Heparin inhibition of antibody-dependent complement-mediated lysis

The effect of heparin on the monoclonal antibody-dependent complement-mediated lysis of human lymphoid cell lines and peripheral blood T-lymphocytes was studied. T-lymphoid cell lines (CEM and MOLT-3) were lysed by optimal concentrations of monoclonal antibodies and rabbit complement. Heparin at concentrations as low as 0.5 U/ml partially inhibited the complement-mediated lysis of all antibody-cell combinations while a heparin concentration of 25 U/ml produced complete inhibition. Lysis mediated by an IgG monoclonal antibody (J5) to the common acute lymphoblastic leukemia antigen (CALLA) was more sensitive to heparin inhibition than that due to an IgM antibody (VIL A1). Bovine and porcine heparin were equally inhibitory. Peripheral blood T-lymphocytes collected in heparin (100 U/ml) were resistant to complete lysis when treated with 17F12 and complement immediately after isolation; complete lysis was achieved only when they were incubated for 2 h prior to treatment. The role of monoclonal antibody and complement in the in vitro lysis of normal and leukemic lymphocytes is discussed.