Characterization of a monoclonal IgA rheumatoid factor. II. Evidence for reactivity with a specific IgG Fc fragment determinant

Evidence is provided which supports the concept that a previously characterized monoclonal IgA-λ rheumatoid factor with a medium-binding avidity reacts with a select Fc region antigenic determinant. The interaction between this rheumatoid factor and anti-Rh-coated human erythrocytes is inhibited by IgG1 Fc fragment, IgG1 heavy chains, and a single peptide pool isolated from this tryptic digest by paper chromatography. Cyanogen bromide cleavage of the isolated heavy chains abolishes this reactivity. A methionine residue is assumed to be near, involved in, or necessary for reactivity between the IgA and its antigenic determinant. The data thus provide further evidence for a specific autoantigenic, rheumatoid factor-reactive determinant.