Endothelial cells are a target of both complement and kinin system

Ant Colony-Inspired Adaptive Peptide Nanoregulators Remodeling the Endothelial Barrier to Alleviate Inflammatory Responses

Endothelial barrier disruption exacerbates inflammation and tissue injury, posing dual challenges of reconstructing tight junctions and precisely regulating the local microenvironment. Traditional multidrug therapies often struggle with rapid drug leakage due to barrier dysfunction and limited synergy between therapeutic agents. Here, a strategy is proposed inspired by the "ant colony collaboration", developing an "all-in-one" conformationally adaptive peptide nanoregulator (VJP NPs) through the intelligent integration of three functional peptides. VJP NPs strategically harness the overexpression of vascular cell adhesion protein 1 (VCAM-1), enabling selective targeting of the inflamed endothelium under the guidance of the VHPK peptide while accumulating within the inflammatory microenvironment. The nanoregulators disassemble in response to high ROS levels, efficiently scavenging excess ROS. Simultaneously, they release the PMX peptide, competitively binding to the complement receptor C5aR to regulate the complement cascade. Furthermore, they release the JIP peptide to restore the endothelial barrier, reducing immune cell infiltration. As demonstrated in a mouse model of acute lung injury (ALI), VJP NPs markedly promote pulmonary vascular endothelial barrier repair, effectively attenuating inflammatory responses and alleviating tissue injury. This peptide-based nanoplatform boosts peptide delivery efficiency via a nanoprodrug strategy and amplifies synergistic therapeutic effects, highlighting its potential in endothelial barrier restoration and inflammation modulation.

Organ dysfunction induced by hemorrhagic shock: From mechanisms to therapeutic medicines

Hemorrhagic shock (HS) leads to organ dysfunction, which increases the incidence of unfavorable outcomes in patients. However, adjuvant drug therapy for HS has not been widely accepted, and the benefits of vasopressors are generally considered to have insufficient evidence. Energy homeostasis disruption and excessive immune system activation are the main mechanisms underlying HS-induced organ dysfunction. Recent reports on HS animal models and clinical trials have revealed potential drugs that target the immune response, oxidative damage, and energy homeostasis in HS, providing new insights for the treatment of HS-induced organ dysfunction. In this review, we first discuss the pathophysiology of organ dysfunction involved in HS injury and then systematically review potential drugs that regulate immunity, the inflammatory response, oxidative damage, energy homeostasis, and cell death. We also review the available drugs with clinical evidence of HS-induced organ dysfunction efficacy. Treatment strategies combined with an improved understanding of the organ injury mechanisms of HS may help identify and develop targeted therapeutic modalities that mitigate severe organ dysfunction and reduce mortality caused by HS injury.

[Berberine ameliorates coronary artery endothelial cell injury in Kawasaki disease through complement and coagulation cascades]

OBJECTIVES

To explore the role of berberine (BBR) in ameliorating coronary endothelial cell injury in Kawasaki disease (KD) by regulating the complement and coagulation cascade.

METHODS

Human coronary artery endothelial cells (HCAEC) were divided into a healthy control group, a KD group, and a BBR treatment group (n=3 for each group). The healthy control group and KD group were supplemented with 15% serum from healthy children and KD patients, respectively, while the BBR treatment group received 15% serum from KD patients followed by the addition of 20 mmol/L BBR. Differential protein expression was analyzed and identified using isobaric tags for relative and absolute quantitation technology and liquid chromatography-tandem mass spectrometry, followed by GO functional enrichment analysis and KEGG signaling pathway enrichment analysis of the differential proteins. Western blot was used to detect differential protein expression.

RESULTS

A total of 518 differential proteins were identified between the KD group and the healthy control group (300 upregulated proteins and 218 downregulated proteins). A total of 422 differential proteins were identified between the BBR treatment group and the KD group (221 upregulated proteins and 201 downregulated proteins). Bioinformatics analysis showed that compared to the healthy control group, the differential proteins in the KD group were enriched in the complement and coagulation cascade and ribosome biogenesis in eukaryotes. Compared to the KD group, the differential proteins in the BBR treatment group were also enriched in the complement and coagulation cascade and ribosome biogenesis in eukaryotes. Western blot results indicated that compared to the healthy control group, the expression of complement C1q subcomponent subunit C (C1QC), kininogen-1 (KNG1), complement C1s subcomponent (C1S), and C4b-binding protein alpha chain (C4BPA) was increased in the KD group (P<0.05). Compared to the KD group, the expression of KNG1, C1S, C1QC, and C4BPA was decreased in the BBR treatment group (P<0.05).

