Immunization of Macaca fascicularis (Macaca irus) monkeys with Streptococcus mutans: specificity of antibody responses in saliva

M fascicularis monkeys were immunized subcutaneously in the vicinity of the major salivary glands and by retrograde infusion into the parotid duct, with a vaccine containing Formalin-killed S mutans strain 6715 cells and culture-fluid antigens. Indirect immunofluorescent staining was used to titrate and classify antibodies. Subcutaneous immunization induced only a serum response, whereas intraductal infusion stimulated both an IgA antibody response in the parotid fluid and a serum response. Immunized and nonimmunized control groups were orally infected with S mutans strain 6715. The establishment in dental plaque was quantitated by recovery of the infecting organism on selective media and by immunofluorescent staining of plaque smears taken from individual tooth surfaces. The establishment of S mutans strain 6715 was noticeably inhibited in immune monkeys. Immunofluorescent assays for antibody also showed that serum and parotid fluid containing serum IgA antibodies cross reacted with other d serotype and a serotype strains but not representative b and c strains. Immune and control groups were then orally infected with S mutans strain GS-5, a c serotype strain, and no inhibition in establishment was detected of the non-cross-reacting type c organism in the immune group. A latter series of booster immunizations via the intraductal route resulted in a significant decrease in parotid fluid flow. Histological investigations showed inflammatory cell infiltration and replacement of epithelium by connective tissue in the glands from immunized monkeys. A separate group of monkeys, younger than the first, was immunized with the same vaccine via the duct only. In this group, immunizations were given at shorter intervals, but the immunization response was similar to that observed in the first group. The investigations reviewed here and new experiments reported show that immunization of monkeys with S mutan strain 6715 via the parotid duct elicited a reproducible IgA antibody response in the parotid fluid as well as a serum antibody response. Inhibition of colonization on tooth surfaces in immune monkeys showed specificity for the immunizing strain suggesting that inhibition was antibody mediated.