The lack of effect of the hematopoietic CD200 deficiency on lesion size suggests that the residual presence of CD200 on stromal cells in the hematopoietic CD200 chimera protects from the increase of plaque burden even in the presence of monocytosis, likely by dampening their recruitment within the vascular compartment. Our data show that the CD200-CD200R pathway restrains activation of CD200R+ lesional macrophages, their production of CCR2 ligands, and monocyte recruitment in vitro and in vivo in an air pouch model. Loss of CD200 leads to an excessive accumulation of classical Ly6Chi monocytes and CCR2+ macrophages within the atherosclerotic aorta, as assessed by mass cytometry. Moreover, we uncover a previously uncharacterized effect of the CD200/CD200R pathway in limiting dysregulated monopoiesis and Ly6Chi monocytosis in hypercholesterolemic mice. Bone marrow chimera experiments demonstrate that this CD200-CD20R pathway enables 2 complementary and tissue-dependent strategies to CEP-32496 limit atherogenesis: CD200 expression by bone marrowCderived cells limits systemic monocytosis, while CD200 expression by nonhematopoietic cells, for example, endothelial cells, prevents local plaque growth. We show that CD200R signaling controls monopoiesis and macrophage activation through inhibiting phosphorylation of STAT1 (signal transducer and activator of transcription 1). Finally, CD200R expression on classical monocytes in peripheral blood of patients with coronary artery disease is usually associated with a lower burden of coronary artery disease and a more favorable Virtual Histology plaque profile. Conclusions: The CD200 checkpoint is usually a key-limiting factor for monopoiesis, monocyte-macrophage activation, and recruitment in atherosclerosis with conserved features in human and mouse. It thus offers a novel potential therapeutic pathway to treat cardiovascular disease. test, Mann-Whitney test, 1-way ANOVA, Kruskal-Wallis test or Spearman correlation as appropriate and as indicated in Table II in the Data Supplement. The significant findings from the planned assessments are reported in the Figures. Results CD200 and CD200R Expression in Atherosclerosis Expression of CD200 and CD200R during atherogenesis was assessed in aortic roots of chow-fed apolipoprotein E-deficient (Deficiency Promotes Atherosclerotic Lesion Development and Vulnerable Plaque Morphology Next, the effect of CD200 deficiency was studied in atherosclerosis-prone deficiency increases atherogenesis and affects plaque phenotype in 27-wk-old apolipoprotein E-deficient ((n=6). Bars show group medianinterquartile range. Atherosclerotic plaque phenotype is usually important for predicting the development of complications of atherosclerosis. The larger aortic root lesion size in Deficiency Affects the Aortic Immune Cell Scenery in Deficiency Promotes Monocyte-Macrophage Recruitment To elucidate the molecular mechanism of increased lesional macrophage content in deficiency affected the ability of monocytes to migrate in vitro and in vivo. Using an in vitro transwell chamber model, we found that CD200 deficiency promoted CCL2-directed monocyte migration in vitro (Physique ?(Figure3B).3B). The effect of CD200 on recruitment to tissue was then assessed in a well-characterized air pouch model15 (Figure ?(Figure3C).3C). Compared with deficiency promotes monocyte-macrophage recruitment. A, Fold change in CD68 (left graph) and CCR2 (C-C chemokine receptor type 2; right graph) gene expression in aortic arch (n=6C8), thoracic aorta (n=6C8), and abdominal aorta (n=6C7) in 27-wk-old deficiency increases monocytosis and monopoiesis in apolipoprotein E-deficient (test or spearman correlation. Values are meanSD. A significant and selective decrease in CD200R level was observed on classical monocytes in subjects with high CAD burden compared with subjects with CEP-32496 a low CAD burden (Figure ?(Figure8D).8D). CD200Rs mean fluorescent density on classical monocytes was also used to correlate with plaque characteristics as assessed via virtual histology (total atheroma volume, % atheroma burden, and % necrosis), and the results suggest significant and moderately high inverse correlations between CD200R level on classical monocytes and total atheroma volume, percentage of atheroma burden and percent necrosis in the plaque (Figure ?(Figure8E)8E) suggesting that CD200R expression on CEP-32496 classical monocytes is associated with a more favorable plaque phenotype. Discussion Monocyte and macrophage supply and recruitment are pivotal events Rabbit Polyclonal to PLCG1 in atherogenesis. CD200 is an inhibitory immune checkpoint known to control macrophage activation through interaction with its cognate receptor CD200R.2 We demonstrate that CD200 promotes arterial homeostasis by limiting excessive supply and activation of monocyte-macrophages during atherogenesis via local and systemic cell-dependent mechanisms (Graphical Abstract). Defective resolution of inflammation is a key driver of atherogenesis21 and downregulation of the myeloid lineage is an attractive therapeutic strategy. However, macrophage subsets in atherosclerosis are heterogeneous,10 and vascular resident macrophages have homeostatic functions.22 Thus, a blanket approach targeting all vascular macrophages could be counterproductive. Classical (Ly6Chi) monocytes are the largest subset in mouse blood, and they are the precursors for most lesional macrophages in atherosclerosis.11,12,23 Ly6Clo monocytes patrol the endothelium and support vessel wall repair. 24 The number of circulating monocytes correlates with lesion size in experimental atherosclerosis,12,13 and leucocytosis is a risk factor for CVD.25 One potential therapeutic strategy for CVD would be to target the supply and activation of monocyte-derived macrophage subsets into and within the arterial wall. CD200 limits atherogenesis by restraining the activation of CD200R+.