T-cell-mediated concomitant immunity to syngeneic tumors. I. Activated macrophages as the expressors of nonspecific immunity to unrelated tumors and bacterial parasites.

Progressive growth of the SA1 sarcoma was shown to result in the generation of a state of concomitant resistance to growth of a second implant of the same tumor. The responding lymph nodes of concomitantly immune mice were shown to contain theta-positive T cells that could specifically neutralize the growth of tumor cells in a normal test recipient. Nevertheless, the concomitantly immune host itself was capable to a limited extent of suppressing the growth of unrelated tumors. The generation of immunity, moreover, was associated with the generation of a powerful state of macrophage-mediated, nonspecific resistance to the bacterial parasite, Listeria monocytogenes. It was concluded that systemic macrophage activation was the consequence of the generation of T-cell-mediated immunity to the progressively growing tumor, and that this not only gave the host the capacity to inhibit the growth of unrelated tumors, but also to protect itself against microbial infection. The results gives credence to the view that macrophages play a central role in defense against microbial and neoplastic growth.