CONCLUSIONS

The complement and coagulation cascade may be involved in the regulation of BBR treatment for coronary injury in KD, and C1QC, KNG1, C1S, and C4BPA may serve as biomarkers for this treatment.

Genetic associations of central serous chorioretinopathy subtypes, neovascular age-related macular degeneration, and polypoidal choroidal vasculopathy

PURPOSE

To evaluate the genetic associations of different subtypes of central serous chorioretinopathy (CSCR), neovascular age-related macular degeneration (nAMD), and polypoidal choroidal vasculopathy (PCV).

DESIGN

A case-control genetic association study.

METHODS

This study enrolled 217 CSCR, 341 nAMD, 288 PCV patients, and 1380 controls. The CSCR patients were classified into those with focal or diffuse leakage, with or without pigment epithelial detachment (PED), and with or without macular neovascularization (MNV). Associations between 11 variants from 8 genes, ADAMTS9, ANGPT2, ARMS2, CFH, NR3C2, PGF, TNFRSF10A and VIPR2, and diseases/subtypes were analyzed by logistic regression analysis adjusted for age and sex, and inter-phenotype comparison by heterogeneity test.

RESULTS

The CFH rs800292-A conferred a protective effect for CSCR with MNV (OR=0.44, P = 0.002) and a risk effect for CSCR without MNV (OR=1.31, P = 0.023). CSCR patients carrying rs800292-G had a 3.23-fold of increased risk towards developing secondary MNV (P = 1.45 ×10-4). CFH rs3753394, rs800292 and rs1329428 showed similar effects among CSCR with MNV, nAMD and PCV, but opposite effects on CSCR without MNV. TNFRSF10A rs13278062-T was associated with overall CSCR but not with CSCR subtypes, nAMD or PCV. Moreover, CFH and ARMS2 SNPs showed heterogeneous effects in CSCR without MNV against CSCR with MNV, nAMD and PCV.

CONCLUSIONS

Genetic associations of CSCR with MNV resembled nAMD and PCV compared to CSCR without MNV, indicating differential genetic effects on neovascularization and choroidopathy. Further investigation of the functional roles of CFH, ARMS2, and TNFRSF10A in CSCR, nAMD and PCV should help elucidate the mechanisms of these maculopathies.

Genetic associations of central serous chorioretinopathy: a systematic review and meta-analysis

AIMS

To identify single-nucleotide polymorphisms (SNPs) associated with central serous chorioretinopathy (CSCR) by a systematic review and meta-analysis, and to compare the association profiles between CSCR, neovascular age-related macular degeneration (nAMD) and polypoidal choroidal vasculopathy (PCV).

METHODS

We searched the EMBASE, PubMed and Web of Science for genetic studies of CSCR from the starting dates of the databases to 12 September 2020. We then performed meta-analyses on all SNPs reported by more than two studies and calculated the pooled OR and 95% CIs. We also conducted sensitivity analysis and adopted the funnel plot to assess potential publication bias.

RESULTS

Totally 415 publications were reviewed, among them 10 were eligible for meta-analysis. We found 10 SNPs that have been reported at least twice. Meta-analysis and sensitivity analysis confirmed significant associations between CSCR and six SNPs in three genes, namely age-related maculopathy susceptibility 2 (ARMS2) (rs10490924, OR=1.37; p=0.00064), complement factor H (CFH) (rs800292, OR=1.44; p=7.80×10^-5; rs1061170, OR=1.34; p=0.0028; rs1329428, OR=1.40; p=0.012; and rs2284664, OR=1.36; p=0.0089) and tumour necrosis factor receptor superfamily, member 10a (TNFRSF10A) (rs13278062, OR=1.34; p=1.44×10^-15). Among them, only TNFRSF10A rs13278062 showed the same trend of effect on CSCR, nAMD and PCV, while the SNPs in ARMS2 and CFH showed opposite trends in the SNP associations.

CONCLUSIONS

This study confirmed the associations of ARMS2, CFH and TNFRSF10A with CSCR, and revealed that ARMS2, CFH and TNFRSF10A may affect different phenotypic expressions of CSCR, nAMD and PCV.

