Background-Strong evidence supports a role for CD40 ligand (CD40L) as marker and mediator of inflammatory diseases such as atherosclerosis. Despite extensive characterization of CD40, the classic receptor of CD40L, its role in immune defense against inflammatory diseases remains uncertain. The present study aimed to characterize the contribution of CD40 signaling to atherogenesis. Methods and Results-Surprisingly, mice deficient in both CD40 and the low-density lipoprotein receptor did not develop smaller lesions in the aortic arch, root, and thoracoabdominal aorta compared with mice deficient only in the low-density lipoprotein receptor that consumed an atherogenic diet for 8 and 16 weeks. By flow cytometry, radioactive binding assays, and immunoprecipitation, we demonstrate that CD40L interacts with the integrin Mac-1, which results in Mac-1-dependent adhesion and migration of inflammatory cells as well as myeloperoxidase release in vitro. Furthermore, mice deficient in CD40L show significantly reduced thioglycolate-elicited invasion of inflammatory cells into the peritoneal cavity compared with mice deficient in CD40 and wild-type controls. Inhibition of Mac-1 in low-density lipoprotein receptor-deficient mice attenuates lesion development and reduces lesional macrophage accumulation. Conclusions-These observations identify the interaction of CD40L and Mac-1 as an alternative pathway for CD40L-mediated inflammation. This novel mechanism expands understanding of inflammatory signaling during atherogenesis.

Rationale: Tumor necrosis factor receptor-associated factors (TRAFs) are cytoplasmic adaptor proteins for the TNF/interleukin-1/Toll-like receptor superfamily. Ligands of this family comprise multiple important cytokines such as TNF␣, CD40L, and interleukin-1␤ that promote chronic inflammatory diseases such as atherosclerosis. We recently reported overexpression of TRAF5 in murine and human atheromata and that TRAF5 promotes inflammatory functions of cultured endothelial cells and macrophages.Objective: This study tested the hypothesis that TRAF5 modulates atherogenesis in vivo. Methods and Results: Surprisingly, TRAF5؊/؊ /LDLR ؊/؊ mice consuming a high-cholesterol diet for 18 weeks developed significantly larger atherosclerotic lesions than did TRAF5 ؉/؉ /LDLR ؊/؊ controls. Plaques of TRAF5-deficient animals contained more lipids and macrophages, whereas smooth muscle cells and collagen remained unchanged. Deficiency of TRAF5 in endothelial cells or in leukocytes enhanced adhesion of inflammatory cells to the endothelium in dynamic adhesion assays in vitro and in murine vessels imaged by intravital microscopy in vivo. TRAF5 deficiency also increased expression of adhesion molecules and chemokines and potentiated macrophage lipid uptake and foam cell formation. These findings coincided with increased activation of JNK and appeared to be independent of TRAF2. Finally, patients with stable or acute coronary heart disease had significantly lower amounts of TRAF5 mRNA in blood compared with healthy controls. Key Words: TRAF5 Ⅲ inflammation Ⅲ atherosclerosis Ⅲ monocyte recruitment Ⅲ foam cells A therosclerosis is one of the leading causes of death worldwide. The concept that inflammatory and immunologic mechanisms drive atherogenesis emerged from both extensive laboratory studies and from clinical observations demonstrating associations between biomarkers of inflammation and cardiovascular events. 1,2 These findings have spurred the quest for antiinflammatory or immunomodulatory treatments to fight atherosclerosis and its sequelae. Selective modulation of key signaling pathways may afford a fruitful strategy to achieve that goal. Conclusions:Tumor necrosis factor (TNF) receptor-associated factors (TRAFs) represent important signal transducers for the TNF/ interleukin (IL)-1/Toll-like receptor (TLR) superfamily, several members of which potently promote atherogenesis. We and others found expression of TRAFs in cells typically resident in the atherosclerotic plaques. [3][4][5][6] However, only a few reports have investigated TRAF-dependent functions in the context of vascular disease: TRAF3 and TRAF2 have been implicated in transducing shear stress, 7,8 and Luo et al recently demonstrated that activation of TNFR2 mediates ischemia-induced atherogenesis by inducing TRAF2-dependent survival pathways. 9 Endothelial cells (ECs) and smooth muscle cells from unstable plaque regions of human carotid arteries overexpress TRAF4. 4 TRAF6 promotes neointima formation on balloon injury in the carotid artery of mice as well as deve...