Inter-α-trypsin inhibitor heavy chain 4 (ITIH4) as a compensatory protease inhibitor in hereditary angioedema.

BACKGROUND: Hereditary angioedema (HAE) is a genetic disorder that manifests as recurrent angioedema attacks, most frequently due to absent or reduced C1 inhibitor (C1INH) activity. C1INH is a crucial regulator of enzymatic cascades in the complement, fibrinolytic, and contact systems. Inter-α-trypsin inhibitor heavy chain 4 (ITIH4) is an abundant plasma protease inhibitor that can inhibit enzymes in the proteolytic pathways associated with HAE. Nothing is known about its role in HAE. OBJECTIVE: We investigated ITIH4 activation in HAE, establishing it as a potential biomarker, and explored its involvement in HAE-associated proteolytic pathways. METHODS: Specific immunoassays for noncleaved ITIH4 (intact ITIH4) and an assay detecting both intact and cleaved ITIH4 (total ITIH4) were developed. We initially tested serum samples from HAE patients (n = 20), angiotensin-converting enzyme inhibitor-induced edema patients (ACEI) (n = 20), and patients with HAE of unknown cause (HAE-UNK) (n = 20). Validation involved an extended cohort of 80 HAE patients (60 with HAE-C1INH type 1, 20 with HAE-C1INH type 2), including samples taken during attack and quiescent disease periods, as well as samples from 100 healthy controls. RESULTS: In 63% of HAE patients, intact ITIH4 assay showed lower signals than total ITIH4 assay. This difference was not observed in ACEI and HAE-UNK patients. Western blot analysis confirmed cleaved ITIH4 with low intact ITIH4 samples. In serum samples lacking intact endogenous ITIH4, we observed immediate cleavage of added recombinant ITIH4, suggesting continuous enzymatic activity in the serum. Confirmatory HAE cohort analysis revealed significantly lower intact ITIH4 levels in both type 1 and type 2 HAE patients compared to controls, with consistently low intact/total ITIH4 ratios during clinical HAE attacks. CONCLUSION: The disease-specific low intact ITIH4 levels highlight its unique nature in HAE. ITIH4 may exhibit compensatory mechanisms in HAE, suggesting its utility as a diagnostic and prognostic biomarker. The variations during quiescent and active disease periods raise intriguing questions about the dynamics of proteolytic pathways in HAE.

Complement MASP-1 Modifies Endothelial Wound Healing.

Endothelial wound-healing processes are fundamental for the maintenance and restoration of the circulatory system and are greatly affected by the factors present in the blood. We have previously shown that the complement protein mannan-binding lectin-associated serine protease-1 (MASP-1) induces the proinflammatory activation of endothelial cells and is able to cooperate with other proinflammatory activators. Our aim was to investigate the combined effect of mechanical wounding and MASP-1 on endothelial cells. Transcriptomic analysis showed that MASP-1 alters the expression of wound-healing-related and angiogenesis-related genes. Both wounding and MASP-1 induced Ca2+ mobilization when applied individually. However, MASP-1-induced Ca2+ mobilization was inhibited when the treatment was preceded by wounding. Mechanical wounding promoted CREB phosphorylation, and the presence of MASP-1 enhanced this effect. Wounding induced ICAM-1 and VCAM-1 expression on endothelial cells, and MASP-1 pretreatment further increased VCAM-1 levels. MASP-1 played a role in the subsequent stages of angiogenesis, facilitating the breakdown of the endothelial capillary network on Matrigel®. Our findings extend our general understanding of endothelial wound healing and highlight the importance of complement MASP-1 activation in wound-healing processes.

The Lectin Pathway of the Complement System-Activation, Regulation, Disease Connections and Interplay with Other (Proteolytic) Systems.

The complement system is the other major proteolytic cascade in the blood of vertebrates besides the coagulation-fibrinolytic system. Among the three main activation routes of complement, the lectin pathway (LP) has been discovered the latest, and it is still the subject of intense research. Mannose-binding lectin (MBL), other collectins, and ficolins are collectively termed as the pattern recognition molecules (PRMs) of the LP, and they are responsible for targeting LP activation to molecular patterns, e.g., on bacteria. MBL-associated serine proteases (MASPs) are the effectors, while MBL-associated proteins (MAps) have regulatory functions. Two serine protease components, MASP-1 and MASP-2, trigger the LP activation, while the third component, MASP-3, is involved in the function of the alternative pathway (AP) of complement. Besides their functions within the complement system, certain LP components have secondary ("moonlighting") functions, e.g., in embryonic development. They also contribute to blood coagulation, and some might have tumor suppressing roles. Uncontrolled complement activation can contribute to the progression of many diseases (e.g., stroke, kidney diseases, thrombotic complications, and COVID-19). In most cases, the lectin pathway has also been implicated. In this review, we summarize the history of the lectin pathway, introduce their components, describe its activation and regulation, its roles within the complement cascade, its connections to blood coagulation, and its direct cellular effects. Special emphasis is placed on disease connections and the non-canonical functions of LP components.

