Macrophage inflammatory responses in rats and mice with autochthonous and transplanted tumors induced by 3-methylcholanthrene.

Autochthonous and transplanted tumors induced by 3-methylcholanthrene-impregnated paraffin pellets in DA rats and C57BL/6 mice were analyzed for effects on macrophage inflammatory responses. Tumors emerged in 40% of carcinogen-treated rats with a mean latency of 8.1 months. During the latent period, rats treated with carcinogen versus rats treated only with paraffin had a higher frequency of depressed macrophage responses, which, however, did not alter either tumor latency or incidence. Tumors emerged in 70% of carcinogen-treated mice with a mean latency of 110 days. Prior to tumor emergence, mice treated with carcinogen or paraffin had a higher frequency of depressed responses than untreated control mice, and such abnormalities in the presence of carcinogen were positively associated with tumor development. Macrophage responses were not altered in rats or mice bearing large autochthonous tumors, although emerging tumors in rats but not in mice were associated with a modest inhibition in macrophage responses. Autochthonous tumors that did not induce macrophage abnormalities did so in syngeneic recipients upon tumor transplantation.