Lysis of Antibody Coated Human Red Cells in the Presence of Human Serum

When peripheral blood lymphocytes and human red cells coated with lgG were incubated in vitro in culture medium, antibodydependent lymphocyte-mediated lysis was observed. This lysis was markedly inhibited by the addition of purified monoclonal IgG1 (1000 Lg/ml) to the culture medium. In contrast. lysis by lymphocytes of sensitized red cells in the presence of undiluted human serum was equal to or greater than lysis in medium alone, even in the presence of IgGi at 1000 sg/ml. despite the high concentration of lgG in human serum (6000-1 9.000 sg/ml). Serum heated to 56#{176}Cfor 30 mm also restored lysis in the presence of IgGi . When serum was separated into three fractions by passage through a Sephadex G-200 column. the third fraction, which contained proteins with a molecular weight of less than 1 00.000 d (but neither of the other two fractions nor purified human albumin). restored lymphocyte-mediated lysis in the presence of IgGi.