Idiotypic specificity of a human monoclonal anti-Rhesus(D) antibody

A human monoclonal IgG anti-Rhesus(D) (H2D5D2) obtained after transformation of lymphoid cells by Epstein-Barr virus was purified from culture supernatant by affinity chromatography. Rabbits were immunized with the monoclonal anti-D. The rabbit antisera, after appropriate absorption, reacted only against the immunizing monoclonal anti-D. The antiidiotypic antibodies (anti-id ab) were purified and gave a complete inhibition of the monoclonal anti-D, whereas no inhibition was observed with monoclonal or polyclonal IgG or with sera containing high titres of anti-D. Polyclonal anti-D obtained from 118 immunized blood donors were coated on Rh-positive red cells. Agglutination by anti-id ab was observed in 4 cases (3.4%), indicating a cross-reactivity between the monoclonal anti-D and the polyclonal anti-D present in the sera of some immunized donors.