Lipid-like agent from human neoplastic cells suppresses cell-mediated immunity

Summary A lipid-like factor (LLF) of a phospholipid nature was isolated from spent cell-free media of explants and cell cultures from lipids collected from human mammary carcinoma and malignant melanoma cells. LLF modulates macrophage properties and inhibits macrophage chemotactic activity, spreading, lipopolysaccharide-induced tumoricidal activities, and macrophage migration. LLF is unique to tumor cells and is not present in detectable quantities in normal mammary epithelial cells or skin fibroblasts. LLF also inhibits human normal lymphocytes' response to mitogenic stimulation. Partial purification of LLF from human mammary carcinoma is attained by a combination of chloroform extraction and filtration through Amicon molecular membranes. LLF activity is not sensitive to trypsin, pronase, bovine spleen phosphodiesterase II, alkaline phosphatase, or ribonuclease, but it is completely inactivated with phospholipase and lipoprotein lipase.