Anti-recombinant V antigen serum promotes uptake of Yersinia enterocolitica serotype O8 by macrophages

Phagocytosis resistance even in the presence of opsonizing antibodies is a key feature of pathogenic Yersinia spp. Nevertheless, antibodies against th e secreted V antigen and the outer membrane protein YadA are known to media te protection against Y. enterocolitica serotype O8 in a mouse model with i ntravenous infection. To investigate the impact of anti-V antigen serum on the interaction of Y. enterocolitica and phagocytic cells, gentamicin kill assays and immunofluorescence staining were performed. In contrast to anti- YadA, the presence of V antigen-specific antibodies resulted in an increase d uptake of yersiniae by macrophages. The inhibition of phagocytosis by cyt ochalasin D suppressed the anti-V antigen-mediated uptake. The uptake-promo ting effect of anti-V antigen was more distinct for macrophages than for po lymorphonuclear leukocytes. The findings of the passive immunization experi ments using an orogastric infection model were in agreement with those of c ell-culture experiments. In the first 3 days of infection both antisera exh ibit no protective effect on the multiplication of the bacteria in the Peye r's patches. Only mice passively immunized with anti-V antigen survived let hal oral infections with Y. enterocolitica serotype O8. taken together, the results support the assumption that V antigen might be part of the translo cation apparatus and that anti-V antigen inhibits the Yop translocation. In addition, antisera against in-frame-deleted recombinant V antigen were gen erated. Protection experiments using these antisera suggested that the type -specific region (amino acids 235-232) of the V antigen might not be a prot ective epitope.