Factor(s) from Ehrlich Ascites cells responsible for delayed rejection of skin allografts in mice and its assay on lymphocytes in vitro.

Cell free Ehrlich ascitic fluid from tumor bearing mice and the nutrient medium from Ehrlich cells maintained in vitro contain a factor(s) which when transferred to normal mice delays rejection of skin allografts and enhances the growth of a syngeneic transplantable tumor. Both types of prepartions inhibit DNA synthesis in lymphocytes stimulated by PHA. These results suggest that Ehrlich tumor cells release a factor which impairs the normal lymphocytic response to allo and tumor antigens.