Cross-talk between the complement system and endothelial cells in physiologic conditions and in vascular diseases

Inhibiting MMP13 Attenuates Deep Vein Thrombosis in a Mouse Model by Reducing the Expression of Pdpn

OBJECTIVE

Matrix metalloproteinase 13 (MMP13) is an extracellular matrix protease that affects the progression of atherosclerotic plaques and arterial thrombi by degrading collagens, modifying protein structures and regulating inflammatory responses, but its role in deep vein thrombosis (DVT) has not been determined. The purpose of this study was to investigate the potential effects of MMP13 and MMP13-related genes on the formation of DVT.

METHODS

We altered the expression level of MMP13 in vivo and conducted a transcriptome study to examine the expression and relationship between MMP13 and MMP13-related genes in a mouse model of DVT. After screening genes possibly related to MMP13 in DVT mice, the expression levels of candidate genes in human umbilical vein endothelial cells (HUVECs) and the venous wall were evaluated. The effect of MMP13 on platelet aggregation in HUVECs was investigated in vitro.

RESULTS

Among the differentially expressed genes, interleukin 1 beta, podoplanin (Pdpn), and factor VIII von Willebrand factor (F8VWF) were selected for analysis in mice. When MMP13 was inhibited, the expression level of PDPN decreased significantly in vitro. In HUVECs, overexpression of MMP13 led to an increase in the expression level of PDPN and induced platelet aggregation, while transfection of PDPN-siRNA weakened the ability of MMP13 to increase platelet aggregation.

CONCLUSIONS

Inhibiting the expression of MMP13 could reduce the burden of DVT in mice. The mechanism involves downregulating the expression of Pdpn through MMP13, which could provide a novel gene target for DVT diagnosis and treatment.

Mechanisms of endothelial activation, hypercoagulation and thrombosis in COVID-19: a link with diabetes mellitus

Early since the onset of the COVID-19 pandemic, the medical and scientific community were aware of extra respiratory actions of SARS-CoV-2 infection. Endothelitis, hypercoagulation, and hypofibrinolysis were identified in COVID-19 patients as subsequent responses of endothelial dysfunction. Activation of the endothelial barrier may increase the severity of the disease and contribute to long-COVID syndrome and post-COVID sequelae. Besides, it may cause alterations in primary, secondary, and tertiary hemostasis. Importantly, these responses have been highly decisive in the evolution of infected patients also diagnosed with diabetes mellitus (DM), who showed previous endothelial dysfunction. In this review, we provide an overview of the potential triggers of endothelial activation related to COVID-19 and COVID-19 under diabetic milieu. Several mechanisms are induced by both the viral particle itself and by the subsequent immune-defensive response (i.e., NF-κB/NLRP3 inflammasome pathway, vasoactive peptides, cytokine storm, NETosis, activation of the complement system). Alterations in coagulation mediators such as factor VIII, fibrin, tissue factor, the von Willebrand factor: ADAMST-13 ratio, and the kallikrein-kinin or plasminogen-plasmin systems have been reported. Moreover, an imbalance of thrombotic and thrombolytic (tPA, PAI-I, fibrinogen) factors favors hypercoagulation and hypofibrinolysis. In the context of DM, these mechanisms can be exacerbated leading to higher loss of hemostasis. However, a series of therapeutic strategies targeting the activated endothelium such as specific antibodies or inhibitors against thrombin, key cytokines, factor X, complement system, the kallikrein-kinin system or NETosis, might represent new opportunities to address this hypercoagulable state present in COVID-19 and DM. Antidiabetics may also ameliorate endothelial dysfunction, inflammation, and platelet aggregation. By improving the microvascular pathology in COVID-19 and post-COVID subjects, the associated comorbidities and the risk of mortality could be reduced.

Shedding light on the molecular and regulatory mechanisms of TLR4 signaling in endothelial cells under physiological and inflamed conditions

Toll-like receptor 4 (TLR4) are part of the innate immune system. They are capable of recognizing pathogen-associated molecular patterns (PAMPS) of microbes, and damage-associated molecular patterns (DAMPs) of damaged tissues. Activation of TLR4 initiates downstream signaling pathways that trigger the secretion of cytokines, type I interferons, and other pro-inflammatory mediators that are necessary for an immediate immune response. However, the systemic release of pro-inflammatory proteins is a powerful driver of acute and chronic inflammatory responses. Over the past decades, immense progress has been made in clarifying the molecular and regulatory mechanisms of TLR4 signaling in inflammation. However, the most common strategies used to study TLR4 signaling rely on genetic manipulation of the TLR4 or the treatment with agonists such as lipopolysaccharide (LPS) derived from the outer membrane of Gram-negative bacteria, which are often associated with the generation of irreversible phenotypes in the target cells or unintended cytotoxicity and signaling crosstalk due to off-target or pleiotropic effects. Here, optogenetics offers an alternative strategy to control and monitor cellular signaling in an unprecedented spatiotemporally precise, dose-dependent, and non-invasive manner. This review provides an overview of the structure, function and signaling pathways of the TLR4 and its fundamental role in endothelial cells under physiological and inflammatory conditions, as well as the advances in TLR4 modulation strategies.

Research progress of NF-κB signaling pathway and thrombosis

Venous thromboembolism is a very common and costly health problem. Deep-vein thrombosis (DVT) can cause permanent damage to the venous system and lead to swelling, ulceration, gangrene, and other symptoms in the affected limb. In addition, more than half of the embolus of pulmonary embolism comes from venous thrombosis, which is the most serious cause of death, second only to ischemic heart disease and stroke patients. It can be seen that deep-vein thrombosis has become a serious disease affecting human health. In recent years, with the deepening of research, inflammatory response is considered to be an important pathway to trigger venous thromboembolism, in which the transcription factor NF-κB is the central medium of inflammation, and the NF-κB signaling pathway can regulate the pro-inflammatory and coagulation response. Thus, to explore the mechanism and make use of it may provide new solutions for the prevention and treatment of thrombosis.

Plasma factor D is cross-sectionally associated with low-grade inflammation, endothelial dysfunction and cardiovascular disease: The Maastricht study

BACKGROUND AND AIMS

The complement system, particularly the alternative complement pathway, may contribute to vascular damage and development of cardiovascular disease (CVD). We investigated the association of factor D, the rate-limiting protease in alternative pathway activation, with adverse cardiovascular outcomes.

METHODS

In 2947 participants (50.6% men, 59.9 ± 8.2 years, 26.5% type 2 diabetes [T2D], oversampled) we measured markers of low-grade inflammation (LGI, composite score, in SD) and, endothelial dysfunction (ED, composite score, in SD), carotid intima-media thickness (cIMT, μm), ankle-brachial index (ABI), CVD (yes/no) and plasma concentrations of factor D (in SD). Associations were estimated using multiple linear and logistic regression, adjusting for demographic, lifestyle, and dietary factors.

RESULTS

Factor D (per SD) significantly associated with LGI (0.171 SD [0.137; 0.205]), ED (0.158 SD [0.123; 0.194]) and CVD (OR 1.15 [1.04; 1.27]) but not significantly with cIMT (-6.62 μm [-13.51; 0.27]) or ABI (-0.003 [-0.007; 0.001]). Interaction analyses show that factor D more strongly associated with ED in non-diabetes (0.237 SD [0.189; 0.285] than in T2D (0.095 SD [0.034; 0.157]), pinteraction <0.05. These results were largely corroborated by additional analyses with C3 and C3a. In contrast, factor D inversely associated with cIMT in non-diabetes (-13.37 μm [-21.84; -4.90]), but not in T2D (4.49 [-7.91; 16.89]), pinteraction <0.05.

CONCLUSIONS

Plasma factor D is independently associated with LGI, ED, and prevalent CVD but not with ABI or cIMT. Hence, greater plasma factor D concentration in CVD may potentially induce complement activation which, in turn, might contribute to further disease progression via a process that may involve inflammation and endothelial dysfunction but was not directly related to atherosclerosis or arterial injury. The observation that, in participants without diabetes, factor D associated with worse ED but smaller cIMT warrants further investigation.

