Serum antibody responses to Streptococcus mutans antigens in humans systemically infected with oral streptococci

Sera from patients with subacute bacterial endocarditis (SBE) due to Streptococcus mutans or other oral streptococci and from normal subjects were assayed by enzyme‐linked immunosorbent assay for antibodies to defined S. mutans antigens. Antibodies of IgG and IgA isotypes to Ag I/II and Ag III were greatly elevated in S. mutans‐SBE sera, and the IgA antibodies in 3 sera included both polymeric and monomeric forms. Elevated IgM and IgG anti‐lipoteichoic acid and IgG and IgA anti‐serotype c polysaccharide antibodies were also found. The sera of 4 of 6 patients infected with other oral streptococci also displayed antibodies to S. mutans Ag I/II. Sera of 3 patients infected with Streptococcus mitis or Streptococcus orallis. but none of the s. mutans‐infected cases, showed elevated antibodies to human heart sarcolemma, and all SBE sera had elevated rheumatoid factor. These results suggest that the known surface protein antigens of S. mutans are immunodominant in humans, and are not likely to be heart cross‐reactive.