Dimeric IgA specifically disables intracellular mutated oncodrivers.

A prevailing belief in the immunotherapy field has been that antibody therapy can effectively target only extracellular antigens. In this issue of Immunity, Biswas et al. demonstrate therapeutically effective targeting, neutralization, and removal of mutated oncodriver proteins from within epithelial cancer cells by treatment with pIgR-dependent, transcytosing dimeric-IgA antibodies.

Single-cell functional genomics reveals determinants of sensitivity and resistance to natural killer cells in blood cancers.

Cancer cells can evade natural killer (NK) cell activity, thereby limiting anti-tumor immunity. To reveal genetic determinants of susceptibility to NK cell activity, we examined interacting NK cells and blood cancer cells using single-cell and genome-scale functional genomics screens. Interaction of NK and cancer cells induced distinct activation and type I interferon (IFN) states in both cell types depending on the cancer cell lineage and molecular phenotype, ranging from more sensitive myeloid to less sensitive B-lymphoid cancers. CRISPR screens in cancer cells uncovered genes regulating sensitivity and resistance to NK cell-mediated killing, including adhesion-related glycoproteins, protein fucosylation genes, and transcriptional regulators, in addition to confirming the importance of antigen presentation and death receptor signaling pathways. CRISPR screens with a single-cell transcriptomic readout provided insight into underlying mechanisms, including regulation of IFN-γ signaling in cancer cells and NK cell activation states. Our findings highlight the diversity of mechanisms influencing NK cell susceptibility across different cancers and provide a resource for NK cell-based therapies.

Single-Cell Survey of Human Lymphatics Unveils Marked Endothelial Cell Heterogeneity and Mechanisms of Homing for Neutrophils.

Lymphatic vessels form a critical component in the regulation of human health and disease. While their functional significance is increasingly being recognized, the comprehensive heterogeneity of lymphatics remains uncharacterized. Here, we report the profiling of 33,000 lymphatic endothelial cells (LECs) in human lymph nodes (LNs) by single-cell RNA sequencing. Unbiased clustering revealed six major types of human LECs. LECs lining the subcapsular sinus (SCS) of LNs abundantly expressed neutrophil chemoattractants, whereas LECs lining the medullary sinus (MS) expressed a C-type lectin CD209. Binding of a carbohydrate Lewis X (CD15) to CD209 mediated neutrophil binding to the MS. The neutrophil-selective homing by MS LECs may retain neutrophils in the LN medulla and allow lymph-borne pathogens to clear, preventing their spread through LNs in humans. Our study provides a comprehensive characterization of LEC heterogeneity and unveils a previously undefined role for medullary LECs in human immunity.

A form of inherited hyperferritinemia associated with bi-allelic pathogenic variants of STAB1.

Hyperferritinemia is a frequent finding in several conditions, both genetic and acquired. We previously studied eleven healthy subjects from eight different families presenting with unexplained hyperferritinemia. Their findings suggested the existence of an autosomal-recessive disorder. We carried out whole-exome sequencing to detect the genetic cause of hyperferritinemia. Immunohistochemistry and flow cytometry assays were performed on liver biopsies and monocyte-macrophages to confirm the pathogenic role of the identified candidate variants. Through a combined approach of whole-exome sequencing and homozygosity mapping, we found bi-allelic STAB1 variants in ten subjects from seven families. STAB1 encodes the multifunctional scavenger receptor stabilin-1. Immunohistochemistry and flow cytometry analyses showed absent or markedly reduced stabilin-1 in liver samples, monocytes, and monocyte-derived macrophages. Our findings show a strong association between otherwise unexplained hyperferritinemia and bi-allelic STAB1 mutations suggesting the existence of another genetic cause of hyperferritinemia without iron overload and an unexpected function of stabilin-1 in ferritin metabolism.

Clinical landscape of macrophage-reprogramming cancer immunotherapies.

