Increased resistance in splenectomized mice to a methylcholanthrene-induced tumour

Prior splenectomy increased the resistance of BALB/c mice to a syngeneic methylcholanthrene-induced ascitic tumour inoculated i.p. The survival rate of splenectomized mice was 81-6% while those of normal and sham-operated controls were 11-5% and 20% respectively. The effect of splenectomy, however, was seen only within the dose range of 10(3) to 10(4) tumour cells. This effect of splenectomy was abolished by the transfer to mice of serum from tumour-bearing mice, and of spleen cells from normal donors, immediately after the inoculation of tumour cells. Cell-free ascitis fluid did not abolish the effect of splenectomy. The findings suggest that there is a subpopulation of spleen cells which produces a tumour growth enhancing factor which is found in the serum of tumour-bearing mice.