Simultaneous detection of two mechanisms of immune destruction of penicillin-treated human red blood cells.

Two separate processes of putative red-cell destruction in penicillin-induced immune hemolysis were measured simultaneously by a rapid (3 hour) assay utilizing 51Cr-labelled red blood cells (RBC). Antibody-dependent, cell-mediated cytotoxicity (ADCC) was estimated by release of 51Cr; and antibody-dependent phagocytosis (ADPh) by quantitation of 51Cr uptake into mononuclear phagocytes as well as by counts of engulfed RBC. Attacking cells were obtained by Ficoll-Hypaque separation of peripheral blood from normal donors. Phagocytosis as well as lysis were proportional to anti-penicillin antiserum concentration, to incubation time, and to the concentration of the attacking cells. Enrichment of mononuclear phagocytes in the attacking cell population by albumin gradient separation led to an increase in phagocytosis as well as in cytotoxicity. Depletion of mononuclear phagocytes resulted in a decline in both processes. Dilution of antiserum abolished ADCC but affected ADPh only slightly. Iodoacetate as well as colchicine inhibited both activities. These results indicate that both processes may be operative in the immune destruction of RBC in vivo.