Background-Current paradigm attributes the low incidence of cardiovascular disorders in Mediterranean countries despite a high saturated fat intake, the "French paradox," to the antioxidant capacity of red wine polyphenols.Conceivably, other antiinflammatory pathways may contribute to at least a similar extent to the atheroprotective activity of these polyphenols. We have investigated whether gallic acid (GA), an abundant red wine polyphenol, modulates the activity of P-selectin, an adhesion molecule that is critically involved in the recruitment of inflammatory cells to the vessel wall and thus in atherosclerosis. Methods and Results-GA potently inhibited the binding of a peptide antagonist (IC 50 , 7.2 mol/L) and biotin-PAA-Le a -SO 3 H, an established high-affinity ligand, to P-selectin (IC 50 , 85 mol/L). Under dynamic flow conditions, GA markedly and dose dependently attenuated the rolling of monocytic HL60 cells over P-selectin-transfected Chinese hamster ovary cells (EC 50 , 14.5 mol/L) while increasing the velocity of P-selectin-dependent rolling of human blood leukocytes over a platelet monolayer. In vivo tests established that GA administration to normolipidemic C57/Bl6 and aged atherosclerotic apolipoprotein E-deficient mice impaired the baseline rolling of conjugates between activated platelets and circulating monocytes over femoral vein endothelium, as judged by online video microscopy (ED 50 , 1.7Ϯ0.3 and 1.5Ϯ0.4 mg · kg Ϫ1 · h Ϫ1 , respectively). Conclusions-Our findings provide a solid mechanistic foundation through which GA intervenes in major inflammatory pathobiologies by binding and antagonizing P-selectin.