Suppressor CD4+ T cells expressing HLA-G are expanded in the peripheral blood from patients with acute decompensation of cirrhosis.

OBJECTIVE: Identifying components of immuneparesis, a hallmark of chronic liver failure, is crucial for our understanding of complications in cirrhosis. Various suppressor CD4+ T cells have been established as potent inhibitors of systemic immune activation. Here, we establish the presence, regulation and mechanism of action of a suppressive CD4+ T cell subset expressing human leucocyte antigen G (HLA-G) in patients with acute decompensation of cirrhosis (AD). DESIGN: Flow cytometry was used to determine the proportion and immunophenotype of CD4+HLA-G+ T cells from peripheral blood of 20 healthy controls (HCs) and 98 patients with cirrhosis (28 with stable cirrhosis (SC), 20 with chronic decompensated cirrhosis (CD) and 50 with AD). Transcriptional and functional signatures of cell-sorted CD4+HLA-G+ cells were delineated by NanoString technology and suppression assays, respectively. The role of immunosuppressive cytokine interleukin (IL)-35 in inducing this population was investigated through in vitro blockade experiments. Immunohistochemistry (IHC) and cultures of primary human Kupffer cells (KCs) were performed to assess cellular sources of IL-35. HLA-G-mediated T cell suppression was explored using neutralising antibodies targeting co-inhibitory pathways. RESULTS: Patients with AD were distinguished by an expansion of a CD4+HLA-G+CTLA-4+IL-35+ immunosuppressive population associated with disease severity, clinical course of AD, infectious complications and poor outcome. Transcriptomic analyses excluded the possibility that these were thymic-derived regulatory T cells. IHC analyses and in vitro cultures demonstrate that KCs represent a potent source of IL-35 which can induce the observed HLA-G+ phenotype. These exert cytotoxic T lymphocyte antigen-4-mediated impaired responses in T cells paralleled by an HLA-G-driven downregulation of T helper 17-related cytokines. CONCLUSION: We have identified a cytokine-driven peripherally derived suppressive population that may contribute to immuneparesis in AD.

Impaired Transmigration of Myeloid-Derived Suppressor Cells across Human Sinusoidal Endothelium Is Associated with Decreased Expression of CD13.

Human monocytic myeloid-derived suppressor cells (MO-MDSCs) within the hepatic compartment suppress inflammation and impair immune surveillance in liver cancer. It is currently not known whether recruitment of MO-MDSCs from blood via hepatic sinusoidal endothelium (HSEC) contributes to their enrichment within the hepatic compartment. We compared the transmigratory potential of MO-MDSCs and monocytes after adhesion to hepatic endothelial monolayers in flow-based assays that mimic in vivo shear stress in the sinusoids. Despite comparable binding to HSEC monolayers, proportionally fewer MO-MDSCs underwent transendothelial migration, indicating that the final steps of extravasation, where actin polymerization plays an important role, are impaired in MO-MDSCs. In this article, we found reduced levels of CD13 on MO-MDSCs, which has recently been reported to control cell motility in monocytes, alongside reduced VLA-4 expression, an integrin predominantly involved in adherence to the apical side of the endothelium. CD13 and VLA-4 blocking and activating Abs were used in flow-based adhesion assays, live-cell imaging of motility, and actin polymerization studies to confirm a role for CD13 in impaired MO-MDSC transmigration. These findings indicate that CD13 significantly contributes to tissue infiltration by MO-MDSCs and monocytes, thereby contributing to the pathogenesis of hepatic inflammation.

Stabilin-1 expression defines a subset of macrophages that mediate tissue homeostasis and prevent fibrosis in chronic liver injury.

