Abstract
Investigations of experimentally induced (i.e. viral, chemical) neoplasms have begun to elucidate the significance of non-lymphoid cells in the interaction between host and tumor (1,2,3,4,5,6,7). Macrophages have been identified as effector cells in a number of tumor systems (1,2,4), and recent reports have suggested that these cells are capable of suppressing immune activity in tumor bearing hosts (3,5,6,7). We have been investigating the nature of tumor-immune system interactions occurring in the AKR mouse during the development and spontaneous regression of a syngeneic tumor. Studies carried out in our laboratory suggest that the role of the macrophage in host defense against this tumor may change during the periods of development and regression, and that failure to do so may result in irreversible tumor growth.