Linking nutrient sensing, mitochondrial function, and PRR immune cell signaling in liver disease

Caloric overconsumption in vertebrates promotes adipose and liver fat accumulation while perturbing the gut microbiome. This triad triggers pattern recognition receptor (PRR)-mediated immune cell signaling and sterile inflammation. Moreover, immune system activation perpetuates metabolic consequences, including the progression of nonalcoholic fatty liver disease (NAFLD) to nonalcoholic hepatic steatohepatitis (NASH). Recent findings show that sensing of nutrient overabundance disrupts the activity and homeostasis of the central cellular energy-generating organelle, the mitochondrion. In parallel, whether caloric excess-initiated PRR signaling and mitochondrial perturbations are coordinated to amplify this inflammatory process in NASH progression remains in question. We hypothesize that altered mitochondrial function, classic PRR signaling, and complement activation in response to nutrient overload together play an integrated role across the immune cell landscape, leading to liver inflammation and NASH progression.

The relevance of complement in pemphigoid diseases: A critical appraisal

Pemphigoid diseases are autoimmune chronic inflammatory skin diseases, which are characterized by blistering of the skin and/or mucous membranes, and circulating and tissue-bound autoantibodies. The well-established pathomechanisms comprise autoantibodies targeting various structural proteins located at the dermal-epidermal junction, leading to complement factor binding and activation. Several effector cells are thus attracted and activated, which in turn inflict characteristic tissue damage and subepidermal blistering. Moreover, the detection of linear complement deposits in the skin is a diagnostic hallmark of all pemphigoid diseases. However, recent studies showed that blistering might also occur independently of complement. This review reassesses the importance of complement in pemphigoid diseases based on current research by contrasting and contextualizing data from in vitro, murine and human studies.

Cobra Venom Factor Boosts Arteriogenesis in Mice

Arteriogenesis, the growth of natural bypass blood vessels, can compensate for the loss of arteries caused by vascular occlusive diseases. Accordingly, it is a major goal to identify the drugs promoting this innate immune system-driven process in patients aiming to save their tissues and life. Here, we studied the impact of the Cobra venom factor (CVF), which is a C3-like complement-activating protein that induces depletion of the complement in the circulation in a murine hind limb model of arteriogenesis. Arteriogenesis was induced in C57BL/6J mice by femoral artery ligation (FAL). The administration of a single dose of CVF (12.5 µg) 24 h prior to FAL significantly enhanced the perfusion recovery 7 days after FAL, as shown by Laser Doppler imaging. Immunofluorescence analyses demonstrated an elevated number of proliferating (BrdU+) vascular cells, along with an increased luminal diameter of the grown collateral vessels. Flow cytometric analyses of the blood samples isolated 3 h after FAL revealed an elevated number of neutrophils and platelet-neutrophil aggregates. Giemsa stains displayed augmented mast cell recruitment and activation in the perivascular space of the growing collaterals 8 h after FAL. Seven days after FAL, we found more CD68+/MRC-1+ M2-like polarized pro-arteriogenic macrophages around growing collaterals. These data indicate that a single dose of CVF boosts arteriogenesis by catalyzing the innate immune reactions, relevant for collateral vessel growth.

Protein palmitoylation regulates extracellular vesicle production and function in sepsis

Extracellular vesicles (EVs) are bioactive membrane-encapsulated particles generated by a series of events involving membrane budding, fission and fusion. Palmitoylation, mediated by DHHC palmitoyl acyltransferases, is a lipidation reaction that increases protein lipophilicity and membrane localization. Here, we report palmitoylation as a novel regulator of EV formation and function during sepsis. Our results showed significantly decreased circulating EVs in mice with DHHC21 functional deficiency (Zdhhc21dep/dep), compared to wild-type (WT) mice 24 h after septic injury. Furthermore, WT and Zdhhc21dep/dep EVs displayed distinct palmitoyl-proteomic profiles. Ingenuity pathway analysis indicated that sepsis altered several inflammation related pathways expressed in EVs, among which the most significantly activated was the complement pathway; however, this sepsis-induced complement enrichment in EVs was greatly blunted in Zdhhc21dep/dep EVs. Functionally, EVs isolated from WT mice with sepsis promoted neutrophil adhesion, transmigration, and neutrophil extracellular trap production; these effects were significantly attenuated by DHHC21 loss-of-function. Furthermore, Zdhhc21dep/dep mice displayed reduced neutrophil infiltration in lungs and improved survival after CLP challenges. These findings indicate that blocking palmitoylation via DHHC21 functional deficiency can reduce sepsis-stimulated production of complement-enriched EVs and attenuates their effects on neutrophil activity.

Distinct Roles of Classical and Lectin Pathways of Complement in Preeclamptic Placentae

Pre-eclampsia is a pregnancy complication characterized by defective vascular remodeling in maternal decidua responsible for reduced blood flow leading to functional and structural alterations in the placenta. We have investigated the contribution of the complement system to decidual vascular changes and showed that trophoblasts surrounding unremodeled vessels prevalent in preeclamptic decidua fail to express C1q that are clearly detected in cells around remodeled vessels predominant in control placenta. The critical role of C1q is supported by the finding that decidual trophoblasts of female C1qa^-/- pregnant mice mated to C1qa^+/+ male mice surrounding remodeled vessels express C1q of paternal origin. Unlike C1qa^-/- pregnant mice, heterozygous C1qa^+/- and wild type pregnant mice share a high percentage of remodeled vessels. C1q was also found in decidual vessels and stroma of normal placentae and the staining was stronger in preeclamptic placentae. Failure to detect placental deposition of C1r and C1s associated with C1q rules out complement activation through the classical pathway. Conversely, the intense staining of decidual endothelial cells and villous trophoblast for ficolin-3, MASP-1 and MASP-2 supports the activation of the lectin pathway that proceeds with the cleavage of C4 and C3 and the assembly of the terminal complex. These data extend to humans our previous findings of complement activation through the lectin pathway in an animal model of pre-eclampsia and provide evidence for an important contribution of C1q in decidual vascular remodeling.

Targeting vascular inflammation through emerging methods and drug carriers

Acute inflammation is a common dangerous component of pathogenesis of many prevalent conditions with high morbidity and mortality including sepsis, thrombosis, acute respiratory distress syndrome (ARDS), COVID-19, myocardial and cerebral ischemia-reperfusion, infection, and trauma. Inflammatory changes of the vasculature and blood mediate the course and outcome of the pathology in the tissue site of insult, remote organs and systemically. Endothelial cells lining the luminal surface of the vasculature play the key regulatory functions in the body, distinct under normal vs. pathological conditions. In theory, pharmacological interventions in the endothelial cells might enable therapeutic correction of the overzealous damaging pro-inflammatory and pro-thrombotic changes in the vasculature. However, current agents and drug delivery systems (DDS) have inadequate pharmacokinetics and lack the spatiotemporal precision of vascular delivery in the context of acute inflammation. To attain this level of precision, many groups design DDS targeted to specific endothelial surface determinants. These DDS are able to provide specificity for desired tissues, organs, cells, and sub-cellular compartments needed for a particular intervention. We provide a brief overview of endothelial determinants, design of DDS targeted to these molecules, their performance in experimental models with focus on animal studies and appraisal of emerging new approaches. Particular attention is paid to challenges and perspectives of targeted therapeutics and nanomedicine for advanced management of acute inflammation.

Endothelial Cell Phenotype, a Major Determinant of Venous Thrombo-Inflammation

Reduced blood flow velocity in the vein triggers inflammation and is associated with the release into the extracellular space of alarmins or damage-associated molecular patterns (DAMPs). These molecules include extracellular nucleic acids, extracellular purinergic nucleotides (ATP, ADP), cytokines and extracellular HMGB1. They are recognized as a danger signal by immune cells, platelets and endothelial cells. Hence, endothelial cells are capable of sensing environmental cues through a wide variety of receptors expressed at the plasma membrane. The endothelium is then responding by expressing pro-coagulant proteins, including tissue factor, and inflammatory molecules such as cytokines and chemokines involved in the recruitment and activation of platelets and leukocytes. This ultimately leads to thrombosis, which is an active pro-inflammatory process, tightly regulated, that needs to be properly resolved to avoid further vascular damages. These mechanisms are often dysregulated, which promote fibrinolysis defects, activation of the immune system and irreversible vascular damages further contributing to thrombotic and inflammatory processes. The concept of thrombo-inflammation is now widely used to describe the complex interactions between the coagulation and inflammation in various cardiovascular diseases. In endothelial cells, activating signals converge to multiple intracellular pathways leading to phenotypical changes turning them into inflammatory-like cells. Accumulating evidence suggest that endothelial to mesenchymal transition (EndMT) may be a major mechanism of endothelial dysfunction induced during inflammation and thrombosis. EndMT is a biological process where endothelial cells lose their endothelial characteristics and acquire mesenchymal markers and functions. Endothelial dysfunction might play a central role in orchestrating and amplifying thrombo-inflammation thought induction of EndMT processes. Mechanisms regulating endothelial dysfunction have been only partially uncovered in the context of thrombotic diseases. In the present review, we focus on the importance of the endothelial phenotype and discuss how endothelial plasticity may regulate the interplay between thrombosis and inflammation. We discuss how the endothelial cells are sensing and responding to environmental cues and contribute to thrombo-inflammation with a particular focus on venous thromboembolism (VTE). A better understanding of the precise mechanisms involved and the specific role of endothelial cells is needed to characterize VTE incidence and address the risk of recurrent VTE and its sequelae.