Storage of Transfusion Platelet Concentrates Is Associated with Complement Activation and Reduced Ability of Platelets to Respond to Protease-Activated Receptor-1 and Thromboxane A2 Receptor.

Platelet activation and the complement system are mutually dependent. Here, we investigated the effects of storage time on complement activation and platelet function in routinely produced platelet concentrates. The platelet concentrates (n = 10) were stored at 22 °C for seven days and assessed daily for complement and platelet activation markers. Additionally, platelet function was analyzed in terms of their responsiveness to protease-activated receptor-1 (PAR-1) and thromboxane A2 receptor (TXA2R) activation and their capacity to adhere to collagen. Complement activation increased over the storage period for all analyzed markers, including the C1rs/C1-INH complex (fold change (FC) = 1.9; p < 0.001), MASP-1/C1-INH complex (FC = 2.0; p < 0.001), C4c (FC = 1.8, p < 0.001), C3bc (FC = 4.0; p < 0.01), and soluble C5b-9 (FC = 1.7, p < 0.001). Furthermore, the levels of soluble platelet activation markers increased in the concentrates over the seven-day period, including neutrophil-activating peptide-2 (FC = 2.5; p < 0.0001), transforming growth factor beta 1 (FC = 1.9; p < 0.001) and platelet factor 4 (FC = 2.1; p < 0.0001). The ability of platelets to respond to activation, as measured by surface expression of CD62P and CD63, decreased by 19% and 24% (p < 0.05) for PAR-1 and 69-72% (p < 0.05) for TXA2R activation, respectively, on Day 7 compared to Day 1. The extent of platelet binding to collagen was not significantly impaired during storage. In conclusion, we demonstrated that complement activation increased during the storage of platelets, and this correlated with increased platelet activation and a reduced ability of the platelets to respond to, primarily, TXA2R activation.

Differentiating between activation via the lectin or the classical complement pathway in patients with systemic lupus erythematosus.

Complement activation is a hallmark of systemic lupus erythematosus (SLE) and can proceed through the classical (CP), lectin (LP), or alternative pathway (AP). When managing SLE patients, pathway-specific complement activation is rarely monitored as clinical assays are unavailable. In this study, we aim to differentiate between CP- or LP-mediated complement activation in SLE patients by quantifying pathway-specific protein complexes, namely C1s/C1-inhibitor (C1-INH) (CP-specific activation) and MASP-1/C1-INH (LP-specific activation). Levels for both complexes were assessed in 156 SLE patients and 50 controls using two newly developed ELISAs. We investigated whether pathway-specific complement activation was associated with disease activity and lupus nephritis (LN). Disease activity stratification was performed using SLEDAI scores assessed at inclusion. C1s/C1-INH concentrations were significantly increased in active SLE patients (SLEDAI ≥6) when compared with SLE patients with low disease activity (SLEDAI <6, P < 0.01) and correlated with SLEDAI score (r = .29, P < 0.01). In active LN, MASP-1/C1-INH plasma concentrations were significantly increased compared with nonactive LN (P = 0.02). No differences in MASP-1/C1-INH plasma concentrations were observed between active SLE patients and patients with low disease activity (P = 0.11) nor did we observe a significant correlation with disease activity (r = 0.12, P = 0.15). Our data suggest that the CP and the LP are activated in SLE. The CP is activated in active SLE disease, whereas activation of the LP might be more specific to disease manifestations like LN. Our results warrant further research into specific complement pathway activation in SLE patients to potentially improve specific-targeted and tailored-treatment approaches.

BRAF increases endothelial cell stiffness through reorganization of the actin cytoskeleton.

