Immunologic control of a retrovirus-associated murine adenocarcinoma. VII. Tumor cell destruction by macrophages and IgG2A.

The mechanism by which IgG2A from a syngeneic antitumor hyperimmune serum mediates destruction of target cells in the presence of thioglycollate-elicited peritoneal macrophages was investigated by using an in vitro assay system. Labeled tumor cells were found to exhibit a biphasic pattern of binding to the effector cells; this binding pattern was dependent on the presence of specific antibody. The initial binding phase produced no apparent changes in the target cell population. Target cells coated with specific antibody exhibited a similar early binding phase, but excess free antibody was required for the subsequent binding phase and its associated release of radiolabel and cell destruction. Several features of this process observed distinguished it from more conventional forms of antibody-dependent cell-mediated cytoxicity. These included 1) the preference for antibodies of the IgG2A isotype, 2) the association of cell destruction with the release of nuclear but not cytoplasmic label, and 3) the requirement of excess free antibody for target cell killing.