Therapeutic Targeting of the Complement System: From Rare Diseases to Pandemics

Depletion of complement factor 3 delays the neuroinflammatory response to intracortical microelectrodes

The neuroinflammatory response to intracortical microelectrodes (IMEs) used with brain-machine interfacing (BMI) applications is regarded as the primary contributor to poor chronic performance. Recent developments in high-plex gene expression technologies have allowed for an evolution in the investigation of individual proteins or genes to be able to identify specific pathways of upregulated genes that may contribute to the neuroinflammatory response. Several key pathways that are upregulated following IME implantation are involved with the complement system. The complement system is part of the innate immune system involved in recognizing and eliminating pathogens - a significant contributor to the foreign body response against biomaterials. Specifically, we have identified Complement 3 (C3) as a gene of interest because it is the intersection of several key complement pathways. In this study, we investigated the role of C3 in the IME inflammatory response by comparing the neuroinflammatory gene expression at the microelectrode implant site between C3 knockout (C3-/-) and wild-type (WT) mice. We have found that, like in WT mice, implantation of intracortical microelectrodes in C3-/- mice yields a dramatic increase in the neuroinflammatory gene expression at all post-surgery time points investigated. However, compared to WT mice, C3 depletion showed reduced expression of many neuroinflammatory genes pre-surgery and 4 weeks post-surgery. Conversely, depletion of C3 increased the expression of many neuroinflammatory genes at 8 weeks and 16 weeks post-surgery, compared to WT mice. Our results suggest that C3 depletion may be a promising therapeutic target for acute, but not chronic, relief of the neuroinflammatory response to IME implantation. Additional compensatory targets may also be required for comprehensive long-term reduction of the neuroinflammatory response for improved intracortical microelectrode performance.

G protein-coupled receptors (GPCRs): advances in structures, mechanisms, and drug discovery

G protein-coupled receptors (GPCRs), the largest family of human membrane proteins and an important class of drug targets, play a role in maintaining numerous physiological processes. Agonist or antagonist, orthosteric effects or allosteric effects, and biased signaling or balanced signaling, characterize the complexity of GPCR dynamic features. In this study, we first review the structural advancements, activation mechanisms, and functional diversity of GPCRs. We then focus on GPCR drug discovery by revealing the detailed drug-target interactions and the underlying mechanisms of orthosteric drugs approved by the US Food and Drug Administration in the past five years. Particularly, an up-to-date analysis is performed on available GPCR structures complexed with synthetic small-molecule allosteric modulators to elucidate key receptor-ligand interactions and allosteric mechanisms. Finally, we highlight how the widespread GPCR-druggable allosteric sites can guide structure- or mechanism-based drug design and propose prospects of designing bitopic ligands for the future therapeutic potential of targeting this receptor family.

The potential application of complement inhibitors-loaded nanosystem for autoimmune diseases via regulation immune balance

The complement is an important arm of the innate immune system, once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammation. Recent studies have shown that over-activated complement is the main proinflammatory system of autoimmune diseases (ADs). In addition, activated complements interact with autoantibodies, immune cells exacerbate inflammation, further worsening ADs. With the increasing threat of ADs to human health, complement-based immunotherapy has attracted wide attention. Nevertheless, efficient and targeted delivery of complement inhibitors remains a significant challenge owing to their inherent poor targeting, degradability, and low bioavailability. Nanosystems offer innovative solutions to surmount these obstacles and amplify the potency of complement inhibitors. This prime aim to present the current knowledge of complement in ADs, analyse the function of complement in the pathogenesis and treatment of ADs, we underscore the current situation of nanosystems assisting complement inhibitors in the treatment of ADs. Considering technological, physiological, and clinical validation challenges, we critically appraise the challenges for successfully translating the findings of preclinical studies of these nanosystem assisted-complement inhibitors into the clinic, and future perspectives were also summarised. (The graphical abstract is by BioRender.).

Mechanistic study of C5F10O-induced lung toxicity in rats: An eco-friendly insulating gas alternative to SF6

The global warming and other environmental problems caused by SF6 emissions can be reduced due to the widespread use of eco-friendly insulating gas, perfluoropentanone (C5F10O). However, there is an exposure risk to populations in areas near C5F10O equipment, so it is important to clarify its biosafety and pathogenesis before large-scale application. In this paper, histopathology, transcriptomics, 4D-DIA proteomics, and LC-MS metabolomics of rats exposed to 2000 ppm and 6000 ppm C5F10O are analyzed to reveal the mechanisms of toxicity and health risks. Histopathological shows that inflammatory cell infiltration, epithelial cell hyperplasia, and alveolar atrophy accompanied by alveolar wall thickening are present in both low-dose and high-dose groups. Analysis of transcriptomic and 4D-DIA proteomic show that Cell cycle and DNA replication can be activated by both 2000 ppm and 6000 ppm C5F10O to induce cell proliferation. In addition, it also leads to the activation of pathways such as Antigen processing and presentation, Cell adhesion molecules and Complement and coagulation cascades, T cell receptor signal path, Th1 and T cell receptor signal path, Th1 and Th2 cell differentiation, complement and coagulation cascades. Finally, LC-MS metabolomics analysis confirms that the metabolic pathways associated with glycerophospholipids, arachidonic acid, and linoleic acid are disrupted and become more severe with increasing doses. The mechanism of lung toxicity caused by C5F10O is systematically expounded based on the multi-omics analysis and provided biosafety references for further promotion and application of C5F10O.

Ficolin-A/2 Aggravated Severe Lung Injury through Neutrophil Extracellular Traps Mediated by Gasdermin D-Induced Pyroptosis

Neutrophil extracellular traps (NETs) and pyroptosis are critical events in lung injury. This study investigated whether ficolin-A influences NET formation through pyroptosis to exacerbate lipopolysaccharide (LPS)-induced lung injury. The expression of ficolin-A/2, NETs, and pyroptosis-related molecules was investigated in animal and cell models. Knockout and knockdown (recombinant protein) methods were used to elucidate regulatory mechanisms. The Pearson correlation coefficient was used to analyze the correlation between ficolins and pyroptosis- and NET-related markers in clinical samples. In this study, ficolin-2 (similar to ficolin-A) showed significant overexpression in patients with acute respiratory distress syndrome. In vivo, knockout of ficolin-A, but not ficolin-B, attenuated lung inflammation and inhibited NET formation in the LPS-induced mouse model. DNase I further alleviated lung inflammation and NET formation in ficolin-A knockout mice. In vitro, neutrophils derived from Fcna-/- mice showed less pyroptosis and necroptosis than those from the control group after LPS stimulation. Additionally, gasdermin D knockdown or Nod-like receptor protein 3 inhibitor reduced NET formation. Addition of recombinant ficolin-2 protein to human peripheral blood neutrophils promoted NET formation and pyroptosis after LPS stimulation, whereas ficolin-2 knockdown had the opposite effect. Acute respiratory distress syndrome patients showed increased levels of pyroptosis- and NET-related markers, which were correlated positively with ficolin-2 levels. In conclusion, these results suggested that ficolin-A/2 exacerbated NET formation and LPS-induced lung injury via gasdermin D-mediated pyroptosis.

The Complement System and C4b-Binding Protein: A Focus on the Promise of C4BPα as a Biomarker to Predict Clopidogrel Resistance

The complement system plays a dual role in the body, either as a first-line defense barrier when balanced between activation and inhibition or as a potential driver of complement-associated injury or diseases when unbalanced or over-activated. C4b-binding protein (C4BP) was the first circulating complement regulatory protein identified and it functions as an important complement inhibitor. C4BP can suppress the over-activation of complement components and prevent the complement system from attacking the host cells through the binding of complement cleavage products C4b and C3b, working in concert as a cofactor for factor I in the degradation of C4b and C3b, and consequently preventing or reducing the assembly of C3 convertase and C5 convertase, respectively. C4BP, particularly C4BP α-chain (C4BPα), exerts its unique inhibitory effects on complement activation and opsonization, systemic inflammation, and platelet activation and aggregation. It has long been acknowledged that crosstalk or interplay exists between the complement system and platelets. Our unpublished preliminary data suggest that circulating C4BPα exerts its antiplatelet effects through inhibition of both complement activity levels and complement-induced platelet reactivity. Plasma C4BPα levels appear to be significantly higher in patients sensitive to, rather than resistant to, clopidogrel, and we suggest that a plasma C4BPα measurement could be used to predict clopidogrel resistance in the clinical settings.

