Monocytes are major participants in inflammatory responses and are central mediators of chronic inflammation. Monocytes are believed to significantly contribute to atherosclerotic lesion pathology. In atherosclerotic lesions, monocyte/macrophages have been shown to expressthe lipid-oxidizing enzyme, 15-lipoxygenase (15LO) that produces potent inflammatory mediators by oxidizing phospholipids, cholesterol esters and free fatty acids. Unique among the products of this enzyme are oxidized linoleate (13-S-HPODE), which we have shown to be the major oxidized fatty acid in atherosclerotic lesions with most present in esterified form. Normal monocytes do not express 15LO, but are induced to do so by exposure to the cytokine IL-13 and expression of this enzyme has been correlated with disease progression in animal models of atherosclerosis. Studies proposed in the first aim of this application will identify novel IL-13-triggered signal transduction pathways responsible for inducing 15LO gene expression in primary human monocytes and relate them to the dual phosphorylation of StatS, a critical transcription factor regulating 15LO. We will also investigate the direct versus indirect role of StatS in specific transcriptional activation of 15LO. The studies proposed in Aim 2 will explore the hypothesis that the induction of 15LO is a critical regulatory step for many of the pathways observed to regulate the expression of the scavenger receptor CD36. The novelty of these studies is derived from elucidating the interaction of the 15LO and CD36 pathways through the use of innovative approaches to specifically dissect the roles of these pathways in intact, primary human monocytes. These include the discovery by our group that monocytes are particularly conducive to antisense oligodeoxyribonucleotide manipulation of specific protein expression and also due to a recent breakthrough allowing efficient transfection of primary human monocytes. We will also define the mechanisms involved in our recent finding that treatment of monocytes with oxidized phospholipids causes dramatic inhibition of 15LO expression. Select oxidized phospholipids may thereforeinterfere with the lipoxygenase expression in atherosclerotic lesions. These studies will substantially enhance our understanding of the signaling mechanisms involved in the expression of 15LO and their impact on the expression of CD36 as well as defining the mechanism of CD36 inhibition of 15LO expression. Modulation of these pathways will impact formation of oxidized phospholipids, oxidized cholesterol ester and oxidized fatty acids as well as modulate lesion macrophage foam cell formation and progression of atherosclerotic lesions. The identification of new pathways that regulate 15LO and CD36 expression will likely suggest novel therapies that may be employed to interfere with this pathway and its role in chronic inflammatory disease such as atherosclerosis.