Human alpha 2-macroglobulin: a major serum factor cytotoxic for tumor cells.

Human alpha 2-macroglobulin (alpha 2M) was established here as a major serum factor which inhibits the DNA synthesis of a mouse ovarian tumor cell line in culture. This inhibitory activity was species non-specific, dose-dependent and unaffected by serum concentrations in culture. alpha 2 M was cytotoxic to both murine and human tumor cell lines in culture, as determined by 2 different viability staining techniques, morphological observation and long-term in vitro culture. This report implicates alpha 2 M or an alpha 2 M-associated substance as a major cytotoxic serum factor that may be involved in endogenous cancer control processes in mammalian species.