Macrophages are key regulators of fibrosis development and resolution. Elucidating the mechanisms by which they mediate this process is crucial for establishing their therapeutic potential. Here, we use experimental models of liver fibrosis to show that deficiency of the scavenger receptor, stabilin-1, exacerbates fibrosis and delays resolution during the recovery phase. We detected a subset of stabilin-1(+) macrophages that were induced at sites of cellular injury close to the hepatic scar in mouse models of liver fibrosis and in human liver disease. Stabilin-1 deficiency abrogated malondialdehyde-LDL (MDA-LDL) uptake by hepatic macrophages and was associated with excess collagen III deposition. Mechanistically, the lack of stabilin-1 led to elevated intrahepatic levels of the profibrogenic chemokine CCL3 and an increase in GFAP(+) fibrogenic cells. Stabilin-1(-/-) macrophages demonstrated a proinflammatory phenotype during liver injury and the normal induction of Ly6C(lo) monocytes during resolution was absent in stabilin-1 knockouts leading to persistence of fibrosis. Human stabilin-1(+) monocytes efficiently internalized MDA-LDL and this suppressed their ability to secrete CCL3, suggesting that loss of stabilin-1 removes a brake to CCL3 secretion. Experiments with cell-lineage-specific knockouts revealed that stabilin-1 expression in myeloid cells is required for the induction of this subset of macrophages and that increased fibrosis occurs in their absence. This study demonstrates a previously unidentified regulatory pathway in fibrogenesis in which a macrophage scavenger receptor protects against organ fibrosis by removing fibrogenic products of lipid peroxidation. Thus, stabilin-1(+) macrophages shape the tissue microenvironment during liver injury and healing.

Vascular adhesion protein-1 is elevated in primary sclerosing cholangitis, is predictive of clinical outcome and facilitates recruitment of gut-tropic lymphocytes to liver in a substrate-dependent manner.

OBJECTIVE: Primary sclerosing cholangitis (PSC) is the classical hepatobiliary manifestation of IBD. This clinical association is linked pathologically to the recruitment of mucosal T cells to the liver, via vascular adhesion protein (VAP)-1-dependent enzyme activity. Our aim was to examine the expression, function and enzymatic activation of the ectoenzyme VAP-1 in patients with PSC. DESIGN: We examined VAP-1 expression in patients with PSC, correlated levels with clinical characteristics and determined the functional consequences of enzyme activation by specific enzyme substrates on hepatic endothelium. RESULTS: The intrahepatic enzyme activity of VAP-1 was elevated in PSC versus immune-mediated disease controls and non-diseased liver (p<0.001). The adhesion of gut-tropic α4ß7+lymphocytes to hepatic endothelial cells in vitro under flow was attenuated by 50% following administration of the VAP-1 inhibitor semicarbazide (p<0.01). Of a number of natural VAP-1 substrates tested, cysteamine-which can be secreted by inflamed colonic epithelium and gut bacteria-was the most efficient (yielded the highest enzymatic rate) and efficacious in its ability to induce expression of functional mucosal addressin cell adhesion molecule-1 on hepatic endothelium. In a prospectively evaluated patient cohort with PSC, elevated serum soluble (s)VAP-1 levels predicted poorer transplant-free survival for patients, independently (HR: 3.85, p=0.003) and additively (HR: 2.02, p=0.012) of the presence of liver cirrhosis. CONCLUSIONS: VAP-1 expression is increased in PSC, facilitates adhesion of gut-tropic lymphocytes to liver endothelium in a substrate-dependent manner, and elevated levels of its circulating form predict clinical outcome in patients.

MerTK expressing hepatic macrophages promote the resolution of inflammation in acute liver failure.

OBJECTIVE: Acute liver failure (ALF) is characterised by overwhelming hepatocyte death and liver inflammation with massive infiltration of myeloid cells in necrotic areas. The mechanisms underlying resolution of acute hepatic inflammation are largely unknown. Here, we aimed to investigate the impact of Mer tyrosine kinase (MerTK) during ALF and also examine how the microenvironmental mediator, secretory leucocyte protease inhibitor (SLPI), governs this response. DESIGN: Flow cytometry, immunohistochemistry, confocal imaging and gene expression analyses determined the phenotype, functional/transcriptomic profile and tissue topography of MerTK+ monocytes/macrophages in ALF, healthy and disease controls. The temporal evolution of macrophage MerTK expression and its impact on resolution was examined in APAP-induced acute liver injury using wild-type (WT) and Mer-deficient (Mer-/-) mice. SLPI effects on hepatic myeloid cells were determined in vitro and in vivo using APAP-treated WT mice. RESULTS: We demonstrate a significant expansion of resolution-like MerTK+HLA-DRhigh cells in circulatory and tissue compartments of patients with ALF. Compared with WT mice which show an increase of MerTK+MHCIIhigh macrophages during the resolution phase in ALF, APAP-treated Mer-/- mice exhibit persistent liver injury and inflammation, characterised by a decreased proportion of resident Kupffer cells and increased number of neutrophils. Both in vitro and in APAP-treated mice, SLPI reprogrammes myeloid cells towards resolution responses through induction of a MerTK+HLA-DRhigh phenotype which promotes neutrophil apoptosis and their subsequent clearance. CONCLUSIONS: We identify a hepatoprotective, MerTK+, macrophage phenotype that evolves during the resolution phase following ALF and represents a novel immunotherapeutic target to promote resolution responses following acute liver injury.

