Antitumor and antitumor-promoting actions of macrophages and their relationship with estrogen

Silica provides, in fact, a remarkable example of selective toxicity for macrophage by a substance of simple chemical composition and low chemical reactivity. Intraperitoneal injection of silica resulted in an increase of growth rate of subcutaneously implanted mouse sarcoma 180 (S180) in female BALB/c mice and of tumor incidence of two-stage mouse skin carcinogenesis in female ICR mice, but did not show any significant effects on tumor growth and carcinogenesis in male mice. In contrast, local administration of homologous macrophages led to the decrease of growth rate of subcutaneously implanted mouse S180 in female BALB/c mice and of tumor incidence of two-stage mouse skin carcinogenesis in female ICR mice. On the other hand, estradiol, estradiol plus macrophages or a large number of macrophages alone inhibited the tumor growth in male mice. It should be noted that estradiol plus macrophages had the most potent antitumor action among them. These results suggest that macrophages, especially estrogen-activated macrophages, may play an important role in antitumor and antitumor-promoting actions of organisms.