BINDING OF HUMAN MONOCLONAL IGG RHEUMATOID FACTORS TO FC IS INFLUENCED BY CARBOHYDRATE

Objective. The precise nature of the epitope on the Fc portion of the IgG molecule to which IgG rheumatoid factors (RF) bind has not been id entified. As patients with rheumatoid arthritis (RA) have abnormal gly cosylation of the Fc portion of IgG, we investigated the impact of the sugar present in the Fc on the binding of IgG RF. Methods. Binding of monoclonal IgG RF to Fc fragments with varying oligosaccharide chains was detected using an immunoblot assay. Results. We demonstrated that the binding of human hybridoma derived monoclonal IgG RF was strongly influenced by the presence of carbohydrate and was maximal when the c arbohydrate molecule was intact. The RF did not bind directly to the c arbohydrate moiety itself. Conclusion. This suggests that conformation al changes in the polypeptide chain induced by the carbohydrate are re sponsible for the observed binding patterns.