Endothelial activation and dysfunction in COVID-19: from basic mechanisms to potential therapeutic approaches

On 12 March 2020, the outbreak of coronavirus disease 2019 (COVID-19) was declared a pandemic by the World Health Organization. As of 4 August 2020, more than 18 million confirmed infections had been reported globally. Most patients have mild symptoms, but some patients develop respiratory failure which is the leading cause of death among COVID-19 patients. Endothelial cells with high levels of angiotensin-converting enzyme 2 expression are major participants and regulators of inflammatory reactions and coagulation. Accumulating evidence suggests that endothelial activation and dysfunction participate in COVID-19 pathogenesis by altering the integrity of vessel barrier, promoting pro-coagulative state, inducing endothelial inflammation, and even mediating leukocyte infiltration. This review describes the proposed cellular and molecular mechanisms of endothelial activation and dysfunction during COVID-19 emphasizing the principal mediators and therapeutic implications.

Neuroimmune crosstalk in the pathophysiology of hypertension

Hypertension is an important risk factor for cardiovascular morbidity and mortality and for events such as myocardial infarction, stroke, heart failure and chronic kidney disease and is a major determinant of disability-adjusted life-years. Despite the importance of hypertension, the pathogenesis of essential hypertension, which involves the complex interaction of several mechanisms, is still poorly understood. Evidence suggests that interplay between bone marrow, microglia and immune mediators underlies the development of arterial hypertension, in particular through mechanisms involving cytokines and peptides, such as neuropeptide Y, substance P, angiotensin II and angiotensin-(1-7). Chronic psychological stress also seems to have a role in increasing the risk of hypertension, probably through the activation of neuroimmune pathways. In this Review, we summarize the available data on the possible role of neuroimmune crosstalk in the origin and maintenance of arterial hypertension and discuss the implications of this crosstalk for recovery and rehabilitation after cardiac and cerebral injuries.

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.

Thrombomodulin enhances complement regulation through strong affinity interactions with factor H and C3b-Factor H complex

INTRODUCTION

Coagulation and complement systems are simultaneously activated at sites of tissue injury, leading to thrombin generation and opsonisation with C3b. Thrombomodulin (TM) is a cell-bound regulator of thrombin activation, but can also enhance the regulatory activity of complement factor H (FH), thus accelerating the degradation of C3b into inactive iC3b.

OBJECTIVES

This study sought to determine the biophysical interaction affinities of two recombinant TM analogs with thrombin, FH and C3b in order to analyze their ability to regulate serum complement activity.

METHODS

Surface plasmon resonance (SPR) analysis was used to determine binding affinities of TM analogs with FH and C3b, and compared to thrombin as positive control. The capacity of the two recombinant TM analogs to regulate complement in serum was tested in standard complement hemolytic activity assays.

RESULTS

SPR analysis showed that both TM analogs bind FH and C3b-Factor H with nanomolar and C3b with micromolar affinity; binding affinity for its natural ligand thrombin was several fold higher than for FH. At a physiological relevant concentration, TM inhibits complement hemolytic activity in serum via FH dependent and independent mechanisms.

CONCLUSIONS

TM exhibits significant binding affinity for complement protein FH and C3b-FH complex and its soluble form is capable at physiologically relevant concentrations of inhibiting complement activation in serum.

Amniotic Fluid Embolism: Anaphylactic Reactions With Idiosyncratic Adverse Response

PROBLEM

Amniotic fluid embolism (AFE) is a rare but severe emergency in obstetrics. The aim of the present study was to investigate the pathophysiology of AFE.

METHODS

A search was conducted between 1966 and 2014 through the English-language literature (online MEDLINE PubMed database) using the keyword amniotic fluid embolism combined with anaphylaxis, anaphylactoid, complement activation, mast cells, fetal antigens, and idiosyncratic.

RESULTS

Amniotic fluid embolism is a rare clinical entity but a severe obstetric emergency that can be lethal even in previously healthy women in labor or in the early postpartum period. There appears to be at least 2 mechanisms. First, adverse reactions in AFE are usually unexpected and fetal antigen dose dependent. Given the disastrous entry of amniotic fluid into the maternal circulation, they experience a sudden cardiopulmonary collapse (mechanical obstruction subtype). Second, anaphylactic and anaphylactoid reactions of the remaining AFE are also relatively unexpected and fetal antigen dose independent and can occur at the first exposure to amniotic fluid components. They are associated with complement activation and subsequent postpartum hemorrhage. Cardiac mast cells constitute a central pathogenesis of anaphylactic (immunoglobulin E-dependent) and anaphylactoid (immunoglobulin E-independent) reactions.

