Crohn disease arthropathy: antigens in synovial fluid share epitopes with strains of two species of viridans streptococci.

Background: There is evidence to suggest that Crohn disease is caused by an immunologic response to an unknown intestinal luminal antigen, probably of bacterial origin. The reported demonstration of yersinia antigen in the synovial fluid of patients with yersinosis therefore prompted a search for bacterial antigens in the synovial fluid of patients with Crohn arthropathy.
Methods: Antisera were raised in rabbits to synovial fluids obtained from seven patients with Crohn arthropathy and from seven 'control' subjects with other forms of arthropathy. These antisera were used to probe sonicates of the bacteria cultured from the gastric juice of patients with gastric Crohn disease.
Results: The antisera made from the Crohn synovial fluids, but none of those made from the controls, reacted uniquely with antigens in sonicates of strains of two species of viridans streptococci (Streptococcus parasanguis and an atypical S. oralis) isolated from four of the five patients with gastric Crohn disease.
Conclusions: These findings suggest that the arthropathy of Crohn disease and, possibly, the intestinal disease itself may involve an immunologically mediated inflammatory response to these antigens.