The complement system as a key modulator of the oral microbiome in health and disease

In this review, we address the interplay between the complement system and host microbiomes in health and disease, focussing on oral bacteria known to contribute to homeostasis or to promote dysbiosis associated with dental caries and periodontal diseases. Host proteins modulating complement activities in the oral environment and expression profiles of complement proteins in oral tissues were described. In addition, we highlight a sub-set of bacterial proteins involved in complement evasion and/or dysregulation previously characterized in pathogenic species (or strains), but further conserved among prototypical commensal species of the oral microbiome. Potential roles of these proteins in host-microbiome homeostasis and in the emergence of commensal strain lineages with increased virulence were also addressed. Finally, we provide examples of how commensal bacteria might exploit the complement system in competitive or cooperative interactions within the complex microbial communities of oral biofilms. These issues highlight the need for studies investigating the effects of the complement system on bacterial behaviour and competitiveness during their complex interactions within oral and extra-oral host sites.

Emerging role of complement in COVID-19 and other respiratory virus diseases

The complement system, a key component of innate immunity, provides the first line of defense against bacterial infection; however, the COVID-19 pandemic has revealed that it may also engender severe complications in the context of viral respiratory disease. Here, we review the mechanisms of complement activation and regulation and explore their roles in both protecting against infection and exacerbating disease. We discuss emerging evidence related to complement-targeted therapeutics in COVID-19 and compare the role of the complement in other respiratory viral diseases like influenza and respiratory syncytial virus. We review recent mechanistic studies and animal models that can be used for further investigation. Novel knockout studies are proposed to better understand the nuances of the activation of the complement system in respiratory viral diseases.

A guide to complement biology, pathology and therapeutic opportunity

Complement has long been considered a key innate immune effector system that mediates host defence and tissue homeostasis. Yet, growing evidence has illuminated a broader involvement of complement in fundamental biological processes extending far beyond its traditional realm in innate immunity. Complement engages in intricate crosstalk with multiple pattern-recognition and signalling pathways both in the extracellular and intracellular space. Besides modulating host-pathogen interactions, this crosstalk guides early developmental processes and distinct cell trajectories, shaping tissue immunometabolic and regenerative programmes in different physiological systems. This Review provides a guide to the system-wide functions of complement. It highlights illustrative paradigm shifts that have reshaped our understanding of complement pathobiology, drawing examples from evolution, development of the central nervous system, tissue regeneration and cancer immunity. Despite its tight spatiotemporal regulation, complement activation can be derailed, fuelling inflammatory tissue pathology. The pervasive contribution of complement to disease pathophysiology has inspired a resurgence of complement therapeutics with major clinical developments, some of which have challenged long-held dogmas. We thus highlight major therapeutic concepts and milestones in clinical complement intervention.

TMT-based quantitative proteomics reveals the protective mechanism of tenuigenin after experimental intracerebral hemorrhage in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Tenuigenin (TNG) is an extract obtained from Polygalae Radix. It possesses anti-inflammatory, antioxidant, and neuroprotective properties. However, the potential mechanism of TNG in intracerebral hemorrhage (ICH) has not been well studied.

AIM OF THE STUDY

In the present study, we aimed to identify the prospective mechanism of TNG in treating ICH.

MATERIALS AND METHODS

A total of 120 mice were divided into five groups: Sham group, ICH + vehicle group, ICH + TNG(8 mg/kg), ICH + TNG(16 mg/kg), and ICH + TNG(32 mg/kg). The modified Garcia test and beam walking test were carried out at 24 h and 72 h after ICH. Brain water content, haematoma volume and hemoglobin content examinations were performed at 72 h after ICH. TMT-based quantitative proteomics combined with bioinformatics analysis methods was used to distinguish differentially expressed proteins (DEPs) to explore potential pharmacological mechanisms. Western blotting was performed to validate representative proteins.

RESULTS

Our results showed that the optimal dose of TNG was 16 mg/kg, which could markedly improve neurological functions, and reduce cerebral oedema, haematoma volume and hemoglobin levels 72 h after ICH. A total of 404 DEPs (353 up-and 51 downregulated) were identified in the ICH + vehicle vs. sham group, while 342 DEPs (306 up-and 36 downregulated) and 76 DEPs (28 up-and 48 downregulated) were quantified in the TNG vs. sham group and TNG vs. ICH + vehicle group, respectively. In addition, a total of 26 DEPs were selected according to strict criteria. Complement and coagulation cascades were the most significantly enriched pathways, and two proteins (MBL-C and Car1) were further validated as hub molecules.

CONCLUSIONS

Our results suggested that the therapeutic effects of TNG on ICH were closely associated with the complement system, and that MBL-C and Car1 might be potential targets of TNG for the treatment of ICH.

Complement in human disease: approved and up-and-coming therapeutics

The complement system is recognised as a protector against blood-borne pathogens and a controller of immune system and tissue homoeostasis. However, dysregulated complement activity is associated with unwanted or non-resolving immune responses and inflammation, which induce or exacerbate the pathogenesis of a broad range of inflammatory and autoimmune diseases. Although the merit of targeting complement clinically has long been acknowledged, the overall complement drug approval rate has been modest. However, the success of the humanised anti-C5 antibody eculizumab in effectively treating paroxysmal nocturnal haemoglobinuria and atypical haemolytic syndrome has revitalised efforts to target complement therapeutically. Increased understanding of complement biology has led to the identification of novel targets for drug development that, in combination with advances in drug discovery and development technologies, has resulted in a surge of interest in bringing new complement therapeutics into clinical use. The rising number of approved drugs still almost exclusively target rare diseases, but the substantial pipeline of up-and-coming treatment options will possibly provide opportunities to also expand the clinical targeting of complement to common diseases.

The complement cascade in lung injury and disease

BACKGROUND

The complement system is an important arm of immune defense bringing innate and adaptive immunity. Although originally regarded as a major complementary defense mechanism against pathogens, continuously emerging evidence has uncovered a central role of this complex system in several diseases including lung pathologies.

MAIN BODY

Complement factors such as anaphylatoxins C3a and C5a, their receptors C3aR, C5aR and C5aR2 as well as complement inhibitory proteins CD55, CD46 and CD59 have been implicated in pathologies such as the acute respiratory distress syndrome, pneumonia, chronic obstructive pulmonary disease, asthma, interstitial lung diseases, and lung cancer. However, the exact mechanisms by which complement factors induce these diseases remain unclear. Several complement-targeting monoclonal antibodies are reported to treat lung diseases.

CONCLUSIONS

The complement system contributes to the progression of the acute and chronic lung diseases. Better understanding of the underlying mechanisms will provide groundwork to develop new strategy to target complement factors for treatment of lung diseases.

Structural Characterization and Anticomplement Activity of an Acidic Heteropolysaccharide from Lysimachia christinae Hance

A novel acidic heteropolysaccharide (LCP-90-1) was isolated and purified from a traditional "heat-clearing" Chinese medicine, Lysimachia christinae Hance. LCP-90-1 (Mw, 20.65 kDa) was composed of Man, Rha, GlcA, Glc, Gal, and Ara, with relative molar ratios of 1.00: 3.00: 11.62: 1.31: 1.64: 5.24. The backbone consisted of 1,4-α-D-GlcpA, 1,4-α-D-Glcp, 1,4-β-L-Rhap, and 1,3,5-α-L-Araf, with three branches of β-D-Galp-(1 → 4)-β-L-Rhap-(1→, α-L-Araf-(1→ and α-D-Manp-(1→ attached to the C-5 position of 1,3,5-α-L-Araf. LCP-90-1 exhibited potent anticomplement activity (CH50: 135.01 ± 0.68 µg/mL) in vitro, which was significantly enhanced with increased glucuronic acid (GlcA) content in its degradation production (LCP-90-1-A, CH50: 28.26 ± 0.39 µg/mL). However, both LCP-90-1 and LCP90-1-A were inactivated after reduction or complete acid hydrolysis. These observations indicated the important role of GlcA in LCP-90-1 and associated derivatives with respect to anticomplement activity. Similarly, compared with LCP-90-1, the antioxidant activity of LCP-90-1-A was also enhanced. Thus, polysaccharides with a high content of GlcA might be important and effective substances of L. christinae.

