Effects of neoplasms on inflammation: depression of macrophage accumulation after tumor implantation.

The local accumulation of macrophages at sites of neoplasms may be a critical event in immunologically mediated tumor killing. Individuals with neoplasms, however, have been noted to have depressed monocyte chemotactic responsiveness in vitro. To determine the effect of neoplasms on macrophage migration, mice were implanted subcutaneously with either sarcoma or hepatoma cells and their macrophage migratory function quantified in vivo and in vitro. The ability of tumor-bearing animals to mobilize macrophages to an inflammatory site in vivo was depressed by as much as 61% by 6 days after tumor implantation. The in vitro chemotactic responsiveness of macrophages recovered from the peritoneal cavities of tumor-bearing animals was also markedly depressed. Macrophage migration was not affected by implantation of normal syngeneic or allogeneic tissues. In addition, the accumulation of polymorphonuclear leukocytes in vivo was not depressed in tumor-bearing animals. These findings suggest that neoplasms themselves may depress the host's ability to localize macrophages at inflammatory sites in vivo and thereby hinder immunologically mediated tumor destruction.