Multispecificity of monoclonal rheumatoid factor.

Abstract

The study involved a monoclonal rheumatoid factor referred to as RF-AN, obtained by Steinitz and his associates from IgG-reactive human lymphocytes 'immortalized' by infection with Epstein-Barr virus. RF-AN combined with red blood cells (RBC) sensitized by either human or rabbit IgG antibodies. The monoclonal character of RF-AN strongly suggested that the same molecule of this factor combined with IgG of both species. Additional evidence for this contention was obtained from absorption and mixed agglutination experiments. RBC sensitized by either human or rabbit antibodies would remove serological activity of RF-AN for both human and rabbit IgG. RF-AN produced exclusively mixed agglutinates when reacted with a mixture of human RBC sensitized by human antibodies and chicken RBC sensitized by rabbit antibodies. Furthermore, it was shown that inhibition with aggregated human Fraction II gave strictly 'specific' results in that it abolished the reaction of RF-AN with RBC sensitized by human antibodies, but not by rabbit antibodies. This result was interpreted as indicating that RF-AN has a multispecific character, i.e., has separate combining sites for human and rabbit IgG. Interestingly, specific inhibition could not be achieved with aggregated rabbit Fraction II and this preparation affected reactivity of RF-AN with RBC sensitized by human antibodies as well as by rabbit antibodies.