Purification, characterization, and immunogenicity of cell-associated glucan from Streptococcus mutans

Appropriate immunization with whole cell vaccines of S mutans appear to induce antibodies that inhibit implantation of S mutans on tooth surfaces and associated dental caries. To better understand the mechanisms by which vaccination prevents S mutans implantation and dental caries, and to prepare antigens whose effectiveness and safety can be tested in animal models of caries, we set out to purify and chemically characterize the CAG of S mutans. The CAG of S mutans strain 6715 was prepared by extracting cells with potasssium hydroxide at 100 C. After neutralization and extensive washing, the water-insoluble product was characterized by a battery of chemical analyses and found to be a relatively pure glucan. The CAG was weakly immunogenic in rabbits when administered in Freund's complete adjuvant. In monkeys (M irus) immunized via the parotid duct with an aqueous solution of CAG, a definite but weak serum IgG, IgM, IgA, and salivary IgA antibody response was observed. Absorption experiments showed that the CAG induced antibodies that cross reacted with Sephadex G-25 and others that reacted with unique determinants on CAG. Retention of native antigenic determinants through the purification procedures was verified by the observations that antiserums to CAG reacted with whole cells of S mutans and by the fact that antiserums to S mutans cells reacted with CAG.