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In this study we describe the preparation of a Streptococcus mutans vaccine consisting of a purified polysaccharide antigen, derived from S. mutans OMZ175 serotype f, covalently coupled through reductive amination to a previously isolated 74,000-molecular-weight (74K) cell wall protein which interacts with saliva proteins (74K-SR). We also investigated the local and systemic immune response to the poly-74K-SR conjugate after oral administration of the conjugate associated with liposomes. Intragastric administration of liposome-associated poly-74K-SR conjugate in rats produced a local immunoglobulin A (IgA) response directed against the polysaccharide and the cell surface protein, whereas liposome-associated polysaccharide was unable to induce any detectable local IgA response. The antigenicity of the polysaccharide in the conjugate was not affected by the coupling reaction, while that of the cell surface protein was reduced. We showed that the immunogenicity of S. mutans polysaccharide could be improved by chemical coupling with a carrier cell surface protein. If such a conjugate were orally administered with liposomes it could constitute a potential vaccine against dental caries.

The aim of the present study was to develop an immunization procedure which preferentially stimulated the IgA system of rats, with release of IgA in secretions. Rats immunized by intragastric route with liposome-associated soluble antigen extracted from Streptococcus mutans cell wall, showed a significantly higher IgA (and IgG) response than did rats injected with the soluble antigen alone. In saliva, maximal antibody titres were obtained 11 days after the beginning of intubations for IgA, and 16 days for IgG. After a booster immunization, the secondary response occurred very quickly in saliva and, like the primary response, it was almost exclusively of the IgA class. This demonstrates, on one hand the existence of immunological memory in the IgA system and, on the other, the efficiency of liposomes as insoluble adjuvants in eliciting an immunological response.