Macrophages and their products may exert either inhibitory or stimulatory effects on malignant cells,thus preventing or supporting
tumor growth, however, the mechanisms of this interaction are not fully understood. It was the aim of the present study to elucidate the role of macrophage activation during the growth and rejection of highly immunogenic murine
leukemia P388/adria cell line which was made resistant by suboptimal treatment of mice with
adriablastin during the serial passaging of parental P388 cells. The functional activity of peritoneal macrophages and the serum level of
cytokines IL-1 beta,
IL-6 and
TNF-alpha were studied in different groups of mice. Mice from group 1 (control) received saline. Mice from group 2 (
tumor bearers) with fast subcutaneous (s.c) 100%
tumor growth were compared with animals from group 3 that had been twice previously immunized with lethally irradiated P388/adria cells and later inoculated with viable
tumor cells.
Tumors grew in only 25% of group 3 animals with a significant delay. The activity of peritoneal macrophages was studied by NO2- production and the NBT-test. Both tests revealed the early high systemic activation of macrophages in group 2. This coincided with the elevation of serum
TNF-alpha and
IL-6 levels. This effect was not dependent on whether alive or lethally irradiated
tumor cells were inoculated. The NO2- production by peritoneal macrophages correlated well with the dynamics of serum
cytokine levels while the NBT-test did not. Studies on group 3 showed total abrogation of early macrophage and
cytokine reactions. The production of inhibitory factors by macrophages in previously immunized mice is suggested. The fact that the early activation of macrophages and increase of serum levels of proinflammatory
cytokines occurred in animals with fast growing
tumors, which was decreased or absent in animals with
tumor delay or rejections, allows us to suppose that this reaction plays more a supporting than a protecting role for
tumor growth.