To determine the effects of saturated and unsaturated fatty acids in phosphatidylcholine (PC) on macrophage activity, peritoneal lavage cells were cultured in the presence of phosphatidylcholine rich in saturated or unsaturated fatty acids (sat PC and unsat PC, respectively), both used at concentrations of 32 and 64 microM. The treatment of peritoneal macrophages with 64 microM unsat PC increased the production of hydrogen peroxide by 48.3% compared to control (148.3 +/- 16.3 vs 100.0 +/- 1.8%, N = 15), and both doses of unsat PC increased adhesion capacity by nearly 50%. Moreover, 64 microM unsat PC decreased neutral red uptake by lysosomes by 32.5% compared to the untreated group (67.5 +/- 6.8 vs 100.0 +/- 5.5%, N = 15), while both 32 and 64 microM unsat PC decreased the production of lipopolysaccharide-elicited nitric oxide by 30.4% (13.5 +/- 2.6 vs 19.4 +/- 2.5 microM) and 46.4% (10.4 +/- 3.1 vs 19.4 +/- 2.5 microM), respectively. Unsat PC did not affect anion production in non-stimulated cells or phagocytosis of unopsonized zymosan particles. A different result pattern was obtained for macrophages treated with sat PC. Phorbol 12-miristate 13-acetate-elicited superoxide production and neutral red uptake were decreased by nearly 25% by 32 and 64 microM sat PC, respectively. Sat PC did not affect nitric oxide or hydrogen peroxide production, adhesion capacity or zymosan phagocytosis. Thus, PC modifies macrophage activity, but this effect depends on cell activation state, fatty acid saturation and esterification to PC molecule and PC concentration. Taken together, these results indicate that the fatty acid moiety of PC modulates macrophage activity and, consequently, is likely to affect immune system regulation in vivo.