Serum antibodies to type II collagen in rheumatoid arthritis: comparison of 6 immunological methods and clinical features.

A collaborative study of 75 selected patients with rheumatoid arthritis (RA) employing 6 different methods for the detection of antibodies to type II collagen showed highly significant correlations between all the assays. The radioimmunoassays showed a greater sensitivity than either the passive haemagglutination or immunofluorescent techniques, and when the native collagen molecule was heat-denatured a higher number of patients showed increased antibody levels. In 33 patients the measurement of serum antibody levels to human, bovine, and rat native type II collagen showed a lack of species specificity, indicating that heterologous collagens can be employed in these assays. A retrospective analysis of the clinical, laboratory, and radiological features in the 41 patients with raised antibody levels and the 34 patients with normal antibody levels showed very few differences, but there was a significantly lower incidence of subcutaneous nodules (24% versus 56%) in patients with raised antibody levels. This study emphasizes the need to standardize assays for the measurement of serum antibody levels to native type II collagen. More extensive studies will be required before the clinical significance of these antibodies can be fully established.