Tumour-associated macrophages (TAMs) sustain a tumour-supporting and immunosuppressive milieu and therefore aggravate cancer prognosis. To modify TAM behaviour and unlock their anti-tumoural potential, novel TAM-reprogramming immunotherapies are being developed at an accelerating rate. At the same time, scientific discoveries have highlighted more sophisticated TAM phenotypes with complex biological functions and contradictory prognostic associations. To understand the evolving clinical landscape, we reviewed current and past clinically evaluated TAM-reprogramming cancer therapeutics and summarised almost 200 TAM-reprogramming agents investigated in more than 700 clinical trials. Observable overall trends include a high frequency of overlapping strategies against the same therapeutic targets, development of more complex strategies to improve previously ineffective approaches and reliance on combinatory strategies for efficacy. However, strong anti-tumour efficacy is uncommon, which encourages re-directing efforts on identifying biomarkers for eligible patient populations and comparing similar treatments earlier. Future endeavours will benefit from considering the shortcomings of past treatment strategies and accommodating the emerging complexity of TAM biology.

Prolonged Systemic Inflammatory Response Syndrome After Cardiac Surgery.

OBJECTIVES: Cardiac surgery induces systemic inflammatory response syndrome (SIRS), leading to higher morbidity and mortality. There are no individualized predictors for worse outcomes or biomarkers for the multifactorial, excessive inflammatory response. The interest of this study was to evaluate whether a systematic use of the SIRS criteria could be used to predict postoperative outcomes beyond infection and sepsis, and if the development of an exaggerated inflammation response could be observed preoperatively. DESIGN: The study was observational, with prospectively enrolled patients. SETTING: This was a single institution study in a hospital setting combined with laboratory findings. PARTICIPANTS: The study included a cohort of 261 volunteer patients. INTERVENTIONS: Patients underwent cardiac surgery with cardiopulmonary bypass, and were followed up to 90 days. Biomarker profiling was run preoperatively. MEASUREMENTS AND MAIN RESULTS: Altogether, 17 of 261 (6.4%) patients had prolonged SIRS, defined as fulfilling at least 2 criteria on 4 consecutive postoperative days. During hospitalization, postoperative atrial fibrillation (POAF) was found in 42.2% of patients, and stroke and transient ischemic attack in 3.8% of patients. Prolonged SIRS was a significant predictor of POAF (odds ratio [OR] 4.5, 95% CI 1.2-17.3), 90-day stroke (OR 4.5, 95% CI 1.1-18.0), and mortality (OR 10.7, 95% CI 1.7-68.8). Biomarker assays showed that preoperative nerve growth factor and interleukin 5 levels were associated with prolonged SIRS (OR 5.6, 95%, CI 1.4-23.2 and OR 0.7, 95%, CI 0.4-1.0, respectively). CONCLUSIONS: Nerve growth factor and interleukin 5 can be used to predict prolonged systemic inflammatory response, which is associated with POAF, stroke, and mortality.

Polymorphism in interferon alpha/beta receptor contributes to glucocorticoid response and outcome of ARDS and COVID-19.