The pathogenesis and potential therapeutic targets in sepsis

Sepsis is defined as "a life-threatening organ dysfunction caused by dysregulated host systemic inflammatory and immune response to infection." At present, sepsis continues to pose a grave healthcare concern worldwide. Despite the use of supportive measures in treating traditional sepsis, such as intravenous fluids, vasoactive substances, and oxygen plus antibiotics to eradicate harmful pathogens, there is an ongoing increase in both the morbidity and mortality associated with sepsis during clinical interventions. Therefore, it is urgent to design specific pharmacologic agents for the treatment of sepsis and convert them into a novel targeted treatment strategy. Herein, we provide an overview of the molecular mechanisms that may be involved in sepsis, such as the inflammatory response, immune dysfunction, complement deactivation, mitochondrial damage, and endoplasmic reticulum stress. Additionally, we highlight important targets involved in sepsis-related regulatory mechanisms, including GSDMD, HMGB1, STING, and SQSTM1, among others. We summarize the latest advancements in potential therapeutic drugs that specifically target these signaling pathways and paramount targets, covering both preclinical studies and clinical trials. In addition, this review provides a detailed description of the crosstalk and function between signaling pathways and vital targets, which provides more opportunities for the clinical development of new treatments for sepsis.

Activation of the complement system by nanoparticles and strategies for complement inhibition

The complement system is a multicomponent and multifunctional arm of the innate immune system. Complement contributes to non-specific host defence and maintains homeostasis through multifaceted processes and pathways, including crosstalk with the adaptive immune system, the contact (coagulation) and the kinin systems, and alarmin high-mobility group box 1. Complement is also present intracellularly, orchestrating a wide range of housekeeping and physiological processes in both immune and nonimmune cells, thus showing its more sophisticated roles beyond innate immunity, but its roles are still controversial. Particulate drug carriers and nanopharmaceuticals typically present architectures and surface patterns that trigger complement system in different ways, resulting in both beneficial and adverse responses depending on the extent of complement activation and regulation as well as pathophysiological circumstances. Here we consider the role of complement system and complement regulations in host defence and evaluate the mechanisms by which nanoparticles trigger and modulate complement responses. Effective strategies for the prevention of nanoparticle-mediated complement activation are introduced and discussed.

Functional Analysis of a Novel Complement C5a Receptor 1-Blocking Monoclonal Antibody

INTRODUCTION

The complement system anaphylatoxin C5a is a critical player in inflammation. By binding to complement C5a receptor 1 (C5aR1/CD88), C5a regulates many cellular functions, mainly as a potent pro-inflammatory inducer. We describe the generation and selection of a potent antagonistic C5aR1 mouse monoclonal antibody (mAb).

METHODS

Initial C5aR1 hybridoma clone selection was performed with a cell-binding study in human whole blood. In-house C5aR1 mAb assessment for C5aR1 inhibition was done via the iLite® C5a assay. C5aR1 mAb specificity was investigated on C5aR1his- and C5aR2his-expressing Flp-In™-CHO cells. Physiological C5aR1 inhibition was assessed via a C5a-driven calcium flux assay and stimulation assay based on isolated polymorphonuclear leukocytes (PMNs) and a whole blood model stimulated with Escherichia coli.

RESULTS

The supernatant of hybridoma clones targeting the N-terminal section of C5aR1 displayed efficient binding to C5aR1 in whole blood, which was confirmed for purified mAbs. The C5aR1 mAb 18-41-6 was selected following the assay of in-house C5aR1 mAbs via the iLite® C5a assay. The mAb 18-41-6 was specific for C5aR1. Full-size and/or F(ab')2 preparations of mAb 18-41-6 were found to efficiently abrogate C5a-induced calcium flux in neutrophils and to significantly reduce the upregulation of the activation markers CD11b (neutrophils, monocytes) and CD66b (neutrophils).

CONCLUSION

Our results demonstrate that mAb 18-41-6 is a valuable tool for investigating the C5a-C5aR1 axis and a potential therapeutic candidate for inflammatory disease treatment.

Increased infiltration of CD4+ T cell in the complement deficient lymphedema model

BACKGROUND

Lymphedema is an intractable disease that can be caused by injury to lymphatic vessels, such as by surgical treatments for cancer. It can lead to impaired joint mobility in the extremities and reduced quality of life. Chronic inflammation due to infiltration of various immune cells in an area of lymphedema is thought to lead to local fibrosis, but the molecular pathogenesis of lymphedema remains unclear. Development of effective therapies requires elucidation of the immunological mechanisms involved in the progression of lymphedema. The complement system is part of the innate immune system which has a central role in the elimination of invading microbes and acts as a scavenger of altered host cells, such as apoptotic and necrotic cells and cellular debris. Complement-targeted therapies have recently been clinically applied to various diseases caused by complement overactivation. In this context, we aimed to determine whether complement activation is involved in the development of lymphedema.

RESULTS

Our mouse tail lymphedema models showed increased expression of C3, and that the classical or lectin pathway was locally activated. Complement activation was suggested to be involved in the progression of lymphedema. In comparison of the C3 knockout (KO) mouse lymphedema model and wild-type mice, there was no difference in the degree of edema at three weeks postoperatively, but the C3 KO mice had a significant increase of TUNEL+ necrotic cells and CD4+ T cells. Infiltration of macrophages and granulocytes was not significantly elevated in C3 KO or C5 KO mice compared with in wild-type mice. Impaired opsonization and decreased migration of macrophages and granulocytes due to C3 deficiency should therefore induce the accumulation of dead cells and may lead to increased infiltration of CD4+ T cells.

CONCLUSIONS

Vigilance for exacerbation of lymphedema is necessary when surgical treatments have the potential to injure lymphatic vessels in patients undergoing complement-targeted therapies or with complement deficiency. Future studies should aim to elucidate the molecular mechanism of CD4+ T cell infiltration by accumulated dead cells.

A Systematic Investigation of Complement and Coagulation-Related Protein in Autism Spectrum Disorder Using Multiple Reaction Monitoring Technology

Autism spectrum disorder (ASD) is one of the common neurodevelopmental disorders in children. Its etiology and pathogenesis are poorly understood. Previous studies have suggested potential changes in the complement and coagulation pathways in individuals with ASD. In this study, using multiple reactions monitoring proteomic technology, 16 of the 33 proteins involved in this pathway were identified as differentially-expressed proteins in plasma between children with ASD and controls. Among them, CFHR3, C4BPB, C4BPA, CFH, C9, SERPIND1, C8A, F9, and F11 were found to be altered in the plasma of children with ASD for the first time. SERPIND1 expression was positively correlated with the CARS score. Using the machine learning method, we obtained a panel composed of 12 differentially-expressed proteins with diagnostic potential for ASD. We also reviewed the proteins changed in this pathway in the brain and blood of patients with ASD. The complement and coagulation pathways may be activated in the peripheral blood of children with ASD and play a key role in the pathogenesis of ASD.

Revealing the signaling of complement receptors C3aR and C5aR1 by anaphylatoxins

The complement receptors C3aR and C5aR1, whose signaling is selectively activated by anaphylatoxins C3a and C5a, are important regulators of both innate and adaptive immune responses. Dysregulations of C3aR and C5aR1 signaling lead to multiple inflammatory disorders, including sepsis, asthma and acute respiratory distress syndrome. The mechanism underlying endogenous anaphylatoxin recognition and activation of C3aR and C5aR1 remains elusive. Here we reported the structures of C3a-bound C3aR and C5a-bound C5aR1 as well as an apo-C3aR structure. These structures, combined with mutagenesis analysis, reveal a conserved recognition pattern of anaphylatoxins to the complement receptors that is different from chemokine receptors, unique pocket topologies of C3aR and C5aR1 that mediate ligand selectivity, and a common mechanism of receptor activation. These results provide crucial insights into the molecular understanding of C3aR and C5aR1 signaling and structural templates for rational drug design for treating inflammation disorders.

Serum mannan-binding lectin-associated serine proteases in early pregnancy for gestational diabetes in Chinese pregnant women

Aims

This study aimed to explore associations of mannan-binding lectin-associated serine protease (MASP) levels in early pregnancy with gestational diabetes mellitus (GDM). We also examined interactions of MASPs and deoxycholic acid (DCA)/glycoursodeoxycholic acid (GUDCA) for the GDM risk and whether the interactive effects if any on the GDM risk were mediated via lysophosphatidylcholine (LPC) 18:0.

Materials and methods

A 1:1 case-control study (n = 414) nested in a prospective cohort of pregnant women was conducted in Tianjin, China. Binary conditional logistic regressions were performed to examine associations of MASPs with the GDM risk. Additive interaction measures were used to examine interactions between MASPs and DCA/GUDCA for the GDM risk. Mediation analyses and Sobel tests were used to examine mediation effects of LPC18:0 between the copresence of MASPs and DCA/GUDCA on the GDM risk.

