Radioimmunoassays for anti-F(ab')z antibodies, which feature the use of goat anti-human Fc antibody for correcting potentiation of IgM anti-F(ab')z antibody titers by endogenous IgM anti-Fc antibodies (rheumatoid factors), are described. Individuals with classic rheumatoid arthritis had significantly more IgM anti-F(ab')2 antibody (P < 0.001) and IgG anti-F(ab')2 antibody (P = 0.05) than did individuals with systemic lupus erythematosus or normal volunteers. There is some similarity in patterns of isotype distribution of anti-F(ab')z antibodies and rheumatoid factors.
Elevated levels of antibodies to epitopes located on the Fab or F(ab');! portions of IgG are often found in the sera of patients with rheumatoid arthritis (RA) and other diseases (1-6). The biologic significance of these findings is just beginning to emerge.
For example, it was shown only recently that anti-F(ab');! antibodies react with allotypic and/or idiotypic epitopes on the surface of subpopulations of B lymphocytes of normal donors (7). There is also recent evidence that some anti-F(ab')2 activity is directed against a repertoire of idiotypes that is commonly included in pooled human IgG (5). Earlier it was suggested that anti-F(ab')2 antibodies, like the classic anti-Fc rheumatoid factors (RF), arise from stimula-From the