CONCLUSIONS

Recent immunologic studies provide a new approach to the study of the pathophysiology of AFE.

Plasma Kallikrein-Kinin system mediates immune-mediated renal injury in trichloroethylene-sensitized mice

Trichloroethylene (TCE) is a major environmental pollutant. An immunological response is a newly-recognized mechanism for TCE-induced kidney damage. However, the role of the plasma kallikrein-kinin system (KKS) in immune-mediated kidney injury has never been examined. This study aimed to explore the role of the key components of the KKS, i.e. plasma kallikrein (PK), bradykinin (BK) and its receptors B1R and B2R, in TCE-induced kidney injury. A mouse model of skin sensitization was used to explore the mechanism of injury with or without a PK inhibitor PKSI. Kidney function was evaluated by measuring blood urea nitrogen (BUN) and creatinine (Cr) in conjunction with histopathologic characterization. Plasma BK was determined by ELISA; Renal C5b-9 membrane attack complex was evaluated by immunohistochemistry. Expression of BK and PK in the kidney was detected by immunofluorescence. mRNA and protein levels of B1R and B2R were assessed by real-time qPCR and Western blot. As expected, numerous inflammatory cell infiltration and tubular epithelial cell vacuolar degeneration were observed in TCE-sensitized mice. Moreover, serum BUN and Cr and plasma BK were increased. In addition, deposition of BK, PK and C5b-9 were observed and B1R and B2R mRNA and proteins levels were up-regulated. Pre-treatment with PKSI, a highly selective inhibitor of PK, alleviated TCE-induced renal damage. In addition, PKSI attenuated TCE-induced up-regulation of BK, PK and its receptors and C5b-9. These results provided the first evidence that activation of the KKS contributed to immune-mediated renal injury induced by TCE and also helped to identify the KKS as a potential therapeutic target for mitigating chemical sensitization-induced renal damage.

Scientific and Regulatory Policy Committee Points-to-consider Paper*

Drug-induced vascular injury (DIVI) is a recurrent challenge in the development of novel pharmaceutical agents. Although DIVI in laboratory animal species has been well characterized for vasoactive small molecules, there is little available information regarding DIVI associated with biotherapeutics such as peptides/proteins or antibodies. Because of the uncertainty about whether DIVI in preclinical studies is predictive of effects in humans and the lack of robust biomarkers of DIVI, preclinical DIVI findings can cause considerable delays in or even halt development of promising new drugs. This review discusses standard terminology, characteristics, and mechanisms of DIVI associated with biotherapeutics. Guidance and points to consider for the toxicologist and pathologist facing preclinical cases of biotherapeutic-related DIVI are outlined, and examples of regulatory feedback for each of the mechanistic types of DIVI are included to provide insight into risk assessment.

Versatility of the complement system in neuroinflammation, neurodegeneration and brain homeostasis

The immune response after brain injury is highly complex and involves both local and systemic events at the cellular and molecular level. It is associated to a dramatic over-activation of enzyme systems, the expression of proinflammatory genes and the activation/recruitment of immune cells. The complement system represents a powerful component of the innate immunity and is highly involved in the inflammatory response. Complement components are synthesized predominantly by the liver and circulate in the bloodstream primed for activation. Moreover, brain cells can produce complement proteins and receptors. After acute brain injury, the rapid and uncontrolled activation of the complement leads to massive release of inflammatory anaphylatoxins, recruitment of cells to the injury site, phagocytosis and induction of blood brain barrier (BBB) damage. Brain endothelial cells are particularly susceptible to complement-mediated effects, since they are exposed to both circulating and locally synthesized complement proteins. Conversely, during neurodegenerative disorders, complement factors play distinct roles depending on the stage and degree of neuropathology. In addition to the deleterious role of the complement, increasing evidence suggest that it may also play a role in normal nervous system development (wiring the brain) and adulthood (either maintaining brain homeostasis or supporting regeneration after brain injury). This article represents a compendium of the current knowledge on the complement role in the brain, prompting a novel view that complement activation can result in either protective or detrimental effects in brain conditions that depend exquisitely on the nature, the timing and the degree of the stimuli that induce its activation. A deeper understanding of the acute, subacute and chronic consequences of complement activation is needed and may lead to new therapeutic strategies, including the ability of targeting selective step in the complement cascade.

