Specificity of secretory antibodies to bacterial immunogens

The present investigation examined the specificity of the salivary immune response of axenic and conventional mice to topically administered Salmonella typhi, S. gallinarum, and S. typhimurium. Specific antibacterial antibodies were determined by passive hemagglutination and bacterial agglutination. Reciprocal antibody titers up to 320 were detected in saliva from mice immunized and assayed with homologous antigens. Antibodies to heterologous immunogens exhibited lower mean titers of 10 to 20 under identical conditions. High concentrations of specific antibodies to the somatic (O) antigen were detected in the saliva of mice administered these microorganisms; however, no significant differences in serum antibody levels were detectable after oral immunization. Only low levels of specific antiflagellar (H) antibodies were demonstrated in the saliva of immunized mice, whereas mean reciprocal titers of 20 were observed in the serum. Antibodies to the Vi antigen of S. typhi were detected in the saliva and serum of only those mice administered formalin-treated S. typhi. Examination of the classes of antibody elicited by these organisms indicated that immunoglobulin A (IgA) was the predominant class in saliva against the O antigens. The salivary response to the H antigens was comprised of both IgG and IgA, whereas the specific serum immunoglobulins were consistent with a primary humoral immune reaction. Local antibodies formed in response to the Vi antigen were exclusively IgG. Serum immunoglobulins produced after peroral administration of the somatic and virulence antigens were limited to the IgM class.