Search

Spatially heterogeneous synapse loss is a characteristic of many psychiatric and neurological disorders, but the underlying mechanisms are unclear. Here, we show that spatially-restricted complement activation mediates stress-induced heterogeneous microglia activation and synapse loss localized to the upper layers of the medial prefrontal cortex (mPFC) in male mice. Single cell RNA sequencing also reveals a stress-associated microglia state marked by high expression of the apolipoprotein E gene (Apoehigh) localized to the upper layers of the mPFC. Mice lacking complement component C3 are protected from stress-induced layer-specific synapse loss, and the Apoehigh microglia population is markedly reduced in the mPFC of these mice. Furthermore, C3 knockout mice are also resilient to stress-induced anhedonia and working memory behavioral deficits. Our findings suggest that region-specific complement and microglia activation can contribute to the disease-specific spatially restricted patterns of synapse loss and clinical symptoms found in many brain diseases. Synapse loss is central to the pathogenesis of stress-related disorders. Here, the authors show that targeted synapse removal by microglia and complement during stress contributes to the effects of stress on behavior. [ABSTRACT FROM AUTHOR]

Proteasome inhibitors (PIs) are crucial in treating multiple myeloma but carry a risk of thrombotic microangiopathy (TMA), especially with carfilzomib use. This systematic review includes 44 studies with 115 cases of PI-induced TMA, where carfilzomib was implicated in 101 cases. Treatment approaches varied: 28 patients received supportive care, 43 underwent therapeutic plasma exchange (TPE), 9 were treated exclusively with eculizumab (ECU), and 13 received both TPE and ECU. Notably, eculizumab significantly improved outcomes for patients unresponsive to initial TPE, achieving complete remission in seven cases. The need for dialysis emerged as a significant predictor of outcomes, often indicating a poor prognosis. For patients suspected of having PI-TMA, it is advisable to discontinue the offending medication promptly, even without definitive laboratory confirmation. In cases where diagnosis is challenging, kidney biopsy may assist if conditions permit. Comprehensive evaluation of the complement system, including genetic mutations, function, and associated complement inhibitory factor antibodies, should be included in the assessment of PI-TMA. Early administration of eculizumab may be beneficial in cases of suspected complement abnormalities or suboptimal response to initial treatments. Highlights: This review systematically addresses for the first time the clinical manifestations, treatments, and prognostic outcomes associated with PI-related TMA. Based on existing research, it is proposed that activation of the complement pathway may be the underlying mechanism of PI-TMA, with further elaboration provided. A comprehensive management model for PI-TMA has been proposed. [ABSTRACT FROM AUTHOR]

Selective inhibition of the transcription elongation factor (P‐TEFb) complex represents a promising approach in cancer therapy, yet CDK9 inhibitors (CDK9i) are currently limited primarily to certain hematological malignancies. Herein, while initial responses to CDK9‐targeted therapies are observed in vitro across various KRAS‐mutant cancer types, their efficacy is far from satisfactory in nude mouse xenograft models. Mechanistically, CDK9 inhibition leads to compensatory activation of ERK‐MYC signaling, accompanied by the recovery of proto‐oncogenes, upregulation of immediate early genes (IEGs), stimulation of the complement C1r‐C3‐C3a cascade, and induction of tumor immunosuppression. The "paradoxical" regulation of PP2Ac activity involving the CDK9/Src interplay contributes to ERK phosphorylation and pause‐release of RNA polymerase II (Pol II). Co‐targeting of CDK9 and KRAS/MAPK signaling pathways eliminates ERK‐MYC activation and prevents feedback activation mediated by receptor tyrosine kinases, leading to more effective control of KRAS‐mutant cancers and overcoming KRASi resistance. Moreover, modulating the tumor microenvironment (TME) by complement system intervention enhances the response to CDK9i and potently suppresses tumor growth. Overall, the preclinical investigations establish a robust framework for conducting clinical trials employing KRASi/SOS1i/MEKi or immunomodifiers in combination with CDK9i to simultaneously target cancer cells and their crosstalk with the TME, thereby yielding improved responses in KRAS‐mutant patients. [ABSTRACT FROM AUTHOR]

The complement cascade is an ancient and highly conserved arm of the immune system. The accumulating evidence highlights elevated activity of the complement cascade in cancer microenvironment and emphasizes its effects on the immune, cancer, and cancer stroma cells, pointing to a role in inflammation-mediated etiology of neoplasms. The role the cascade plays in development, progression, and relapse of solid tumors is increasingly recognized, however its role in hematological malignancies, especially those of myeloid origin, has not been thoroughly assessed and remains obscure. As the role of inflammation and autoimmunity in development of myeloid malignancies is becoming recognized, in this review we focus on summarizing the links that have been identified so far for complement cascade involvement in the pathobiology of myeloid malignancies. Complement deficiencies are primary immunodeficiencies that cause an array of clinical outcomes including an increased risk of a range of infectious as well as local or systemic inflammatory and thrombotic conditions. Here, we discuss the impact that deficiencies in complement cascade initiators, mid- and terminal-components and inhibitors have on the biology of myeloid neoplasms. The emergent conclusions indicate that the links between complement cascade, inflammatory signaling, and the homeostasis of hematopoietic system exist, and efforts should continue to detail the mechanistic involvement of complement cascade in the development and progression of myeloid cancers. [ABSTRACT FROM AUTHOR]

Schistosomiasis-induced pulmonary hypertension (PH) presents a significant global health burden, yet the underlying mechanisms remain poorly understood. Here, we investigate the involvement of platelets and the complement system in the initiation events leading to Schistosoma-induced PH. We demonstrate that Schistosoma exposure leads to thrombocytopenia, platelet accumulation in the lung, and platelet activation. In addition, we observed increased plasma complement anaphylatoxins C3a and C5a, indicative of complement system activation, and elevated platelet expression of C1q, C3, decay activating factor (DAF), and complement C3a and C5a receptors. Our findings suggest the active involvement of platelets in responding to complement system signals induced by Schistosoma exposure and form the basis for future mechanistic studies on how complement may regulate platelet activation and promote the development of Schistosoma-induced PH. NEW & NOTEWORTHY: Schistosomiasis-induced pulmonary hypertension (PH) is a significant global health burden, yet the underlying mechanisms remain poorly understood. We demonstrate that Schistosoma exposure leads to platelet accumulation in the lung and platelet activation. We observed increased plasma levels of C3a and C5a, indicative of complement system activation, and elevated expression of platelet complement proteins and receptors. These findings underscore the role of platelets and complement in the inflammatory responses associated with Schistosoma-induced PH. [ABSTRACT FROM AUTHOR]

