Effect of macrophages on the growth of syn- and xenogeneic tumors

Human colorectal tumors transplanted in immune-suppressed mice (xenogeneic system) and metastasizing Lewis lung carcinoma (syngeneic system) were used to study the effect of macrophages on tumor progression. Carrageenan modifying the structure of macrophage cell coat and damaging the membrane of lysosomes led to severe disturbances in macrophage functions. The inhibition of macrophage activity by Carrageenan produced an enhancement in tumor take in both systems. In another set of experiments peritoneal macrophages were injected into tumor-bearing mice. In both systems the non-stimulated macrophages given i.v., produced a delay in tumor growth. These results indicated that the activity of macrophages influences markedly the tumor progression--even in hosts with damaged T cell population.