Specific lysis of human colon tumor cells by antibodies to CEA and isoantigen A: dependence on rabbit serum or neuraminidase.

The 51Cr cytotoxicity test was used to measure specific antibody reactions against carcinoembryonic antigen (CEA) and isoantigen A on the surface of human colon tumor cells. When human serum or guinea pig serum was used as a source of complement, no anti-CEA or anti-isoantigen A cytotoxicity was demonstrable despite binding of specific antibodies and activation of complement at least through the C3 component on the cell surface. In contrast, specific anti-CEA and anti-isoantigen A cytotoxicity was demonstrated when rabbit serum was used as a source of complement. Specific antibody-mediated cell lysis was also achieved with guinea pig complement if the cells were treated with neuraminidase before testing. These results support the concept that certain tumor cells have surface properties that render them resistant to immune lysis.