Proteins secreted by activated platelets can adhere to the vessel wall and promote the development of atherosclerosis and thrombosis. Despite this biologic significance, however, the complement of proteins comprising the platelet releasate is largely unknown. Using a proteomics approach, we have identified more than 300 proteins released by human platelets following thrombin activation. Many of the proteins identified were not previously attributed to platelets, including secretogranin III, a potential monocyte chemoattractant precursor; cyclophilin A, a vascular smooth muscle cell growth factor; calumenin, an inhibitor of the vitamin K epoxide reductase-warfarin interaction, as well as proteins of unknown function that map to expressed sequence tags. Secretogranin III, cyclophilin A, and calumenin were confirmed to localize in platelets and to be released upon activation. Furthermore, while absent in normal vasculature, they were identified in human atherosclerotic lesions. Therefore, these and other proteins released from platelets may contribute to atherosclerosis and to the thrombosis that complicates the disease. Moreover, as soluble extracellular proteins, they may prove suitable as novel therapeutic targets.

Background-The formation of prostacyclin (PGI 2 ), thromboxane (TX) A 2 , and isoprostanes is markedly enhanced in atherosclerosis. We examined the relative contribution of cyclooxygenase (COX)-1 and -2 to the generation of these eicosanoids in patients with atherosclerosis. Methods and Results-The study population consisted of 42 patients with atherosclerosis who were undergoing surgical revascularization. COX-2 mRNA was detected in areas of atherosclerosis but not in normal blood vessel walls, and there was evidence of COX-1 induction. The use of immunohistochemical studies localized the COX-2 to proliferating vascular smooth muscle cells and macrophages. Twenty-four patients who did not previously receive aspirin were randomized to receive either no treatment or nimesulide at 24 hours before surgery and then for 3 days. Eighteen patients who were receiving aspirin were continued on a protocol of either aspirin alone or a combination of aspirin and nimesulide. Urinary levels of 11-dehydro-TXB 2 and 2,3-dinor-6-keto-PGF 1␣ , metabolites of TXA 2 and PGI 2 , respectively, were elevated in patients with atherosclerosis compared with normal subjects (3211Ϯ533 versus 679Ϯ63 pg/mg creatinine, PϽ0.001; 594Ϯ156 versus 130Ϯ22 pg/mg creatinine, PϽ0.05, respectively), as was the level of the isoprostane 8-iso-PGF 2␣ . Nimesulide reduced 2,3-dinor-6-keto-PGF 1␣ excretion by 46Ϯ5% (378.3Ϯ103 to 167Ϯ37 pg/mg creatinine, PϽ0.01) preoperatively and blunted the increase after surgery. Nimesulide had no significant effect on 11-dehydro-TXB 2 before (2678Ϯ694 to 2110Ϯ282 pg/mg creatinine) or after surgery. The levels of both products were lower in patients who were taking aspirin, and no further reduction was seen with the addition of nimesulide. None of the treatments influenced urinary 8-iso-PGF 2␣ excretion. Conclusions-Both COX-1 and -2 are expressed and contribute to the increase in PGI 2 in patients with atherosclerosis, whereas TXA 2 is generated by COX-1. (Circulation. 2000;102:840-845.)