Endothelial-to-mesenchymal transition and renal fibrosis in ischaemia/reperfusion injury are mediated by complement anaphylatoxins and Akt pathway

BACKGROUND

Increasing evidence demonstrates a phenotypic plasticity of endothelial cells (ECs). Endothelial-to-mesenchymal transition (EndMT) contributes to the development of tissue fibrosis. However, the pathogenic factors and signalling pathways regulating this process in ischaemia/reperfusion (I/R) injury are still poorly understood.

METHODS

We investigated the possible role of complement in the induction of this endothelial dysfunction in a swine model of renal I/R injury by using recombinant C1 inhibitor in vivo.

RESULTS

Here, we showed that I/R injury reduced the density of renal peritubular capillaries and induced tissue fibrosis with generation of CD31(+)/α-SMA(+) and CD31(+)/FPS-1(+) cells indicating EndMT. When we inhibited complement, the process of EndMT became rare, with preserved density of peritubular capillaries and significant reduction in renal fibrosis. When we activated ECs by anaphylatoxins in vitro, C3a and C5a led to altered endothelial phenotype with increased expression of fibroblast markers and decrease expression of specific endothelial markers. The activation of Akt pathway was pivotal for the C3a and C5a-induced EndMT in vitro. In accordance, inhibition of complement in vivo led to the abrogation of Akt signalling, with hampered EndMT and tissue fibrosis.

CONCLUSIONS

Our data demonstrate a critical role for complement in the acute induction of EndMT via the Akt pathway. Therapeutic inhibition of these systems may be essential to prevent vascular damage and tissue fibrosis in transplanted kidney.

Alternative complement pathway assessment in patients with atypical HUS

The atypical Hemolytic Uremic Syndrome (aHUS) is a rare thrombotic microangiopathy leading to end stage renal disease in approximately 60% of patients. Over the last decade, a clear link has been demonstrated between this disease and defective complement regulation. The hallmark of the aHUS is the association with mutations in complement alternative pathway genes. Endothelial damage is related to complement dysregulation, but the exact mechanism is just starting to be elucidated. Screening for and characterization of mutations in the components of the C3 convertase (C3 and FB) or its regulators (FH, FI, MCP, and Thrombomodulin) or anti-FH antibodies has become an indispensable part of the disease's diagnostic. This review will initially summarize current knowledge on the understanding of complement activation and regulation, followed by a description on the genetic analysis as well as the methods used for complement protein quantification. Another part of this review will focus on the mechanisms of action of aHUS-associated mutations. We will emphasize on when and why some mutations lead to protein deficiency, while others result in - to dysfunctional but normally expressed proteins. Finally, we will discuss how the therapy of aHUS patients can be modified according to the functional consequences of each particular genetic defect.

The role of endothelial cell injury in thrombotic microangiopathy

Thrombotic microangiopathy (TMA) refers to a clinical and pathologic syndrome in which endothelial injury results in the manifestations of thrombocytopenia, microangiopathic hemolytic anemia, and kidney injury. A host of causes may induce endothelial injury and TMA, including enteric bacterial toxins, deficiency or dysfunction of complement regulatory proteins, deficiency or inhibition of von Willebrand factor-cleaving proteases, and factors that inhibit endothelial cell proliferation and turnover. This has led specialists to concentrate on these specific inciting factors in terms of designing treatment and management. However, a key and less recognized factor is the underlying level of endothelial health. Many persons with hereditary causes may remain disease free for years or may never develop disease. Others with acute inciting events, such as Escherichia coli O157 enteritis, never manifest TMA. Experimental studies document the importance of specific factors, such as endothelial nitric oxide levels, in helping protect animals from TMA. This suggests that one might approach the management of TMA not simply with specific treatments aimed at the underlying hereditary cause or inciting event, but rather at general measures that may improve overall endothelial health. We propose studies to determine whether interventions that improve endothelial health, such as the administration of angiotensin-converting enzyme inhibitors, statins, vitamin C, allopurinol, or nitric oxide-producing drugs, may be able to prevent TMA, even in persons with underlying hereditary conditions that otherwise would predispose them to these diseases.

Novel pathogenic mechanism and therapeutic approaches to angioedema associated with C1 inhibitor deficiency

BACKGROUND

Activation of bradykinin-mediated B2 receptor has been shown to play an important role in the onset of angioedema associated with C1 inhibitor deficiency. This finding has led to the development of novel therapeutic drugs such as the B2 receptor antagonist icatibant. However, it is unclear whether other receptors expressed on endothelial cells contribute to the release of kinins and vascular leakage in these patients. The recognition of their role may have obvious therapeutic implications.