Diversity in Phenotypes Associated With Host Persistence and Systemic Virulence in Streptococcus sanguinis Strains

Streptococcus sanguinis is a pioneer commensal species of dental biofilms, abundant in different oral sites and commonly associated with opportunist cardiovascular infections. In this study, we addressed intra-species functional diversity to better understand the S. sanguinis commensal and pathogenic lifestyles. Multiple phenotypes were screened in nine strains isolated from dental biofilms or from the bloodstream to identify conserved and strain-specific functions involved in biofilm formation and/or persistence in oral and cardiovascular tissues. Strain phenotypes of biofilm maturation were independent of biofilm initiation phenotypes, and significantly influenced by human saliva and by aggregation mediated by sucrose-derived exopolysaccharides (EPS). The production of H2O2 was conserved in most strains, and consistent with variations in extracellular DNA (eDNA) production observed in few strains. The diversity in complement C3b deposition correlated with the rates of opsonophagocytosis by human PMN and was influenced by culture medium and sucrose-derived EPS in a strain-specific fashion. Differences in C3b deposition correlated with strain binding to recognition proteins of the classical pathway, C1q and serum amyloid protein (SAP). Importantly, differences in strain invasiveness into primary human coronary artery endothelial cells (HCAEC) were significantly associated with C3b binding, and in a lesser extent, with binding to host glycoproteins (such as fibrinogen, plasminogen, fibronectin, and collagen). Thus, by identifying conserved and strain-specific phenotypes involved in host persistence and systemic virulence, this study indicates potential new functions involved in systemic virulence and highlights the need of including a wider panel of strains in molecular studies to understand S. sanguinis biology.

Multiple inducers of endothelial NOS (eNOS) dysfunction in sickle cell disease

A characteristic aspect of the robust, systemic inflammatory state in sickle cell disease is dysfunction of endothelial nitric oxide synthase (eNOS). We identify 10 aberrant endothelial cell inputs, present in the specific sickle context, that are known to have the ability to cause eNOS dysfunction. These are: endothelial arginase depletion, asymmetric dimethylarginine, complement activation, endothelial glycocalyx degradation, free fatty acids, inflammatory mediators, microparticles, oxidized low density lipoproteins, reactive oxygen species, and Toll‐like receptor 4 signaling ligands. The effect of true eNOS dysfunction on clinical testing using flow‐mediated dilation can be simulated by two known examples of endothelial dysfunction mimicry (hemoglobin consumption of NO; and oxidation of smooth muscle cell soluble guanylate cyclase). This lends ambiguity to interpretation of such clinical testing. The presence of these multiple perturbing factors argues that a therapeutic approach targeting only a single injurious endothelial input (or either example of mimicry) would not be sufficiently efficacious. This would seem to argue for identifying therapeutics that directly protect eNOS function or application of multiple therapeutic approaches.

Cellular and Molecular Crosstalk of Graft Endothelial Cells During AMR: Effector Functions and Mechanisms

Graft endothelial cell (EC) injury is central to the pathogenesis of antibody-mediated rejection (AMR). The ability of donor-specific antibodies (DSA) to bind C1q and activate the classical complement pathway is an efficient predictor of graft rejection highlighting complement-dependent cytotoxicity as a key process operating during AMR. In the past 5 y, clinical studies further established the cellular and molecular signatures of AMR revealing the key contribution of other, IgG-dependent and -independent, effector mechanisms mediated by infiltrating NK cells and macrophages. Beyond binding to alloantigens, DSA IgG can activate NK cells and mediate antibody-dependent cell cytotoxicity through interacting with Fcγ receptors (FcγRs) such as FcγRIIIa (CD16a). FcRn, a nonconventional FcγR that allows IgG recycling, is highly expressed on ECs and may contribute to the long-term persistence of DSA in blood. Activation of NK cells and macrophages results in the production of proinflammatory cytokines such as TNF and IFNγ that induce transient and reversible changes in the EC phenotype and functions promoting coagulation, inflammation, vascular permeability, leukocyte trafficking. MHC class I mismatch between transplant donor and recipient can create a situation of "missing self" allowing NK cells to kill graft ECs. Depending on the microenvironment, cellular proximity with ECs may participate in macrophage polarization toward an M1 proinflammatory or an M2 phenotype favoring inflammation or vascular repair. Monocytes/macrophages participate in the loss of endothelial specificity in the process of endothelial-to-mesenchymal transition involved in renal and cardiac fibrosis and AMR and may differentiate into ECs enabling vessel and graft (re)-endothelialization.

COVID-19-related coagulopathy: A review of pathophysiology and pharmaceutical management

December 2019 will never be forgotten in the history of medicine when an outbreak of pneumonia of unknown etiology in Wuhan, China sooner or later prompted the World Health Organization to issue a public health warning emergency. This is not the first nor will it be the last time that a member of β-coronaviruses (CoVs) is waging a full-scale war against human health. Notwithstanding the fact that pneumonia is the primary symptom of the novel coronavirus (2019nCoV; designated as SARS-CoV-2), the emergence of severe disease mainly due to the injury of nonpulmonary organs at the shadow of coagulopathy leaves no choice, in some cases, rather than a dreadful death. Multiple casual factors such as inflammation, endothelial dysfunction, platelet and complement activation, renin-angiotensin-aldosterone system derangement, and hypoxemia play a major role in the pathogenesis of coagulopathy in coronavirus disease 2019 (COVID-19) patients. Due to the undeniable role of coagulation dysfunction in the initiation of several complications, assessment of coagulation parameters and the platelet count would be beneficial in early diagnosis and also timely prediction of disease severity. Although low-molecular-weight heparin is considered as the first-line of treatment in COVID-19-associated coagulopathy, several possible therapeutic options have also been proposed for better management of the disease. In conclusion, this review would help us to gain insight into the pathogenesis, clinical manifestation, and laboratory findings associated with COVID-19 coagulopathy and would summarize management strategies to alleviate coagulopathy-related complications.

Proteomic and Biological Analysis of an In Vitro Human Endothelial System in Response to Drug Anaphylaxis

Anaphylaxis is a life-threatening systemic hypersensitivity reaction. During anaphylaxis, mediator release by effector cells causes endothelial barrier breakdown, increasing vascular permeability and leakage of fluids, which may lead to tissue edema. Although endothelial cells (ECs) are key players in this context, scant attention has been paid to the molecular analysis of the vascular system, and further analyses of this cell type are necessary, especially in humans. The protein expression pattern of human microvascular ECs was analyzed in response to sera from anaphylactic patients (EC-anaphylaxis) and sera from non-allergic subjects (EC-control) after 2 hours of contact. Firstly, a differential quantitative proteomic analysis of the protein extracts was performed by mass spectrometry using an isobaric labeling method. Second, the coordinated behavior of the identified proteins was analyzed using systems biology analysis (SBA). The proteome of the EC-anaphylaxis system showed 7,707 proteins, of which 1,069 were found to be significantly altered between the EC-control and EC-anaphylaxis groups (p-value < 0.05). Among them, a subproteome of 47 proteins presented a high rate of change (|ΔZq| ≥ 3). This panel offers an endothelial snapshot of the anaphylactic reaction. Those proteins with the highest individual changes in abundance were hemoglobin subunits and structural support proteins. The interacting network analysis of this altered subproteome revealed that the coagulation and complement systems are the main biological processes altered in the EC-anaphylactic system. The comprehensive SBA resulted in 5,512 functional subcategories (biological processes), 57 of which were significantly altered between EC-control and EC-anaphylaxis. The complement system, once again, was observed as the main process altered in the EC system created with serum from anaphylactic patients. Findings of the current study further our understanding of the underlying pathophysiological mechanisms operating in anaphylactic reactions. New target proteins and relevant signaling pathways operating in the in vitro endothelial-serum system have been identified. Interestingly, our results offer a protein overview of the micro-EC-anaphylaxis environment. The relevance of the coagulation, fibrinolytic, contact and complement systems in human anaphylaxis is described. Additionally, the untargeted high-throughput analysis used here is a novel approach that reveals new pathways in the study of the endothelial niche in anaphylaxis.