Results

High MASP-2 was independently associated with GDM [odds ratio (OR): 2.62, 95% confidence interval (CI): 1.44-4.77], while the effect of high MASP-1 on GDM was attributable to high MASP-2 (P for Sobel test: 0.003). Low DCA markedly increased the OR of high MASP-2 alone from 2.53 (1.10-5.85) up to 10.6 (4.22-26.4), with a significant additive interaction. In addition, high LPC18:0 played a significant mediating role in the links from low DCA to GDM and from the copresence of high MASP-2 and low DCA to GDM (P for Sobel test <0.001) but not in the link from high MASP-2 to GDM.

Conclusions

High MASP-1 and MASP-2 in early pregnancy were associated with GDM in Chinese pregnant women. MASP-2 amplifies the risk of low DCA for GDM, which is mediated via LPC18:0.

Efficacy and safety of avacincaptad pegol in patients with geographic atrophy (GATHER2): 12-month results from a randomised, double-masked, phase 3 trial

BACKGROUND

Geographic atrophy is an advanced form of dry age-related macular degeneration that can lead to irreversible vision loss and high burden of disease. We aimed to assess efficacy and safety of avacincaptad pegol 2 mg in reducing geographic atrophy lesion growth.

METHODS

GATHER2 is a randomised, double-masked, sham-controlled, 24-month, phase 3 trial across 205 retina clinics, research hospitals, and academic institutions globally. To be eligible, patients had to be aged 50 years or older with non-centrepoint-involving geographic atrophy and best corrected visual acuity between 20/25 and 20/320 in the study eye. Eligible patients were randomly assigned (1:1) to monthly avacincaptad pegol 2 mg administered as a 100 μL intravitreal injection or sham for the first 12 months. Randomisation was performed using an interactive response technology system with stratification by factors known to be of prognostic importance in age-related macular degeneration. Patients, investigators, study centre staff, sponsor personnel, and data analysts were masked to treatment allocation. The primary endpoint was geographic atrophy lesion size measured by fundus autofluorescence at baseline, month 6, and month 12. Efficacy and safety analyses were done in the modified intention-to-treat and safety populations, respectively. This trial is registered with ClinicalTrials.gov, NCT04435366.

FINDINGS

Between June 22, 2020, and July 23, 2021, 1422 patients were screened for eligibility, of whom 448 were enrolled and randomly assigned to avacincaptad pegol 2 mg (n=225) or sham (n=223). One patient in the sham group did not receive study treatment and was excluded from analyses. There were 154 (68%) female patients and 71 (32%) male patients in the avacincaptad pegol 2 mg group, and 156 (70%) female patients and 66 (30%) male patients in the sham group. From baseline to month 12, the mean rate of square-root-transformed geographic atrophy area growth was 0·336 mm/year (SE 0·032) with avacincaptad pegol 2 mg and 0·392 mm/year (0·033) with sham, a difference in growth of 0·056 mm/year (95% CI 0·016-0·096; p=0·0064), representing a 14% difference between the avacincaptad pegol 2 mg group and the sham group. Ocular treatment-emergent adverse events in the study eye occurred in 110 (49%) patients in the avacincaptad pegol 2 mg group and 83 (37%) in the sham group. There were no endophthalmitis, intraocular inflammation, or ischaemic optic neuropathy events over 12 months. To month 12, macular neovascularisation in the study eye occurred in 15 (7%) patients in the avacincaptad pegol 2 mg group and nine (4%) in the sham group, with exudative macular neovascularisation occurring in 11 (5%) in the avacincaptad pegol 2 mg group and seven (3%) in the sham group.

INTERPRETATION

Monthly avacincaptad pegol 2 mg was well tolerated and showed significantly slower geographic atrophy growth over 12 months than sham treatment, suggesting that avacincaptad pegol might slow disease progression and potentially change the trajectory of disease for patients with geographic atrophy.

FUNDING

Iveric Bio, An Astellas Company.

Revisiting the role of the complement system in intracerebral hemorrhage and therapeutic prospects

Intracerebral hemorrhage (ICH) is a stroke subtype characterized by non-traumatic rupture of blood vessels in the brain, resulting in blood pooling in the brain parenchyma. Despite its lower incidence than ischemic stroke, ICH remains a significant contributor to stroke-related mortality, and most survivors experience poor outcomes that significantly impact their quality of life. ICH has been accompanied by various complex pathological damage, including mechanical damage of brain tissue, hematoma mass effect, and then leads to inflammatory response, thrombin activation, erythrocyte lysis, excitatory amino acid toxicity, complement activation, and other pathological changes. Accumulating evidence has demonstrated that activation of complement cascade occurs in the early stage of brain injury, and the excessive complement activation after ICH will affect the occurrence of secondary brain injury (SBI) through multiple complex pathological processes, aggravating brain edema, and pathological brain injury. Therefore, the review summarized the pathological mechanisms of brain injury after ICH, specifically the complement role in ICH, and its related pathological mechanisms, to comprehensively understand the specific mechanism of different complements at different stages after ICH. Furthermore, we systematically reviewed the current state of complement-targeted therapies for ICH, providing a reference and basis for future clinical transformation of complement-targeted therapy for ICH.

Differences in Physico-Chemical Properties and Immunological Response in Nanosimilar Complex Drugs: The Case of Liposomal Doxorubicin

This study aims to highlight the impact of physicochemical properties on the behaviour of nanopharmaceuticals and how much carrier structure and physiochemical characteristics weigh on the effects of a formulation. For this purpose, two commercially available nanosimilar formulations of Doxil and their respective carriers were compared as a case study. Although the two formulations were "similar", we detected different toxicological effects (profiles) in terms of in vitro toxicity and immunological responses at the level of cytokines release and complement activation (iC3b fragment), that could be correlated with the differences in the physicochemical properties of the formulations. Shedding light on nanosimilar key quality attributes of liposome-based materials and the need for an accurate characterization, including investigation of the immunological effects, is of fundamental importance considering their great potential as delivery system for drugs, genes, or vaccines and the growing market demand.

Inhibition of cleavage of human complement component C5 and the R885H C5 variant by two distinct high affinity anti-C5 nanobodies

The human complement system plays a crucial role in immune defense. However, its erroneous activation contributes to many serious inflammatory diseases. Since most unwanted complement effector functions result from C5 cleavage into C5a and C5b, development of C5 inhibitors, such as clinically approved monoclonal antibody eculizumab, are of great interest. Here, we developed and characterized two anti-C5 nanobodies, UNbC5-1 and UNbC5-2. Using surface plasmon resonance, we determined a binding affinity of 119.9 pM for UNbC5-1 and 7.7 pM for UNbC5-2. Competition experiments determined that the two nanobodies recognize distinct epitopes on C5. Both nanobodies efficiently interfered with C5 cleavage in a human serum environment, as they prevented red blood cell lysis via membrane attack complexes (C5b-9) and the formation of chemoattractant C5a. The cryo-EM structure of UNbC5-1 and UNbC5-2 in complex with C5 (3.6 Å resolution) revealed that the binding interfaces of UNbC5-1 and UNbC5-2 overlap with known complement inhibitors eculizumab and RaCI3, respectively. UNbC5-1 binds to the MG7 domain of C5, facilitated by a hydrophobic core and polar interactions, and UNbC5-2 interacts with the C5d domain mostly by salt bridges and hydrogen bonds. Interestingly, UNbC5-1 potently binds and inhibits C5 R885H, a genetic variant of C5 that is not recognized by eculizumab. Altogether, we identified and characterized two different, high affinity nanobodies against human C5. Both nanobodies could serve as diagnostic and/or research tools to detect C5 or inhibit C5 cleavage. Furthermore, the residues targeted by UNbC5-1 hold important information for therapeutic inhibition of different polymorphic variants of C5.