OBJECTIVE

Our aim was to investigate the involvement of B1 and gC1q receptors in in vitro and in vivo models of vascular leakage induced by plasma samples obtained from patients with C1 inhibitor deficiency.

METHODS

The vascular leakage was evaluated in vitro on endothelial cells by a transwell model system and in vivo on rat mesentery microvessels by intravital microscopy.

RESULTS

We observed that the attack phase plasma from C1 inhibitor-deficient patients caused a delayed fluorescein-labeled albumin leakage as opposed to the rapid effect of bradykinin, whereas remission plasma elicited a modest effect compared with control plasma. The plasma permeabilizing effect was prevented by blocking the gC1q receptor-high-molecular-weight kininogen interaction, was partially inhibited by B2 receptor or B1 receptor antagonists, and was totally prevented by the mixture of the 2 antagonists. Involvement of B1 receptor was supported by the finding that albumin leakage caused by attack phase plasma was enhanced by IL-1beta and was markedly reduced by brefeldin A.

CONCLUSION

Our data suggest that both B1 receptor and gC1q receptor are involved in the vascular leakage induced by hereditary and acquired angioedema plasma.

The complement system in systemic autoimmune disease

Complement is part of the innate immune system. Its major function is recognition and elimination of pathogens via direct killing and/or stimulation of phagocytosis. Activation of the complement system is, however, also involved in the pathogenesis of the systemic autoimmune diseases. Activation via the classical pathway has long been recognized in immune complex-mediated diseases such as cryoglobulinemic vasculitis and systemic lupus erythematosus (SLE). In SLE, the role of complement is somewhat paradoxical. It is involved in autoantibody-initiated tissue damage on the one hand, but, on the other hand, it appears to have protective features as hereditary deficiencies of classical pathway components are associated with an increased risk for SLE. There is increasing evidence that the alternative pathway of complement, even more than the classical pathway, is involved in many systemic autoimmune diseases. This is true for IgA-dominant Henoch Schönlein Purpura, in which additional activation of the lectin pathway contributes to more severe disease. In anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis the complement system was considered not to be involved since immunoglobulin deposition is generally absent in the lesions. However, recent studies, both in human and animal models, demonstrated complement activation via the alternative pathway as a major pathogenic mechanism. Insight into the role of the various pathways of complement in the systemic autoimmune diseases including the vasculitides opens up new ways of treatment by blocking effector pathways of complement. This has been demonstrated for monoclonal antibodies to C5 or C5a in experimental anti-phospholipid antibody syndrome and ANCA-associated vasculitis.

The contact/kinin and complement systems in vasculitis

Vasculitides are a group of conditions with marked inflammation in and around vessel walls and vascular leakage. These conditions may involve the presence of auto-antibodies such as ANCA or may be mediated by other autoimmune or pathogenic mechanisms. Regardless of the primary trigger, vasculitides entail activation of the complement system as well as the contact/kinin system. In vivo and in vitro data support the involvement of these systems showing activation of the alternative, classical and lectin complement pathways as well as release of bradykinin at sites of vascular inflammation. This short review will summarize some of the data regarding the participation of these systems and the interplay between the complement and kinin systems as well as their interaction with the endothelium and neutrophils. Although these systems do not play a primary role in induction of vasculitis, the peptides released contribute to inflammation and vascular leakage and may thus be identified as potential therapeutic targets.

Kallikreins and lupus nephritis

The kidney kallikrein-kinin system plays important roles in inflammation, coagulation, angiogenesis, and regulation of vessel tone and permeability. In this issue of the JCI, Liu et al. provide data that suggest a protective role for kallikrein in animal models of anti-glomerular basement membrane(GBM) antibody-induced nephritis, an experimental model of Goodpasture disease (see the related article beginning on page 911). Furthermore, human systemic lupus erythematosus and lupus nephritis were shown to be associated with kallikrein 1 (KLK1) and the KLK3 promoter. The authors suggest that kallikrein genes are involved in the development of SLE and lupus nephritis and may exert a renoprotective role. It is possible, however, that the kallikrein-kinin system may play dual roles: protecting the kidney against ischemia and interstitial fibrosis while also mediating vasodilation, inflammation, and activation of the innate immune response.