Antibody to Mycobacterium tuberculosis 65 kDa heat shock protein in patients with rheumatoid arthritis--a survey of antigen-specific antibody isotypes and subclasses in an endemic area of previous tuberculosis infection.

OBJECTIVE To clarify the significance of the humoral immune response triggered by the Mycobacterium tuberculosis (M.tb) 65 kDa heat shock protein (hsp) in the pathogenesis of rheumatoid arthritis (RA). METHODS M.tb 65 kDa hsp-specific IgG, IgA, IgM, and IgG subclass antibodies in serum or synovial fluid (SF) of RA and other disease patients were determined by enzyme linked immunosorbent assay (ELISA). RESULTS RA patients did not show any characteristic increase in mycobacterial 65 kDa hsp-specific antibodies compared with healthy individuals. In contrast, antigen-specific IgG and IgG2 antibody titres in the serum of RA patients were significantly lower than those of patients with tuberculosis and normal controls. In addition, there was also no significant difference in antibody titre between the serum and SF of RA patients, nor was any significant difference found between the SF of RA and Reiter's patients. CONCLUSION The failure to detect a significant increase in IgG anti-M.tb 65 kDa hsp antibodies in RA patients does not exclude the possibility of microbial immunity in the aetiology of RA. Nevertheless, anti-M.tb 65 kDa hsp antibodies clearly do not appear to be the disease specific markers for RA and their relatively reduced concentrations may argue against their playing a major role in the disease pathogenesis.