Ficolin A knockout alleviates sepsis-induced severe lung injury in mice by restoring gut Akkermansia to inhibit S100A4/STAT3 pathway

Acute lung injury (ALI) is a life-threatening disease with high morbidity and mortality. Our previous results demonstrated that Ficolin A (FcnA) protected against lipopolysaccharide (LPS)-induced mild ALI via activating complement, however the mechanism of severe lung damage caused by sepsis remains unclear. This study aimed to investigate whether FcnA modulated gut microbiota to affect the progression of sepsis-induced severe ALI. Fcna^-/- and Fcnb^-/- C57BL/6 mice were applied to establish the ALI model by injection of LPS intraperitoneally. Mice were treated with antibiotics, fecal microbiota transplantation (FMT), and intratracheal administration of recombinant protein S100A4. Changes in body weight of mice were recorded, and lung injury were assessed. Then lung tissue wet/dry weight was calculated. We found knockout of FcnA, but not FcnB, alleviated sepsis-induced severe ALI evidenced by increased body weight change, decreased wet/dry weight of lung tissue, reduced inflammatory infiltration, decreased lung damage score, decreased Muc-2, TNF-α, IL-1β, IL-6, and Cr levels, and increased sIgA levels. Furthermore, knockout of FcnA restored gut microbiota homeostasis in mice. Correlation analysis showed that Akkermansia was significantly negatively associated with TNF-α, IL-1β, and IL-6 levels in serum and bronchoalveolar lavage fluid (BALF). Moreover, knockout of FcnA regulated gut microbiota to protect ALI through S100A4. Finally, we found knockout of FcnA alleviated ALI by inhibiting S100A4 via gut Akkermansia in mice, which may provide further insights and new targets into treating sepsis-induced severe lung injury.

Increased Expression of Anaphylatoxin C5a-Receptor-1 in Neutrophils and Natural Killer Cells of Preterm Infants

Preterm infants are susceptible to infection and their defense against pathogens relies largely on innate immunity. The role of the complement system for the immunological vulnerability of preterm infants is less understood. Anaphylatoxin C5a and its receptors C5aR1 and -2 are known to be involved in sepsis pathogenesis, with C5aR1 mainly exerting pro-inflammatory effects. Our explorative study aimed to determine age-dependent changes in the expression of C5aR1 and C5aR2 in neonatal immune cell subsets. Via flow cytometry, we analyzed the expression pattern of C5a receptors on immune cells isolated from peripheral blood of preterm infants (n = 32) compared to those of their mothers (n = 25). Term infants and healthy adults served as controls. Preterm infants had a higher intracellular expression of C5aR1 on neutrophils than control individuals. We also found a higher expression of C5aR1 on NK cells, particularly on the cytotoxic CD56^dim subset and the CD56^- subset. Immune phenotyping of other leukocyte subpopulations revealed no gestational-age-related differences for the expression of and C5aR2. Elevated expression of C5aR1 on neutrophils and NK cells in preterm infants may contribute to the phenomenon of "immunoparalysis" caused by complement activation or to sustained hyper-inflammatory states. Further functional analyses are needed to elucidate the underlying mechanisms.

Role of gC1qR as a modulator of endothelial cell permeability and contributor to post-stroke inflammation and edema formation

Ischemic stroke is a leading cause of death and disability worldwide. A serious risk of acute ischemic stroke (AIS) arises after the stroke event, due to inflammation and edema formation. Inflammation and edema in the brain are mediated by bradykinin, the formation of which is dependent upon a multi-ligand receptor protein called gC1qR. There are currently no preventive treatments for the secondary damage of AIS produced by inflammation and edema. This review aims to summarize recent research regarding the role of gC1qR in bradykinin formation, its role in inflammation and edema following ischemic injury, and potential therapeutic approaches to preventing post-stroke inflammation and edema formation.

MASP3 Deficiency in Mice Reduces but Does Not Abrogate Alternative Pathway Complement Activity Due to Intrinsic Profactor D Activity

Complement factor D (FD) is a rate-limiting enzyme of the alternative pathway (AP). Recent studies have suggested that it is synthesized as an inactive precursor and that its conversion to enzymatically active FD is catalyzed by mannan-binding lectin-associated serine protease 3 (MASP3). However, whether MASP3 is essential for AP complement activity remains uncertain. It has been shown that Masp1/3 gene knockout did not prevent AP complement overactivation in a factor H-knockout mouse, and a human patient lacking MASP3 still retained AP complement activity. In this study, we have assessed AP complement activity in a Masp3-knockout mouse generated by CRISPR/Cas9 editing of the Masp1/3 gene. We confirmed specific Masp3 gene inactivation by showing intact MASP1 protein expression and absence of mature FD in the mutant mice. Using several assays, including LPS- and zymosan-induced C3b deposition and rabbit RBC lysis tests, we detected plasma concentration-dependent AP complement activity in Masp3 gene-inactivated mice. Thus, although not measurable in 5% plasma, significant AP complement activity was detected in 20-50% plasma of Masp3 gene-inactivated mice. Furthermore, whereas FD gene deletion provided more than 90% protection of CD55/Crry-deficient RBCs from AP complement-mediated extravascular hemolysis, Masp3 gene deletion only provided 30% protection in the same study. We also found pro-FD to possess intrinsic catalytic activity, albeit at a much lower level than mature FD. Our data suggest that MASP3 deficiency reduces but does not abrogate AP complement activity and that this is explained by intrinsic pro-FD activity, which can be physiologically relevant in vivo.

Inflammatory mechanisms and intervention strategies for sepsis-induced myocardial dysfunction

Sepsis-induced myocardial dysfunction (SIMD) is the leading cause of death in patients with sepsis in the intensive care units. The main manifestations of SIMD are systolic and diastolic dysfunctions of the myocardium. Despite our initial understanding of the SIMD over the past three decades, the incidence and mortality of SIMD remain high. This may be attributed to the large degree of heterogeneity among the initiating factors, disease processes, and host states involved in SIMD. Previously, organ dysfunction caused by sepsis was thought to be an impairment brought about by an excessive inflammatory response. However, many recent studies have shown that SIMD is a consequence of a combination of factors shaped by the inflammatory responses between the pathogen and the host. In this article, we review the mechanisms of the inflammatory responses and potential novel therapeutic strategies in SIMD.

The anaphylatoxin C5a: Structure, function, signaling, physiology, disease, and therapeutics

The complement system is one of the oldest known tightly regulated host defense systems evolved for efficiently functioning cell-based immune systems and antibodies. Essentially, the complement system acts as a pivot between the innate and adaptive arms of the immune system. The complement system collectively represents a cocktail of ∼50 cell-bound/soluble glycoproteins directly involved in controlling infection and inflammation. Activation of the complement cascade generates complement fragments like C3a, C4a, and C5a as anaphylatoxins. C5a is the most potent proinflammatory anaphylatoxin, which is involved in inflammatory signaling in a myriad of tissues. This review provides a comprehensive overview of human C5a in the context of its structure and signaling under several pathophysiological conditions, including the current and future therapeutic applications targeting C5a.

Ependyma in Neurodegenerative Diseases, Radiation-Induced Brain Injury and as a Therapeutic Target for Neurotrophic Factors

The neuron loss caused by the progressive damage to the nervous system is proposed to be the main pathogenesis of neurodegenerative diseases. Ependyma is a layer of ciliated ependymal cells that participates in the formation of the brain-cerebrospinal fluid barrier (BCB). It functions to promotes the circulation of cerebrospinal fluid (CSF) and the material exchange between CSF and brain interstitial fluid. Radiation-induced brain injury (RIBI) shows obvious impairments of the blood-brain barrier (BBB). In the neuroinflammatory processes after acute brain injury, a large amount of complement proteins and infiltrated immune cells are circulated in the CSF to resist brain damage and promote substance exchange through the BCB. However, as the protective barrier lining the brain ventricles, the ependyma is extremely vulnerable to cytotoxic and cytolytic immune responses. When the ependyma is damaged, the integrity of BCB is destroyed, and the CSF flow and material exchange is affected, leading to brain microenvironment imbalance, which plays a vital role in the pathogenesis of neurodegenerative diseases. Epidermal growth factor (EGF) and other neurotrophic factors promote the differentiation and maturation of ependymal cells to maintain the integrity of the ependyma and the activity of ependymal cilia, and may have therapeutic potential in restoring the homeostasis of the brain microenvironment after RIBI or during the pathogenesis of neurodegenerative diseases.

Thromboinflammatory response is increased in pancreas transplant alone versus simultaneous pancreas-kidney transplantation and early pancreas graft thrombosis is associated with complement activation

Background

Pancreas transplant alone (PTA) recipients are more affected by pancreas graft thrombosis, and graft loss compared to simultaneous pancreas-kidney (SPK) recipients. The pathophysiology is unknown, but an increased immune response has been suggested in the PTA recipients. In this observational study, we compared perioperative thromboinflammation between PTA (n=32) and SPK (n=35) recipients, and between PTA recipients with (n=14) versus without (n=18) early graft thrombosis.