Mesenchymal stem cells (MSCs) inhibit T-cell activation and proliferation but their effects on individual T-cell-effector pathways and on memory versus naïve T cells remain unclear. MSC influence on the differentiation of naïve and memory CD41 T cells toward the Th17 phenotype was examined. CD4 1 T cells exposed to Th17-skewing conditions exhibited reduced CD25 and IL-17A expression following MSC co-culture. Inhibition of IL-17A production persisted upon re-stimulation in the absence of MSCs. These effects were attenuated when cell-cell contact was prevented. Th17 cultures from highly purified naïve-and memoryphenotype responders were similarly inhibited. Th17 inhibition by MSCs was reversed by indomethacin and a selective COX-2 inhibitor. Media from MSC/Th17 co-cultures contained increased prostaglandin E2 (PGE2) levels and potently suppressed Th17 differentiation in fresh cultures. MSC-mediated Th17 inhibition was reversed by a selective EP4 antagonist and was mimicked by synthetic PGE2 and a selective EP4 agonist. Activation-induced IL-17A secretion by naturally occurring, effector-memory Th17 cells from a urinary obstruction model was also inhibited by MSC co-culture in a COX-dependent manner. Overall, MSCs potently inhibit Th17 differentiation from naïve and memory T-cell precursors and inhibit naturally-occurring Th17 cells derived from a site of inflammation. Suppression entails cellcontact-dependent COX-2 induction resulting in direct Th17 inhibition by PGE2 via EP4.Key words: Immunosuppression . Mesenchymal stem cells . Stem cells . T helper cells . Th17 cells Supporting Information available online IntroductionThe immune suppressive properties of mesenchymal stem cells (MSCs) have garnered increasing attention over the past decade and constitute a central mechanism for MSC therapeutic benefits [1][2][3][4]. Specific modulatory effects of MSCs from human and experimental animal sources have been described for the differentiation, activation, proliferation and effector functions of multiple innate and adaptive immune cells [5][6][7][8][9][10][11]. Among these, MSC-mediated inhibition of primary T-cell activation and proliferation, suppression of DC maturation and promotion of regulatory phenotypes in 2840monocyte/macrophages and T cells have been most extensively characterised [7-9, 11, 12].In keeping with a paracrine or ''trophic'' model of MSC function in vivo [13], various MSC-produced soluble mediators have been implicated in these immunomodulatory effects including IL-10, IL-6, HGF, TGF-b, chemokine ligand-2 (CCL2), HLA-G, NO, tumor necrosis factor-inducible gene 6 protein (TSG-6), prostaglandin E2 (PGE2) and kyneurenine [1,2,7,9,12,[14][15][16]. For some such mediators, expression by MSCs may be dependent on pre-exposure to exogenous factors (e.g. IFN-g, TNF) or on contact-dependent MSC/target cell cross-talk [2,7,[16][17][18][19]. The potential for harnessing MSC immunomodulatory properties has been highlighted by results in pre-clinical models of autoimmunity, allotransplantation, sepsis and acu...

Atherosclerosis is an inflammatory disease caused by endothelial injury, lipid deposition, and oxidative stress. This progressive disease can be converted into an acute clinical event by plaque rupture and thrombosis. In the context of atherosclerosis, the underlying cause of myocardial infarction and stroke, macrophages uniquely possess a dual functionality, regulating lipid accumulation and metabolism and sustaining the chronic inflammatory response, two of the most well-documented pathways associated with the pathogenesis of the disease. Macrophages are heterogeneous cell populations and it is hypothesized that, during the pathogenesis of atherosclerosis, macrophages in the developing plaque can switch from a pro-inflammatory (MΦ1) to an anti-inflammatory (MΦ2) phenotype and vice versa, depending on the microenvironment. The aim of this study was to identify changes in macrophage subpopulations in the progression of human atherosclerotic disease. Established atherosclerotic plaques from symptomatic and asymptomatic patients with existing coronary artery disease undergoing carotid endarterectomy were recruited to the study. Comprehensive histological and immunohistochemical analyses were performed to quantify the cellular content and macrophage subsets of atherosclerotic lesion. In parallel, expression of MΦ1 and MΦ2 macrophage markers were analyzed by real-time PCR and Western blot analysis. Gross analysis and histological staining demonstrated that symptomatic plaques presented greater hemorrhagic activity and the internal carotid was the most diseased segment, based on the predominant prevalence of fibrotic and necrotic tissue, calcifications, and hemorrhagic events. Immunohistochemical analysis showed that both MΦ1 and MΦ2 macrophages are present in human plaques. However, MΦ2 macrophages are localized to more stable locations within the lesion. Importantly, gene and protein expression analysis of MΦ1/MΦ2 markers evidenced that MΦ1 markers and Th1-associated cytokines are highly expressed in symptomatic plaques, whereas expression of the MΦ2 markers, mannose receptor (MR), and CD163 and Th2 cytokines are inversely related with disease progression. These data increase the understanding of atherosclerosis development, identifying the cellular content of lesions during disease progression, and characterizing macrophage subpopulation within human atherosclerotic plaques.