Apoptosis in antibody-dependent monocyte-mediated cytotoxicity with monoclonal antibody 17-1A against human colorectal carcinoma cells: enhancement with interferon gamma.

Antibody-dependent cell-mediated cytotoxicity (ADCC) has been considered to be one of the main effector mechanisms by which unconjugated monoclonal antibody (mAb) 17-1A can exert an antitumor effect in vivo. Since the apoptotic pathway as well as the necrotic pathway have been shown to be utilized in various cytotoxic effector mechanism, we investigated the role of apoptosis in ADCC mediated by monocytes (ADMC) using mAb 17-1A as an antibody and the human colorectal carcinoma cell line, COLO205, as target cells in vitro. The implications of the apoptosis during ADMC was demonstrated by means of both a DNA fragmentation assay and a TdT-mediated dUTP-biotin nick end labeling (TUNEL) assay. Furthermore, interferon gamma (IFN gamma) was also found to enhance the induction of apoptosis significantly. The addition of superoxide dismutase did not reduce the level of the apoptosis, although superoxide anion (O2-) was observed to be produced. However, the release of tumor necrosis factor alpha (TNF alpha) was significantly enhanced during ADMC, while, in addition, apoptosis was significantly inhibited by the addition of anti-TNF alpha antibody. These findings indicated that apoptosis might be implicated in ADMC with mAb 17-1A, which was augmented by IFN gamma, while, in addition, TNF alpha may also be one of the major mediators of apoptosis.