Background Lipoprotein-associated phospholipase A2 (Lp-PLA2) is mainly secreted by macrophages,serving as a specific marker of atherosclerotic plaque and exerting pro-atherogenic effects.It is known that high-density lipoprotein (HDL) plays an important role against atherosclerosis by inhibiting pro-inflammatory factors,however,the relationship between HDL and Lp-PLA2 remains elusive.Methods In this study,reverse transcription-polymerase chain reaction (RT-PCR),West blotting,and a platelet-activating factor (PAF) acetylhydrolase assay were performed to determine the Lp-PLA2 mRNA level,protein expression and activity in human monocyte-derived macrophages upon HDL treatment of different concentrations and durations.To investigate the underlying mechanism of HDL-induced Lp-PLA2 action,pioglitazone,a peroxisome proliferator-activated receptor-y (PPARy) ligand,was introduced to human monocyte-derived macrophages and mRNA and protein levels of Lp-PLA2,as well as its activity,were determined.Results Lp-PLA2 mRNA levels,protein expression and activity were significantly inhibited in response to HDL treatment in a dose and time dependent manner in human monocyte-derived macrophages.Pioglitazone treatment (1-10 ng/ml) upregulated the Lp-PLA2 mRNA level,protein expression and activity in human monocyte-derived macrophages,while the effects were markedly reversed by HDL.In addition,pioglitazone resulted in a significant increase in PPARY phosphorylation in human monocyte-derived macrophages,which could be inhibited by HDL.Conclusion These findings indicate that HDL suppresses the expression and activity of Lp-PLA2 in human monocyte-derived macrophages,and the underlying mechanisms may be mediated through the PPARY pathway.