The dynamics of the actin cytoskeleton and its connection to endothelial cell-cell junctions determine the barrier function of endothelial cells. The proper regulation of barrier opening/closing is necessary for the normal function of vessels, and its dysregulation can result in chronic and acute inflammation leading to edema formation. By using atomic force microscopy, we show here that thrombin-induced permeability of human umbilical vein endothelial cells, associated with actin stress fiber formation, stiffens the cell center. The depletion of the MEK/ERK kinase BRAF reduces thrombin-induced permeability prevents stress fiber formation and cell stiffening. The peripheral actin ring becomes stabilized by phosphorylated myosin light chain, while cofilin is excluded from the cell periphery. All these changes can be reverted by the inhibition of ROCK, but not of the MEK/ERK module. We propose that the balance between the binding of cofilin and myosin to F-actin in the cell periphery, which is regulated by the activity of ROCK, determines the local dynamics of actin reorganization, ultimately driving or preventing stress fiber formation.

Cooperation of Complement MASP-1 with Other Proinflammatory Factors to Enhance the Activation of Endothelial Cells.

Endothelial cells play an important role in sensing danger signals and regulating inflammation. Several factors are capable of inducing a proinflammatory response (e.g., LPS, histamine, IFNγ, and bradykinin), and these factors act simultaneously during the natural course of the inflammatory reaction. We have previously shown that the complement protein mannan-binding lectin-associated serine protease-1 (MASP-1) also induces a proinflammatory activation of the endothelial cells. Our aim was to investigate the possible cooperation between MASP-1 and other proinflammatory mediators when they are present in low doses. We used HUVECs and measured Ca2+ mobilization, IL-8, E-selectin, VCAM-1 expression, endothelial permeability, and mRNA levels of specific receptors. LPS pretreatment increased the expression of PAR2, a MASP-1 receptor, and furthermore, MASP-1 and LPS enhanced each other's effects in regulating IL-8, E-selectin, Ca2+ mobilization, and changes in permeability in a variety of ways. Cotreatment of MASP-1 and IFNγ increased the IL-8 expression of HUVECs. MASP-1 induced bradykinin and histamine receptor expression, and consequently, increased Ca2+ mobilization was found. Pretreatment with IFNγ enhanced MASP-1-induced Ca2+ mobilization. Our findings highlight that well-known proinflammatory mediators and MASP-1, even at low effective doses, can strongly synergize to enhance the inflammatory response of endothelial cells.

The emerging roles of mannose-binding lectin-associated serine proteases (MASPs) in the lectin pathway of complement and beyond.

Mannose-binding lectin (MBL)-associated serine proteases (MASPs) are the enzymatic constituents of the lectin pathway of the complement system. They are complexed with large pattern recognition molecules (PRMs) such as MBL, other collectins, and ficolins. The main function of two of the three MASPs has crystallized lately: MASP-1 autoactivates first, then it activates MASP-2, and finally both participate in the formation of the C4b2a convertase. In addition to this, both enzymes are involved in several other processes which are subject to intense research nowadays. Notably, MASP-1, as a promiscuous enzyme, has been implicated in the coagulation cascade, in the kinin generating contact system, and in cellular activation through protease-activated receptor (PAR) cleavage on endothelial cells. The third protease MASP-3 has emerged recently as the protease responsible for pro-factor D activation in resting blood, providing a fundamental link between two complement pathways. At present all three MASPs have at least one well-defined role and several other possible functions were implicated. Defect or more likely over-activation of MASPs may culminate into diseases such as ischemia-reperfusion injury (IRI); hence, MASPs are all potential targets of drug development.

Flow-mediated vasodilation assay indicates no endothelial dysfunction in hereditary angioedema patients with C1-inhibitor deficiency.

