Analysis of heart‐reactive antibodies induced in rabbits by immunization with Streptococcus mutans

The induction of antibodies that react with human heart muscle in rabbits immunized with Streptococcus mutans and related organisms has been investigated in order to re‐examine the reported antigenic cross‐reactivity between the major cell wall protein antigen I/II of S. mutans and heart tissue. Serum from 2 of 8 rabbits hyperimmunized with whole cells of S. mutans, S. sohrinus, S. rattus, or V. mitis, assayed by immunofluorescence and radioimmunoassay, revealed antibodies reactive with sarcolemma that could be attributed to immunization. Antisera raised against several crude and purified antigens of S. mutans did not reveal heart‐reactive antibodies, that could be attributed to antigenic similarity between heart and these antigens. An assay designed to detect antibodies that could simultaneously bind to both heart and antigen I/II of S. mutans failed to reveal cross‐reactivity due to this antigen, although antibodies separately expressing these binding activities were demonstrable. IgM rheumatoid factor was elevated in several antiscra to S. mutans, and could have contributed to some previous observations ascribed to antigenic cross‐reactivity between S. Mutans and human heart muscle.