Fatty acid ethyl ester effects on interleukin-2 production, cyclic AMP synthesis, and calcium influx in human mononuclear cells

Background: Fatty acid ethyl esters (FAEE), nonoxidative ethanol metabolites, are produced by the esterification of fatty acids and ethanol. Plasma and serum FAEE correlate linearly with blood ethanol levels and are present in organs most commonly damaged by ethanol abuse. Our previous studies have shown that there is significant synthesis of FAEE by human mononuclear cells within seconds of exposure to physiologic doses of ethanol. Objectives: We studied the effects of FAEE on selected early events of mononuclear cell activation that follow stimulation with phytohemagglutinin (PHA). Fatty acid ethyl esters induced changes in cytosolic free calcium ([Ca2+]) levels, the production and secretion of interleukin-2 (IL-2) by the cells, and intracellular cAMP concentrations. Methods: A mononuclear fraction of human white blood cells (WBC) was incubated with physiologic doses of FAEE. For experiments involving IL-2 production and calcium influx, PHA-stimulated cells were incubated with 10, 25, 50, or 100 mu M ethyl oleate, a representative FAEE species, for 60 minutes. Interleukin-2 was measured by enzyme immunometeric assay and maximum levels of Ca2+ were monitored by spectrofluorimetry. In other experiments, mononuclear cells were incubated with 10, 25, and 50 mu M ethyl oleate for 0.08 to 120 minutes, and then the concentration of cAMP was determined by a cAMP competitive enzyme immunoassay system. Results: Fatty acid ethyl esters inhibited the PHA-induced IL-2 production and secretion in activated human mononuclear cells. Fatty acid ethyl esters also inhibited PHA-induced [Ca2+] influx into cells in a dose-dependent fashion. There was a rapid increase in the intracellular cAMP concentration of mononuclear cells induced by FAEE, with FAEE dose dependence. The cAMP concentration decreased as the incubation time with FAEE was increased. Conclusions: Fatty acid ethyl esters inhibited PHA-stimulated IL-2 production and Ca2+ influx into human mononuclear cells and elevated intracellular cAMP concentration. These changes in mononuclear cell signaling may be associated with the immunosuppression associated with alcohol abuse.