BACKGROUND: Hereditary angioedema with C1 inhibitor deficiency (C1-INH-HAE) is a rare, potentially life-threatening disorder characterized by recurrent edematous attacks. The edema formation is the consequence of interaction of bradykinin and various vasoactive peptides with endothelium. Besides these agents, danazol, a modified testosterone derivative used in these patients to prevent edematous attacks, can also affect the function of the endothelium, because it shifts the blood lipid profile to a pro-atherogenic phenotype. OBJECTIVE: To assess the endothelial function in C1-INH-HAE patients and in healthy matched controls. METHODS: To evaluate the endothelial function, we used the flow-mediated dilation method measured in the region of the brachial artery in 33 C1-INH-HAE patients and in 30 healthy matched controls. Laboratory measurements of standard biochemical parameters were performed on computerized laboratory analyzers. RESULTS: No difference was found in endothelial function (reactive hyperemia, RH) between patients (median, 9.0; 25%-75% percentile, 6.3-12.9) and controls (median, 7.37; 25%-75% percentile, 4.52-9.93). Although we found elevated cardiovascular risk (high body mass index and low-density lipoprotein/high-density lipoprotein ratio) in danazol-treated C1-INH-HAE patients, RH values did not differ between danazol-treated and nontreated patients. Furthermore, risk factors correlated with the endothelial function only in healthy controls and patients not treated with danazol. CONCLUSION: In summary, our results did not indicate any signs of endothelial dysfunction in C1-INH-HAE patients. Moreover, the normal endothelial function in danazol-treated patients with pro-atherogenic lipid profile suggests that elevated bradykinin level or other factor(s) involved in the pathogenesis of edematous attacks may have a protective role against endothelial dysfunction and atherosclerosis.

Novel Vasoregulatory Aspects of Hereditary Angioedema: the Role of Arginine Vasopressin, Adrenomedullin and Endothelin-1.

The elevation of bradykinin (BK) level during attacks of hereditary angioedema due to C1-Inhibitor deficiency (C1-INH-HAE) is well known. We previously demonstrated that endothelin-1 (ET-1) level also increases during C1-INH-HAE attacks. Although BK and ET-1 are both potent vasoactive peptides, the vasoregulatory aspect of the pathomechanism of C1-INH-HAE has not yet been investigated. Hence we studied the levels of vasoactive peptides in controls and in C1-INH-HAE patients, as well as evaluated their changes during C1-INH-HAE attacks. The levels of arginine vasopressin (AVP), adrenomedullin (ADM) and ET-1 were measured in the plasma of 100 C1-INH-HAE patients in inter-attack periods and of 111 control subjects, using BRAHMS Kryptor technologies. In 18 of the 100 C1-INH-HAE patients, the levels of vasoactive peptides were compared in blood samples obtained during attacks, or in inter-attack periods. AVP, ADM and ET-1 levels were similar in inter-attack samples from C1-INH-HAE patients and in the samples of controls, although cardiovascular risk has an effect on the levels of vasoactive peptides in both groups. The levels of all three vasoactive peptides increased during C1-INH-HAE attacks. Moreover, the levels of ET-1 and ADM as well as their changes during attacks were significantly correlated. This study demonstrated that vascular regulation by vasoactive peptides is affected during C1-INH-HAE attacks. Our results suggest that the cooperation of several vasoactive peptides may be necessary to counterbalance the actions of excess BK, and to terminate the attacks. This may reveal a novel pathophysiological aspect of C1-INH-HAE.

Tesmilifene modifies brain endothelial functions and opens the blood-brain/blood-glioma barrier.

Tesmilifene, a tamoxifen analog with antihistamine action, has chemopotentiating properties in experimental and clinical cancer studies. In our previous works, tesmilifene increased the permeability of the blood-brain barrier (BBB) in animal and culture models. Our aim was to investigate the effects of tesmilifene on brain microvessel permeability in the rat RG2 glioma model and to reveal its mode of action in brain endothelial cells. Tesmilifene significantly increased fluorescein extravasation in the glioma. Short-term treatment with tesmilifene reduced the resistance and increased the permeability for marker molecules in a rat triple co-culture BBB model. Tesmilifene also affected the barrier integrity in brain endothelial cells co-cultured with RG2 glioblastoma cells. Tesmilifene inhibited the activity of P-glycoprotein and multidrug resistance-associated protein-1 efflux pumps and down-regulated the mRNA expression of tight junction proteins, efflux pumps, solute carriers, and metabolic enzymes important for BBB functions. Among the possible signaling pathways that regulate BBB permeability, tesmilifene activated the early nuclear translocation of NFκB. The MAPK/ERK and PI3K/Akt kinase pathways were also involved. We demonstrate for the first time that tesmilifene increases permeability marker molecule extravasation in glioma and inhibits efflux pump activity in brain endothelial cells, which may have therapeutic relevance. Tesmilifene, a chemopotentiator in experimental and clinical cancer studies increases vascular permeability in RG2 glioma in rats and permeability for marker molecules in a culture model of the blood-brain barrier. Tesmilifene inhibits the activity of efflux pumps and down-regulates the mRNA expression of tight junction proteins, transporters, and metabolic enzymes important for the blood-brain barrier functions, which may have therapeutic relevance.

