Crossreaction of monoclonal antiidiotypic antibodies specific for human antithyroglobulin antibody with the Fc portion of human IgG.

We established 2 monoclonal antiidiotypic antibodies that reacted not only with a private idiotope on human antithyroglobulin antibody but also with the Fc portion of human IgG. These antiidiotypic antibodies (B2 and B6) bound to IgG F(ab')2 antithyroglobulin derived from a patient with chronic thyroiditis and normal human IgG, but did not bind to IgG F(ab')2 nonantithyroglobulin derived from the patient and normal human IgG F(ab')2. The antiidiotypic properties and the rheumatoid factor (RF) like properties of B2 and B6 were confirmed by inhibition assay. Our results suggest that RF may be produced as antiidiotypic antibodies specific for other antigens than IgG.