Objective. It has been postulated that superantigens might play a role in the human rheumatic diseases, by activation of self‐reactive T cells or by induction of autoantibodies. The Mycoplasma arthritidis superantigen MAM, which is derived from a naturally occurring murine arthitogenic mycoplasma, uses certain Vβ chains of the murine T cell receptor (TCR) that have been proposed to be involved in murine collagen‐induced arthritis (CIA). The present study was designed to determine whether MAM influences the course of arthritis mediated by immunization with porcine type II collagen (PII).

Methods. MAM or phosphate buffered saline (PBS) was injected locally or systemically into mice convalescing from CIA or mice suboptimally immunized with collagen.

Results. In contrast to PBS, MAM caused an exacerbation of arthritis in mice that were recovering from CIA. MAM also triggered arthritis onset in mice that had been suboptimally immunized with PII up to 160 days previously. Injection of MAM during the onset phase of CIA also triggered and enhanced the severity of arthritis in mice given low doses of PII.

Conclusion. MAM can both trigger and exacerbate murine autoimmune arthritis induced by immunization with type II collagen. Since T cells bearing the same Vβ TCRs as are used by MAM have been found to comprise a major portion of the activated cells in the synovial tissue of patients with rheumatoid arthritis, it is possible that superantigens similar to MAM may play a role in this human disease.