The precise molecular processes underlying the complement's activation, which follows exposure to physical stress still remain to be fully elucidated. However, some possible mechanisms could play a role in initiating changes in the complement's activity, which are observed post-exposure to physical stress stimuli. These are mainly based on metabolic shifts that occur in the microenvironment of muscle tissue while performing its function with increased intensity, as well as the adipose tissue's role in sterile inflammation and adipokine secretion. This review aims to discuss the current opinions on the possible link between the complement activation and diet, age, sex, and health disorders with a particular emphasis on endocrinopathies and, furthermore, the type of physical activity and overall physical fitness. It has been indicated that regular physical activity incorporated into therapeutic strategies potentially improves the management of particular diseases, such as, e.g., autoimmune conditions. Moreover, it represents a favorable influence on immunoaging processes. A better understanding of the complement system's interaction with physical activity will support established clinical therapies targeting complement components. [ABSTRACT FROM AUTHOR]

Antibodies that trigger the complement system play a pivotal role in the immune defense against pathogenic bacteria and offer potential therapeutic avenues for combating antibiotic‐resistant bacterial infections, a rising global concern. To gain a deeper understanding of the key parameters regulating complement activation by monoclonal antibodies, we developed a novel bioassay for quantifying classical complement activation at the monoclonal antibody level, and employed this assay to characterize rare complement‐activating antibacterial antibodies on the single‐antibody level in postimmunization murine antibody repertoires. We characterized monoclonal antibodies from various antibody isotypes against specific pathogenic bacteria (Bordetella pertussis and Neisseria meningitidis) to broaden the scope of our findings. We demonstrated activation of the classical pathway by individual IgM‐ and IgG‐secreting cells, that is, monoclonal IgM and IgG2a/2b/3 subclasses. Additionally, we could observe different epitope density requirements for efficient C1q binding depending on antibody isotype, which is in agreement with previously proposed molecular mechanisms. In short, we found that antibody density most crucially regulated C1q recruitment by monoclonal IgG isotypes, but not IgM isotypes. This study provides additional insights into important parameters for classical complement initiation by monoclonal antibodies, a knowledge that might inform antibody screening and vaccination efforts. [ABSTRACT FROM AUTHOR]

Infections are one of the most significant healthcare and economic burdens across the world as underscored by the recent coronavirus pandemic. Moreover, with the increasing incidence of antimicrobial resistance, there is an urgent need to better understand host–pathogen interactions to design effective treatment strategies. The complement system is a key arsenal of the host defense response to pathogens and bridges both innate and adaptive immunity. However, in the contest between pathogens and host defense mechanisms, the host is not always victorious. Pathogens have evolved several approaches, including co‐opting the host complement regulators to evade complement‐mediated killing. Furthermore, deficiencies in the complement proteins, both genetic and therapeutic, can lead to an inefficient complement‐mediated pathogen eradication, rendering the host more susceptible to certain infections. On the other hand, overwhelming infection can provoke fulminant complement activation with uncontrolled inflammation and potentially fatal tissue and organ damage. This review presents an overview of critical aspects of the complement‐pathogen interactions during infection and discusses perspectives on designing therapies to mitigate complement dysfunction and limit tissue injury. [ABSTRACT FROM AUTHOR]

We describe initial, current, and future aspects of complement activation and inhibition in the rare hematological disease paroxysmal nocturnal hemoglobinuria (PNH). PNH is a rare but severe hematological disorder characterized by complement‐mediated intravascular hemolysis resulting in anemia and severe thrombosis. Insights into the complement‐mediated pathophysiology ultimately led to regulatory approval of the first‐in‐class complement inhibitor, eculizumab, in 2007. This anti‐complement C5 therapy resulted in the stabilization of many hematologic parameters and dramatically reduced the often fatal, coagulant‐resistant thrombotic events. Despite the remarkable clinical success, a substantial proportion of PNH patients experience suboptimal clinical responses during anti‐C5 therapy. We describe the identification and mechanistic dissection of four unexpected processes responsible for such suboptimal clinical responses: (1) pharmacokinetic and (2) pharmacodynamic intravascular breakthrough hemolysis, (3) continuing low‐level residual intravascular hemolysis, and (4) extravascular hemolysis. Novel complement therapeutics mainly targeting different complement proteins proximal in the cascade attempt to address these remaining problems. With five approved complement inhibitors in the clinic and many more being evaluated in clinical trials, PNH remains one of the complement diseases with the highest intensity of clinical research. Mechanistically unexpected breakthrough events occur not only with C5 inhibitors but also with proximal pathway inhibitors, which require further mechanistic elaboration. [ABSTRACT FROM AUTHOR]

Systemic lupus erythematosus (SLE) is marked by excessive complement activation, contributing to tissue damage. Complement activation can be detected in many organs including the skin, kidney, and brain. The involvement of the central nervous system is particularly relevant to understanding neuropsychiatric SLE (NPSLE), one of the poorest understood manifestations of SLE for which no biomarkers are available. We studied the levels of complement inhibitors in SLE in relation to disease activity and as possible biomarkers to identify NPSLE. Serum levels of complement inhibitors C1‐inhibitor (C1‐INH), C4b‐binding protein (C4BP), Factor I, and Factor H were measured in 345 SLE patients (including 102 with NPSLE) and 108 healthy controls. Compared with controls, SLE patients had higher C1‐INH and C4BP but lower Factor I and H levels. All inhibitors positively correlated with total C3 and C4 levels. While correlating with the SLE Disease Activity Index (SLEDAI), no distinction in inhibitor levels was found between SLE and NPSLE patients. Over time, C1‐INH and Factor H levels normalized, but no significant changes were observed for C4BP and Factor I. In SLE the levels of circulating complement inhibitors are inversely correlated to complement consumption but do not serve as biomarkers for NPSLE. [ABSTRACT FROM AUTHOR]

The complement system is a set of over 50 proteins that constitutes an essential part of the innate immune system. Complement system activation involves an organized proteolytic cascade. Overactivation of complement system activation is the main pathogenic mechanism of several diseases and contributes to the manifestations of many other conditions. This review describes the normal complement system and the role for complement dysregulation in critical illnesses, notably sepsis and acute respiratory distress syndrome. Complement activation is involved in the immune system response to pathogens but, when excessive, can contribute to tissue damage, runaway inflammation, and capillary leakage syndrome. Complement overactivation may play a key role in severe forms of coronavirus disease 2019 (COVID-19). Two diseases whose manifestations are mainly caused by complement overactivation, namely, atypical hemolytic and uremic syndrome (aHUS) and myasthenia gravis, are discussed. A diagnostic algorithm for aHUS is provided. Early complement-inhibiting therapy has been proven effective. When renal transplantation is required, complement-inhibiting drugs can be used prophylactically to prevent aHUS recurrence. Similarly, acetylcholine-receptor autoantibody-positive generalized myasthenia gravis involves complement system overactivation and responds to complement inhibition. The two main complement inhibitors used in to date routine are eculizumab and ravulizumab. The main adverse event is Neisseria infection, which is rare and preventable, but can be fatal. The complement system is crucial to health but, when overactivated, can cause or contribute to disease. Effective complement inhibitors are now available, although additional data are required to determine optimal regimens. Further research is also needed to better understand the complement system, develop advanced diagnostic tools, and identify markers that allow the personalization of treatment strategies. [ABSTRACT FROM AUTHOR]

