Protooncogene expression in normal and tumor-infiltrating phagocytes.

Expression of cellular protooncogene was investigated in freshly isolated human leukocytes and in tumor-associated macrophages isolated from murine fibrosarcomas. Normal leukocytes express high levels of c-fos and c-raf-1 transcripts. Expression of c-fos and c-raf-1 in leukocytes differ in many respects; in particular, agents that stimulate leukocyte functions augment c-fos expression but have no effects on c-raf-1 transcription. Tumor-associated macrophages constitutively express c-fos protooncogene at levels higher than peritoneal macrophages. Moreover, in contrast to what happens in peritoneal macrophages, tumor-associated macrophages do not respond to endotoxin with an increase in c-fos expression.