The effects of mesoporphyrin on experimental arthritis in mice.

The effects of mesoporphyrin, a novel porphyrin derivative, on type II collagen-induced arthritis in mice were studied. Mesoporphyrin (10-30 mg/kg) and prednisolone (5 mg/kg; reference drug) reduced the incidence and severity of type II collagen-induced arthritis in mice, as assayed by clinical observation and histopathological studies. Although both agents inhibited type II collagen-induced delayed type hypersensitivity in arthritic mice, only prednisolone inhibited humoral immunity to type II collagen. The effects of mesoporphyrin on T cell dependent allergic inflammation were examined, in order to study the mechanism by which it inhibits arthritis. Staphylococcal enterotoxin B (SEB; superantigen)-potentiated collagen-induced arthritis and sheep red blood cell-induced delayed type hypersensitivity reaction were clearly inhibited by mesoporphyrin. Moreover, the superantigen-induced CD-25 expression on T cells was inhibited by mesoporphyrin. These results indicate that mesoporphyrin inhibits type II collagen-induced arthritis by inhibiting the activation of T cells.