Omega‐3 fatty acid modification of membrane structure and function. II. Alteration by docosahexaenoic acid of tumor cell sensitivity to immune cytolysis

Abstract

Docosahexaenoic acid (DHA, 22: 6) is a long‐chain omega‐3 fatty acid abundant in cold water fish; it is the most unsaturated fatty acid found in biologic systems and is reported to alter membrane structure. To explore DHA's effect on membrane function, we have fused tumor cells with synthetic phosphatidylcholine (PC) containing stearic acid in the sn‐1 position and DHA in the sn‐2 position (18: 0, 22: 6 PC) and have found the lipid‐modified tumor cells to be more sensitive to cytolysis by alloreactive cytotoxic T lymphocytes. Cold target competition experiments suggested that fusion of tumor plasma membranes with 18: 0, 22: 6 PC produced a qualitative change in expression of surface antigens recognized by cytotoxic T lymphocytes. We monitored the expression of various epitopes on tumor cells by complement‐mediated lysis and radioimmu‐noassay with monoclonal antibodies against H‐2 class I antigens. Our results suggest that membrane‐bound DHA increases the expression of some epitopes while decreasing the expression of others and that different tumor lines vary in the magnitude of DHA's effect. Our findings are consistent with a model in which DHA‐containing phospholipids segregate into membrane domains, in turn altering the expression of membrane proteins.