Analysis of the Yersinia enterocolitica 0:8 V antigen for cross protectivity

The plasmid encoded V antigen (Vag) of pathogenic Yersinia spp. is a major virulence factor as well as a protective immunogen. Recently, two main types of Vag, represented by either Yersinia enterocolitica 0:8 or Yersinia pseudotuberculosis, have been identified and it has been suggested, that antibodies generated against one type are unable to protect against Yersinia spp. carrying the other type. By using a recombinant Vag (rVagHis) of the Y. enterocolitica 0:8 type we show here, that actively immunized mice were completely protected against challenge with both, Y. enterocolitica 0:8 and Y. pseudotuberculosis serotype III. In addition, passive protection was possible with polyclonal rabbit anti-rVagHisIgG. However, while a single antibody dose (200 microgramg) was sufficient to protect against challenge with Y. enterocolitica 0:8, repetitive injections at intervals of 2 to 3 days were needed to protect against challenge with Y. pseudotuberculosis III. The apparent difference in protection correlated with a rapid disappearance of anti-rVagHisIgG from the circulation by days 3 to 4. The data therefore indicate, that expression of distinct types of Vag by Yersinia spp. does not necessarily exclude immunoprotection in mice immunized with the other type of Vag. It rather appears, that differences in immunoprotection between Yersinia species relate to the amount of cross-protective antibody. Finally, as revealed by the lack of complement-mediated killing and the lack of immunostaining of Yersiniae with anti-rVagHisantibodies, evidence is provided to indicate that immunoprotection does not occur via opsonisation or complement lysis.