Recent studies have demonstrated that kynurenic acid (KYNA), a compound produced endogenously by the interferon-␥-induced degradation of tryptophan by indoleamine 2,3-dioxygenase, activates the previously orphaned G protein-coupled receptor, GPR35. This receptor is expressed in immune tissues, although its potential function in immunomodulation remains to be explored. We determined that GPR35 was most highly expressed on human peripheral monocytes. In an in vitro vascular flow model, KYNA triggered the firm arrest of monocytes to both fibronectin and ICAM-1, via ␤ 1 integrin-and ␤ 2 integrin-mediated mechanisms, respectively. Incubation of monocytes with pertussis toxin prior to use in flow experiments significantly reduced the KYNA-induced monocyte adhesion, suggesting that adhesion is triggered by a G i -mediated process. Furthermore, KYNA-triggered adhesion of monocytic cells was reduced by short hairpin RNA-mediated silencing of GPR35. Although GPR35 is expressed at slightly lower levels on neutrophils, KYNA induced firm adhesion of these cells to an ICAM-1-expressing monolayer as well. KYNA also elicited neutrophil shedding of surface L-selectin, another indicator of leukocyte activation. Taken together, these data suggest that KYNA could be an important early mediator of leukocyte recruitment.Leukocyte recruitment into tissue compartments is a tightly regulated process orchestrated by chemokines (1). Chemokines convert leukocyte rolling or tethering on the vascular endothelium to firm arrest via the activation of leukocyte surface integrins (2, 3). As chemoattractants, chemokines subsequently play an important role in the directional migration of leukocytes through tissues.Chemoattractant receptors are a subtype of G protein-coupled receptors (GPCRs), 3 one of the largest known families of human proteins. Chemoattractant receptors bind a variety of agonists, including proteins such as interleukin-8 (IL-8, CXCL8) (4) and monocyte chemoattractant protein-1 (MCP-1, CCL2) (5), small peptides such as fMLP (6), as well as bioactive lipids including leukotriene B 4 (7). As such, chemoattractant receptors mirror the entire family of GPCRs, which can be activated by ligands ranging in size from metabolites to large proteins (8).Because GPCRs serve as targets for therapeutic intervention, considerable activity has gone into the identification of both putative GPCR genes and the ligands for the resulting receptors (8). Recently, the tryptophan metabolite kynurenic acid (KYNA) was identified as an agonist for the previously "orphaned" receptor GPR35. KYNA was shown to elicit intracellular release of Ca 2ϩ in Chinese hamster ovary cells in which GPR35 was co-expressed in the context of a chimeric G protein signaling apparatus. HEK93 cells transfected with GPR35 and G qo proteins accumulated inositol phosphate upon exposure to KYNA. KYNA also induced internalization of GPR35 on HeLa cells, which is commonly seen following the activation of GPRs with agonists such as chemokines (9).KYNA is produced endogenously as a resu...

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Background-Vascular disease can manifest as stenotic plaques or ectatic aneurysms, although the mechanisms culminating in these divergent disease manifestations remain poorly understood. T-helper type 1 cytokines, including interferon-␥ and CXCL10, have been strongly implicated in atherosclerotic plaque development. Methods and Results-Here, we specifically examined their role in the formation of abdominal aortic aneurysms in the angiotensin II-induced murine model. Unexpectedly, we found increased suprarenal aortic diameters, abdominal aortic aneurysm incidence, and aneurysmal death in apolipoprotein E-and interferon-␥-deficient (Apoe Ϫ/Ϫ /Ifng Ϫ/Ϫ ) mice compared with Apoe Ϫ/Ϫ controls, although atherosclerotic luminal plaque formation was attenuated. The interferon-␥-inducible T-cell chemoattractant CXCL10 was highly induced by angiotensin II infusion in Apoe Ϫ/Ϫ mice, but this induction was markedly attenuated in Apoe Ϫ/Ϫ /Ifng Ϫ/Ϫ mice. Apoe Ϫ/Ϫ /Cxcl10 Ϫ/Ϫ mice had decreased luminal plaque but also increased aortic size, worse morphological grades of aneurysms, and a higher incidence of death due to aortic rupture than Apoe Ϫ/Ϫ controls. Furthermore, abdominal aortic aneurysms in Apoe Ϫ/Ϫ /Cxcl10 Ϫ/Ϫ mice were enriched for non-T-helper type 1-related signals, including transforming growth factor-␤1. Treatment of Apoe Ϫ/Ϫ /Cxcl10 Ϫ/Ϫ mice with anti-transforming growth factor-␤ neutralizing antibody diminished angiotensin II-induced aortic dilation. Conclusions-The present study defines a novel pathway in which interferon-␥ and its effector, CXCL10, contribute to divergent pathways in abdominal aortic aneurysm versus plaque formation, inhibiting the former pathology but promoting the latter. Thus, efforts to develop antiinflammatory strategies for atherosclerosis must carefully consider potential effects on all manifestations of vascular disease. Key Words: aneurysm Ⅲ atherosclerosis Ⅲ immunology Ⅲ inflammation Ⅲ mice, knockout T he pathophysiological mechanisms that lead to stenotic plaques versus aneurysms, 2 distinct vascular lesions, remain poorly understood. Clinically, abdominal aortic aneurysms (AAAs) are more strongly correlated with a family history 1 and smoking 2 than are coronary stenoses. Diabetes mellitus, a strong risk factor for coronary plaques, actually protects against AAA formation in population-based studies. 3,4 Clinical Perspective p 435Chronic inflammation of the vascular wall is believed to contribute to both manifestations of arterial pathology. 5,6 Atherosclerotic plaques are marked primarily by intimal infiltration of macrophages and T cells, at least at earlier disease stages. In contrast, aneurysmal segments are characterized by macrophage, T-cell, and B-cell accumulation primarily in the media and adventitia at all stages of disease evolution. 6 Human atherosclerotic stenoses specifically express mediators characteristic of a T-helper type 1 (Th1) immune response, including interferon (IFN)-␥, as well as the IFN-␥-inducible T-cell chemoattractant IP-10 (IFN-␥-inducible Protein...