Human liver sinusoidal endothelial cells promote intracellular crawling of lymphocytes during recruitment: A new step in migration.

The recruitment of lymphocytes via the hepatic sinusoidal channels and positioning within liver tissue is a critical event in the development and persistence of chronic inflammatory liver diseases. The hepatic sinusoid is a unique vascular bed lined by hepatic sinusoidal endothelial cells (HSECs), a functionally and phenotypically distinct subpopulation of endothelial cells. Using flow-based adhesion assays to study the migration of lymphocytes across primary human HSECs, we found that lymphocytes enter into HSECs, confirmed by electron microscopy demonstrating clear intracellular localization of lymphocytes in vitro and by studies in human liver tissues. Stimulation by interferon-γ increased intracellular localization of lymphocytes within HSECs. Furthermore, using confocal imaging and time-lapse recordings, we demonstrated "intracellular crawling" of lymphocytes entering into one endothelial cell from another. This required the expression of intracellular adhesion molecule-1 and stabilin-1 and was facilitated by the junctional complexes between HSECs. CONCLUSION: Lymphocyte migration is facilitated by the unique structure of HSECs. Intracellular crawling may contribute to optimal lymphocyte positioning in liver tissue during chronic hepatitis. (Hepatology 2017;65:294-309).

CD151 supports VCAM-1-mediated lymphocyte adhesion to liver endothelium and is upregulated in chronic liver disease and hepatocellular carcinoma.

CD151, a member of the tetraspanin family of receptors, is a lateral organizer and modulator of activity of several families of transmembrane proteins. It has been implicated in the development and progression of several cancers, but its role in chronic inflammatory disease is less well understood. Here we show that CD151 is upregulated by distinct microenvironmental signals in a range of chronic inflammatory liver diseases and in primary liver cancer, in which it supports lymphocyte recruitment. CD151 was highly expressed in endothelial cells of the hepatic sinusoids and neovessels developing in fibrotic septa and tumor margins. Primary cultures of human hepatic sinusoidal endothelial cells (HSECs) expressed CD151 at the cell membrane and in intracellular vesicles. CD151 was upregulated by VEGF and HepG2 conditioned media but not by proinflammatory cytokines. Confocal microscopy confirmed that CD151 colocalized with the endothelial adhesion molecule/immunoglobulin superfamily member, VCAM-1. Functional flow-based adhesion assays with primary human lymphocytes and HSECs demonstrated a 40% reduction of lymphocyte adhesion with CD151 blockade. Inhibition of lymphocyte adhesion was similar between VCAM-1 blockade and a combination of CD151/VCAM-1 blockade, suggesting a collaborative role between the two receptors. These studies demonstrate that CD151 is upregulated within the liver during chronic inflammation, where it supports lymphocyte recruitment via liver endothelium. We propose that CD151 regulates the activity of VCAM-1 during lymphocyte recruitment to the human liver and could be a novel anti-inflammatory target in chronic liver disease and hepatocellular cancer prevention.NEW & NOTEWORTHY Chronic hepatitis is characterized by lymphocyte accumulation in liver tissue, which drives fibrosis and carcinogenesis. Here, we demonstrate for the first time that the tetraspanin CD151 supports lymphocyte adhesion to liver endothelium. We show that CD151 is upregulated in chronic liver disease and hepatocellular carcinoma (HCC) and is regulated on endothelium by tissue remodeling and procarcinogenic factors. These regulatory and functional studies identify CD151 as a potential therapeutic target to treat liver fibrosis and HCC.

Bidirectional transendothelial migration of monocytes across hepatic sinusoidal endothelium shapes monocyte differentiation and regulates the balance between immunity and tolerance in liver.

