Experimental immunization of rats with a Streptococcus mutans 59-kilodalton glucan-binding protein protects against dental caries.

Glucan-binding proteins (GBPs) are theoretically important in the molecular pathogenesis of dental caries caused by Streptococcus mutans. The present study evaluated the ability of antibody induced by the S. mutans 59-kDa GBP (GBP59) to affect dental caries caused by experimental infection with S. mutans in a rodent model. Groups of 20-day-old rats were injected twice at 9-day intervals subcutaneously in the salivary gland vicinity with GBP59, glucosyltransferase (GTF), or phosphate-buffered saline (sham injection), each incorporated in an adjuvant. Two weeks after the second injection, GBP59- and GTF-injected rats contained significant levels of salivary immunoglobulin A and serum immunoglobulin G antibody to the respective injected antigens. However, cross-reacting antibody to S. mutans GTF or GBP59 was not induced by the respective antigen. Rats were then orally infected with S. mutans. After 71 days of infection, GBP59- and GTF-injected groups had smaller numbers of S. mutans on their molar surfaces, compared with the sham-injected infected group. Total, sulcal, and smooth-surface molar caries in the GBP59- and GTF-immunized S. mutans-infected groups were each significantly lower (P < or = 0.003) than the respective measures of caries in the sham injected infected group. The results of this investigation demonstrate that immunization with S. mutans GBP59 induces an immune response in rats that can interfere with the accumulation of S. mutans and can reduce the level of dental caries caused by this cariogenic streptococcus. Furthermore, the protective immunity induced by either GBP59 or GTF appears to result from antibodies to independent epitopes since these two S. mutans components do not have a close antigenic relationship.