Antibody‐dependent Cell‐mediated Cytotoxicity and Phagocytosis of Autologous Red Blood Cells in Alphamethyldopa‐induced Haemolysis

7 alphamethyldopa (AMD)-treated patients with positive direct antiglobulin test (DAT) were investigated. Peripheral blood mononuclear phagocytes of 2 patients suffering from haemolysis caused lysis and phagocytosis of autologous DAT-positive red blood cells (RBC). Eluates from RBC of both patients contained antibodies of IgG1 subclass and supported antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent phagocytosis (ADPh) of the patients' RBC after remission. Both cytotoxic activities were proportional to the serum concentration and to the number of attacking cells. The 5 patients without overt haemolysis did not show in vitro lysis or phagocytosis of autologous RBC. These results suggest that ADCC as well as ADPh participate in the destruction of RBC in AMD-induced haemolysis in vivo.