BACKGROUND: The use of glucocorticoids has given contradictory results for treating acute respiratory distress syndrome (ARDS). The use of intravenous Interferon beta (IFN ß) for the treatment of ARDS was recently tested in a phase III ARDS trial (INTEREST), in which more than half of the patients simultaneously received glucocorticoids. Trial results showed deleterious effects of glucocorticoids when administered together with IFN ß, and therefore, we aimed at finding the reason behind this. METHODS: We first sequenced the genes encoding the IFN α/ß receptor of the patients, who participated in the INTEREST study (ClinicalTrials.gov Identifier:  NCT02622724 , November 24, 2015) in which the patients were randomized to receive an intravenous injection of IFN ß-1a (144 patients) or placebo (152 patients). Genetic background was analyzed against clinical outcome, concomitant medication, and pro-inflammatory cytokine levels. Thereafter, we tested the influence of the genetic background on IFN α/ß receptor expression in lung organ cultures and whether, it has any effect on transcription factors STAT1 and STAT2 involved in IFN signaling. RESULTS: We found a novel disease association of a SNP rs9984273, which is situated in the interferon α/ß receptor subunit 2 (IFNAR2) gene in an area corresponding to a binding motif of the glucocorticoid receptor (GR). The minor allele of SNP rs9984273 associates with higher IFNAR expression, more rapid decrease of IFN γ and interleukin-6 (IL-6) levels and better outcome in IFN ß treated patients with ARDS, while the major allele associates with a poor outcome especially under concomitant IFN ß and glucocorticoid treatment. Moreover, the minor allele of rs9984273 associates with a less severe form of coronavirus diseases (COVID-19) according to the COVID-19 Host Genetics Initiative database. CONCLUSIONS: The distribution of this SNP within clinical study arms may explain the contradictory results of multiple ARDS studies and outcomes in COVID-19 concerning type I IFN signaling and glucocorticoids.

Clever-1 positive macrophages in breast cancer.

PURPOSE: Common Lymphatic Endothelial and Vascular Endothelial Receptor 1 (Clever-1) is expressed by a subset of immunosuppressive macrophages and targeting the receptor with therapeutic antibodies has been shown to activate T-cell-mediated anti-cancer immunity. The aim of this research was to study Clever-1 expression in breast cancer. Specifically, how Clever-1 + macrophages correlate with clinicopathologic factors, Tumor Infiltrating Lymphocytes (TILs) and prognosis. METHODS: Tissue microarray blocks were made from 373 primary breast cancer operation specimens. Hematoxylin and Eosin (H&E-staining) and immunohistochemical staining with Clever-1, CD3, CD4 and CD8 antibodies were performed. Differences in quantities of Clever-1 + macrophages and TILs were analyzed. Clever-1 + cell numbers were correlated with 25-year follow-up survival data and with breast cancer clinicopathologic parameters. RESULTS: Low numbers of intratumoral Clever-1 + cells were found to be an independent adverse prognostic sign. Increased numbers of Clever-1 + cells were found in high grade tumors and hormone receptor negative tumors. Tumors that had higher amounts of Clever-1 + cells also tended to have higher amounts of TILs. CONCLUSION: The association of intratumoral Clever-1 + macrophages with better prognosis might stem from the function of Clever as a scavenger receptor that modulates tumor stroma. The association of Clever-1 + macrophages with high number of TILs and better prognosis indicates that immunosuppression by M2 macrophages is not necessarily dampening adaptive immune responses but instead keeping them in control to avoid excess inflammation.

Vascular adhesion protein-1 defines a unique subpopulation of human hematopoietic stem cells and regulates their proliferation.

Although the development of hematopoietic stem cells (HSC) has been studied in great detail, their heterogeneity and relationships to different cell lineages remain incompletely understood. Moreover, the role of Vascular Adhesion Protein-1 in bone marrow hematopoiesis has remained unknown. Here we show that VAP-1, an adhesin and a primary amine oxidase producing hydrogen peroxide, is expressed on a subset of human HSC and bone marrow vasculature forming a hematogenic niche. Bulk and single-cell RNAseq analyses reveal that VAP-1+ HSC represent a transcriptionally unique small subset of differentiated and proliferating HSC, while VAP-1- HSC are the most primitive HSC. VAP-1 generated hydrogen peroxide acts via the p53 signaling pathway to regulate HSC proliferation. HSC expansion and differentiation into colony-forming units are enhanced by inhibition of VAP-1. Contribution of VAP-1 to HSC proliferation was confirmed with mice deficient of VAP-1, mice expressing mutated VAP-1 and using an enzyme inhibitor. In conclusion, VAP-1 expression allows the characterization and prospective isolation of a new subset of human HSC. Since VAP-1 serves as a check point-like inhibitor in HSC differentiation, the use of VAP-1 inhibitors enables the expansion of HSC.