Methods

We measured C-reactive protein (CRP), plasma markers of activated coagulation and complement, and cytokines preoperatively and daily during the first postoperative week.

Results

Preoperatively, coagulation and complement activation markers were comparable between PTA and SPK recipients, while cytokine concentrations were higher in SPK recipients (TNF, IL-8, IP-10, MCP-1, MIP-1α; all p&lt;0.05). On the first postoperative day, PTA recipients had higher coagulation activation, measured as thrombin-antithrombin complex (TAT), than SPK recipients (p=0.008). In the first postoperative week, PTA recipients showed higher relative cytokine release (IL-6, IL-8, G-CSF, IP-10, MCP-1, and MIP-1α; all p&lt;0.05) while SPK recipients showed higher absolute cytokine concentrations (TNF, IL-1ra, IL-8, MIP-1α, and IL-4; all p&lt;0.05). PTA and SPK recipients showed similar terminal complement complex (TCC, sC5b-9) activation. On the first postoperative day, TCC (OR 1.2 [95% CI 1.0-1.5] for 0.1 CAU/ml increase, p=0.02) and CRP (OR 1.2 [95% CI 1.0-1.3] for 10 mg/L increase, p=0.04) were associated with an increased risk of early graft thrombosis. TCC was specific for graft thrombosis, while CRP increased with several complications. PTA recipients with compared to those without graft thrombosis had higher TCC pre- (p=0.04) and postoperatively (p=0.03).

Conclusion

The relative increase in postoperative thromboinflammatory response was more pronounced in PTA recipients. Complement activation was associated with an increased risk of graft thrombosis. This study indicates that innate immune activation rather than elevated levels may affect early postoperative pancreas graft thrombosis.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT01957696, identifier NCT01957696

Ficolin-3 and MASP-2 gene variants in Siberian arctic populations: Summarized evidence of selective pressure for the high frequency of lectin complement pathway deficiency

Herewith, we provide novel original data about the prevalence of FCN3 rs532781899 and MASP2 rs72550870 variants among the newborns of aboriginal Siberian Arctic populations (Nenets and Dolgan-Nganasans) and Russians of East Siberia. This novel data has been analysed along with the genetic data about other proteins of the lectin pathway of the complement system (mannose-binding lectin and ficolin-2) obtained earlier. A total of 926 specimens of dried blood spots of the newborns were genotyped. The newborns represented four populations: Nenets, Dolgan-Nganasans, Mixed aboriginal population, and Russians (Caucasians) to study the prevalence of single nucleotide polymorphisms of FCN3 rs532781899 and MASP2 rs72550870. The prevalence of the deletion allele of the rs532781899 variant in the FCN3 gene associated with the decreased production of ficolin-3 was found to be increased in Russians compared to the Nenets aboriginal populations (P = .002). The prevalence of the rs72550870*G allele in the MASP2 gene associated with low serum protease activity was found to be increased in Russians compared with Nenets and Dolgan-Nganasans (P < .001 and P = .03, respectively). The results of the current study and our previous findings corroborate with a hypothesis that human evolution has been directed toward the accumulation of genotypes associated with low activity of the lectin complement activation pathway.

Microglia PKM2 Mediates Neuroinflammation and Neuron Loss in Mice Epilepsy through the Astrocyte C3-Neuron C3R Signaling Pathway

Epilepsy is a neurological disease and approximately 30% of patients have failed to respond to current anti-epilepsy drugs. The neuroinflammation mechanism has raised increasing concerns and been regarded as the novel treatment strategy in epilepsy, but the target molecules require further research. Pyruvate kinase isoform 2 (PKM2) is well studied in peripheral inflammation, but its role in epilepsy neuroinflammation remains unclear. We knocked down microglia PKM2 in the hippocampus using a stereotaxic adeno-associated virus (AAV) microinjection and established a pilocarpine-induced status epilepticus (PISE) model. Racine score was used to evaluate the seizure grade. Next, we used WB, Multiplex tyramide signal amplification (TSA) staining and other methods to determine neuroinflammation and the complement component 3 (C3)-C3aR interaction in primary microglia. Results showed that microglia PKM2 knockdown reduced epilepsy grade and rescued neuron loss. Mechanistically, PKM2 knockdown inhibited microglia activation and inflammation factor secretion through suppressing p65 expression and phosphorylation. The reduced microglia C1q, TNF-α, and IL-1α were responsible for the decreased astrocyte C3 expression and the following neuron damage caused by the C3-C3aR interaction. Our data suggest that microglia PKM2 inhibition ameliorates neuroinflammation and neuron loss through C3-C3aR interaction in epilepsy, which provides an attractive target for the intervention of damaged neuron-glia crosstalk in epilepsy.

Dual inhibition of complement C5 and CD14 attenuates inflammation in a cord blood model

BACKGROUND

Escherichia coli and Group B streptococci (GBS) are the main causes of neonatal early-onset sepsis (EOS). Despite antibiotic therapy, EOS is associated with high morbidity and mortality. Dual inhibition of complement C5 and the Toll-like receptor co-factor CD14 has in animal studies been a promising novel therapy for sepsis.

METHODS

Whole blood was collected from the umbilical cord after caesarean section (n = 30). Blood was anti-coagulated with lepirudin. C5 inhibitor (eculizumab) and anti-CD14 was added 8 min prior to, or 15 and 30 min after adding E. coli or GBS. Total bacterial incubation time was 120 min (n = 16) and 240 min (n = 14). Cytokines and the terminal complement complex (TCC) were measured using multiplex technology and ELISA.

RESULTS

Dual inhibition significantly attenuated TCC formation by 25-79% when adding inhibitors with up to 30 min delay in both E. coli- and GBS-induced inflammation. TNF, IL-6 and IL-8 plasma concentration were significantly reduced by 28-87% in E. coli-induced inflammation when adding inhibitors with up to 30 min delay. The dual inhibition did not significantly reduce TNF, IL-6 and IL-8 plasma concentration in GBS-induced inflammation.

CONCLUSION

Dual inhibition of C5 and CD14 holds promise as a potential future treatment for severe neonatal EOS.

IMPACT

Neonatal sepsis can cause severe host inflammation with high morbidity and mortality, but there are still no effective adjunctive immunologic interventions available. Adding CD14 and complement C5 inhibitors up to 30 min after incubation of E. coli or Group B streptococci in a human umbilical cord blood model significantly reduced complement activation and cytokine release. Dual inhibition of C5 and CD14 is a potential future therapy to modulate systemic inflammation in severe cases of neonatal sepsis.

The neoepitope of the complement C5b-9 Membrane Attack Complex is formed by proximity of adjacent ancillary regions of C9

The Membrane Attack Complex (MAC) is responsible for forming large β-barrel channels in the membranes of pathogens, such as gram-negative bacteria. Off-target MAC assembly on endogenous tissue is associated with inflammatory diseases and cancer. Accordingly, a human C5b-9 specific antibody, aE11, has been developed that detects a neoepitope exposed in C9 when it is incorporated into the C5b-9 complex, but not present in the plasma native C9. For nearly four decades aE11 has been routinely used to study complement, MAC-related inflammation, and pathophysiology. However, the identity of C9 neoepitope remains unknown. Here, we determined the cryo-EM structure of aE11 in complex with polyC9 at 3.2 Å resolution. The aE11 binding site is formed by two separate surfaces of the oligomeric C9 periphery and is therefore a discontinuous quaternary epitope. These surfaces are contributed by portions of the adjacent TSP1, LDLRA, and MACPF domains of two neighbouring C9 protomers. By substituting key antibody interacting residues to the murine orthologue, we validated the unusual binding modality of aE11. Furthermore, aE11 can recognise a partial epitope in purified monomeric C9 in vitro, albeit weakly. Taken together, our results reveal the structural basis for MAC recognition by aE11.

Paroxysmal nocturnal hemoglobinuria: Where we stand

For the last 20 years, therapy of paroxysmal nocturnal hemoglobinuria (PNH) relied-up until recently-on antibody based terminal complement inhibitionon. PNH pathophysiology-a mutational defect leading to partial or complete absence of complement-regulatory proteins on blood cells-leads to intravascular hemolysis and consequences such as thrombosis and other sequelae. A plethora of new drugs interfering with the proximal and terminal complement cascade are under recent development and the first "proof-of-pinciple" proximal complement inhibitor targeting C3 has been approved in 2021. "PNH: where we stand" will try to give a brief account on where we came from and where we stand focusing on approved therapeutic options. The associated improvements as well as potential consequences of actual and future treatments as well as their impact on the disease will continue to necessitate academic and scientific focus on improving treatment options as well as on side effects and outcomes relevant to individual patient lives and circumstances in order to develop effective, safe, and available treatment for all hemolytic PNH patients globally.

