MULTIPLE EPITOPES RECOGNIZED BY HUMAN MONOCLONAL IGM ANTI-D ANTIBODIES

Abstract. Bivalent 7S subunits were obtained from 7 purified IgM human monoclonal anti‐D antibodies with 33–63% of the total protein‐retaining functional binding activity. The number of sites per red cell recognized by these subunits ranged between 9,400 and 28,500. The values are taken to indicate that a number of different epitopes on the D polypeptide are being recognized. There was competition between IgG and IgM antibodies for binding to the red cells, indicating that both classes of antibody are recognizing epitopes on the same D polypeptide. The value of the functional affinity constants for the binding of the 7S subunits varied between 1.0 and 8.8 times 107 M‐1 and there was a 3‐ to 16‐fold increase on reduction of the ionic strength (0.05 M NaCl). Using agglutination in microwells, the end‐point of the titres for the native pentamer IgM antibodies occurred at concentrations in the range 7–26 ng/ml, with one exception where the concentration required was 165 ng/ml. © 1990 S. Karger AG, Basel