Immunologic control of a retrovirus-associated murine adenocarcinoma. VIII. Corynebacterium parvum-activated natural killer cells as potent antibody-dependent cell-mediated cytotoxicity effectors.

The antibody-dependent lytic activity of Corynebacterium parvum-induced peritoneal exudate cells was examined in vitro by utilizing AD755a tumor targets and a homologous anti-AD755a hyperimmune serum. Maximum antibody-dependent cell-mediated cytolysis (ADCC) of tumor targets was achieved within 4 hours of incubation. ADCC activity was found primarily in the plastic nonadherent cell population and was greatly enriched following removal of phagocytic cells by carbonyl iron. Phenotypically, the cells active in short-term ADCC were Qa-5+, ASGM-1+, Thy 1.2+, and NK 1.1+ and were unaffected by treatment with Lyt 1.2, Lyt 2.2, MAC-1, or I-Ab antibodies plus complement. Cells active in antibody-independent lysis of AD755a targets were phenotypically identical to antibody-dependent effectors. Although indicative of a natural killer (NK) cell phenotype, C. parvum-induced effectors differed from "spontaneous" splenic NK cells in their relative sensitivity to anti-Thy 1.2 as well as to anti-NK 1.1 treatment. Unlike the IgG2a-dependent lysis of AD755a-derived cells by inflammatory macrophages, all IgG isotypes of antiAD755a serum were equally effective in ADCC mediated by C. parvum NK cells. Finally, treatment of C. parvum-inoculated animals with anti-ASGM-1 serum eliminated in vitro NK activity and abrogated the in vivo therapeutic effects of hyperimmune serum. These findings, together with other correlations detailed herein, strongly suggested that C. parvum-activated NK cells appeared to represent a unique subset of NK cells that can serve as potent effectors in the antibody-dependent killing of AD755a tumor cells.