Tumour growth and non-specific immunity in rats: the mechanisms involved in inhibition of tumour growth.

Various non-specific stimulants of phagocytosis, such as peptone, starch, glycogen, BCG, inhibit the growth of Walker carcinosarcoma in rats. This was confirmed by comparison of the histological appearance of tumour beds and tumours of peptone-treated and control rats. In rats given peptone or BCG, tumour inhibition was detectable only during a limited period of time. Experiments on the effect of pretreatment with peptone on the growth of Walker ascites tumour cells revealed a clear-cut inhibition, and suggest that tumour cells may be successfully eliminated during the lag phase. Data showing that activated macrophages labelled with Cr significantly accumulate around the tumour implant support the view that macrophages are of prime importance in the elimination of tumour cells in this model system.