Endothelial cell activation during edematous attacks of hereditary angioedema types I and II.

BACKGROUND: Hereditary angioedema (HAE) caused by C1-inhibitor (C1-INH) deficiency (HAE-C1-INH) is a potentially life-threatening rare disease caused by the decreased activity of C1-INH. Lack of C1-INH leads to overproduction of bradykinin, a potent vasoactive peptide. Although angioedema is induced by bradykinin, the function and activation of endothelial cells (ECs), the targets of bradykinin, have not yet been studied during HAE attacks. OBJECTIVE: We studied whether EC function is altered during HAE attacks in comparison with attack-free intervals. METHODS: Forty-six consecutive samples obtained during attacks from 18 patients with HAE-C1-INH were compared with inter-attack samples of the same patients. The patients' sera were tested for von Willebrand factor (VWF) antigen, VWF collagen-binding activity, soluble E-selectin, and endothelin-1 levels by using ELISA and BRAHMS Kryptor technologies. RESULTS: Levels of all 4 EC markers (VWF antigen, VWF collagen-binding activity, soluble E-selectin, and endothelin-1) were significantly increased during HAE attacks. Their increases were even more obvious in the subgroup of patients without any pre-existing risk factors for endothelial dysfunction. CONCLUSION: In this study we demonstrated that ECs are activated during HAE attacks. Our results might suggest the need for revising the knowledge on the pathogenesis of HAE-C1-INH and for reconsidering the role of ECs as a possible novel therapeutic target in patients with this disease.

Detrimental interactions of hypoxia and complement MASP-1 in endothelial cells as a model for atherosclerosis-related diseases.

Both hypoxia and the complement lectin pathway (CLP) are involved in atherosclerosis and atherosclerosis-related stroke and acute myocardial infarction (AMI). We have previously shown that mannose-binding lectin-associated serine protease-1 (MASP-1), the most abundant enzyme of CLP, induces an inflammatory phenotype of endothelial cells (ECs) by cleaving protease activated receptors (PARs). In the absence of data, we aimed to investigate whether hypoxia and MASP-1 interact at the level of ECs, to better understand their role in atherosclerosis-related diseases. Hypoxia attenuated the wound healing ability of ECs, increased ICAM-1 and decreased ICAM-2 expression and upregulated PAR2 gene expression. Hypoxia and MASP-1 increased GROα and IL-8 production, and endothelial permeability without potentiating each other's effects, whereas they cooperatively disrupted vascular network integrity, activated the Ca2+, CREB and NFκB signaling pathways, and upregulated the expression of E-selectin, a crucial adhesion molecule in neutrophil homing. VCAM-1 expression was not influenced either by hypoxia, or by MASP-1. In summary, hypoxia potentiates the effect of MASP-1 on ECs, at least partially by increasing PAR expression, resulting in interaction at several levels, which may altogether exacerbate stroke and AMI progression. Our findings suggest that MASP-1 is a potential drug target in the acute phase of atherosclerosis-related diseases.

Decreased adhesion to endothelium leads to elevated neutrophil granulocyte count in hereditary angioedema patients.

As many aspects of hereditary angioedema (HAE) due to C1-inhibitor (C1-INH) deficiency (C1-INH-HAE) cannot be explained with elevated bradykinin level alone, it has recently become clear that other factors also play an important role in the pathogenesis. One of these factors could be elevated neutrophil granulocyte (NG) counts, which are associated with increased NG activation in C1-INH-HAE patients; however, their origin has not been elucidated so far. Here, we aimed to investigate whether the excess of NGs is due to disturbed maturation, biased circulating/marginated pool equilibrium or decreased elimination. We enrolled 20 attack-free C1-INH-HAE patients together with 21 healthy controls and collected blood samples. We compared cell surface maturation markers, adhesion molecules, cytokine receptors, and Ca2+-mobilization of NG by flow cytometry, activation markers by ELISA, and NG/endothelial cell adhesion by automated pipetting system. Cell-surface markers showed normal maturation of NGs in C1-INH-HAE patients. Adhesion of NGs to endothelial cells pretreated with lipopolysaccharide or phorbol 12-myristate 13-acetate was significantly weaker in samples from C1-INH-HAE patients and bradykinin had no effect on the adhesion. NGs from C1-INH-HAE patients were in an activated state when assessed by soluble activation markers without any stimulation. Our data support that the maturation of NGs in C1-INH-HAE patients is normal, whereas adhesion properties of patient-derived NGs to the endothelium are reduced compared to those from healthy controls, indicating a bias between the circulating and marginated pools of NGs in patients. Bradykinin may not be responsible for reduced adhesion properties of NGs.

