Rheumatoid arthritis and Proteus: a possible aetiological association.

The presence of specific anti-Proteus antibodies in active, rheumatoid arthritis (RA) patients, has been demonstrated by four different techniques: indirect bacterial agglutination, ELISA, Western blotting and immunofluorescence. Furthermore, anti-HLA-DR4 tissue typing sera have been shown to bind to Proteus microorganisms, thereby suggesting some molecular similarity or cross-reactivity between bacteria and HLA antigens. The concept is proposed that Proteus-reactive arthritis occurs during active phases of RA and tissue damage is mediated through immunological activity involving HLA antigens.