Purpose: To study the role of the complement system's C3 and C4 fractions in the pathogenesis of different types of uveitis. Methods: A prospective case-control study. 118 patients were enrolled. The control group comprised 60 patients who were otherwise healthy people undergoing cataract or pterygium surgery, whereas the uveitis patients group consisted of 58 people. The levels of C3 and C4 fractions in the blood and in the aqueous humor for both groups were evaluated and compared. Results: No statistically significant differences were found in the levels of the C3 and C4 fractions in the blood between the groups. However, a statistically significant difference was observed in the levels of C3 and C4 in the aqueous humor between the case and control groups, as C3 and C4 fractions were not detected in the control group. The analysis of the mean gradient between the C4 levels in the blood samples and in the aqueous samples did not reveal a statistically significant difference between the case and control groups. However, upon performing an analogous mean gradient analysis of C3 levels, a statistically significant elevation in the value of the mean gradient was observed in the case group as compared to the control group. Conclusion: Our findings are in line with our initial hypothesis, that the complement system's C3 and C4 fractions may have a role in the pathogenesis of uveitis. [ABSTRACT FROM AUTHOR]

The common carp is one of the most economically valuable freshwater fish worldwide and its aquaculture can be severely affected by the koi sleepy disease (KSD)/carp edema virus disease (CEVD). This study explores a natural outbreak of CEVD in a pond containing both clinically healthy and diseased fish of various origins exposed to the virus. We investigated mRNA expression of genes associated with known antiviral immune mechanisms, such as type I interferon signalling and cell‐mediated cytotoxicity, and performed a comprehensive protein expression analysis to highlight differences between the two groups in various organs. Significant differences in expression profiles of common carp with and without clinical signs were found to be strongly dependent on the organ from which the sample originated. Components of the complement cascade, including various C3 proteins, exhibited upregulation only in less affected organs, specifically the head kidney and spleen. Other complement proteins such as B/C2 and C9 showed upregulation in the kidney, spleen, and gills but not in the skin. Conversely, lysozymes C and G, were observed to be upregulated in the most affected organs of the skin and gills. This study submits the first description of the immune system related proteome using a mass spectrometry on the samples isolated from fish infected with CEV. It also offers a unique comparison of immune reaction of CEV infected and healthy fish under an infectious pressure. [ABSTRACT FROM AUTHOR]

Objective. The complement system has been associated with the etiopathogenesis of rheumatoid arthritis (RA). Insulin resistance (IR) and metabolic syndrome (MetS) are prevalent among patients with RA. The aim of this study was to explore the relationship between a comprehensive evaluation of the complement system and IR, as well as MetS, in patients with RA. Methods. A total of 339 nondiabetic patients with RA were recruited. Functional assays of the 3 complement pathways were assessed. Additionally, serum levels of the following individual components of the complement system were measured: C1q (classical); lectin (lectin); C2, C4, and C4b (classical lectin); factor D and properdin (alternative); C3 and C3a (common); C5, C5a, and C9 (terminal); as well as the factor I and C1 inhibitor regulators. IR and β cell function indices were calculated using the homeostatic model assessment. Criteria for MetS were applied. Multivariable linear regression analysis was performed to investigate the association between the complement system and IR in patients with RA. Results. Many elements of the upstream and common complement pathways, but not the functional tests of the 3 routes, correlated positively with higher levels of IR and β cell function. However, after multivariable adjustment for factors associated with IR, these relationships were lost. Conversely, the presence of MetS in patients with RA maintained a relationship with higher levels of C1q, C4, C3, properdin, and factor I after adjusting for confounders. Conclusion. There is a positive correlation between the complement system and MetS among nondiabetic patients with RA. This association is independent of traditional IR factors. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) are metabolic by-products that constitute an indispensable component of physiological processes, albeit their heightened presence may proffer substantial perils to biological entities. Such a proliferation gives rise to a gradual escalation of oxidative stress within the organism, thereby compromising mitochondrial functionality and inflicting harm upon various bodily systems, with a particular predilection for the central nervous system. In its nascent stages, it is plausible that inflammation has been a facilitator in the progression of the malady. The precise role of inflammation in Alzheimer's disease (AD) remains somewhat enigmatic, although it is conceivable that activated microglia and astrocytes might be implicated in the removal of amyloid-β (Aβ) deposits. Nonetheless, prolonged microglial activation is associated with Tau phosphorylation and Aβ aggregation. Research studies have indicated that AD brains upregulate complementary molecules, inflammatory cytokines, acute phase reacting agents, and other inflammatory mediators that may cause neurodegeneration. In this review, oxidative damage products will be discussed as potential peripheral biomarkers for AD and its early stages. The disordered excretion of pro-inflammatory cytokines, chemokines, oxygen, and nitrogen-reactive species, along with the stimulation of the complement system by glial cells, has the potential to disrupt the functionality of neuronal termini. This perturbation, in turn, culminates in compromised synaptic function, a phenomenon empirically linked to the manifestation of cognitive impairments. The management of neurodegenerative conditions in the context of dementia necessitates therapeutic interventions that specifically target the excessive production of inflammatory and oxidative agents. Furthermore, we shall deliberate upon the function of microglia and oxidative injury in the etiology of AD and the ensuing neurodegenerative processes. [ABSTRACT FROM AUTHOR]

Introduction: The role of complement system in late stage of IgA nephropathy (IgAN) remains unknown. We therefore investigated the effects of complement system on worsening kidney function in advanced (stage 4 CKD) IgAN. Methods: Renal specimens of 69 IgAN patients who underwent renal biopsy during stage 4 CKD between 2010 and 2021, were stained using immunofluorescence (IF) and immunohistochemistry (IHC) for glomerular complement components. The primary outcome was progression to end-stage renal disease (ESRD). Associations of complement components with baseline clinicopathological characteristics and outcomes were assessed using multivariable Cox regression and Spearman analyses. Results: During a median follow-up of 18.0 months, 26 (37.7%) patients progressed to ESRD and none died. C1q and C3 deposition were detected in 12 and 66 patients, respectively. Higher eGFR [hazards ratio (HR), 0.852, 95% confidence interval (CI), 0.756–0.959; P = 0.008], higher C3 intensity (HR, 2.955, 95%CI, 1.063–8.220; P = 0.038) and T1-2 score (HR, 2.576, 95%CI, 1.205–5.576, P = 0.015) were predictive of time to ESRD in CKD 4 stage IgAN. Significant expressions of C1q (P = 0.005), C4d (P < 0.001), factor B (P < 0.001), C3 (P = 0.042) and C5b-9 (P = 0.004) were identified in ESRD group than in non-ESRD group by IHC, while MBL expression was low. Although they were not associated with baseline 24 h-UP, higher factor B and C1q expressions were both correlated with a lower baseline eGFR (P < 0.001 and = 0.04, respectively) and the deterioration of kidney function during follow-up (P = 0.046 and 0.015, respectively). Conclusion: Complement deposition in IgAN patients with stage 4 CKD portends a faster deterioration of kidney function. Activation of classical and alternative complement pathways plays a major role in this stage. [ABSTRACT FROM AUTHOR]

