Roles of V antigen in promoting virulence and immunity in yersiniae

It is established that yersiniae harboring an approximately 45-megadalton Vwa-plasmid can produce V and W antigens (Vwa+), and that sera containing anti-V provides passive protection to mice against Yersinia pestis. This observation was extended by the use of monospecific anti-V prepared by injecting rabbits with partially purified V, absorption of antisera with a Vwa- extract, and then separation of gamma-globulin by traditional processes of fractionation or by affinity chromatography. These preparations provided passive protection against 10 minimum lethal doses of virulent Y. pestis KIM, Yersinia pseudotuberculosis PB1, and Yersinia enterocolitica WA. Kinetics of elimination of these Vwa+ yersiniae from organs and blood of passively immunized mice closely resembled those of avirulent Vwa- mutants from normal mice. Injection into mice of sterile crude extracts of Y. pseudotuberculosis PB1 containing V promoted significant survival and retention of Vwa- mutants of Y. pestis, Y. pseudotuberculosis, and Y. enterocolitica. This effect was eliminated by the removal of V before injection by precipitation with monospecific antibody. These results indicate that V antigen per se is the major virulence factor mediated by Vwa-plasmids.