Klebsiella antibodies in ankylosing spondylitis and Proteus antibodies in rheumatoid arthritis.

Antibodies to Klebsiella, but not to other bacteria, have been shown to be present in patients with active ankylosing spondylitis (AS) by seven different techniques. Antibodies to Proteus, but not to E. coli or Klebsiella, have been shown to be present in patients with active rheumatoid arthritis (RA) by three different techniques. It is suggested AS and RA are forms of reactive arthritis, to Klebsiella and Proteus respectively, probably mediated by cross-reactivity to HLA antigens.