Urate-lowering treatment (ULT) to target with xanthine oxidase inhibitors (XOIs) paradoxically causes early increase in gouty arthritis flares. Because delayed reduction in flare burden is mechanistically unclear, we tested for ULT inflammation responsiveness markers. Unbiased proteomics analyzed blood samples (baseline, 48 weeks ULT) in two, independent ULT out trial cohorts (n = 19, n = 30). STRING-db and multivariate analyses supplemented determinations of altered proteins via Wilcoxon matched pairs signed rank testing in XOI ULT responders. Mechanistic studies characterized proteomes of cultured XOI-treated murine bone marrow macrophages (BMDMs). At 48 weeks ULT, serum urate normalized in all gout patients, and flares declined in association with significantly altered proteins (p < 0.05) in clustering and proteome networks in sera and peripheral blood mononuclear cells. Sera demonstrated altered complement activation and regulatory gene ontology biologic processes. In both cohorts, a treatment-emergent serum interactome included key gouty inflammation mediators (C5, IL-1B, CXCL8, IL6). Last, febuxostat treatment decreased complement activation biologic process proteins in cultured BMDMs. Reduced gout flares are linked with a XOI treatment-emergent serum protein interactome that includes inflammation regulators, associated with altered complement activation and regulatory biologic processes. Serum and leukocyte proteomics could help identify when gouty inflammatory processes begin to subside in response to ULT. Trial Registration: ClinicalTrials.gov Identifier NCT02579096, posted October 19, 2015. [ABSTRACT FROM AUTHOR]

In patients with major depressive disorder, various functional areas are impaired, negatively impacting the quality of life. Remission can restore pre-depression functions; however, some patients may still have residual impairments. Distinguishing between near-normal recovery and residual impairment helps identify those at a high risk of relapse risk and helps tailor treatment. Accordingly, we aimed to discover and validate biomarkers that distinguish between near-normal recovery and residual impairment in remission states through serum proteome analysis. Pooled serum and individual serum samples from three groups (depression status, remission status with residual impairment, and remission status with normal recovery) were analyzed using liquid chromatography-tandem mass spectrometry. The combination of four proteins—antithrombin-III, serum amyloid A4 protein, C1q subcomponent subunit B, and serum amyloid P-component—was selected as a candidate biomarker. The trend of protein changes suggests complement C1q subcomponent subunit B and serum amyloid P-component as potential biomarkers for distinguishing remission from residual impairment. Changes in complement C1q subcomponent subunit B and serum amyloid P-component suggest that the complement system and inflammation-related immune mechanisms are associated with residual impairment in remittent major depressive disorder. [ABSTRACT FROM AUTHOR]

Extracorporeal membrane oxygenation (ECMO) provides critical support for patients with severe cardiopulmonary dysfunction. Unfractionated heparin (UFH) is used for anticoagulation to maintain circuit patency and avoid thrombotic complications, but it increases the risk of bleeding. Extracellular vesicles (EVs), nano-sized subcellular spheres with potential pro-coagulant properties, are released during cellular stress and may serve as potential targets for monitoring anticoagulation, particularly in thromboinflammation. We investigated the impact of UFH dose during ECMO therapy at the coagulation–inflammation interface level, focusing on complement activation and changes in circulating large EV (lEV) subsets. In a post hoc analysis of a multicenter randomized controlled trial comparing two anticoagulation management algorithms, we examined lEV levels and complement activation in 23 veno-venous-ECMO patients stratified by UFH dose. Blood samples were collected at different time points and grouped into three phases of ECMO therapy: initiation (day 1), mid (days 3–4), and late (days 6–7). Immunoassays detected complement activation, and flow cytometry analyzed lEV populations with an emphasis on mitochondria-carrying subsets. Patients receiving <15 IU/kg/h UFH exhibited higher levels of the complement activation product C5a and soluble terminal complement complex (sC5b-9). Lower UFH doses were linked to increased endothelial-derived lEVs, while higher doses were associated with elevated RBC-derived and mitochondria-positive lEVs. Our findings suggest the potential theranostic relevance of EV detection at the coagulation–inflammation interface. Further research is needed to standardize EV detection methods and validate these findings in larger ECMO patient cohorts. [ABSTRACT FROM AUTHOR]

Chronic antibody-mediated rejection in kidney transplantation is a common cause of graft loss in the late post-transplant period. In this process, the role of the classical complement activation pathway is crucial due to the formation of immune complexes between donor-specific antibodies (DSAs) and donor antigens and the attachment of the C1q complement fragment. This study aimed to determine the levels of circulating C1q immunocomplexes (CIC-C1q) and complement activation (CH50), in sensitized kidney transplant recipients (KTRs). In this cross-sectional study we used serum samples from KTRs with de novo or preformed DSAs (n = 14), KTRs without DSAs (n = 28), and 22 subjects with no history of chronic kidney disease (controls). C1q immunocomplexes and CH50 concentration in serum were measured with the enzyme immunoassay (EIA) kit MicroVue CIC-C1q (Quidel, Athens, OH, USA) and EIA kit MicroVue CH50 (Quidel, OH, USA), respectively. Higher concentrations of CIC-C1q was observed in KTRs with DSAs in comparison with controls and with KTRs with no DSAs (6.8 ± 2.7 and 4.8 ± 1.9 vs. 5.0 ± 1.2 μg Eq/mL, respectively, p < 0.01). We found no difference in CIC-C1q between KTRs with no DSAs and controls. CIC-C1q levels were positively correlated with DSA titer. CH50 levels were decreased in KTRs with DSAs in comparison with controls and KTRs with no DSAs (39 ± 15 vs. 68 ± 40 and 71 ± 34 U Eq/mL, respectively, p < 0.01). There was no difference in CH50 between DSA-negative KTRs and controls. Kidney transplant recipients with DSAs had increased serum levels of C1q immunocomplexes and increased classical pathway complement activation. [ABSTRACT FROM AUTHOR]

Background Borna disease virus 1 (BoDV-1) causes rare but severe zoonotic infections in humans, presenting as encephalitis. The case-fatality risk is very high and no effective countermeasures have been established so far. An immunopathology is presumed, while data on immune responses in humans are limited. Evidence of a role of the complement system in various neurological disorders and in viral infections of the central nervous system is increasing and specific inhibitors are available as therapeutic options. Methods In this study, we investigated factors of the complement system in the cerebrospinal fluid (CSF) of patients with BoDV-1 infections (n = 17) in comparison to noninflammatory control CSF samples (n = 11), using a bead-based multiplex assay. In addition, immunohistochemistry was performed using postmortem brain tissue samples. Results We found an intrathecal elevation of complement factors of all complement pathways and an active cascade during human BoDV-1 infections. The increase of certain complement factors such as C1q was persistent, and C3 complement deposits were detected in postmortem brain sections. Intrathecal complement levels were negatively correlated with survival. Conclusions Further investigations are warranted to clarify whether targeting the complement cascade by specific inhibitors might be beneficial for patients suffering from severe BoDV-1 encephalitis. [ABSTRACT FROM AUTHOR]

