Abstract
OBJECTIVE: To determine the relevance of the functional affinity of IgM rheumatoid factor (RF) to the clinical and serological characteristics of patients with rheumatoid arthritis. METHODS: The functional affinity of IgM RF of 57 seropositive rheumatoid arthritis patients was evaluated by an enzyme linked immunosorbent assay based on the use of a chaotropic agent. The inhibition index was taken as an estimate of functional affinity. The patient group was divided into high functional affinity subgroup 1 (functional affinity < 0.5, n = 37) and low functional affinity subgroup 2 (functional affinity > 0.5, n = 20). The medical records of all patients were reviewed with a particular note of the disease activity and the articular damage score. RESULTS: The disease duration was shorter (P < 0.01) in subgroup 1 patients [7.9 (SD 6.4) years] than in subgroup 2 patients [13.4 (11.29) years], so that Ritchie's, Lee's, and Steinbrocker's indices were lower in the former than in the latter (P < 0.01, 0.001, and 0.01, respectively). In contrast, erythrocyte sedimentation rates, C reactive protein concentrations, antinuclear antibody, and HLA DR4 prevalences were similar in the two subgroups. CONCLUSIONS: Different forms of RF are present during progression of the disease.