokine synthesis. To elucidate further the pathogenetic mechanism(s) of V, in vitrosystems are needed to measure and analyse relevant functional activities of V. We studied the effect of V on the migration of neutrophils to a chemoattractant both in vivo and in vitro. Peripheral injection of V was associated with a reduction in the number of PMN migrating into s.c. sponges and i.p. exudates. Similarly, pre-incubating human peripheral blood neutrophils with >/=ng/ml V significantly inhibited the in vitro chemotactic response to the peptide chemoattractant FMLP. The inhibitory activity of V was inactivated by heat and was neutralized by rabbit polyclonal anti-V IgG as well as by sera from mice surviving infection with Y. pestis. Recombinant polyhistidine-tagged V fusion proteins retained biological activity compared to V proteins lacking the tag. Inhibition of chemotaxis appears to be the first demonstration of an in vitro biological effect of V and may be a useful model to elucidate its molecular mechanism of action.