Demonstration of anticollagen antibodies in rheumatoid arthritis synovial fluids by 14C-radioimmunoassay.

Twenty-seven synovial fluids from rheumatoid arthritis (RA) patients and 17 synovial fluids from controls were investigated in a new radioimmunoassay for anticollagen antibodies. In vitro labeled human 14C-collagen of type I in native or denatured state was used as antigen. Passive hemagglutination was used in comparison. Parameters for defining positive results in radioimmunoassay were evaluated on the basis of control synovial fluids. Synovial fluids from 20 RA patients (74%) showed antibodies to denatured collagen; synovial fluids from 8 RA patients (30%) also demonstrated antibodies to native collagen. Control fluids of posttraumatic effusions were negative; among the other controls synovial fluid from 1 psoriatic arthritis patient reacted positively. Inhibition experiments showed that antibodies to denatured collagen cross-reacted with native collagen. Inhibition with human denatured type III collagen displayed strong cross-reactivity of anti-type I collagen antibodies with type III collagen.