Complement biomarkers reflect the pathological status of neuromyelitis optica spectrum disorders

Complement is involved in the pathogenesis of neuroimmune disease, but the detailed pathological roles of the complement pathway remain incompletely understood. Recently, eculizumab, a humanized anti-C5 monoclonal antibody, has been clinically applied against neuroimmune diseases such as myasthenia gravis and neuromyelitis optica spectrum disorders (NMOSD). Clinical application of eculizumab is also being investigated for another neuroimmune disease, Guillain-Barré syndrome (GBS). However, while the effectiveness of eculizumab for NMOSD is extremely high in many cases, there are some cases of myasthenia gravis and GBS in which eculizumab has little or no efficacy. Development of effective biomarkers that reflect complement activation in these diseases is therefore important. To identify biomarkers that could predict disease status, we retrospectively analyzed serum levels of complement factors in 21 patients with NMOSD and 25 patients with GBS. Ba, an activation marker of the alternative complement pathway, was elevated in the acute phases of both NMOSD and GBS. Meanwhile, sC5b-9, an activation marker generated by the terminal complement pathway, was elevated in NMOSD but not in GBS. Complement factor H (CFH), a complement regulatory factor, was decreased in the acute phase as well as in the remission phase of NMOSD, but not in any phases of GBS. Together, these findings suggest that complement biomarkers, such as Ba, sC5b-9 and CFH in peripheral blood, have potential utility in understanding the pathological status of NMOSD.

The Factor H protein family: The switchers of the complement alternative pathway

The factor H (FH) protein family is emerging as a complex network of proteins controlling the fate of the complement alternative pathway (AP) and dictating susceptibility to a wide range of diseases including infectious, inflammatory, autoimmune, and degenerative diseases and cancer. Composed, in man, of seven highly related proteins, FH, factor H-like 1, and 5 factor H-related proteins, some of the FH family proteins are devoted to down-regulating the AP, while others exert an opposite function by promoting AP activation. Recent findings have provided insights into the molecular mechanisms defining their biological roles and their pathogenicity, illustrating the relevance that the balance between the regulators and the activators within this protein family has in defining the outcome of complement activation on cell surfaces. In this review we will discuss the emerging roles of the factor H protein family, their impact in the complement cascade, and their involvement in the pathogenesis of complement-mediated diseases associated with the AP dysregulation.

Complement C3b contributes to Escherichia coli-induced platelet aggregation in human whole blood

Introduction

Platelets have essential functions as first responders in the immune response to pathogens. Activation and aggregation of platelets in bacterial infections can lead to life-threatening conditions such as arterial thromboembolism or sepsis-associated coagulopathy.

Methods

In this study, we investigated the role of complement in Escherichia coli (E. coli)-induced platelet aggregation in human whole blood, using Multiplate^® aggregometry, flow cytometry, and confocal microscopy.

Results and Discussion

We found that compstatin, which inhibits the cleavage of complement component C3 to its components C3a and C3b, reduced the E. coli-induced platelet aggregation by 42%-76% (p = 0.0417). This C3-dependent aggregation was not C3a-mediated as neither inhibition of C3a using a blocking antibody or a C3a receptor antagonist, nor the addition of purified C3a had any effects. In contrast, a C3b-blocking antibody significantly reduced the E. coli-induced platelet aggregation by 67% (p = 0.0133). We could not detect opsonized C3b on platelets, indicating that the effect of C3 was not dependent on C3b-fragment deposition on platelets. Indeed, inhibition of glycoprotein IIb/IIIa (GPIIb/IIIa) and complement receptor 1 (CR1) showed that these receptors were involved in platelet aggregation. Furthermore, aggregation was more pronounced in hirudin whole blood than in hirudin platelet-rich plasma, indicating that E. coli-induced platelet aggregation involved other blood cells. In conclusion, the E. coli-induced platelet aggregation in human whole blood is partly C3b-dependent, and GPIIb/IIIa and CR1 are also involved in this process.

The biological alterations of synapse/synapse formation in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common complication caused by sepsis, and is responsible for increased mortality and poor outcomes in septic patients. Neurological dysfunction is one of the main manifestations of SAE patients. Patients may still have long-term cognitive impairment after hospital discharge, and the underlying mechanism is still unclear. Here, we first outline the pathophysiological changes of SAE, including neuroinflammation, glial activation, and blood-brain barrier (BBB) breakdown. Synapse dysfunction is one of the main contributors leading to neurological impairment. Therefore, we summarized SAE-induced synaptic dysfunction, such as synaptic plasticity inhibition, neurotransmitter imbalance, and synapses loss. Finally, we discuss the alterations in the synapse, synapse formation, and mediators associated with synapse formation during SAE. In this review, we focus on the changes in synapse/synapse formation caused by SAE, which can further understand the synaptic dysfunction associated with neurological impairment in SAE and provide important insights for exploring appropriate therapeutic targets of SAE.

New insights into immunomodulatory properties of lactic acid bacteria fermented herbal medicines

The COVID-19 pandemic has brought more attention to the immune system, the body’s defense against infectious diseases. The immunomodulatory ability of traditional herbal medicine has been confirmed through clinical trial research, and has obvious advantages over prescription drugs due to its high number of potential targets and low toxicity. The active compounds of herbal drugs primarily include polysaccharides, saponins, flavonoids, and phenolics and can be modified to produce new active compounds after lactic acid bacteria (LAB) fermentation. LAB, primary source of probiotics, can produce additional immunomodulatory metabolites such as exopolysaccharides, short-chain fatty acids, and bacteriocins. Moreover, several compounds from herbal medicines can promote the growth and production of LAB-based immune active metabolites. Thus, LAB-mediated fermentation of herbal medicines has become a novel strategy for regulating human immune responses. The current review discusses the immunomodulatory properties and active compounds of LAB fermented herbal drugs, the interaction between LAB and herbal medicines, and changes in immunoregulatory components that occur during fermentation. This study also discusses the mechanisms by which LAB-fermented herbal medicines regulate the immune response, including activation of the innate or adaptive immune system and the maintenance of intestinal immune homeostasis.

The complement system and complement-like factors in sea cucumber

The complement system is an important part of innate immunity and plays an essential role in immune responses. Complement system consists of a series of proteins, its activation results in opsonization and phagocytosis of pathogens. Although the complement system has been studied extensively in vertebrates, considerably less is known about complement in invertebrates, especially in sea cucumber. Here, we reviewed the complement-like factors including Component 3 (C3), Complement factor B (Bf), Mannan-binding lectin (MBL) and globular Complement component 1q Receptor (gC1qR), which had been found in the complement system of sea cucumber. Furthermore, we compared the features of complement components among marine invertebrates and described the evolution of sea cucumber complement system obviously. This review can offer theoretical basis for disease control of the sea cucumber and will provide new insights into immune system of marine invertebrates. Meantime, the complete framework of sea cucumber complement may benefit the aquaculture industry.

Single-cell RNAseq provides insight into altered immune cell populations in human fracture nonunions

Nonunion describes bone fractures that fail to heal, resulting in the fracture callus failing to fully ossify or, in atrophic cases, not forming altogether. Fracture healing is regulated, in part, by the balance of proinflammatory and anti-inflammatory processes occurring within the bone marrow and surface cell populations. We sought to further understand the role of osteoimmunology (i.e., study of the close relationship between the immune system and bone) by examining immune cell gene expression via single-cell RNA sequencing of intramedullary canal tissue obtained from human patients with femoral nonunions. Intramedullary canal tissue samples obtained by reaming were collected at the time of surgical repair for femur fracture nonunion (n = 5) or from native bone controls when harvesting autologous bone graft (n = 4). Cells within the samples were isolated and analyzed using the Chromium Single-Cell System (10x Genomics Inc.) and Illumina sequencers. Twenty-three distinct cell clusters were identified, with higher cell proportions in the nonunion samples for monocytes and CD14 + dendritic cells (DCs), and lower proportions of T cells, myelocytes, and promyelocytes in nonunion samples. Gene expression differences were identified in each of the cell clusters from cell types associated with osteoimmunology, including CD14 + DC, monocytes, T cells, promyelocytes, and myelocytes. These results provide human-derived gene profiles that can further our understanding of pathways that may be a cause or a consequence of nonunion, providing the clinical rationale to focus on specific components of osteoimmunology. Clinical significance: The novel single-cell approach may lead to clinically relevant diagnostic biomarkers during earlier stages of nonunion development and/or investigation into therapeutic options.

