Crohn's disease, sarcoidosis and rheumatoid arthritis: Evidence for mycobacterial aetiology

The pathogenesis of Crohn's disease, sarcoidosis and rheumatoid arthritis involves immunopathology that may be caused by a mycobacterial infection. Both Crohn's disease and sarcoidosis are granulomatous diseases with some similarities to forms of tuberculosis. Mycobacterium paratuberculosis has been specifically isolated from Crohn's disease tissue by independent laboratories. However, polymerase chain reaction (PCR) studies for detecting mycobacterial DNA in Crohn's tissue have failed to produce consistent results, No specific agent has been isolated from sarcoid tissue, but PCR studies have implicated Mycobacterium tuberculosis. Again, inconsistent results have been obtained from independent laboratories. Animal models of adjuvant arthritis have been shown to involve T cells that respond to the mycobacterial 65 kDa heat shock protein. Patients with rheumatoid arthritis have also been shown to have mycobacteria-reactive T cells in their joints but it is unclear whether this is specific to the disease. The involvement of mycobacteria in any of these diseases remains unproven.