UNLABELLED: Monocytes are versatile cells that can fulfill proinflammatory and anti-inflammatory functions when recruited to the liver. Recruited monocytes differentiate into tissue macrophages and dendritic cells, which sample antigens and migrate to lymph nodes to elicit T-cell responses. The signals that determine monocyte differentiation and the role of hepatic sinusoidal endothelial cells (HSECs) in this process are poorly understood. HSECs are known to modulate T-cell activation, which led us to investigate whether transendothelial migration of monocytes across HSECs influences their phenotype and function. Subsets of blood-derived monocytes were allowed to transmigrate across human HSECs into a collagen matrix. Most migrated cells remained in the subendothelial matrix, but ~10% underwent spontaneous basal to apical transendothelial migration. The maturation, cytokine secretion, and T-cell stimulatory capacity of reverse transmigrating (RT) and subendothelial (SE) monocytes were compared. SE monocytes were mainly CD16(-) , whereas 75%-80% of RT monocytes were CD16(+) . SE monocytes derived from the CD14(++) CD16(-) subset and exhibited high phagocytic activity, whereas RT monocytes originated from CD14(++) CD16(+) and CD14(+) CD16(++) monocytes, displayed an immature dendritic cell-like phenotype (CD11c(pos) HLA-DR(pos) CD80lo CD86lo ), and expressed higher levels of chemokine (C-C motif) receptor 8. Consistent with a dendritic cell phenotype, RT monocytes secreted inflammatory cytokines and induced antigen-specific CD4(+) T-cell activation. In contrast, SE monocytes suppressed T-cell proliferation and activation and exhibited endotoxin tolerance. Transcriptome analysis underscored the functional differences between SE and RT monocytes. CONCLUSIONS: Migration across HSECs shapes the subsequent fate of monocytes, giving rise to anergic macrophage-like cells in tissue and the release of immunocompetent pre-dendritic cells into the circulation.

Contact-dependent depletion of hydrogen peroxide by catalase is a novel mechanism of myeloid-derived suppressor cell induction operating in human hepatic stellate cells.

Myeloid-derived suppressor cells (MDSC) represent a unique cell population with distinct immunosuppressive properties that have been demonstrated to shape the outcome of malignant diseases. Recently, human hepatic stellate cells (HSC) have been reported to induce monocytic-MDSC from mature CD14(+) monocytes in a contact-dependent manner. We now report a novel and unexpected mechanism by which CD14(+)HLADR(low/-) suppressive cells are induced by catalase-mediated depletion of hydrogen peroxide (H2O2). Incubation of CD14(+) monocytes with catalase led to a significant induction of functional MDSC compared with media alone, and H2O2 levels inversely correlated with MDSC frequency (r = -0.6555, p < 0.05). Catalase was detected in primary HSC and a stromal cell line, and addition of the competitive catalase inhibitor hydroxylamine resulted in a dose-dependent impairment of MDSC induction and concomitant increase of H2O2 levels. The NADPH-oxidase subunit gp91 was significantly increased in catalase-induced MDSC as determined by quantitative PCR outlining the importance of oxidative burst for the induction of MDSC. These findings represent a so far unrecognized link between immunosuppression by MDSC and metabolism. Moreover, this mechanism potentially explains how stromal cells can induce a favorable immunological microenvironment in the context of tissue oxidative stress such as occurs during cancer therapy.

Intestinal CCL25 expression is increased in colitis and correlates with inflammatory activity.

CCL25-mediated activation of CCR9 is critical for mucosal lymphocyte recruitment to the intestine. In immune-mediated liver injury complicating inflammatory bowel disease, intrahepatic activation of this pathway allows mucosal lymphocytes to be recruited to the liver, driving hepatobiliary destruction in primary sclerosing cholangitis (PSC). However, in mice and healthy humans CCL25 expression is restricted to the small bowel, whereas few data exist on activation of this pathway in the inflamed colon despite the vast majority of PSC patients having ulcerative colitis. Herein, we show that colonic CCL25 expression is not only upregulated in patients with active colitis, but strongly correlates with endoscopic Mayo score and mucosal TNFα expression. Moreover, approximately 90% (CD4(+)) and 30% (CD8(+)) of tissue-infiltrating T-cells in colitis were identified as CCR9(+) effector lymphocytes, compared to <10% of T-cells being CCR9(+) in normal colon. Sorted CCR9(+) lymphocytes also demonstrated enhanced cellular adhesion to stimulated hepatic sinusoidal endothelium compared with their CCR9(-) counterparts when under flow. Collectively, these results suggest that CCR9/CCL25 interactions are not only involved in colitis pathogenesis but also correlate with colonic inflammatory burden; further supporting the existence of overlapping mucosal lymphocyte recruitment pathways between the inflamed colon and liver.

Vascular adhesion protein-1 blockade in primary sclerosing cholangitis: Open-label, multicenter, single-arm, phase II trial.

