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[Clinical significance of rheumatoid factor--its complement activating property and isotype].

We investigated the relationship between complement-activating properties of rheumatoid factors (RF) and their isotypes. Active and inactive RA patients without extra-articular symptoms (EAS) and those with EAS were studied. Patients with SLE, liver cirrhosis (LC) and normal volunteers were served as controls. Isotype of RF was measured by ELISA and complement activation (CA) of RF was measured by hemolytic assay. The CA values were significantly higher in RA patients with EAS than those in RA patients without EAS and with other diseases. The IgG and IgM-RF values were significantly higher in active RA without EAS than in inactive RA. Positive correlations between IgM-RF values and CA values were observed in RA with or without EAS, SLE and LC. The Sephadex G-200 gel filtration analysis of sera revealed CA in only 19S IgM fraction. Additionally, we purified 19S IgM-RF from sera of RA, SLE and LC patients by affinity chromatography, and found 19S IgM-RF had CA. These data suggest that serum IgM-RF may play a critical role in the pathogenesis of RA, especially in RA with EAS.