Rheumatoid factor in rabbits with antigen-induced arthritis

Rheumatoid factor was assayed weekly by hemagglutination in sera from rabbits with antigen-induced arthritis and from control immunized animals receiving intra-articular injections of saline. Both groups developed rheumatoid factor. Arthritic animals, however, maintained high titers of rheumatoid factor more persistently than controls. Pre-incubation of positive sera with native or aggregated rabbit IgG was unable to inhibit agglutination, while native and aggregated human IgG were highly effective. Rheumatoid factor was unable to induce arthritis and probably does not potentiate articular tissue damage by immunocomplexes. Although production of rheumatoid factor may be a consequence of the polyclonal activation promoted by the immunization with complete Freund's adjuvant (CFA), the presence of arthritis is associated with persistence of high titers of rheumatoid factor for longer than would be expected from immunization with CFA alone.