Class-specific immune response to Yersinia enterocolitica serotype O9 antigens as determined by enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay (ELISA) using lipopolysaccharide (S-LPS) as the antigen was used to analyze the antibody response in rabbits orogastrically and intravenously infected with virulent (plasmid-bearing) Yersinia enterocolitica O9 strains (pYV+) and with the avirulent (plasmid-cured) derivatives (pYV-). A significative response of immunoglobulin G (IgG), IgA, and IgM antibodies against the S-LPS antigen was evident in sera from the rabbits orogastrically infected with pYV+ strains. This immune response was stronger and persisted longer than those obtained with the corresponding pYV- strains. In contrast, few differences were observed in the titers and evolution of IgG, IgA, and IgM antibodies against the S-LPS antigen in rabbits intravenously infected with pYV+ and pYV- strains. These results suggest that the necessity of the virulence plasmid for the establishment of infection by Y. enterocolitica serotype O9 is conditioned by the infection route used. When the S-LPS ELISA was compared with the radial immunodiffusion test using the native hapten as the antigen, the results showed that the ELISA technique was more sensitive. However, only those sera obtained between 2 and 8 weeks postinfection from rabbits intravenously infected with plasmid-bearing strains were positive in the radial immunodiffusion test.