C3 Deficiency Leads to Increased Angiogenesis and Elevated Pro-Angiogenic Leukocyte Recruitment in Ischemic Muscle Tissue

The complement system is a potent inflammatory trigger, activator, and chemoattractant for leukocytes, which play a crucial role in promoting angiogenesis. However, little information is available about the influence of the complement system on angiogenesis in ischemic muscle tissue. To address this topic and analyze the impact of the complement system on angiogenesis, we induced muscle ischemia in complement factor C3 deficient (C3-/-) and wildtype control mice by femoral artery ligation (FAL). At 24 h and 7 days after FAL, we isolated the ischemic gastrocnemius muscles and investigated them by means of (immuno-)histological analyses. C3-/- mice showed elevated ischemic damage 7 days after FAL, as evidenced by H&E staining. In addition, angiogenesis was increased in C3-/- mice, as demonstrated by increased capillary/muscle fiber ratio and increased proliferating endothelial cells (CD31+/BrdU+). Moreover, our results showed that the total number of leukocytes (CD45+) was increased in C3-/- mice, which was based on an increased number of neutrophils (MPO+), neutrophil extracellular trap formation (MPO+/CitH3+), and macrophages (CD68+) displaying a shift toward an anti-inflammatory and pro-angiogenic M2-like polarized phenotype (CD68+/MRC1+). In summary, we show that the deficiency of complement factor C3 increased neutrophil and M2-like polarized macrophage accumulation in ischemic muscle tissue, contributing to angiogenesis.

Lung histopathological findings in COVID-19 disease - a systematic review

Since December 2019, the global burden of the COVID-19 pandemic has increased rapidly and has impacted nearly every country in the world, affecting those who are elderly or with underlying comorbidities or immunocompromised states. Aim of this systematic review is to summarize lung histopathological characteristics of COVID-19, not only for diagnostic purpose but also to evaluate changes that can reflect pathophysiological pathways that can inform clinicians of useful treatment strategies. We identified following histopathological changes among our patients:: hyaline membranes; endothelial cells/ interstitial cells involvement; alveolar cells, type I pneumocytes/ type II pneumocytes involvement; interstitial and/ or alveolar edema; evidence of hemorrhage, of inflammatory cells, evidence of microthrombi; evidence of fibrin deposition and of viral infection in the tissue samples.The scenario with proliferative cell desquamation is typical of Acute Respiratory Distress Syndrome (ARDS) that can be classified as diffuse alveolar damage (DAD) and not DAD-ARDS. The proposed pathological mechanism concerns the role of both innate and adaptive components of the immune system. COVID-19 lethal cases present themselves as a heterogeneous disease, characterized by the different simultaneous presence of different histological findings, which reflect histological phases with corresponding different pathological pathways (epithelial, vascular and fibrotic changes), in the same patient.

The interaction between the complement system and hemostatic factors

PURPOSE OF REVIEW

To discuss the crosstalk between the complement system and hemostatic factors (coagulation cascade, platelet, endothelium, and Von Willebrand Factor), and the consequences of this interaction under physiologic and pathologic conditions.

RECENT FINDINGS

The complement and coagulation systems are comprised of serine proteases and are genetically related. In addition to the common ancestral genes, the complement system and hemostasis interact directly, through protein-protein interactions, and indirectly, on the surface of platelets and endothelial cells. The close interaction between the complement system and hemostatic factors is manifested both in physiologic and pathologic conditions, such as in the inflammatory response to thrombosis, thrombosis at the inflamed area, and thrombotic complications of complement disorders.

SUMMARY

The interaction between the complement system and hemostasis is vital for homeostasis and the protective response of the host to tissue injury, but also results in the pathogenesis of several thrombotic and inflammatory disorders.

The blood endothelial cell chamber - An innovative system to study immune responses in drug development

The risk for adverse immune-mediated reactions, associated with the administration of certain immunotherapeutic agents, should be mitigated early. Infusion reactions to monoclonal antibodies and other biopharmaceuticals, known as cytokine release syndrome, can arise from the release of cytokines via the drug target cell, as well as the recruitment of immune effector cells. While several in vitro cytokine release assays have been proposed up to date, many of them lack important blood components, required for this response to occur. The blood endothelial cell chamber model is an in vitro assay, composed of freshly drawn human whole blood and cultured human primary endothelial cells. Herein, its potential to study the compatibility of immunotherapeutics with the human immune system was studied by evaluating three commercially available monoclonal antibodies and bacterial endotoxin lipopolysaccharide. We demonstrate that the anti-CD28 antibody TGN1412 displayed an adaptive cytokine release profile and a distinct IL-2 response, accompanied with increased CD3⁺ cell recruitment. Alemtuzumab exhibited a clear cytokine response with a mixed adaptive/innate source (IFNγ, TNFα and IL-6). Its immunosuppressive nature is observed in depleted CD3⁺ cells. Cetuximab, associated with low infusion reactions, showed a very low or absent stimulatory effect on proinflammatory cytokines. In contrast, bacterial endotoxin demonstrated a clear innate cytokine response, defined by TNFα, IL-6 and IL-1β release, accompanied with a strong recruitment of CD14⁺CD16⁺ cells. Therefore, the blood endothelial cell chamber model is presented as a valuable in vitro tool to investigate therapeutic monoclonal antibodies with respect to cytokine release and vascular immune cell recruitment.

Fundamental Basis of COVID-19 Pathogenesis

At the end of 2019, a new coronavirus infection occurred in the People’s Republic of China with an epicentre in the city of Wuhan. On February 11th, 2020, the World Health Organization assigned the official name of the infection caused by the new coronavirus – COVID-19. COVID-19 has affected people from all over the world given that the infection was noted in 200 countries resulting in annunciation of the pandemic situation. Human corona viruses cause mild to moderate respiratory infections. At the end of 2002, a new coronavirus appeared (SARS-CoV), the causal agent of atypical pneumonia, which caused acute respiratory distress syndrome (ARDS). The initial stage of COVID-19 infection is the penetration of SARS-CoV-2 into target cells that have angiotensin converting enzyme type II receptors. The virus enters the body through the respiratory tract and interacts primarily with toll-like receptors (TLRs). The events in SARS-Cov-2 induced infection follow the next scenario: epithelial cells via TLRs recognize and identify SARS-Cov-2, and after that the information is transmitted to the transcriptional NF-κB, which causes expression of the corresponding genes. Activated in this way, the epithelial cells begin to synthesize various biologically active molecules. The results obtained on preclinical material indicate that ROS generation increases and the antioxidant protection decreases, which plays a major role in the pathogenesis of SARS-CoV, as well as in the progression and severity of this respiratory disease.

Incidence of healthcare-associated infections in patients with fever during the first 48 hours after decannulation from veno-venous extracorporeal membrane oxygenation

INTRODUCTION

Fevers following decannulation from veno-venous extracorporeal membrane oxygenation often trigger an infectious workup; however, the yield of this workup is unknown. We investigated the incidence of post-veno-venous extracorporeal membrane oxygenation decannulation fever as well as the incidence and nature of healthcare-associated infections in this population within 48 hours of decannulation.

METHODS

All patients treated with veno-venous extracorporeal membrane oxygenation for acute respiratory failure who survived to decannulation between August 2014 and November 2018 were retrospectively reviewed. Trauma patients and bridge to lung transplant patients were excluded. The highest temperature and maximum white blood cell count in the 24 hours preceding and the 48 hours following decannulation were obtained. All culture data obtained in the 48 hours following decannulation were reviewed. Healthcare-associated infections included blood stream infections, ventilator-associated pneumonia, and urinary tract infections.