The Complement System: A Potential Therapeutic Target in Liver Cancer

Liver cancer is the sixth most common cancer and the fourth most fatal cancer in the world. Immunotherapy has already achieved modest results in the treatment of liver cancer. Meanwhile, the novel and optimal combinatorial strategies need further research. The complement system, which consists of mediators, receptors, cofactors and regulators, acts as the connection between innate and adaptive immunity. Recent studies demonstrate that complement system can influence tumor progression by regulating the tumor microenvironment, tumor cells, and cancer stem cells in liver cancer. Our review concentrates on the potential role of the complement system in cancer treatment, which is a promising strategy for killing tumor cells by the activation of complement components. Conclusions: Our review demonstrates that complement components and regulators might function as biomarkers and therapeutic targets for liver cancer diagnosis and treatment.

Evaluating the clinical utility of measuring levels of factor H and the related proteins

After years of disappointing clinical results, the tide has finally changed and complement targeted-therapies have become a validated and accepted treatment option for several diseases. These accomplishments have revitalized the field and brought renewed attention to the prospects that complement therapeutics can offer. Streamlining diagnostics and therapeutics is imperative in this new era of clinical use of complement therapeutics. However, the incredible success in therapeutics has not been accompanied by the development of novel standardized tools for complement testing. Complement biomarkers can assist in the risk assessment and diagnosis of diseases as well as the prediction of disease progression and treatment response. Recently, a group of complement proteins has been suggested to be highly relevant in various complement-associated disorders, namely the human factor H (FH) protein family. This family of closely related proteins consists of FH, FH-like protein 1, and five factor H-related proteins, and they have been linked to eye, kidney, infectious, vascular, and autoimmune diseases as well as cancer. The goal of this review is to provide a comprehensive overview of the available data on circulating levels of FH and its related proteins in different pathologies. In addition, we examined the current literature to determine the clinical utility of measuring levels of the FH protein family in health and disease. Finally, we discuss future steps that are needed to make their clinical translation a reality.

Complement system-related genes in stomach adenocarcinoma: Prognostic signature, immune landscape, and drug resistance

Stomach adenocarcinoma (STAD) is one of the most common malignant tumors of the digestive tract, and its survival predictors are critical for precision medicine but have not been fully investigated. The complement system is a complex multistep cascade at the interface of innate and adaptive immunity, which augments the function of antibodies and phagocytes. This study aimed to construct and validate a CSRG signature based on TCGA (The Cancer Genome Atlas) STAD dataset and revalidated it in an external GEO (Gene Expression Omnibus) STAD cohort. Subsequently, we assessed the association of risk levels with the stromal and immune cell infiltration level in STAD using the ESTIMATE, single-sample Gene Set Enrichment Analysis (ssGSEA), and Microenvironment Cell Populations-counter (MCP-counter) algorithm. It was found that the CSRG signature, based on three genes (SERPINE1, PROC, and CFHR3), was significantly and independently associated with the OS in TCGA STAD patients (p &lt; 0.001). Subsequently, we found that the high-risk STAD harbors more immune cell infiltration than the low-risk group, and the ESTIMATE results indicated that there exists a more stromal component in the tumor microenvironment of the high-risk groups. Compared to the low-risk group, the high-risk STAD patients had higher expressions of marker genes for immune checkpoint inhibitors (ICIs) and showed higher sensitivity to the chemotherapy agents (rapamycin, nilotinib, 5-fluorouracil, axitinib, DMOG, and JNK inhibitor VIII). The prognostic value of the CSRGs was further validated by nomogram plots, which revealed that it was superior to tumor TNM and pathologic stage. Finally, the three expression levels were evaluated in GES-1, HGC27, and AGS cells by qRT-PCR.

Discovery of functionally distinct anti-C7 monoclonal antibodies and stratification of anti-nicotinic AChR positive Myasthenia Gravis patients

Myasthenia Gravis (MG) is mediated by autoantibodies against acetylcholine receptors that cause loss of the receptors in the neuromuscular junction. Eculizumab, a C5-inhibitor, is the only approved treatment for MG that mechanistically addresses complement-mediated loss of nicotinic acetylcholine receptors. It is an expensive drug and was approved despite missing the primary efficacy endpoint in the Phase 3 REGAIN study. There are two observations to highlight. Firstly, further C5 inhibitors are in clinical development, but other terminal pathway proteins, such as C7, have been relatively understudied as therapeutic targets, despite the potential for lower and less frequent dosing. Secondly, given the known heterogenous mechanisms of action of autoantibodies in MG, effective patient stratification in the REGAIN trial may have provided more favorable efficacy readouts. We investigated C7 as a target and assessed the in vitro function, binding epitopes and mechanism of action of three mAbs against C7. We found the mAbs were human, cynomolgus monkey and/or rat cross-reactive and each had a distinct, novel mechanism of C7 inhibition. TPP1820 was effective in preventing experimental MG in rats in both prophylactic and therapeutic dosing regimens. To enable identification of MG patients that are likely to respond to C7 inhibition, we developed a patient stratification assay and showed in a small cohort of MG patients (n=19) that 63% had significant complement activation and C7-dependent loss of AChRs in this in vitro set up. This study provides validation of C7 as a target for treatment of MG and provides a means of identifying patients likely to respond to anti-C7 therapy based on complement-activating properties of patient autoantibodies.

Simultaneous C5 and CD14 inhibition limits inflammation and organ dysfunction in pig polytrauma

Dysfunctional complement activation and Toll-like receptor signaling immediately after trauma are associated with development of trauma-induced coagulopathy and multiple organ dysfunction syndrome. We assessed the efficacy of the combined inhibition therapy of complement factor C5 and the TLR co-receptor CD14 on thrombo-inflammation and organ damage in an exploratory 72-h polytrauma porcine model, conducted under standard surgical and intensive care management procedures. Twelve male pigs were subjected to polytrauma, followed by resuscitation (ATLS® guidelines) and operation of the femur fracture (intramedullary nailing technique). The pigs were allocated to combined C5 and CD14 inhibition therapy group (n=4) and control group (n=8). The therapy group received intravenously C5 inhibitor (RA101295) and anti-CD14 antibody (rMil2) 30 min post-trauma. Controls received saline. Combined C5 and CD14 inhibition reduced the blood levels of the terminal complement complex (TCC) by 70% (p=0.004), CRP by 28% (p=0.004), and IL-6 by 52% (p=0.048). The inhibition therapy prevented the platelet consumption by 18% and TAT formation by 77% (p=0.008). Moreover, the norepinephrine requirements in the treated group were reduced by 88%. The inhibition therapy limited the organ damage, thereby reducing the blood lipase values by 50% (p=0.028), LDH by 30% (p=0.004), AST by 33%, and NGAL by 30%. Immunofluorescent analysis of the lung tissue revealed C5b-9 deposition on blood vessels in five from the untreated, and in none of the treated animals. In kidney and liver, the C5b-9 deposition was similarly detected mainly the untreated as compared to the treated animals. Combined C5 and CD14 inhibition limited the inflammatory response, the organ damage, and reduced the catecholamine requirements after experimental polytrauma and might be a promising therapeutic approach.

Pharmacological targeting of microglia dynamics in Alzheimer's disease: Preclinical and clinical evidence

Numerous clinical trials of anti-amyloid agents for Alzheimer's disease (AD) were so far unsuccessful thereby challenging the validity of the amyloid hypothesis. This lack of progress has encouraged researchers to investigate alternative mechanisms in non-neuronal cells, among which microglia represent nowadays an attractive target. Microglia play a key role in the developing brain and contribute to synaptic remodeling in the mature brain. On the other hand, the intimate relationship between microglia and synapses led to the so-called synaptic stripping hypothesis, a process in which microglia selectively remove synapses from injured neurons. Synaptic stripping, along with the induction of a microglia-mediated chronic neuroinflammatory environment, promote the progressive synaptic degeneration in AD. Therefore, targeting microglia may pave the way for a new disease modifying approach. This review provides an overview of the pathophysiological roles of the microglia cells in AD and describes putative targets for pharmacological intervention. It also provides evidence for microglia-targeted strategies in preclinical AD studies and in early clinical trials.