Natural resistance mechanisms may play a role in protection against chemical carcinogenesis.

Mice deprived of B lymphocytes by the chronic administration of anti-IgM antibodies have been shown to possess a heightened natural resistance (NR) to micro-organisms, to parental bone marrow, and to natural killer (NK)-sensitive tumors in vitro and in vivo. Experiments described in this communication indicate that the latent period of primary tumors induced by the injection of methylcholanthrene (MC) is also prolonged in these mice. This observation suggests that NR mechanisms may provide protection against primary chemically induced tumors.