V-ANTIGEN OF YERSINIA-PESTIS INHIBITS NEUTROPHIL CHEMOTAXIS

V antigen (V), a secreted protein encoded by the 70kb low-calcium resp onse plasmid of Yersinia pestis, is an essential virulence factor. In animal models, it inhibits the early host inflammatory response to inf ection which is associated with decreased blood and tissue levels of p roinflammatory cytokine synthesis. To elucidate further the pathogenet ic mechanism(s) of V, in vitro systems are needed to measure and analy se 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 th e number of PMN migrating into s.c. sponges and i.p. exudates. Similar ly, pre-incubating human peripheral blood neutrophils with greater tha n or equal to 1 ng/ml V significantly inhibited the in vitro chemotact ic response to the peptide chemoattractant FMLP. The inhibitory activi ty of V was inactivated by heat and was neutralized by rabbit polyclon al anti-V IgG as well as by sera from mice surviving infection with Y. pestis. Recombinant polyhistidine-tagged V fusion proteins retained b iological activity compared to V proteins lacking the tag. Inhibition of chemotaxis appears to be the first demonstration of an in vitro bio logical effect of V and may be a useful model to elucidate its molecul ar mechanism of action.