The aetiology of RA is unknown; however, bacterial exposure, particularly to Escherichia coli, Proteus mirabilis and Klebsiella pneumoniae, has been linked to disease pathogenesis. The strongest association was observed for RF(+) RA. We compare colonization patterns of these bacteria, and the anti-bacterial antibody levels in early onset RF(+) and RF(-) inflammatory arthritis.
Bacteria isolated from stool and urine of early-stage RF(+) and RF(-) patients recruited to the Early Arthritis Registry were biochemically identified and genotyped. IgM and IgA anti-bacterial and RF antibodies were assessed by ELISA.
Differences in the types of colonizing pathogenic E. coli were identified. RF(+) patients were more commonly colonized with phylogenetic Group D E. coli, whereas RF(-) patients were more commonly colonized with phylogenetic Group B2 E. coli and these individuals also had lower joint scores and inflammatory markers yet higher IgA anti-E. coli antibody responses.
These studies link the type of colonizing bacteria in the gut and urine with the immune response (anti-bacterial and RF) in early-onset inflammatory arthritis and provide evidence for a role of the host-pathogen response in the aetiology of RF.