Gaucher disease (GD) is the most common lysosomal storage disease. It is a multisystemic metabolic disease caused by GBA pathogenic mutations. Although the general symptoms have been known for a long time, new treatment possibilities, the detection of different biomarkers, and innovations in diagnosis and follow‐up have paved the way for further studies. Recent studies have shown that the immune system has become an essential factor associated with disease progression. The role of Gaucher cells in the disease is well characterized. In addition to phagocytic macrophage cells, lymphocytes, complement system, and inflammatory pathway elements are also implicated in GD as they were shown to be the underlying factors causing associated pathologies such as Parkinson's. In this article, the relationship between the GD and the immune system has been examined and reviewed in light of new findings. [ABSTRACT FROM AUTHOR]

C4d is the end degradation product of activated complement component C4b that appears during the early steps of the classical and lectin complement pathways. Within the primary sequence of C4d, there is a reactive thioester group that binds covalently to nearby surfaces, thus labeling the locations of complement activation. This feature makes C4d a target for immunohistochemical staining aimed to aid the diagnosis of, among others, the antibody-mediated rejection of transplanted organs, membranous glomerulonephritis, bullous pemphigoid, or inflammatory myopathies. However, the credibility of C4d immunostaining is debatable, as a high background in surrounding tissues and body fluids and diffused patterns of deposits in target structures are experienced with some of the available anti-C4d antibodies. Herein, we present an improved version of a rabbit anti-C4d antibody, originally raised against the C-terminal linear neoepitope of this complement fragment. Minor cross-reactivity with C4b and native C4 proteins, measured by ELISAs, as well as relatively low concentrations necessary for obtaining a specific signal in immunohistochemical analyses of formalin-fixed paraffin-embedded material, makes the improved antibody superior to commercially available rabbit monoclonal anti-C4d antibody SP91 dedicated to ex vivo diagnostics, as demonstrated by the staining of a panel of kidney transplant biopsies. [ABSTRACT FROM AUTHOR]

Multiple Sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system (CNS) and is termed as one of the most common causes of neurological disability in young adults. Axonal loss and neuronal cell damage are the primary causes of disease progression and disability. Yet, little is known about the mechanism of neurodegeneration in the disease, a limitation that impairs the development of more effective treatments for progressive MS. MS is characterized by the presence of oligoclonal bands and raised levels of immunoglobulins in the CNS. The role of complement in the demyelinating process has been detected in both experimental animal models of MS and within the CNS of affected MS patients. Furthermore, both IgG antibodies and complement activation can be detected in the demyelinating plaques and cortical gray matter lesions. We propose here that both immunoglobulins and complement play an active role in the neurodegenerative process of MS. We hypothesize that the increased CNS IgG antibodies form IgG aggregates and bind complement C1q with high affinity, activating the classical complement pathway. This results in neuronal cell damage, which leads to neurodegeneration and demyelination in MS. [ABSTRACT FROM AUTHOR]

Hereditary angioedema is a rare, genetic disorder characterized by painful, debilitating and potentially life-threatening angioedema attacks in subcutaneous and submucosal tissue. While usually unpredictable, attacks can be provoked by a variety of triggers including physical injury and certain medication and are often preceded by prodromal symptoms. Hereditary angioedema has a profound influence on the patients' lives. The fundamental cause of hereditary angioedema in almost all patients is a mutation in the SERPING1 gene leading to a deficiency in C1-inhibitor. Subsequently, the contact activation cascade and kallikrein-kinin pathway are insufficiently inhibited, resulting in excessive bradykinin production triggering vascular leakage. While C1-inhibitor is an important regulator of the intrinsic coagulation pathway, fibrinolytic system and complement cascade, patients do not have an increased risk of coagulopathy, autoimmune conditions or immunodeficiency disorders. Hereditary angioedema is diagnosed based on C1-inhibitor level and function. Genetic analysis is only required in rare cases where hereditary angioedema with normal C1-inhibitor is found. In recent years, new, highly specific therapies have greatly improved disease control and angioedema-related quality of life. This article reviews the clinical picture of hereditary angioedema, the underlying pathophysiology, diagnostic process and currently available as well as investigational therapeutic options. [ABSTRACT FROM AUTHOR]

Multiple myeloma (MM) is an incurable cancer in the bone marrow. The treatment of MM has developed significantly during the last 20 years, which has resulted in increased survival. Daratumumab is the first CD38 antibody approved for the treatment of MM. It has improved the treatment of MM even further. This is an evaluation of the modes of action of daratumumab and a description of the development of resistance with a focus on inhibitory checkpoint receptors on CD8+ T‐cells, complement activation and extracellular vesicles. [ABSTRACT FROM AUTHOR]

Background: Humoral bactericidal activity was first recognized nearly a century ago. However, the extent of inter-individual heterogeneity and the mechanisms underlying such heterogeneity beyond antibody or complement systems have not been well studied. Methods: The plasma bactericidal activity of five healthy volunteers were tested against 30 strains of Gram-negative uropathogens, Klebsiella pneumoniae and Escherichia coli, associated with bloodstream infections. IgG and IgM titers specific to K. pneumoniae strains KP13883 and KPB1 were measured by ELISA, and complement inhibitor was used to measure the contribution of complementinduced killing. Furthermore, MALDI-TOF mass spectrometry was conducted to determine the metabolomic components of plasma with bactericidal properties in 25 healthy individuals using Bayesian inference of Pearson correlation between peak intensity and colony counts of surviving bacteria. Results: Plasma bactericidal activity varied widely between individuals against various bacterial strains. While individual plasma with higher IgM titers specific to K. pneumoniae strain KP13883 showed more efficient killing of the strain, both IgM and IgG titers for K. pneumoniae strain KPB1 did not correlate well with the killing activity. Complement inhibition assays elucidated that the complement-mediated killing was not responsible for the inter-individual heterogeneity in either isolate. Subsequently, using MALDI-TOF mass spectrometry on plasmas of 25 healthy individuals, we identified several small molecules including gangliosides, pediocins, or saponins as candidates that showed negative correlation between peak intensities and colony forming units of the test bacteria. Conclusion: This is the first study to demonstrate the inter-individual heterogeneity of constitutive innate humoral bactericidal function quantitatively and that the heterogeneity can be independent of antibody or the complement system. [ABSTRACT FROM AUTHOR]