Metastable Atrial State Underlies the Primary Genetic Substrate for MYL4 Mutation-Associated Atrial Fibrillation.

BACKGROUND: Atrial fibrillation (AF) is the most common clinical arrhythmia and is associated with heart failure, stroke, and increased mortality. The myocardial substrate for AF is poorly understood because of limited access to primary human tissue and mechanistic questions around existing in vitro or in vivo models. METHODS: Using an MYH6:mCherry knock-in reporter line, we developed a protocol to generate and highly purify human pluripotent stem cell-derived cardiomyocytes displaying physiological and molecular characteristics of atrial cells. We modeled human MYL4 mutants, one of the few definitive genetic causes of AF. To explore non-cell-autonomous components of AF substrate, we also created a zebrafish Myl4 knockout model, which exhibited molecular, cellular, and physiologic abnormalities that parallel those in humans bearing the cognate mutations. RESULTS: There was evidence of increased retinoic acid signaling in both human embryonic stem cells and zebrafish mutant models, as well as abnormal expression and localization of cytoskeletal proteins, and loss of intracellular nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide + hydrogen. To identify potentially druggable proximate mechanisms, we performed a chemical suppressor screen integrating multiple human cellular and zebrafish in vivo endpoints. This screen identified Cx43 (connexin 43) hemichannel blockade as a robust suppressor of the abnormal phenotypes in both models of MYL4 (myosin light chain 4)-related atrial cardiomyopathy. Immunofluorescence and coimmunoprecipitation studies revealed an interaction between MYL4 and Cx43 with altered localization of Cx43 hemichannels to the lateral membrane in MYL4 mutants, as well as in atrial biopsies from unselected forms of human AF. The membrane fraction from MYL4-/- human embryonic stem cell derived atrial cells demonstrated increased phospho-Cx43, which was further accentuated by retinoic acid treatment and by the presence of risk alleles at the Pitx2 locus. PKC (protein kinase C) was induced by retinoic acid, and PKC inhibition also rescued the abnormal phenotypes in the atrial cardiomyopathy models. CONCLUSIONS: These data establish a mechanistic link between the transcriptional, metabolic and electrical pathways previously implicated in AF substrate and suggest novel avenues for the prevention or therapy of this common arrhythmia.

Intravenous Interferon-ß1a for the Treatment of Ischemia-Reperfusion Injury in Acute Myocardial Infarct in Pigs.

BACKGROUND: To investigate the potential of intravenously administered porcine recombinant interferon-ß1a (IFN-ß1a) for myocardial protection during acute ischemia-reperfusion (IR) injury in an experimental animal model. METHODS: Twenty-two piglets (mean ± standard deviation, 26.7 ± 1.65 kg) were assigned to either the IFN group (n = 12) or the control group (n = 10). IR injury was induced by occluding the distal left descending coronary artery for 30 minutes, with a reperfusion period of 6 h. In the IFN group, the animals received 12.5 µg IFN-ß1a intravenously repeatedly; the control group received saline solution. The levels of interleukin-6 (IL-6) and cardiac troponin I (TnI) were measured, and the amount of myocardial damage was quantified by analyzing myocardial apoptosis and the mean fluorescence intensity (MFI) of methylene blue-stained cardiac tissue. RESULTS: In the IFN group, significantly more premature deaths occurred compared with the control group (25% versus 17%, P = .013). Between the groups, the mean heart rate was higher in the IFN group (102 ± 22 versus 80 ± 20 beats per minute, P = .02). IL-6 and TnI levels were comparable between the groups, with no significant difference, and there was no difference between the study groups in myocardial apoptosis in the infarcted myocardium. The percentage of MFI differed significantly between the IFN and control groups (90.75% ± 4.90% versus 96.02% ± 2.73%, P = .01). CONCLUSION: In this acute IR injury animal model, IFN-ß1a did not protect the myocardium from IR injury, but rather increased some of the unfavorable outcomes studied.