BACKGROUND: Primary sclerosing cholangitis is a progressive inflammatory liver disease characterized by biliary and liver fibrosis. Vascular adhesion protein-1 (VAP-1) is important in the inflammatory process driving liver fibrosis. We evaluated the safety and efficacy of VAP-1 blockade with a monoclonal antibody (timolumab, BTT1023) in patients with primary sclerosing cholangitis. METHODS: BUTEO was a prospective, single-arm, open-label, multicenter, phase II trial, conducted in 6 centers in the United Kingdom. Patients with primary sclerosing cholangitis aged 18-75 years had an alkaline phosphatase value of >1.5 times the upper limit of normal. The dose-confirmatory stage aimed to confirm the safety of timolumab through the incidence of dose-limiting toxicity and sufficient trough levels of circulating antibody to block VAP-1 function. The primary outcome of the dose-expansion portion of the trial was patient's response to timolumab at day 99, as measured by a reduction in serum alkaline phosphatase by 25% or more from baseline to day 99. RESULTS: Twenty-three patients were recruited: 7 into the initial dose-confirmatory stage and a further 16 into an expansion stage. Timolumab (8 mg/kg) was confirmed to be safe for the duration of administration with sufficient circulating levels. Only 2 of the 18 evaluable patients (11.1%) achieved a reduction in alkaline phosphatase levels of 25% or more, and both the proportion of circulating inflammatory cell populations and biomarkers of fibrosis remained unchanged from baseline. CONCLUSIONS: The BUTEO trial confirmed 8 mg/kg timolumab had no short-term safety signals and resulted in sufficient circulating levels of VAP-1 blocking timolumab. However, the trial was stopped after an interim assessment due to a lack of efficacy as determined by no significant change in serum liver tests.

Evaluation of Gremlin-1 as a therapeutic target in metabolic dysfunction-associated steatohepatitis.

Gremlin-1 has been implicated in liver fibrosis in metabolic dysfunction-associated steatohepatitis (MASH) via inhibition of bone morphogenetic protein (BMP) signalling and has thereby been identified as a potential therapeutic target. Using rat in vivo and human in vitro and ex vivo model systems of MASH fibrosis, we show that neutralisation of Gremlin-1 activity with monoclonal therapeutic antibodies does not reduce liver inflammation or liver fibrosis. Still, Gremlin-1 was upregulated in human and rat MASH fibrosis, but expression was restricted to a small subpopulation of COL3A1/THY1+ myofibroblasts. Lentiviral overexpression of Gremlin-1 in LX-2 cells and primary hepatic stellate cells led to changes in BMP-related gene expression, which did not translate to increased fibrogenesis. Furthermore, we show that Gremlin-1 binds to heparin with high affinity, which prevents Gremlin-1 from entering systemic circulation, prohibiting Gremlin-1-mediated organ crosstalk. Overall, our findings suggest a redundant role for Gremlin-1 in the pathogenesis of liver fibrosis, which is unamenable to therapeutic targeting.

Cellular localization and trafficking of vascular adhesion protein-1 as revealed by an N-terminal GFP fusion protein.

Recent studies of vascular adhesion protein-1 (VAP-1) have greatly advanced our understanding of the important role this protein plays in the establishment and progression of inflammatory disease. To facilitate more detailed studies on the function of VAP-1, we developed a GFP-fusion protein that enabled us to monitor the trafficking of the protein in three selected cell types: hepatic sinusoidal endothelial cells, liver myofibroblasts and an hepatic stellate cell line (LX-2). The fusion protein was detected as punctate cytoplasmic GFP staining, but was present only at low levels at the cell surface in all cell types studied. The subcellular distribution of the protein was not altered in a catalytically inactive mutant form of the protein (Tyr471Phe) or in the presence of exogenous VAP-1 substrate (methylamine) or inhibitor (semicarbazide). The GFP-VAP-1 protein was localized to the Golgi apparatus (GM-130), endoplasmic reticulum (GRP94) and early endosomes (EEA-1). Additional staining for VAP-1 revealed that the overexpressed protein was also present in vesicles that were negative for GFP fluorescent signal and did not express EEA-1. We propose that these vesicles are responsible for recycling the fusion protein and that the fluorescence of the GFP moiety is quenched at the low pH within these vesicles. This feature of the protein makes it well suited for live cell imaging studies where we wish to track protein that is being actively trafficked within the cell in preference to that which is being recycled.

