A radioimmunoassay for serum and gingival crevicular fluid antibodies to a purified protein of Streptococcus mutans.

A solid-phase radioimmunoassay was developed to measure serum IgG antibodies to a purified protein antigen I/II prepared from Streptococcus mutans. The assay was specific to this antigen and significant binding of 125I-radiolabelled antiserum was found only in sera from rhesus monkeys immunized with the antigen I/II but not in sham-immunized monkeys or those immunized with streptococcal antigen III. A very significant correlation was found in serum IgG antibodies tested by the radioimmunoassay and an immunofluorescent technique (r = 0.88, P less than 0.001). The sensitivity of the double-layer radioimmunoassay was increased 10 times by the addition of a third antibody layer and this enabled gingival crevicular fluid antibodies to be measured. Comparison of paired samples of serum and crevicular fluid revealed a very significant correlation between IgG antibodies to streptococcal antigen I/II in the the two fluids (P less than 0.001). These findings suggest that serum antibodies can reach the tooth surface via gingival crevicular fluid.