A Distinct Cytokine Profile and Stromal Vascular Fraction Metabolic Status without Significant Changes in the Lipid Composition Characterizes Lipedema.

Lipedema is an adipose tissue disorder characterized by the disproportionate increase of subcutaneous fat tissue in the lower and/or upper extremities. The underlying pathomechanism remains unclear and no molecular biomarkers to distinguish the disease exist, leading to a large number of undiagnosed and misdiagnosed patients. To unravel the distinct molecular characteristic of lipedema we performed lipidomic analysis of the adipose tissue and serum of lipedema versus anatomically- and body mass index (BMI)-matched control patients. Both tissue groups showed no significant changes regarding lipid composition. As hyperplastic adipose tissue represents low-grade inflammation, the potential systemic effects on circulating cytokines were evaluated in lipedema and control patients using the Multiplex immunoassay system. Interestingly, increased systemic levels of interleukin 11 (p = 0.03), interleukin 28A (p = 0.04) and interleukin 29 (p = 0.04) were observed. As cytokines can influence metabolic activity, the metabolic phenotype of the stromal vascular fraction was examined, revealing significantly increased mitochondrial respiration in lipedema. In conclusion, despite sharing a comparable lipid profile with healthy adipose tissue, lipedema is characterized by a distinct systemic cytokine profile and metabolic activity of the stromal vascular fraction.

New tools to prevent cancer growth and spread: a 'Clever' approach.

Clever-1 (also known as Stabilin-1 and FEEL-1) is a scavenger receptor expressed on lymphatic endothelial cells, sinusoidal endothelial cells and immunosuppressive monocytes and macrophages. Its role in cancer growth and spread first became evident in Stab1-/- knockout mice, which have smaller primary tumours and metastases. Subsequent studies in mice and humans have shown that immunotherapeutic blockade of Clever-1 can activate T-cell responses, and that this response is mainly mediated by a phenotypic change in macrophages and monocytes from immunosuppressive to pro-inflammatory following Clever-1 inhibition. Analyses of human cancer cohorts have revealed marked associations between the number of Clever-1-positive macrophages and patient outcome. As hardly any reports to date have addressed the role of Clever-1 in immunotherapy resistance and T-cell dysfunction, we performed data mining using several published cancer cohorts, and observed a remarkable correlation between Clever-1 positivity and resistance to immune checkpoint therapies. This result provides impetus and potential for the ongoing clinical trial targeting Clever-1 in solid tumours, which has so far shown a shift towards immune activation when a particular epitope of Clever-1 is blocked.

Adipose Tissue Hypertrophy, An Aberrant Biochemical Profile and Distinct Gene Expression in Lipedema.

BACKGROUND: Lipedema is a common adipose tissue disorder affecting women, characterized by a symmetric subcutaneous adipose tissue deposition, particularly of the lower extremities. Lipedema is usually underdiagnosed, thus remaining an undertreated disease. Importantly, no histopathologic or molecular hallmarks exist to clearly diagnose the disease, which is often misinterpreted as obesity or lymphedema. MATERIALS AND METHODS: The aim of the present study is to characterize in detail morphologic and molecular alterations in the adipose tissue composition of lipedema patients compared with healthy controls. Detailed histopathologic and molecular characterization was performed using lipid and cytokine quantification as well as gene expression arrays. The analysis was conducted on anatomically matched skin and fat tissue biopsies as well as fasting serum probes obtained from 10 lipedema and 11 gender and body mass index-matched control patients. RESULTS: Histologic evaluation of the adipose tissue showed increased intercellular fibrosis and adipocyte hypertrophy. Serum analysis showed an aberrant lipid metabolism without changes in the circulating adipokines. In an adipogenesis gene array, a distinct gene expression profile associated with macrophages was observed. Histologic assessment of the immune cell infiltrate confirmed the increased presence of macrophages, without changes in the T-cell compartment. CONCLUSIONS: Lipedema presents a distinguishable disease with typical tissue architecture and aberrant lipid metabolism, different to obesity or lymphedema. The differentially expressed genes and immune cell infiltration profile in lipedema patients further support these findings.