Chronic activation of human cardiac fibroblasts in vitro attenuates the reversibility of the myofibroblast phenotype.

Activation of cardiac fibroblasts and differentiation to myofibroblasts underlies development of pathological cardiac fibrosis, leading to arrhythmias and heart failure. Myofibroblasts are characterised by increased α-smooth muscle actin (α-SMA) fibre expression, secretion of collagens and changes in proliferation. Transforming growth factor-beta (TGF-ß) and increased mechanical stress can initiate myofibroblast activation. Reversibility of the myofibroblast phenotype has been observed in murine cells but has not been explored in human cardiac fibroblasts. In this study, chronically activated adult primary human ventricular cardiac fibroblasts and human induced pluripotent stem cell derived cFbs (hiPSC-cFbs) were used to investigate the potential for reversal of the myofibroblast phenotype using either subculture on soft substrates or TGF-ß receptor inhibition. Culture on softer plates (25 or 2 kPa Young's modulus) did not alter proliferation or reduce expression of α-SMA and collagen 1. Similarly, culture of myofibroblasts in the presence of TGF-ß inhibitor did not reverse myofibroblasts back to a quiescent phenotype. Chronically activated hiPSC-cFbs also showed attenuated response to TGF-ß receptor inhibition and inability to reverse to quiescent fibroblast phenotype. Our data demonstrate substantial loss of TGF-ß signalling plasticity as well as a loss of feedback from the surrounding mechanical environment in chronically activated human myofibroblasts.

Regulation of mucosal addressin cell adhesion molecule 1 expression in human and mice by vascular adhesion protein 1 amine oxidase activity.

UNLABELLED: Primary sclerosing cholangitis (PSC) and autoimmune hepatitis are hepatic complications associated with inflammatory bowel disease (IBD). The expression of mucosal addressin cell adhesion molecule 1 (MAdCAM-1) on mucosal endothelium is a prerequisite for the development of IBD, and it is also detected on the hepatic vessels of patients with liver diseases associated with IBD. This aberrant hepatic expression of MAdCAM-1 results in the recruitment of effector cells initially activated in the gut to the liver, in which they drive liver injury. However, the factors responsible for the aberrant hepatic expression of MAdCAM-1 are not known. In this study, we show that deamination of methylamine (MA) by vascular adhesion protein 1 (VAP-1) [a semicarbazide-sensitive amine oxidase (SSAO) expressed in the human liver] in the presence of tumor necrosis factor α induces the expression of functional MAdCAM-1 in hepatic endothelial cells and in intact human liver tissue ex vivo. This is associated with increased adhesion of lymphocytes from patients with PSC to hepatic vessels. Feeding mice MA, a constituent of food and cigarette smoke found in portal blood, led to VAP-1/SSAO-dependent MAdCAM-1 expression in mucosal vessels in vivo. CONCLUSION: Activation of VAP-1/SSAO enzymatic activity by MA, a constituent of food and cigarette smoke, induces the expression of MAdCAM-1 in hepatic vessels and results in the enhanced recruitment of mucosal effector lymphocytes to the liver. This could be an important mechanism underlying the hepatic complications of IBD.

Distinct roles for CCR4 and CXCR3 in the recruitment and positioning of regulatory T cells in the inflamed human liver.

Regulatory T cells (T(regs)) are found at sites of chronic inflammation where they mediate bystander and Ag-specific suppression of local immune responses. However, little is known about the molecular control of T(reg) recruitment into inflamed human tissues. We report that up to 18% of T cells in areas of inflammation in human liver disease are forkhead family transcriptional regulator box P3 (FoxP3)(+) T(regs). We isolated CD4(+)CD25(+)CD127(low)FoxP3(+) T(regs) from chronically inflamed human liver removed at transplantation; compared with blood-derived T(regs), liver-derived T(regs) express high levels of the chemokine receptors CXCR3 and CCR4. In flow-based adhesion assays using human hepatic sinusoidal endothelium, T(regs) used CXCR3 and alpha4beta1 to bind and transmigrate, whereas CCR4 played no role. The CCR4 ligands CCL17 and CCL22 were absent from healthy liver, but they were detected in chronically inflamed liver where their expression was restricted to dendritic cells (DCs) within inflammatory infiltrates. These DCs were closely associated with CD8 T cells and CCR4(+) T(regs) in the parenchyma and septal areas. Ex vivo, liver-derived T(regs) migrated to CCR4 ligands secreted by intrahepatic DCs. We propose that CXCR3 mediates the recruitment of T(regs) via hepatic sinusoidal endothelium and that CCR4 ligands secreted by DCs recruit T(regs) to sites of inflammation in patients with chronic hepatitis. Thus, different chemokine receptors play distinct roles in the recruitment and positioning of T(regs) at sites of hepatitis in chronic liver disease.

