Macrophage nonimmunologic recognition: target cell factors related to contact inhibition.

Activated mouse macrophages were not cytotoxic to contact-inhibited nontumorigenic 3T3 fibroblasts, but caused marked destruction to non-contact-inhibited, tumorigenic 3T12 and simian virus 40-transformed fibroblasts. Nonimmunologic recognition and destruction of target cells by activated macrophages is independent of altered morphology, abnormal karyotype, and ability for continuous multiplication in vitro-all characteristics of 3T3 fibroblasts. A modification e f the target cell surface that results in a high in vitro saturation density, agglutinability by plant lectins, and tumorigenicity appears to evoke a cytotoxic response by activated macrophages.