Immune complexes and rheumatoid factors in canine arthritides.

Thirty two domestic dogs with naturally occurring polyarthritis were investigated to determine the contribution of autoimmunity in the pathological mechanisms. Comparisons were made with canine infective arthritis (12 dogs), osteoarthritis (32), and osteoarthritis secondary to rupture of the cranial cruciate ligament (19). Rheumatoid factors, immune complexes, and complement fixation (C1q binding) were measured in sera and synovial fluids. Compared with normal dogs (32), dogs with rheumatoid arthritis (RA) had increased serum and synovial fluid immune complexes and rheumatoid factors. Increases were generally also seen in dogs with other arthropathies, however. Rheumatoid factors were higher in sera than in synovial fluids. Rheumatoid factors correlated with immune complex levels and complexed rheumatoid factor only in the group of dogs with RA. Both rheumatoid factors and immune complexes may contribute to the pathogenesis of canine RA but are considered to arise as a result of non-specific inflammatory mechanisms in the non-rheumatoid groups.