Differences between the activities of human monoclonal IgG1 and IgG3 anti-D antibodies of the Rh blood group system in their abilities to mediate effector functions of monocytes.

Seven IgG1 and seven IgG3 human monoclonal antibodies derived from heterohybridoma or Epstein-Barr virus-transformed lymphocytes and specific for the D antigen of the human Rh blood group system were tested for their ability to bring about red cell attachment to and phagocytosis by monocytes. The antibodies produced by the heterohybridomas were also investigated for their potency to mediate antibody-dependent cellular cytotoxicity (ADCC) by monocytes. When red cells were sensitized with any of the IgG1 anti-D antibodies, most of them were ingested by the phagocytes. By contrast, many of the red cells coated with any of the IgG3 antibodies remained attached to the monocyte surface while only few underwent phagocytosis. Some of the attached red cells remained on the phagocyte exterior for a considerable length of time. The ADCC activities of the IgG3 anti-D antibodies was greater than that of the IgG1 anti-D antibodies. The results mean that in vitro IgG1 anti-D mediates red cell destruction mainly by phagocytosis, while IgG3 anti-D causes their destruction predominantly by prolonged cytolysis. These differences between the effector functions of human monoclonal IgG1 and IgG3 anti-D antibodies might have important implications for their use in the prophylaxis of haemolytic disease of the new-born.