RESULTS

A total of 143 patients survived to decannulation from veno-venous extracorporeal membrane oxygenation and were included in the study. In total, 73 patients (51%) were febrile in the 48 hours following decannulation. Among this cohort, seven healthcare-associated infections were found, including five urinary tract infections, one blood stream infection, and one ventilator-associated pneumonia. In the afebrile cohort (70 patients), four healthcare-associated infections were found, including one catheter-associated urinary tract infection, two blood stream infections, and one ventilator-associated pneumonia. In all decannulated patients, the majority of healthcare-associated infections were urinary tract infections (55%). No central line-associated blood stream infections were identified in either cohort. When comparing febrile to non-febrile cohorts, there was a significant difference between pre- and post-decannulation highest temperature (p < 0.001) but not maximum white blood cell count (p = 0.66 and p = 0.714) between the two groups. Among all positive culture data, the most commonly isolated organism was Klebsiella pneumoniae (41.7%) followed by Escherichia coli (33%). Median hospital length of stay and time on extracorporeal membrane oxygenation were shorter in the afebrile group compared to the febrile group; however, this did not reach a statistical difference.

CONCLUSION

Fever is common in the 48 hours following decannulation from veno-venous extracorporeal membrane oxygenation. Differentiating infection from non-infectious fever in the post-decannulation veno-venous extracorporeal membrane oxygenation population remains challenging. In our febrile post-decannulation cohort, the incidence of healthcare-associated infections was low. The majority were diagnosed with a urinary tract infection. We believe obtaining cultures in febrile patients in the immediate decannulation period from veno-venous extracorporeal membrane oxygenation has utility, and even in the absence of other clinical suspicion, should be considered. However, based on our data, a urinalysis and urine culture may be sufficient as an initial work up to identify the source of infection.

Targeting the Complement Alternative Pathway Permits Graft Versus Leukemia Activity while Preventing Graft Versus Host Disease

PURPOSE

Application of allogeneic hematopoietic cell transplantation (allo-HCT) for patients with hematologic disorders is limited by the development of GVHD. Separation of GVHD and graft-versus-leukemia (GVL) remains a great challenge in the field. We investigated the contribution of individual pathways involved in the complement cascade in GVH and GVL responses to identify specific targets by which to separate these two processes.

EXPERIMENTAL DESIGN

We used multiple preclinical murine and human-to-mouse xenograft models involving allo-HCT recipients lacking components of the alternative pathway (AP) or classical pathway (CP)/lectin pathway (LP) to dissect the role of each individual pathway in GVHD pathogenesis and the GVL effect. For translational purposes, we used the AP-specific complement inhibitor, CR2-fH, which localizes in injured target organs to allow specific blockade of complement activation at sites of inflammation.

RESULTS

Complement deposition was evident in intestines of mice and patients with GVHD. In a preclinical setting, ablation of the AP, but not the CP/LP, significantly improved GVHD outcomes. Complement activation through the AP in host hematopoietic cells, and specifically dendritic cells (DC), was required for GVHD progression. AP deficiency in recipients decreased donor T-cell migration and Th1/Th2 differentiation, while increasing the generation of regulatory T cells. This was because of decreased activation and stimulatory activity of recipient DCs in GVHD target organs. Treatment with CR2-fH effectively prevented GVHD while preserving GVL activity.

CONCLUSIONS

This study highlights the AP as a new therapeutic target to prevent GVHD and tumor relapse after allo-HCT. Targeting the AP by CR2-fH represents a promising therapeutic approach for GVHD treatment.

Hypertension, Thrombosis, Kidney Failure, and Diabetes: Is COVID-19 an Endothelial Disease? A Comprehensive Evaluation of Clinical and Basic Evidence

The symptoms most commonly reported by patients affected by coronavirus disease (COVID-19) include cough, fever, and shortness of breath. However, other major events usually observed in COVID-19 patients (e.g., high blood pressure, arterial and venous thromboembolism, kidney disease, neurologic disorders, and diabetes mellitus) indicate that the virus is targeting the endothelium, one of the largest organs in the human body. Herein, we report a systematic and comprehensive evaluation of both clinical and preclinical evidence supporting the hypothesis that the endothelium is a key target organ in COVID-19, providing a mechanistic rationale behind its systemic manifestations.

Hypoxia-induced complement dysregulation is associated with microvascular impairments in mouse tracheal transplants

BACKGROUND

Complement Regulatory Proteins (CRPs), especially CD55 primarily negate complement factor 3-mediated injuries and maintain tissue homeostasis during complement cascade activation. Complement activation and regulation during alloimmune inflammation contribute to allograft injury and therefore we proposed to investigate a crucial pathological link between vascular expression of CD55, active-C3, T cell immunity and associated microvascular tissue injuries during allograft rejection.

METHODS

Balb/c→C57BL/6 allografts were examined for microvascular deposition of CD55, C3d, T cells, and associated tissue microvascular impairments during rejection in mouse orthotopic tracheal transplantation.

RESULTS

Our findings demonstrated that hypoxia-induced early activation of HIF-1α favors a cell-mediated inflammation (CD4⁺, CD8⁺, and associated proinflammatory cytokines, IL-2 and TNF-α), which proportionally triggers the downregulation of CRP-CD55, and thereby augments the uncontrolled release of active-C3, and Caspase-3 deposition on CD31⁺ graft vascular endothelial cells. These molecular changes are pathologically associated with microvascular deterioration (low tissue O₂ and Blood flow) and subsequent airway epithelial injuries of rejecting allografts as compared to non-rejecting syngrafts.

CONCLUSION

Together, these findings establish a pathological correlation between complement dysregulation, T cell immunity, and microvascular associated injuries during alloimmune inflammation in transplantation.

Pseudolinear C4d deposits in a hereditary glomerulopathy caused by a rare NC1 collagen-4-alpha-5 missense mutation: a "new disease entity"?

C4d positive glomerulopathies with pseudolinear capillary wall deposits caused by basement membrane (GBM) remodeling have sporadically been reported in renal transplants. Here we describe the case of a hypertensive 60 year-old male with a 5 month history of nephrotic range proteinuria in the setting of normal serum creatinine, complement and ANA levels. Work-up showed MGUS (IgG/kappa restricted). A diagnostic renal biopsy to search for monoclonal gammopathy of renal significance demonstrated thickened glomerular capillary walls with strong pseudolinear complement factor C4d deposits by immunofluorescence microscopy (IF); all other IF studies including stains for Col4A3 were unrevealing with only minor abnormalities seen for Col4A5. The strong and unusual C4d staining of undetermined direct diagnostic significance triggered additional electron microscopic studies uncovering marked structural GBM changes suggestive of a hereditary nephropathy. Further genetic testing revealed a very rare X-linked single missense mutation in the NC1 domain of Col4A5 (exon 51) with a single amino acid substitution (COL4A5 p.A1581S) that has thus far not been reported in hereditary nephropathies. Our case provides further support for pseudolinear glomerular C4d deposits as general markers of GBM remodeling, in our case an unexpected hereditary nephropathy in an older male. Pseudolinear C4d: a general signpost for architectural GBM disturbance and a stimulus for in-depth studies including electron microscopy.

Misunderstandings Between Platelets and Neutrophils Build in Chronic Inflammation

Regulated hemostasis, inflammation and innate immunity entail extensive interactions between platelets and neutrophils. Under physiological conditions, vascular inflammation offers a template for the establishment of effective intravascular immunity, with platelets providing neutrophils with an array of signals that increase their activation threshold, thus limiting collateral damage to tissues and promoting termination of the inflammatory response. By contrast, persistent systemic inflammation as observed in immune-mediated diseases, such as systemic vasculitides, systemic sclerosis, systemic lupus erythematosus or rheumatoid arthritis is characterized by platelet and neutrophil reciprocal activation, which ultimately culminates in the generation of thrombo-inflammatory lesions, fostering vascular injury and organ damage. Here, we discuss recent evidence regarding the multifaceted aspects of platelet-neutrophil interactions from bone marrow precursors to shed microparticles. Moreover, we analyse shared and disease-specific events due to an aberrant deployment of these interactions in human diseases. To restore communications between the pillars of the immune-hemostatic continuum constitutes a fascinating challenge for the near future.