C-reactive protein (CRP) binds to phosphocholine (PCh)-containing substances and subsequently activates the complement system to eliminate the ligand. The PCh- binding function of CRP has been conserved throughout evolution from arthropods to humans. Human CRP, in its structurally altered conformation at acidic pH, also binds to amyloid-β (Aβ) and prevents the formation of Aβ fibrils. It is unknown whether the Aβ-binding function of CRP has also been evolutionarily conserved. The aim of this study was to determine whether CRP isolated from American horseshoe crab Limulus polyphemus was also anti-amyloidogenic and whether this function required structural alteration of Limulus CRP (Li-CRP). Two CRP species Li-CRP-I and Li-CRP-II were purified from hemolymph by employing PCh-affinity chromatography and phosphoethanolamine-affinity chromatography, respectively. Both Li-CRP-I and Li-CRP-II bound to immobilized Aβ at physiological pH. Unlike human CRP, Li-CRP did not require any changes in its overall structure to bind to Aβ. Both Li-CRP-I and Li-CRP-II bound to Aβ in the fluid phase also and prevented the fibrillation of Aβ. Additionally, ion-exchange chromatography of purified Li-CRP indicated that a variety of Li-CRP molecules of different subunit compositions were present in Limulus hemolymph, raising the possibility that the presence of various Li-CRP species in hemolymph facilitates the recognition of a range of proteins with differing amyloidogenicity. We conclude that the binding of CRP to Aβ is an ancient function of CRP. In invertebrates, the Aβ-binding function of CRP can protect the host from toxicity caused by amyloidogenic and pathogenic proteins. In humans, the Aβ-binding function of CRP can protect against inflammatory diseases in which the host proteins are ectopically deposited on either host cells or foreign cells in an inflammatory milieu since immobilized proteins may expose Aβ-like structures after deposition at places where they are not supposed to be. [ABSTRACT FROM AUTHOR]

The objective of this study was to analyze complement activation in antiphospholipid antibody (aPL)-positive patients without other systemic autoimmune rheumatic diseases, using C3/C4 and cell-bound complement activation products (CB-CAPs) (B-lymphocytes [BC4d], erythrocytes [EC4d], and platelets [PC4d]). Persistently aPL-positive patients with or without aPL- related clinical manifestations (thrombotic APS [TAPS], microvascular APS [MAPS], obstetric APS, thrombocytopenia [TP], and/or hemolytic anemia [HA]) were enrolled in a single center study. Blood and clinical data were collected at baseline; a subgroup of patients completed 6- or 12-month follow-up. At baseline, 4/31 (13%) patients had decreased C3/C4, while 7/29 (24%) had elevated BC4d, 11/33 (33%) EC4d, and 12/32 (38%) PC4d. Based on different aPL profiles, all patients with decreased C3/C4 or elevated BC4d, EC4d, and PC4d had triple aPL or isolated lupus anticoagulant positivity. Based on different aPL clinical phenotypes, the number of patients with strongly positive EC4d and PC4d were proportionally higher in those with MAPS/TP/HA, compared to TAPS or no APS. Compared to baseline, the frequencies of BC4d, EC4d, and PC4d positivity were not significantly different in the subgroup of patients during their 6- or 12-month follow-up. There was a weak correlation between C3/C4 and CB-CAPs, especially for PC4d. In summary, complement activation in aPL- positive patients varies based on aPL profiles and clinical phenotypes. Given the higher percentage of aPL-positive patients with abnormal CB-CAPs, compared to C3/C4, and the poor inverse correlation between CB-CAPs and C3/C4, our study generates the hypothesis that CB-CAPs have a role in assessing disease activity and thrombosis risk in aPL-positive patients. [ABSTRACT FROM AUTHOR]

In arthropods, hematophagy has arisen several times throughout evolution. This specialized feeding behavior offered a highly nutritious diet obtained during blood feeds. On the other hand, blood‐sucking arthropods must overcome problems brought on by blood intake and digestion. Host blood complement acts on the bite site and is still active after ingestion, so complement activation is a potential threat to the host's skin feeding environment and to the arthropod gut enterocytes. During evolution, blood‐sucking arthropods have selected, either in their saliva or gut, anticomplement molecules that inactivate host blood complement. This review presents an overview of the complement system and discusses the arthropod's salivary and gut anticomplement molecules studied to date, exploring their mechanism of action and other aspects related to the arthropod–host–pathogen interface. The possible therapeutic applications of arthropod's anticomplement molecules are also discussed. [ABSTRACT FROM AUTHOR]

Purpose: This review focuses on extensive macular atrophy with pseudodrusen-like appearance (EMAP), a recently described maculopathy presenting with pseudodrusen-like lesions and chorioretinal atrophy more pronounced in the vertical axis. Methods: Narrative review of the literature published until May 2024. Results: The early onset age of EMAP (50–55 years) and its distinctive natural history, which includes night blindness followed by severe vision loss, differentiate it from atrophic age-related macular degeneration (AMD). A clear pathogenesis has not been determined, but risk factors include female gender and complement system abnormalities (altered levels of C3 and CH50). Moreover, lifelong exposure to pesticides has been suggested as risk factor for direct neuronal degeneration involving rods and cones. In the early phase of the disease, reticular pseudodrusen-like lesions appear in the superior perifovea and tend to coalescence horizontally into a flat, continuous, reflective material localized between the retinal pigmented epithelium and Bruch's membrane. Over time, EMAP causes profound RPE and outer retinal atrophy in the macular area, with a recent classification reporting a 3-stages evolution pattern. Blue autofluorescence showed rapidly evolving atrophy with either hyperautofluorescent or isoautofluorescent borders. Significant similarities between the diffuse-trickling phenotype of geographic atrophy and EMAP have been reported. Macular neovascularization is a possible complication. Conclusion: EMAP is specific form of early-onset atrophic macular degeneration with rapid evolution and no treatment. Further studies are needed to assess the best management. Key messages: What is known • Extensive Macular Atrophy with Pseudodrusen (EMAP) is a rapidly-progressive macular atrophy developing in the fifth-decade and leading to legal blindness. • Typical characteristics at multimodal imaging are reticular pseudodrusen-like lesions starting at the superior perifovea and vertically-oriented macular atrophy. What is new • Dysregulated complement cascade and pesticide-related toxicity have been proposed as possible etiologies. • In the late stages of the disease 50% of EMAP patients were legally blind by US standards and, after 7 years on average, atrophy reaches the mid-periphery. [ABSTRACT FROM AUTHOR]

