IgG Fc receptors in sera from patients with rheumatoid arthritis and systemic lupus erythematosus.

A murine monoclonal antibody to receptors for IgG (FcR) in human placenta was used in a competitive ELISA to demonstrate soluble FcR in human sera. Sera from 20 blood donors, 30 patients with systemic lupus erythematosus and 50 patients with rheumatoid arthritis were examined. Soluble FcR were demonstrated in all sera. However, significantly lower amounts of FcR were demonstrated in the patient groups as compared to blood donors. Whether this is due to increased consumption or reduced production has to be further investigated. The findings may be of significance in the pathogenesis of these diseases.