Molecular basis for the immunosuppressive action of stearic acid on T cells.

Abstract

Studies were performed to determine the mechanism by which stearic acid (18: 0) selectively inhibits T-dependent immune responses in vitro. Incubation of mitogen-activated B and T cells with 18:0 resulted in dissimilar patterns of incorporation of the saturated fatty acid into their membranes. High-performance liquid chromatography (HPLC) analyses of T cells showed an accumulation of desaturated 18:0-containing phosphatidylcholine (PC) that replaced normal cellular PC. Less significant quantities of the same PC species were seen to accumulate in B-cell membranes; rather, they increased their proportion of oleic acid (18: 1)-containing PC. The different lipid compositions of the lymphocyte cell membranes after exposure to 18:0 were correlated with their plasma membrane potentials. In T cells, the accumulation ofdesaturated, 18: 0-containing PC coincided with a rapid (within 8 hr) collapse ofmembrane integrity, as determined by flow cytometry. The collapse of membrane integrity was found to be time and dose dependent. No such depolarization was observed in B cells which, by virtue of their desaturating ability, were able to avoid incorporating large amounts of desaturated 18: 0-containing phospholipids into their membranes. It is proposed that a lack of stearoyl-CoA desaturase in T cells precludes them from desaturating exogenously derived 18:0, thus leading to increased proportions of 18:0-containing desaturated PC in their cell membranes. The increased abundance of this PC species may enhance membrane rigidity to an extent that plasma membrane integrity is significantly impaired, leading to a loss ofmembrane potential and ultimately cell function and viability. Originally published Immunology, Vol. 70, No. 3, July 1990