Immunogenicity of Bacteroides isolated from mice: relationship between immunogenicity and cell wall antigens.

Three different strains of Bacteroides were isolated from feces and cecal contents of mice. The immunogenicity of the strains was determined by measuring the serum agglutinin titers after intraperitoneal antigen injection. There were marked differences in quantity and quality of produced antibodies among the three strains. One strain (2-2) induced low antibody titers in both the primary and secondary responses, and a significant 2-mercaptoethanol (2-ME)-resistant antibody production occurred. Another strain (Y) induced low antibody titers in the primary response and high titers in the secondary response, but 2-ME-resistant antibody production did not occur. The third strain (2-4) induced very high antibody titers in both the responses, and a large amount of 2-ME-resistant antibody production occurred. Further, heat-ethanol-treated strain Y induced only immunoglobulin M antibody, but periodate-treated strain Y induced no antibody. Heat-ethanol- or periodate-treated strain 2-4 induced immunoglobulin M or G antibody, respectively. These observations suggest that the surface antigens of the two strains are distinctly different: the antigen of strain Y would be mostly O-antigen, whereas those of strain 2-4 would be O-antigen and protein moieties.