Head and neck cancer (HNC) is the seventh most common cancer globally, resulting in 440 000 deaths per year. While there have been advancements in chemoradiotherapy and surgery, relapse occurs in more than half of HNCs, and these patients have a median survival of 10 months and a 2‐year survival of < 20%. Only a subset of patients displays durable benefits from immunotherapies in metastatic and recurrent HNC, making it critical to understand the tumor microenvironment (TME) underpinning therapy responses in HNC. To recognize biological differences within the TME that may be predictive of immunotherapy response, we applied cutting‐edge geospatial whole‐transcriptome profiling (NanoString GeoMx Digital Spatial Profiler) and spatial proteomics profiling (Akoya PhenoCycler‐Fusion) on a tumor microarray consisting of 25 cores from 12 patients that included 4 immunotherapy‐unresponsive (8 cores) and 2 immunotherapy‐responsive patients (5 cores), as well as 6 immunotherapy naïve patients (12 cores). Through high‐plex, regional‐based transcriptomic mapping of the tumor and TME, pathways involved with the complement system and hypoxia were identified to be differentially expressed in patients who went on to experience a poor immunotherapy response. Single‐cell, targeted proteomic analysis found that immune cell infiltration of the cancer cell mass and interactions of CD8 T cells with tumor and other immune cells were associated with positive immunotherapy response. The relative abundance of specific tumor phenotypes and their interactions with various immune cells was identified to be different between response groups. This study demonstrates how spatial transcriptomics and proteomics can resolve novel alterations in the TME of HNC that may contribute to therapy sensitivity and resistance. [ABSTRACT FROM AUTHOR]

Malignant cells are part of a complex network within the tumor microenvironment, where their interaction with host cells and soluble mediators, including complement components, is pivotal. The complement system, known for its role in immune defense and homeostasis, exhibits a dual effect on cancer progression. This dichotomy arises from its antitumoral opsonophagocytosis and cytotoxicity versus its protumoral chronic inflammation mediated by the C5a/C5aR1 axis, influencing antitumor T‐cell responses. Recent studies have revealed distinct co‐expression patterns of complement genes in various cancer types, correlating with prognosis. Notably, some cancers exhibit co‐regulated overexpression of complement genes associated with poor prognosis, while others show favorable outcomes. However, significant intra‐patient heterogeneity further complicates this classification. Moreover, the involvement of locally produced and intracellular complement proteins adds complexity to the tumor microenvironment dynamics. This review highlights the unique interplay of complement components within different cancers and patient cohorts, showing that "one size does not fit all", for complement in cancer. It summarizes the clinical trials for complement targeting in cancer, emphasizing the need for tailored therapeutic approaches. By elucidating the mechanistic basis of complement's context‐dependent role, this review aims to facilitate the development of personalized cancer therapies, ultimately improving patient care and outcomes. [ABSTRACT FROM AUTHOR]

Systemic lupus erythematosus (SLE) can present with a diverse array of hematologic manifestations, among which atypical hemolytic uremic syndrome (aHUS) is a rare entity. SLE-triggered aHUS has significant morbidity and mortality without timely intervention, yet its frequency remains uncertain and optimal strategies for complement-directed therapies are largely expert-driven. We performed a comprehensive literature review and present a case of a 23-year-old female newly diagnosed with SLE/class IV lupus nephritis who developed aHUS that rapidly responded to the C5 antagonist, eculizumab. Review of the current literature identified forty-nine published cases of SLE with concurrent aHUS and revealed a predilection for aHUS in younger SLE patients, concurrent presentation with lupus nephritis, anti-dsDNA positivity, and complement system abnormalities. Over seventy percent of cases used eculizumab as complement-directed therapy with a trend towards faster time to improvement in laboratory parameters, though reported outcomes were highly variable. Early recognition of aHUS in SLE is pivotal in guiding appropriate therapeutic interventions, and prompt initiation of eculizumab may reduce the potential morbidity associated with plasmapheresis and additional immunosuppression. While eculizumab showcases promising results, its optimal timing and duration remain elusive. An understanding of a patients' complement genetics could aid management strategies, and ongoing research into complement-targeted therapies offers promising avenues for both SLE and aHUS treatment. [ABSTRACT FROM AUTHOR]

Extracorporeal membrane oxygenation (ECMO), as an extracorporeal life support technique, can save the lives of reversible critically ill patients when conventional treatments fail. However, ECMO-related acute organ injury is a common complication that increases the risk of death in critically ill patients, including acute kidney injury, acute brain injury, acute lung injury, and so on. In ECMO supported patients, an increasing number of studies have shown that activation of the inflammatory response plays an important role in the development of acute organ injury. Cross-cascade activation of the complement system, the contact system, and the coagulation system, as well as the mechanical forces of the circuitry are very important pathophysiological mechanisms, likely leading to neutrophil activation and the production of neutrophil extracellular traps (NETs). NETs may have the potential to cause organ damage, generating interest in their study as potential therapeutic targets for ECMO-related acute organ injury. Therefore, this article comprehensively summarized the mechanism of neutrophils activation and NETs formation following ECMO treatment and their actions on acute organ injury. [ABSTRACT FROM AUTHOR]

Catastrophic antiphospholipid syndrome (CAPS) is a life-threatening condition of small-vessel thrombosis with acute multiple-organ involvement and visceral damage. In this report, we present a case of a patient with CAPS who is refractory to conventional therapy. For the first time in a patient with CAPS, marked C5b-9 formation was demonstrated on microvascular endothelial cells, suggesting the usefulness of therapeutic complement inhibition in this setting. Eculizumab, a C5-blocking monoclonal antibody, is remarkably effective in the treatment of different forms of thrombotic microangiopathy by controlling complement system hyperactivation. It halted the "thrombotic storm" and promptly achieved full recovery of thrombocytopenia. However, kidney function did not recover, possibly because eculizumabwas administered too late. Conceivably, the timing of treatment is crucial to achieving disease remission before irreversible structural damage occurs in target organs, thereby preventing their complete functional recovery. [ABSTRACT FROM AUTHOR]

Antibody-dependent complement activation plays a key role in the natural human immune response to infections. Currently, the understanding of which antibody-antigen combinations drive a potent complement response on bacteria is limited. Here, we develop an antigen-agnostic approach to stain and single-cell sort human IgG memory B cells recognizing intact bacterial cells, keeping surface antigens in their natural context. With this method we successfully identified 29 antibodies against K. pneumoniae, a dominant cause of hospital-acquired infections with increasing antibiotic resistance. Combining genetic tools and functional analyses, we reveal that the capacity of antibodies to activate complement on K. pneumoniae critically depends on their antigenic target. Furthermore, we find that antibody combinations can synergistically activate complement on K. pneumoniae by strengthening each other's binding in an Fc-independent manner. Understanding the molecular basis of effective complement activation by antibody combinations to mimic a polyclonal response could accelerate the development of antibody-based therapies against problematic infections. Here, van der Lans et al describe an antigen-agnostic approach to identify antibodies against Klebsiella pneumoniae. Functional analysis of these antibodies indicates that their capacity to activate complement depends on their antigenic target. [ABSTRACT FROM AUTHOR]

Systemic lupus erythematosus (SLE) is a chronic, heterogeneous, systemic autoimmune disease characterized by autoantibody production, complement activation, and immune complex deposition. SLE predominantly affects young, middle-aged, and child-bearing women with episodes of flare-up and remission, although it affects males at a much lower frequency (female: male; 7:1 to 15:1). Technological and molecular advancements have helped in patient stratification and improved patient prognosis, morbidity, and treatment regimens overall, impacting quality of life. Despite several attempts to comprehend the pathogenesis of SLE, knowledge about the precise molecular mechanisms underlying this disease is still lacking. The current treatment options for SLE are pragmatic and aim to develop composite biomarkers for daily practice, which necessitates the robust development of novel treatment strategies and drugs targeting specific responsive pathways. In this communication, we review and aim to explore emerging therapeutic modalities, including multiomics-based approaches, rational drug design, and CAR-T-cell-based immunotherapy, for the management of SLE. [ABSTRACT FROM AUTHOR]

