To study the role of microbial infection in rheumatic diseases.
Sera from 39 Chinese patients with rheumatoid arthritis (RA), 52 patients with ankylosing spondylitis (AS) and 51 healthy subjects (HS) were examined for IgG, IgA, and IgM class antibodies against Proteus mirabilis, Escherichia coli, Campylobacter jejuni, Salmonella typhimurium and enteritidis, Yersinia enterocolitica, and Klebsiella pneumoniae (capsular serotypes 31 and 43), using an enzyme-linked immunosorbent assay.
In patients with RA, IgA class antibodies against all bacterial strains used as the antigen were increased when compared to healthy controls. In patients with AS, significantly elevated IgA levels were observed against Campylobacter and Klebsiella K43. IgM class antibodies were less frequently elevated in RA and in AS than IgA class antibodies. In RA patients, IgG antibodies against Klebsiella K43 and Proteus were significantly increased. No differences were observed in IgG class antibodies between AS patients and healthy controls.
Increases in serum bacterial antibodies in RA and AS suggest that in both diseases stimulation of the intestinal immune system by enterobacteria may have a role. However, the question whether this phenomenon is due to increased intestinal permeability and/or represents cross reactions between different enterobacteria remains open.