Proteomic atlas of organ vasculopathies triggered by Staphylococcus aureus sepsis

Sepsis is a life-threatening condition triggered by a dysregulated host response to microbial infection resulting in vascular dysfunction, organ failure and death. Here we provide a semi-quantitative atlas of the murine vascular cell-surface proteome at the organ level, and how it changes during sepsis. Using in vivo chemical labeling and high-resolution mass spectrometry, we demonstrate the presence of a vascular proteome that is perfusable and shared across multiple organs. This proteome is enriched in membrane-anchored proteins, including multiple regulators of endothelial barrier functions and innate immunity. Further, we automated our workflows and applied them to a murine model of methicillin-resistant Staphylococcus aureus (MRSA) sepsis to unravel changes during systemic inflammatory responses. We provide an organ-specific atlas of both systemic and local changes of the vascular proteome triggered by sepsis. Collectively, the data indicates that MRSA-sepsis triggers extensive proteome remodeling of the vascular cell surfaces, in a tissue-specific manner.

Vascular surfaces are rapidly remodeled during systemic inflammatory responses and sepsis. Here, the authors combine in vivo biotinylation and high-resolution mass spectrometry to characterize organ-level changes of the murine vascular cell surface proteome induced by MRSA sepsis.

Blockade of the kallikrein-kinin system reduces endothelial complement activation in vascular inflammation

Background

The complement and kallikrein-kinin systems (KKS) are activated during vascular inflammation. The aim of this study was to investigate if blockade of the KKS can affect complement activation on the endothelium during inflammation.

Methods

Complement deposition on endothelial microvesicles was assayed in vasculitis patient plasma samples and controls. Plasma was perfused over glomerular endothelial cells and complement deposition assayed by flow cytometry. The effect of the kinin system was assessed using kinin receptor antagonists and C1-inhibitor. The in vivo effect was assessed in kidney sections from mice with nephrotoxic serum-induced glomerulonephritis treated with a kinin receptor antagonist.

Findings

Vasculitis patient plasma had significantly more C3- and C9-positive endothelial microvesicles than controls. Perfusion of patient acute-phase plasma samples over glomerular endothelial cells induced the release of significantly more complement-positive microvesicles, in comparison to remission or control plasma. Complement activation on endothelial microvesicles was reduced by kinin B1- and B2-receptor antagonists or by C1-inhibitor (the main inhibitor of the classical pathway and the KKS). Likewise, perfusion of glomerular endothelial cells with C1-inhibitor-depleted plasma induced the release of complement-positive microvesicles, which was significantly reduced by kinin-receptor antagonists or C1-inhibitor. Mice with nephrotoxic serum-induced glomerulonephritis exhibited significantly reduced glomerular C3 deposition when treated with a B1-receptor antagonist.

Interpretation

Excessive complement deposition on the endothelium will promote endothelial injury and the release of endothelial microvesicles. This study demonstrates that blockade of the KKS can reduce complement activation and thereby the inflammatory response on the endothelium.

Funding

Full details are provided in the Acknowledgements/Funding section.

Selective permeability of mouse blood-aqueous barrier as determined by 15N-heavy isotope tracing and mass spectrometry

The blood-aqueous barrier plays a key role in regulating aqueous humor homeostasis by selectively restricting passage of proteins into the eye. The kinetics of aqueous flow are traditionally measured using artificial markers; however, these marker molecules do not address the barrier's selective permeability to plasma proteins. Here we applied stable isotope labeling of all serum proteins with nitrogen-15 (¹⁵N) atoms. Following systemic injection of this "heavy" serum in mice, the ¹⁵N-to-endogenous nitrogen-14 (¹⁴N) ratio of each protein in aqueous was measured by mass spectrometry. By monitoring the kinetic changes in these ratios, we determined the permeability profiles of hundreds of serum proteins. Meanwhile, we subjected one of the eyes to neoangiogenic wound healing by inflicting injury to the corneal limbus and compared the ¹⁵N proteomes between the normal eyes and the recovering eyes at 2 weeks after injury. In the injured eye, we detected markedly enhanced permeability to inhibitory complement regulator proteins, such as Cfh, Cfhr, Cfb, Cfi, Cfd, and Vtn. Many of the proteins in this group are implicated in age-related macular degeneration associated with leakage of the blood-retinal barrier due to inflammation. To rule out the possibility that the observed leakage was due simply to physical damage of the blood vessels, we separately created a neovascularization model using an alkali burn of the avascular cornea. In this latter model, elevated levels of Cfh and Cfb were evident. These findings suggest that ocular neovascularization is associated with enhanced permeability to serum complement regulators.

The Alternative Complement System Mediates Cell Death in Retinal Ischemia Reperfusion Injury

Ischemia reperfusion (IR) injury induces retinal cell death and contributes to visual impairment. Previous studies suggest that the complement cascade plays a key role in IR injury in several systemic diseases. However, the role of the complement pathway in the ischemic retina has not been investigated. The aim of this study is to determine if the alternative complement cascade plays a role in retinal IR injury, and identify which components of the pathway mediate retinal degeneration in response to IR injury. To accomplish this, we utilized the mouse model of retinal IR injury, wherein the intraocular pressure (IOP) is elevated for 45 min, collapsing the retinal blood vessels and inducing retinal ischemia, followed by IOP normalization and subsequent reperfusion. We found that mRNA expression of complement inhibitors complement receptor 1-related gene/protein-y (Crry), Cd55 and Cd59a was down-regulated after IR. Moreover, genetic deletion of complement component 3 (C3^−/−) and complement factor b (Fb^−/−) decreased IR-induced retinal apoptosis. Because vascular dysfunction is central to IR injury, we also assessed the role of complement in a model of shear stress. In human retinal endothelial cells (HRECs), shear stress up-regulated complement inhibitors Cd46, Cd55, and Cd59, and suppressed complement-mediated cell death, indicating that a lack of vascular flow, commonly observed in IR injury, allows for complement mediated attack of the retinal vasculature. These results suggested that in retinal IR injury, the alternative complement system is activated by suppression of complement inhibitors, leading to vascular dysfunction and neuronal cell death.

Acute heart failure following myocardial infarction: complement activation correlates with the severity of heart failure in patients developing cardiogenic shock

AIMS

Heart failure (HF) is an impending complication to myocardial infarction. We hypothesized that the degree of complement activation reflects severity of HF following acute myocardial infarction.

METHODS AND RESULTS

The LEAF trial (LEvosimendan in Acute heart Failure following myocardial infarction) evaluating 61 patients developing HF within 48 h after percutaneous coronary intervention-treated ST-elevation myocardial infarction herein underwent a post hoc analysis. Blood samples were drawn from inclusion to Day 5 and at 42 day follow-up, and biomarkers were measured with enzyme immunoassays. Regional myocardial contractility was measured by echocardiography as wall motion score index (WMSI). The cardiogenic shock group (n = 9) was compared with the non-shock group (n = 52). Controls (n = 44) were age-matched and sex-matched healthy individuals. C4bc, C3bc, C3bBbP, and sC5b-9 were elevated in patients at inclusion compared with controls (P < 0.01). The shock group had higher levels compared with the non-shock group for all activation products except C3bBbP (P < 0.05). At Day 42, all products were higher in the shock group (P < 0.05). In the shock group, sC5b-9 correlated significantly with WMSI at baseline (r = 0.68; P = 0.045) and at Day 42 (r = 0.84; P = 0.036). Peak sC5b-9 level correlated strongly with WMSI at Day 42 (r = 0.98; P = 0.005). Circulating endothelial cell activation markers sICAM-1 and sVCAM-1 were higher in the shock group during the acute phase (P < 0.01), and their peak levels correlated with sC5b-9 peak level in the whole HF population (r = 0.32; P = 0.014 and r = 0.30; P = 0.022, respectively).

CONCLUSIONS

Complement activation discriminated cardiogenic shock from non-shock in acute ST-elevation myocardial infarction complicated by HF and correlated with regional contractility and endothelial cell activation, suggesting a pathogenic role of complement in this condition.

Complement Activation in Inflammatory Skin Diseases

The complement system is a fundamental part of the innate immune system, playing a crucial role in host defense against various pathogens, such as bacteria, viruses, and fungi. Activation of complement results in production of several molecules mediating chemotaxis, opsonization, and mast cell degranulation, which can contribute to the elimination of pathogenic organisms and inflammation. Furthermore, the complement system also has regulating properties in inflammatory and immune responses. Complement activity in diseases is rather complex and may involve both aberrant expression of complement and genetic deficiencies of complement components or regulators. The skin represents an active immune organ with complex interactions between cellular components and various mediators. Complement involvement has been associated with several skin diseases, such as psoriasis, lupus erythematosus, cutaneous vasculitis, urticaria, and bullous dermatoses. Several triggers including auto-antibodies and micro-organisms can activate complement, while on the other hand complement deficiencies can contribute to impaired immune complex clearance, leading to disease. This review provides an overview of the role of complement in inflammatory skin diseases and discusses complement factors as potential new targets for therapeutic intervention.