Serum cytokine levels differ according to major cardiovascular risk factors in patients with lower limb atherosclerosis.

Different cardiovascular risk factors present a heterogenic manifestation of lower limb atherosclerosis. The molecular mechanisms behind this phenomenon remain unknown. We aimed to clarify this phenomenon by studying the association of major cardiovascular risk factors with the profile of serum cytokines in 226 consecutive patients with lower limb atherosclerosis treated at a department of Vascular Surgery during a one-year enrollment period. Increasing age independently associated with higher levels of IFN-γ inducible factors MIG, CTACK and IP-10 (P < 0.001 for all). Patients with chronic kidney disease had higher serum levels of MIF, IL-16 and SCF (P = 0.001 or less for all). Smoking and hypertension associated with IL-17 (P = 0.037 and 0.015, respectively). In addition, smoking associated with growth factors known to induce myeloid progenitor cell proliferation: GM-CSF (P = 0.035), PDGF (P = 0.024), bFGF (P = 0.026), and HGF (P = 0.030). Dyslipidemia also associated with myeloproliferative factors: MIB-1α (P = 0.005) and PDGF (P = 0.01). Type II diabetes associated with Th2 mediated inflammation: IL-5 (P < 0.001), IL-7 (P = 0.004) and IL-13 (P = 0.015). Major cardiovascular risk factors are associated with different circulating cytokines implicating different immunological pathology.

Melanocortin 1 Receptor Deficiency Promotes Atherosclerosis in Apolipoprotein E-/- Mice.

OBJECTIVE: The MC1-R (melanocortin 1 receptor) is expressed by monocytes and macrophages where it mediates anti-inflammatory actions. MC1-R also protects against macrophage foam cell formation primarily by promoting cholesterol efflux through the ABCA1 (ATP-binding cassette transporter subfamily A member 1) and ABCG1 (ATP-binding cassette transporter subfamily G member 1). In this study, we aimed to investigate whether global deficiency in MC1-R signaling affects the development of atherosclerosis. APPROACH AND RESULTS: Apoe-/- (apolipoprotein E deficient) mice were crossed with recessive yellow (Mc1re/e) mice carrying dysfunctional MC1-R and fed a high-fat diet to induce atherosclerosis. Apoe-/- Mc1re/e mice developed significantly larger atherosclerotic lesions in the aortic sinus and in the whole aorta compared with Apoe-/- controls. In terms of plaque composition, MC1-R deficiency was associated with less collagen and smooth muscle cells and increased necrotic core, indicative of more vulnerable lesions. These changes were accompanied by reduced Abca1 and Abcg1 expression in the aorta. Furthermore, Apoe-/- Mc1re/e mice showed a defect in bile acid metabolism that aggravated high-fat diet-induced hypercholesterolemia and hepatic lipid accumulation. Flow cytometric analysis of leukocyte profile revealed that dysfunctional MC1-R enhanced arterial accumulation of classical Ly6Chigh monocytes and macrophages, effects that were evident in mice fed a normal chow diet but not under high-fat diet conditions. In support of enhanced arterial recruitment of Ly6Chigh monocytes, these cells had increased expression of L-selectin and P-selectin glycoprotein ligand 1. CONCLUSIONS: The present study highlights the importance of MC1-R in the development of atherosclerosis. Deficiency in MC1-R signaling exacerbates atherosclerosis by disturbing cholesterol handling and by increasing arterial monocyte accumulation.

Aberrant circulating levels of purinergic signaling markers are associated with several key aspects of peripheral atherosclerosis and thrombosis.

