Chronic peroral immunization of conventional laboratory rats with mutans streptococci leads to stable acquired suppression of salivary antibodies

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Abstract
Prior investigations have demonstrated that salivary antibody responses to mutans streptococci are dose-dependent and temporary. The purpose of this study was to evaluate the stability of antibody suppression established by mutans streptococci. Streptococcus mutans 6715-15 was provided in food to conventional rats for 18 weeks. Antigen was withdrawn for 10 weeks and then resumed for an additional 6 weeks. Saliva and serum from nonimmunized controls and from experimental rats were tested with a quantitative enzyme-linked immunosorbent assay for IgA and IgG antibodies to whole bacterial cells and to soluble antigen. Results show that salivary antibodies were stimulated by primary peroral immunization, that IgA was the dominant isotype and that IgA antibodies were primarily directed against soluble antigen. This study also shows that immunity is not maintained, even while challenge continues, and that once suppression is established, immunized animals do not recover their ability to respond, even if exposure is stopped for 10 weeks before re-exposure.