Extracorporeal membrane oxygenation and cytokine adsorption

Extracorporeal membrane oxygenation (ECMO) is an increasingly used technology for mechanical support of respiratory and cardio-circulatory failure. Excessive systemic inflammatory response is observed during sepsis and after cardiopulmonary bypass (CPB) with similar clinical features. The overwhelming inflammatory response is characterized by highly elevated pro- and anti-inflammatory cytokine levels. The excessive cytokine release during the overwhelming inflammatory response may result in multiple organ damage and failure. During ECMO therapy activation of complement and contact systems occur which may be followed by cytokine release. Controlling excessively increased cytokines may be considered as a valuable treatment option. Hemoadsorption therapy may be used to decrease cytokine levels in case of excessive inflammatory response and due to its unspecific adsorptive characteristics also substances like myoglobin, free hemoglobin or bilirubin. Controlling pro-inflammatory response with hemoadsorption may have positive impact on the endothelial glycocalix and also may be advantageous for maintenance of the vascular barrier function which plays a pivotal role in the development of tissue edema and oxygen mismatch. Hemoadsorption therapy seems to offer a promising new option for the treatment of patients with overwhelming inflammatory response leading to faster hemodynamic and metabolic stabilization finally resulting in preserved organ functions.

The alternative complement pathway is longitudinally associated with adverse cardiovascular outcomes

The alternative pathway of complement activation is highly reactive and can be activated spontaneously in the vasculature. Activation may contribute to vascular damage and development of cardiovascular disease (CVD). We aimed to investigate functional components of the alternative pathway in cardiovascular risk. We studied 573 individuals who were followed-up for seven years. At baseline, we measured the enhancer properdin; the rate-limiting protease factor D (FD); and a marker of systemic activation, Bb. Using generalised estimating equations, we investigated their longitudinal associations with cardiovascular events (CVE, N=89), CVD (N=159), low-grade inflammation (LGI), endothelial dysfunction (ED) and carotid intima-media thickness (cIMT). Furthermore, we investigated associations with incident CVE (N=39) and CVD (N=73) in 342 participants free of CVD at baseline. CVE included myocardial infarction, stroke, cardiac angioplasty and/or cardiac bypass. CVD additionally included ischaemia on an electrocardiogram and/or ankle-brachial index < 0.9. In adjusted analyses, properdin was positively associated with CVE (per 1SD, longitudinal OR=1.36 [1.07; 1.74], OR for incident CVE=1.53 [1.06; 2.20]), but not with CVD. Properdin was also positively associated with ED (β=0.13 [95 %CI 0.06; 0.20]), but not with LGI or cIMT. FD and Bb were positively associated with LGI (per 1SD, FD: β=0.21 [0.12; 0.29], Bb: β=0.14 [0.07; 0.21]), and ED (FD: β=0.20 [0.11; 0.29], Bb: β=0.10 [0.03; 0.18]), but not with cIMT, CVE or CVD. Taken together, this suggests that the alternative complement pathway contributes to processes of vascular damage, and that in particular a high potential to enhance alternative pathway activation may promote unfavourable cardiovascular outcomes in humans.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Endothelial cells: source, barrier, and target of defensive mediators

Endothelium is strategically located at the interface between blood and interstitial tissues, placing thus endothelial cell as a key player in vascular homeostasis. Endothelial cells are in a dynamic equilibrium with their environment and constitute concomitantly a source, a barrier, and a target of defensive mediators. This review will discuss the recent advances in our understanding of the complex crosstalk between the endothelium, the complement system and the hemostasis in health and in disease. The first part will provide a general introduction on endothelial cells heterogeneity and on the physiologic role of the complement and hemostatic systems. The second part will analyze the interplay between complement, hemostasis and endothelial cells in physiological conditions and their alterations in diseases. Particular focus will be made on the prototypes of thrombotic microangiopathic disorders, resulting from complement or hemostasis dysregulation-mediated endothelial damage: atypical hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. Novel aspects of the pathophysiology of the thrombotic microangiopathies will be discussed.

Glomerular C4d deposits can mark structural capillary wall remodelling in thrombotic microangiopathy and transplant glomerulopathy: C4d beyond active antibody-mediated injury: a retrospective study

Peritubular capillary C4d (ptc-C4d) usually marks active antibody-mediated rejection, while pseudolinear glomerular capillary C4d (GBM-C4d) is of undetermined diagnostic significance, especially when seen in isolation without concurrent ptc-C4d. We correlated GBM-C4d with structural GBM abnormalities and active antibody-mediated rejection in 319 renal transplant and 35 control native kidney biopsies. In kidney transplants, ptc-C4d was associated with GBM-C4d in 97% by immunofluorescence microscopy (IF) and 61% by immunohistochemistry (IHC; P < 0.001). Transplant glomerulopathy correlated with GBM-C4d (P < 0.001) and presented with isolated GBM-C4d lacking ptc-C4d in 69% by IF and 40% by IHC. Strong isolated GBM-C4d was found post year-1 in repeat biopsies with transplant glomerulopathy. GBM-C4d staining intensity correlated with Banff cg scores (rs = 0.45, P < 0.001). Stepwise exclusion and multivariate logistic regression corrected for active antibody-mediated rejection showed significant correlations between GBM duplication and GBM-C4d (P = 0.001). Native control biopsies with thrombotic microangiopathies demonstrated GBM-C4d in 92% (IF, P < 0.001) and 35% (IHC). In conclusion, pseudolinear GBM-C4d staining can reflect two phenomena: (i) structural GBM changes with duplication in native and transplant kidneys or (ii) active antibody-mediated rejection typically accompanied by ptc-C4d. While ptc-C4d is a dynamic 'etiologic' marker for active antibody-mediated rejection, isolated strong GBM-C4d can highlight architectural glomerular remodelling.

The inflammatory response to extracorporeal membrane oxygenation (ECMO): a review of the pathophysiology

Extracorporeal membrane oxygenation (ECMO) is a technology capable of providing short-term mechanical support to the heart, lungs or both. Over the last decade, the number of centres offering ECMO has grown rapidly. At the same time, the indications for its use have also been broadened. In part, this trend has been supported by advances in circuit design and in cannulation techniques. Despite the widespread adoption of extracorporeal life support techniques, the use of ECMO remains associated with significant morbidity and mortality. A complication witnessed during ECMO is the inflammatory response to extracorporeal circulation. This reaction shares similarities with the systemic inflammatory response syndrome (SIRS) and has been well-documented in relation to cardiopulmonary bypass. The exposure of a patient’s blood to the non-endothelialised surface of the ECMO circuit results in the widespread activation of the innate immune system; if unchecked this may result in inflammation and organ injury. Here, we review the pathophysiology of the inflammatory response to ECMO, highlighting the complex interactions between arms of the innate immune response, the endothelium and coagulation. An understanding of the processes involved may guide the design of therapies and strategies aimed at ameliorating inflammation during ECMO. Likewise, an appreciation of the potentially deleterious inflammatory effects of ECMO may assist those weighing the risks and benefits of therapy.

The alternative complement pathway aids in vascular regression during the early stages of a murine model of proliferative retinopathy

Proliferative retinopathic diseases often progress in 2 phases: initial regression of retinal vasculature (phase 1) followed by subsequent neovascularization (NV) (phase 2). The immune system has been shown to aid in vascular pruning in such retinopathies; however, little is known about the role of the alternative complement pathway in the initial vascular regression phase. Using a mouse model of oxygen-induced retinopathy (OIR), we observed that alternative complement pathway-deficient mice (Fb(-/-)) exhibited a mild decrease in vascular loss at postnatal day (P)8 compared with age- and strain-matched controls (P = 0.035). Laser capture microdissection was used to isolate the retinal blood vessels. Expression of the complement inhibitors Cd55 and Cd59 was significantly decreased in blood vessels isolated from hyperoxic retinas compared with those from normoxic control mice. Vegf expression was measured at P8 and found to be significantly lower in OIR mice than in normoxic control mice (P = 0.0048). Further examination of specific Vegf isoform expression revealed a significant decrease in Vegf120 (P = 0.00032) and Vegf188 (P = 0.0092). In conjunction with the major modulating effects of Vegf during early retinal vascular development, our data suggest a modest involvement of the alternative complement pathway in targeting vessels for regression in the initial vaso-obliteration stage of OIR.

