Effect of tumour-associated macrophages on the growth of tumours in rats.

Tumours that had grown in syngeneic rats were depleted of macrophages in vitro. A comparison was made with non-depleted tumours of their growth in the feet and spread to the popliteal lymph nodes in untreated, irradiated (500 rads) or carrageenan-treated rats. A non-metastasizing methylcholanthrene-induced fibrosarcoma (D8) grew better in the feet of all three groups after macrophage depletion but metastasized more extensively only in irradiated rats; irradiation increased the growth of non-depleted D8 in the feet. D8M, a metastatic variant of D8, grew less extensively in the feet of normal rats after macrophage depletion. Its metastatic spread was increased by macrophage depletion in carrageenan-treated rats only. Non-depleted D8M grew less well in the feet or irradiated or carrageenan-treated rats than in normal rats. A metastasizing spontaneous adenocarcinoma (ST-2) grew less well in normal rats after macrophage depletion. The non-depleted tumour grew less well in irradiated rats but macrophage depletion had no further effect. Metastasis of ST-2 to the popliteal node of normal rats was abolished by macrophage depletion. The nature of the host macrophage-tumour relationship seems to differ from tumour to tumour.