C1-inhibitor/C1-inhibitor antibody complexes in acquired angioedema due to C1-inhibitor deficiency.

BACKGROUND: Autoantibodies against C1-inhibitor (C1-INH-Ab) have a diagnostic value in acquired angioedema due to C1-inhibitor deficiency (C1-INH-AAE), even though antibodies can circulate in complexes, which can be undetectable by proven methods. Our aim was to measure C1-INH/C1-INH-Ab complexes (CAC) and investigate their connection to C1-INH-Ab and the changes in their titer over time. RESULTS: 19 patients were diagnosed with C1-INH-AAE in the Hungarian Angioedema Center of Reference and Excellence; 79% of them had an underlying disease. Samples were examined with a newly developed in-house complex ELISA method. Patients with high C1-INH-Ab titer had a CAC titer which did not exceed the normal level and the ones with high CAC titer had a C1-INH-Ab titer which did not exceed the normal level. In case of those patients who had C1-INH-Ab and CAC of the same type of immunoglobulin, the increasing titer of C1-INH-Ab went together with the decreasing level of CAC and vice versa. CAC titer was already increased before the diagnosis of the underlying disease. CONCLUSIONS: Free circulating and complex antibodies are in a dynamically changing equilibrium. CAC measurements can help to predict the development of an underlying disease. The efficiency of the treatment for underlying disease can be monitored by the decreasing CAC titers. Our results show that the CAC can be of important additional information besides the complement panel examination in case of C1-INH-AAE. Measurement of CAC is recommended to be done parallelly with C1-INH-Ab, so as to detect both free and bound antibodies.

Class switch towards spike protein-specific IgG4 antibodies after SARS-CoV-2 mRNA vaccination depends on prior infection history.

Vaccinations against SARS-CoV-2 reduce the risk of developing serious COVID-19 disease. Monitoring spike-specific IgG subclass levels after vaccinations may provide additional information on SARS-CoV-2 specific humoral immune response. Here, we examined the presence and levels of spike-specific IgG antibody subclasses in health-care coworkers vaccinated with vector- (Sputnik, AstraZeneca) or mRNA-based (Pfizer-BioNTech, Moderna) vaccines against SARS-CoV-2 and in unvaccinated COVID-19 patients. We found that vector-based vaccines elicited lower total spike-specific IgG levels than mRNA vaccines. The pattern of spike-specific IgG subclasses in individuals infected before mRNA vaccinations resembled that of vector-vaccinated subjects or unvaccinated COVID-19 patients. However, the pattern of mRNA-vaccinated individuals without SARS-CoV-2 preinfection showed a markedly different pattern. In addition to IgG1 and IgG3 subclasses presented in all groups, a switch towards distal IgG subclasses (spike-specific IgG4 and IgG2) appeared almost exclusively in individuals who received only mRNA vaccines or were infected after mRNA vaccinations. In these subjects, the magnitude of the spike-specific IgG4 response was comparable to that of the spike-specific IgG1 response. These data suggest that the priming of the immune system either by natural SARS-CoV-2 infection or by vector- or mRNA-based vaccinations has an important impact on the characteristics of the developed specific humoral immunity.

Complement lectin pathway activation is associated with COVID-19 disease severity, independent of MBL2 genotype subgroups.

Introduction: While complement is a contributor to disease severity in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, all three complement pathways might be activated by the virus. Lectin pathway activation occurs through different pattern recognition molecules, including mannan binding lectin (MBL), a protein shown to interact with SARS-CoV-2 proteins. However, the exact role of lectin pathway activation and its key pattern recognition molecule MBL in COVID-19 is still not fully understood. Methods: We therefore investigated activation of the lectin pathway in two independent cohorts of SARS-CoV-2 infected patients, while also analysing MBL protein levels and potential effects of the six major single nucleotide polymorphisms (SNPs) found in the MBL2 gene on COVID-19 severity and outcome. Results: We show that the lectin pathway is activated in acute COVID-19, indicated by the correlation between complement activation product levels of the MASP-1/C1-INH complex (p=0.0011) and C4d (p<0.0001) and COVID-19 severity. Despite this, genetic variations in MBL2 are not associated with susceptibility to SARS-CoV-2 infection or disease outcomes such as mortality and the development of Long COVID. Conclusion: In conclusion, activation of the MBL-LP only plays a minor role in COVID-19 pathogenesis, since no clinically meaningful, consistent associations with disease outcomes were noted.