Complement Interactions with Blood Cells, Endothelial Cells and Microvesicles in Thrombotic and Inflammatory Conditions

The complement system is activated in the vasculature during thrombotic and inflammatory conditions. Activation may be associated with chronic inflammation on the endothelial surface leading to complement deposition. Complement mutations allow uninhibited complement activation to occur on platelets, neutrophils, monocytes, and aggregates thereof, as well as on red blood cells and endothelial cells. Furthermore, complement activation on the cells leads to the shedding of cell derived-microvesicles that may express complement and tissue factor thus promoting inflammation and thrombosis. Complement deposition on red blood cells triggers hemolysis and the release of red blood cell-derived microvesicles that are prothrombotic. Microvesicles are small membrane vesicles ranging from 0.1 to 1 μm, shed by cells during activation, injury and/or apoptosis that express components of the parent cell. Microvesicles are released during inflammatory and vascular conditions. The repertoire of inflammatory markers on endothelial cell-derived microvesicles shed during inflammation is large and includes complement. These circulating microvesicles may reflect the ongoing inflammatory process but may also contribute to its propagation. This overview will describe complement activation on blood and endothelial cells and the release of microvesicles from these cells during hemolytic uremic syndrome, thrombotic thrombocytopenic purpura and vasculitis, clinical conditions associated with enhanced thrombosis and inflammation.

Targeted complement inhibition and microvasculature in transplants: a therapeutic perspective

Active complement mediators play a key role in graft-versus-host diseases, but little attention has been given to the angiogenic balance and complement modulation during allograft acceptance. The complement cascade releases the powerful proinflammatory mediators C3a and C5a anaphylatoxins, C3b, C5b opsonins and terminal membrane attack complex into tissues, which are deleterious if unchecked. Blocking complement mediators has been considered to be a promising approach in the modern drug discovery plan, and a significant number of therapeutic alternatives have been developed to dampen complement activation and protect host cells. Numerous immune cells, especially macrophages, develop both anaphylatoxin and opsonin receptors on their cell surface and their binding affects the macrophage phenotype and their angiogenic properties. This review discusses the mechanism that complement contributes to angiogenic injury, and the development of future therapeutic targets by antagonizing activated complement mediators to preserve microvasculature in rejecting the transplanted organ.

Parietal and intravascular innate mechanisms of vascular inflammation

Sustained inflammation of the vessel walls occurs in a large number of systemic diseases (ranging from atherosclerosis to systemic vasculitides, thrombotic microangiopathies and connective tissue diseases), which are ultimately characterized by ischemia and end-organ failure. Cellular and humoral innate immunity contribute to a common pathogenic background and comprise several potential targets for therapeutic intervention. Here we discuss some recent advances in the effector and regulatory action of neutrophils and in the outcome of their interaction with circulating platelets. In parallel, we discuss novel insights into the role of humoral innate immunity in vascular inflammation. All these topics are discussed in light of potential clinical and therapeutic implications in the near future.

C1q as a unique player in angiogenesis with therapeutic implication in wound healing

We have previously shown that C1q is expressed on endothelial cells (ECs) of newly formed decidual tissue. Here we demonstrate that C1q is deposited in wound-healing skin in the absence of C4 and C3 and that C1q mRNA is locally expressed as revealed by real-time PCR and in situ hybridization. C1q was found to induce permeability of the EC monolayer, to stimulate EC proliferation and migration, and to promote tube formation and sprouting of new vessels in a rat aortic ring assay. Using a murine model of wound healing we observed that vessel formation was defective in C1qa(-/-) mice and was restored to normal after local application of C1q. The mean vessel density of wound-healing tissue and the healed wound area were significantly increased in C1q-treated rats. On the basis of these results we suggest that C1q may represent a valuable therapeutic agent that can be used to treat chronic ulcers or other pathological conditions in which angiogenesis is impaired, such as myocardial ischemia.

Chronic Inflammation: Synergistic Interactions of Recruiting Macrophages (TAMs) and Eosinophils (Eos) with Host Mast Cells (MCs) and Tumorigenesis in CALTs. M-CSF, Suitable Biomarker for Cancer Diagnosis!

Ongoing debates, misunderstandings and controversies on the role of inflammation in cancer have been extremely costly for taxpayers and cancer patients for over four decades. A reason for repeated failed clinical trials (90% ± 5 failure rates) is heavy investment on numerous genetic mutations (molecular false-flags) in the chaotic molecular landscape of site-specific cancers which are used for "targeted" therapies or "personalized" medicine. Recently, unresolved/chronic inflammation was defined as loss of balance between two tightly regulated and biologically opposing arms of acute inflammation ("Yin"-"Yang" or immune surveillance). Chronic inflammation could differentially erode architectural integrities in host immune-privileged or immune-responsive tissues as a common denominator in initiation and progression of nearly all age-associated neurodegenerative and autoimmune diseases and/or cancer. Analyses of data on our "accidental" discoveries in 1980s on models of acute and chronic inflammatory diseases in conjunctival-associated lymphoid tissues (CALTs) demonstrated at least three stages of interactions between resident (host) and recruited immune cells: (a), acute phase; activation of mast cells (MCs), IgE Abs, histamine and prostaglandin synthesis; (b), intermediate phase; down-regulation phenomenon, exhausted/degranulated MCs, heavy eosinophils (Eos) infiltrations into epithelia and goblet cells (GCs), tissue hypertrophy and neovascularization; and (c), chronic phase; induction of lymphoid hyperplasia, activated macrophages (Mfs), increased (irregular size) B and plasma cells, loss of integrity of lymphoid tissue capsular membrane, presence of histiocytes, follicular and germinal center formation, increased ratios of local IgG1/IgG2, epithelial thickening (growth) and/or thinning (necrosis) and angiogenesis. Results are suggestive of first evidence for direct association between inflammation and identifiable phases of immune dysfunction in the direction of tumorigenesis. Activated MFs (TAMs or M2) and Eos that are recruited by tissues (e.g., conjunctiva or perhaps lung airways) whose principal resident immune cells are MCs and lymphocytes are suggested to play crucial synergistic roles in enhancing growth promoting capacities of host toward tumorigenesis. Under oxidative stress, M-CSF may produce signals that are cumulative/synergistic with host mediators (e.g., low levels of histamine), facilitating tumor-directed expression of decoy receptors and immune suppressive factors (e.g., dTNFR, IL-5, IL-10, TGF-b, PGE2). M-CSF, possessing superior sensitivity and specificity, compared with conventional markers (e.g., CA-125, CA-19-9) is potentially a suitable biomarker for cancer diagnosis and technology development. Systematic monitoring of interactions between resident and recruited cells should provide key information not only about early events in loss of immune surveillance, but it would help making informed decisions for balancing the inherent tumoricidal (Yin) and tumorigenic (Yang) properties of immune system and effective preventive and therapeutic approaches and accurate risk assessment toward improvement of public health.

Complement activation by heme as a secondary hit for atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is characterized by genetic and acquired abnormalities of the complement system leading to alternative pathway (AP) overactivation and by glomerular endothelial damage, thrombosis, and mechanical hemolysis. Mutations per se are not sufficient to induce aHUS, and nonspecific primary triggers are required for disease manifestation. We investigated whether hemolysis-derived heme contributes to aHUS pathogenesis. We confirmed that heme activates complement AP in normal human serum, releasing C3a, C5a, and sC5b9. We demonstrated that heme-exposed endothelial cells also activate the AP, resulting in cell-bound C3 and C5b9. This was exacerbated in aHUS by genetic abnormalities associated with AP overactivation. Heme interacted with C3 close to the thioester bond, induced homophilic C3 complexes, and promoted formation of an overactive C3/C5 convertase. Heme induced decreased membrane cofactor protein (MCP) and decay-accelerating factor (DAF) expression on endothelial cells, giving Factor H (FH) a major role in complement regulation. Finally, heme promoted a rapid exocytosis of Weibel-Palade bodies, with membrane expression of P-selectin known to bind C3b and trigger the AP, and the release of the prothrombotic von Willebrand factor. These results strongly suggest that hemolysis-derived heme represents a common secondary hit amplifying endothelial damage and thrombosis in aHUS.