Secreted by activated natural killer lymphocytes as a 50-kDa glycoprotein lymphokine, Leukoregulin can up regulate the expression of hyaluronan and prostaglandin-endoperoxide H synthase 2 (PTGS2), the inflammatory cyclooxygenase. Leukoregulin shows tumor growth inhibitory activity, enhances membrane permeability, and promotes the uptake of cytotoxic drugs by tumors cells without affecting these processes in normal cells. (NCI) [ ]