Endothelial cell function in patients with hereditary angioedema: elevated soluble E-selectin level during inter-attack periods.

BACKGROUND: The bradykinin pathway in the pathomechanism of hereditary angioedema due to C1-inhibitor deficiency (henceforward "hereditary angioedema") has been thoroughly studied; however, much less is known about endothelial cell function. Enhanced endothelial cell permeability is obvious during edematous attacks, but not during inter-attack periods. Our knowledge about other endothelial characteristics is even more incomplete. OBJECTIVE: Therefore the aim of this study was to characterize endothelial cell function in hereditary angioedema patients during symptom-free, inter-attack periods. METHODS: We measured the serum levels of soluble E-selectin, endothelin-1, and von Willebrand factor along with collagen-binding activity in 49 hereditary angioedema patients and in 50 healthy controls. RESULTS: Endothelin-1 and von Willebrand factor level, as well as its collagen-binding activity, were similar in hereditary angioedema patients and in controls; however, we found elevated soluble E-selectin levels in the patients. Interestingly, soluble E-selectin concentration did not correlate with any of the inflammatory markers or smoking, and it is not the consequence of the known E-selectin/C1-inhibitor interaction (an analytical phenomenon). In a multiple logistic regression model, the difference in soluble E-selectin between hereditary angioedema patients and controls remained highly significant when adjusted for age, gender, smoking, C-reactive protein, and AB0 blood groups. CONCLUSION: These results demonstrate that in hereditary angioedema, the majority of endothelial functions are normal during inter-attack periods; however, soluble E-selectin levels are elevated. The higher soluble E-selectin plasma concentration is unlikely to result from inflammation; rather, it reflects enhanced shedding mechanisms.

A novel pathogenetic factor of laryngeal attack in hereditary angioedema? Involvement of protease activated receptor 1.

BACKGROUND: Hereditary angioedema (HAE) is a rare, life-threatening disease. The knowledge about the molecular pathogenesis of HAE has derived mainly from investigating blood samples. However, limited data are available on the role of the molecular mechanisms in the affected tissues during HAE attack. OBJECTIVE: The aim of our study was to explore the histological changes occurring in HAE attacks. METHODS: Post mortem macro-, microscopic and immunohistological assessment of upper airway tissues of a patient with HAE due to C1 inhibitor deficiency (C1-INH-HAE) type 2 who died from laryngeal HAE attack was compared with a non-HAE patient who died from other condition without any signs of angioedema. RESULTS: Compared to the control patient, we demonstrated stronger T cell/monocyte infiltration and a more intense C1-INH staining in the C1-INH-HAE patient. The expression of both bradykinin receptors (B1/B2) was observed with a slightly lower level in the C1-INH-HAE patient than in the control patient. PAR1 expression was strongly reduced in the C1-INH-HAE patient suggesting overactivation of this hyperpermeability inducing receptor. CONCLUSION: Our unique case and novel results correspond to the knowledge about C1-INH and BDKRs observed in plasma; however, it revealed new information about the pathomechanism of HAE attack focusing on the potential involvement of PAR1 in edema formation. This observation, if it is verified by subcutaneous biopsy studies, may designate a new therapeutic target in HAE.

Evidence, detailed characterization and clinical context of complement activation in acute multisystem inflammatory syndrome in children.

Multisystem inflammatory syndrome in children (MIS-C) is a rare, life-threatening complication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. MIS-C develops with high fever, marked inflammation and shock-like picture several weeks after exposure to, or mild infection with SARS-CoV-2. Deep immune profiling identified activated macrophages, neutrophils, B-plasmablasts and CD8 + T cells as key determinants of pathogenesis together with multiple inflammatory markers. The disease rapidly responds to intravenous immunoglobulin (IVIG) treatment with clear changes of immune features. Here we present the results of a comprehensive analysis of the complement system in the context of MIS-C activity and describe characteristic changes during IVIG treatment. We show that activation markers of the classical, alternative and terminal pathways are highly elevated, that the activation is largely independent of anti-SARS-CoV-2 humoral immune response, but is strongly associated with markers of macrophage activation. Decrease of complement activation is closely associated with rapid improvement of MIS-C after IVIG treatment.