Targeting IL-36 improves age-related coronary microcirculatory dysfunction and attenuates myocardial ischemia/reperfusion injury in mice.

Following myocardial infarction (MI), elderly patients have a poorer prognosis than younger patients, which may be linked to increased coronary microvessel susceptibility to injury. Interleukin-36 (IL-36), a newly discovered proinflammatory member of the IL-1 superfamily, may mediate this injury, but its role in the injured heart is currently not known. We first demonstrated the presence of IL-36(α/ß) and its receptor (IL-36R) in ischemia/reperfusion-injured (IR-injured) mouse hearts and, interestingly, noted that expression of both increased with aging. An intravital model for imaging the adult and aged IR-injured beating heart in real time in vivo was used to demonstrate heightened basal and injury-induced neutrophil recruitment, and poorer blood flow, in the aged coronary microcirculation when compared with adult hearts. An IL-36R antagonist (IL-36Ra) decreased neutrophil recruitment, improved blood flow, and reduced infarct size in both adult and aged mice. This may be mechanistically explained by attenuated endothelial oxidative damage and VCAM-1 expression in IL-36Ra-treated mice. Our findings of an enhanced age-related coronary microcirculatory dysfunction in reperfused hearts may explain the poorer outcomes in elderly patients following MI. Since targeting the IL-36/IL-36R pathway was vasculoprotective in aged hearts, it may potentially be a therapy for treating MI in the elderly population.

CX(3)CR1 and vascular adhesion protein-1-dependent recruitment of CD16(+) monocytes across human liver sinusoidal endothelium.

UNLABELLED: The liver contains macrophages and myeloid dendritic cells (mDCs) that are critical for the regulation of hepatic inflammation. Most hepatic macrophages and mDCs are derived from monocytes recruited from the blood through poorly understood interactions with hepatic sinusoidal endothelial cells (HSECs). Human CD16(+) monocytes are thought to contain the precursor populations for tissue macrophages and mDCs. We report that CD16(+) cells localize to areas of active inflammation and fibrosis in chronic inflammatory liver disease and that a unique combination of cell surface receptors promotes the transendothelial migration of CD16(+) monocytes through human HSECs under physiological flow. CX(3)CR1 activation was the dominant pertussis-sensitive mechanism controlling transendothelial migration under flow, and expression of the CX(3)CR1 ligand CX(3)CL1 is increased on hepatic sinusoids in chronic inflammatory liver disease. Exposure of CD16(+) monocytes to immobilized purified CX(3)CL1 triggered beta1-integrin-mediated adhesion to vascular cell adhesion molecule-1 and induced the development of a migratory phenotype. Following transmigration or exposure to soluble CX(3)CL1, CD16(+) monocytes rapidly but transiently lost expression of CX(3)CR1. Adhesion and transmigration across HSECs under flow was also dependent on vascular adhesion protein-1 (VAP-1) on the HSECs. CONCLUSION: Our data suggest that CD16(+) monocytes are recruited by a combination of adhesive signals involving VAP-1 and CX(3)CR1 mediated integrin-activation. Thus a novel combination of surface molecules, including VAP-1 and CX(3)CL1 promotes the recruitment of CD16(+) monocytes to the liver, allowing them to localize at sites of chronic inflammation and fibrosis.

Hepatic consequences of vascular adhesion protein-1 expression.

The liver is constantly exposed to antigens present in the blood and to particulate antigens delivered from the gut. To maintain effective levels of immune surveillance and yet tolerate food antigens, the hepatic environment has become highly specialised. A low flow environment exists within the hepatic sinusoids that not only facilitates the exchange of toxins and nutrients within the liver parenchyma, but also provides an ideal niche for the recruitment of leukocytes. One such adhesion molecule involved in this process, the vascular adhesion protein-1 (VAP-1), is unusual in the context of the leukocyte adhesion cascade in that it is both an adhesion molecule and a primary amine oxidase. In this review, we examine the biological functions of VAP-1 and examine what role this molecule might play in the establishment and progression of chronic liver disease.