Macrophages isolated from regressing Moloney sarcomas are more cytotoxic than those recovered from progressing sarcomas

Abstract

THERE is increasing evidence that many tumours contain appreciable numbers of macrophages^1–3, and that these inflammatory cells can be cytotoxic for various neoplastic cells in vitro^4,5. Thus at first it seems paradoxical that many tumours are progressive and lethal in spite of a high content of macrophages. But to kill a malignant cell, these inflammatory cells must be brought to an ill-defined state of ‘activation’^6,7. It is therefore conceivable that the macrophages in progressing tumours are less activated, and thus less cytotoxic, than those in spontaneously regressing neoplasms. To test this hypothesis we isolated macrophages from either regressing or progressing Moloney sarcomas and tested them in vitro for their capacity to release chromium-51 (⁵¹Cr) from prelabelled target cells. The former were usually significantly more cytotoxic than the latter.