Antibody-dependent cell-mediated cytotoxicity (ADCC) toward human O+ red cells coated with anti-D antibody:...

We investigated the antibody dependent cell-mediated cytotoxicity (ADCC) of lymphocytes and monocytes toward human O+ red cells coated with anti-D antibody using a 51Cr release assay. Lysis of sensitized red cells by lymphocytes occurred rapidly, but monocyte-mediated lysis occurred slowly. This difference might be due to postphagocytic 51Cr release by monocytes. ADCC of lymphocytes increased in proportion to the effector cell number, but large amounts of antibodies were required. In contrast, ADCC of monocytes was independent of the effector/target ratio and very small amounts of antibodies could produce red cell lysis. Large amounts of fluid phase IgG were required to inhibit the lymphocyte ADCC, whereas the monocyte ADCC was markedly inhibited by small amounts of IgG. Monocyte-mediated lysis was completely inhibited by the addition of 10% human AB serum, but lymphocyte-mediated lysis was only slightly inhibited. Purified IgG1 and IgG3 were much more inhibitory to the lysis by both effectors than IgG2 and IgG4 (IgG2 greater than IgG4). Erythrophagocytosis also was inhibited by IgG1 and IgG3. These studies demonstrate that lymphocytes as well as monocytes can cause the lysis of antibody sensitized red cells, and IgG1 and IgG3 subclasses are more important than IgG2 and IgG4 in causing lysis of anti-D coated red cells.