Effect of X-irradiation on host-cell infiltration and growth of a murine fibrosarcoma.

Whole body X-irradiation (400 rad) of C57BL mice, either before or after i.m. implantation of the syngeneic fibrosarcoma, FS6, influenced both the growth of the tumours and their cellular composition, particularly their macrophage content. Pre-irradiation resulted in slower initial growth of tumours, and a concomitant lack of host-cell infiltration, but when tumours began to grow at a rate parallel to controls infiltration by host cells was demonstrable. Similarly, irradiation of the tumour-bearing host resulted in a temporary cessation of growth, and a decrease in the macrophage content, which did not return to control levels for 2-3 weeks after irradiation. The significance of these results is discussed in relation to the possibility that infiltrating host cells, particularly macrophages, may stimulate the growth of this tumour.