Sequestration of macrophages in growing tumours and its effect on the immunological capacity of the host.

The effects of rat tumours of various macrophage contents on the syngeneic host's ability to produce either: (1) an inflammatory exudate in response to intraperitoneal oyster glycogen or (2) a cutaneous delayed hypersensitivity (DHS) response to PPD or SRBC after appropriate sensitization, were studied as a function of tumour growth.Both these reactions were found to be markedly decreased as the tumours grew. The suppression was greatest in animals bearing tumours of high macrophage content. The suppression of the DHS response could be reversed by a local injection of normal peritoneal macrophages with the eliciting antigen, and lymphocytes from tumour bearing animals exhibiting poor DHS responses were able to adoptively transfer DHS reactivity to normal unsensitized recipients. The monocyte infiltration in response to oyster glycogen was also decreased, and these data indicate a monocyte, rather than a lymphocyte defect in the tumour induced "anergy" in this system.