Defective production of reactive oxygen intermediates by tumor-associated macrophages exposed to phorbol ester.

Macrophages were isolated from poorly immunogenic metastatic sarcomas (mFS6 and MN/MCA1) of C57BL/6 origin. Tumor-associated macrophages (TAM) showed little release of superoxide when exposed to phorbol myristate acetate. When exposed to a phagocytic stimulus (zymosan), TAM released appreciable amounts of superoxide. TAM had a lower number of specific binding sites for phorbol esters than resident or caseinate-elicited peritoneal macrophages, but had normal NADPH-cytochrome C reductase. The tumor environment, possibly through previously demonstrated products of neoplastic cells, may influence the functional status of in situ macrophages and, thus, impair host anti-tumor and anti-microbial defense mechanisms.