RATIONALE: Purinergic signaling plays an important role in inflammation and vascular integrity, but little is known about purinergic mechanisms during the pathogenesis of atherosclerosis in humans. OBJECTIVE: The objective of this study is to study markers of purinergic signaling in a cohort of patients with peripheral artery disease. METHODS AND RESULTS: Plasma ATP and ADP levels and serum nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39) and ecto-5'-nucleotidase/CD73 activities were measured in 226 patients with stable peripheral artery disease admitted for nonurgent invasive imaging and treatment. The major findings were that ATP, ADP, and CD73 values were higher in atherosclerotic patients than in controls without clinically evident peripheral artery disease (P<0.0001). Low CD39 activity was associated with disease progression (P=0.01). In multivariable linear regression models, high CD73 activity was associated with chronic hypoxia (P=0.001). Statin use was associated with lower ADP (P=0.041) and tended to associate with higher CD73 (P=0.054), while lower ATP was associated with the use of angiotensin receptor blockers (P=0.015). CONCLUSIONS: Purinergic signaling plays an important role in peripheral artery disease progression. Elevated levels of circulating ATP and ADP are especially associated with atherosclerotic diseases of younger age and smoking. The antithrombotic and anti-inflammatory effects of statins may partly be explained by their ability to lower ADP. We suggest that the prothrombotic nature of smoking could be a cause of elevated ADP, and this may explain why cardiovascular patients who smoke benefit from platelet P2Y12 receptor antagonists more than their nonsmoking peers.

Regulation of CD73 in the development of lower limb atherosclerosis.

Atherosclerosis is an inflammatory process of the arterial wall. CD73 (also known as ecto-5'-nucleotidase) is a key regulator of cell signaling in response to inflammation and hypoxia, and may be important in the development of atherosclerosis. Recently, we have shown that high CD73 activity can be detected in the serum of patients with peripheral arterial disease (PAD). Using this same PAD patient cohort of 226 subjects with 38 femoral artery samples obtained during surgical endarcterectomy and control artery samples taken during autopsy, we explored the association of serum CD73 activity with overall atherosclerotic burden and the expression of CD73 in mature and developing plaques. Interestingly, we found that CD73 activity had a tendency to increase along with more severe presentation of PAD (from 249 nmol/mL/h in moderate disease to 332 nmol/mL/h in severe disease; P = 0.013) and that CD73 expression is elevated in the vasa vasorum of developing plaques, but completely lost in mature occlusive plaques removed during endarcterectomy (P < 0.001). The current findings implicate that as a result of shedding and loss of CD73 from the arterial wall, CD73 activity is elevated in the serum of patients with widespread atherosclerosis. These findings highlight the importance of a better understanding of the local role of CD73 in the development and maturation of arterial atherosclerotic plaques in man.

Ecto-5'-nucleotidase/CD73 enhances endothelial barrier function and sprouting in blood but not lymphatic vasculature.

CD73/ecto-5'-nucleotidase is a key enzyme in the regulation of purinergic signaling and inflammatory reactions. It hydrolyzes extracellular AMP into adenosine, which dampens immune cell activation, and reduces leukocyte trafficking. By comparing CD73 expression and function in mononuclear and endothelial cells (ECs) of blood and lymph, we show that extracellular purines and CD73 activity have differential effects in these two vascular systems. We found that CD8-positive T lymphocytes and CD19-positive B lymphocytes in human lymph expressed high levels of CD73 and other purinergic enzymes and adenosine receptors. Soluble CD73 was less abundant in human lymph than in serum, whereas CD73 activity was higher in afferent lymphatic ECs than in blood ECs. Adenosine signaling improved barrier function and induced sprouting of human blood, but not lymphatic, ECs in vitro. Similarly, using CD73-deficient mice we found that CD73 controls only blood vascular permeability at selected lymphoid organs under physiological conditions. Thus, both vascular and lymphatic arms of the immune system synthesize the components of purinergic signaling system, but surprisingly they use CD73 differentially to control endothelial permeability and sprouting.