Suppressive factor of tumour origin against macrophage phagocytosis of Staphylococcus aureus.

Peritoneal macrophages from Sarcoma-180-bearing mice against Staphylococcus aureus were studied to determine the in vitro phagocytic capacities. When the phagocytic system was opsonized with normal mouse serum, macrophage phagocytic activity increased markedly soon after tumour graft and then returned to normal. A new antiphagocytic factor was detected in the serum of tumour-bearers soon after tumour implantation. This factor was of tumour origin, stable even at a temperature of 56 degrees C for 30 min and non-dialysable. Peptone-starch-induced macrophages were less sensitive to the factor than their unstimulated counterpart.