Complement C3 (C3) is usually deposited spontaneously on the surfaces of invading bacteria prior to internalization, but the impact of C3 coating on cellular responses is largely unknown. Staphylococcus aureus (S. aureus) is a facultative intracellular pathogen that subverts autophagy and replicates in both phagocytic and nonphagocytic cells. In the present study, we deposited C3 components on the surface of S. aureus by complement opsonization before cell infection and confirmed that C3-coatings remained on the surface of the bacteria after they have invaded the cells, suggesting S. aureus cannot escape or degrade C3 labeling. We found that the C3 deposition on S. aureus notably enhanced cellular autophagic responses, and distinguished these responses as xenophagy, in contrast to LC3-associated phagocytosis (LAP). Furthermore, this upregulation was due to the recruitment of and direct interaction with autophagy-related 16-like 1 (ATG16L1), thereby resulting in autophagydependent resistance to bacterial growth within cells. Interestingly, this autophagic effect occurred only after C3 activation by enzymatic cleavage because full-length C3 without cleavage of the complement cascade reaction, although capable of binding to ATG16L1, failed to promote autophagy. These findings demonstrate the biological function of intracellular C3 upon bacterial infection in enhancing autophagy against internalized S. aureus. [ABSTRACT FROM AUTHOR]

Ethyl carbamate (EC) is a process contaminant found in fermented foods and alcoholic beverages. Metabolic conversion of ethyl carbamate generates vinyl carbamate (VC), a carcinogenic metabolite. EC, as a Group 2A probable human carcinogen, and the more potent VC, are known to cause tumors in rodents. However, their effects on the kidney are unknown and were explored here. Female A/J inbred mice received an intraperitoneal injection of vehicle or VC. Beginning 5 weeks after VC injection, mice showed signs of moribund state. Mouse necropsies revealed renal glomerular injury that histopathologically recapitulated human membranoproliferative glomerulonephritis (MPGN), as evidenced by light microscopy, immunostaining for immunoglobulins and complements, and electron microscopy. To determine the molecular pathomechanisms, a post-hoc analysis was performed on a publicly available RNA-Seq transcriptome of kidneys from control rats and rats treated with fermented wine containing high concentrations of EC. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses of the differentially expressed genes revealed that the complement and coagulation cascades were a top predicted biological process involved. Furthermore, pathway-based data integration and visualization revealed that key regulators of complement activation were altered by high EC treatment. Among these, complement factors (CF) D and H, critical positive and negative regulators of the alternative pathway, respectively, were most affected, with CFD induced by 3.49-fold and CFH repressed by 5.9-fold, underscoring a hyperactive alternative pathway. Consistently, exposure of primary glomerular endothelial cells to EC or VC resulted in induction of CFD and repression of CFH, accompanied by increased fixation of C3 and C5b9. This effect seems to be mediated by Ras, one of the top genes that interact with both EC and VC, as identified by analyzing the chemical-gene/protein interactions database. Indeed, EC or VC-elicited complement activation was associated with activation of Ras signaling, but was abolished by the Ras inhibitor farnesyl thiosalicylic acid. Collectively, our findings suggest that VC, a metabolite of EC, induces glomerular injury in mice akin to human MPGN, possibly via perturbing the expression of complement regulators, resulting in an effect that favors activation of the alternative complement pathway. [ABSTRACT FROM AUTHOR]

Pseudomonas aeruginosa is a leading cause of nosocomial bloodstream infections. The outcome of these infections depends on the virulence of the microorganism as well as host-related conditions and factors. The complement system plays a crucial role in defense against bloodstream infections. P. aeruginosa counteracts complement attack by recruiting Factor H (FH) that inhibits complement amplification on the bacterial surface. Factor H-related proteins (FHRs) are a group of plasma proteins evolutionarily related to FH that have been postulated to interfere this bacterial evasion mechanism. In this study, we demonstrate that FHR-3 competes with purified FH for binding to P. aeruginosa and identify EF-Tu as a common bacterial target for both complement regulator factors. Importantly, elevated levels of FHR-3 in human serum promote complement activation, leading to increased opsonization and killing of P. aeruginosa. Conversely, physiological concentrations of FHR-3 have no significant effect. Our findings suggest that FHR-3 may serve as a protective host factor against P. aeruginosa infections. [ABSTRACT FROM AUTHOR]

Background/Objectives: Through the past several years, a constant interaction has been implicated between complement and coagulation cascades. SARS-CoV-2 infection and bacterial sepsis are potent activators of both cascades. This study aims to compare the extent of complement and intrinsic coagulation pathway activation (and the interplay between them) among patients with COVID-19 and bacterial sepsis. Methods: Serum and plasma samples were collected from 25 ICU patients (11 patients with COVID-19 and 14 patients with bacterial sepsis) at two time points (on admission and either on improvement or deterioration). The activities of coagulation factors XI and XII and complement factors C3a and C5a were measured at both time points. Results: The activities of factors XI and XII were increased in both groups of patients and at both time points. However, there were no statistically significant differences between SARS-CoV-2 and bacterial sepsis patients. On the other hand, both C3a and C5a were significantly higher in the COVID-19 group on admission. This correlation was preserved on reassessment. Conclusions: Complement activation seems to be more enhanced in COVID-19 than bacterial sepsis. However, the lack of statistical significance in factors XI and XII indicates t the presence of additional pathways for complement activation in SARS-CoV-2 infection. [ABSTRACT FROM AUTHOR]

Antibody-dependent complement activation plays a key role in the natural human immune response to infections. Currently, the understanding of which antibody-antigen combinations drive a potent complement response on bacteria is limited. Here, we develop an antigen-agnostic approach to stain and single-cell sort human IgG memory B cells recognizing intact bacterial cells, keeping surface antigens in their natural context. With this method we successfully identified 29 antibodies against K. pneumoniae, a dominant cause of hospital-acquired infections with increasing antibiotic resistance. Combining genetic tools and functional analyses, we reveal that the capacity of antibodies to activate complement on K. pneumoniae critically depends on their antigenic target. Furthermore, we find that antibody combinations can synergistically activate complement on K. pneumoniae by strengthening each other's binding in an Fc-independent manner. Understanding the molecular basis of effective complement activation by antibody combinations to mimic a polyclonal response could accelerate the development of antibody-based therapies against problematic infections. Here, van der Lans et al describe an antigen-agnostic approach to identify antibodies against Klebsiella pneumoniae. Functional analysis of these antibodies indicates that their capacity to activate complement depends on their antigenic target. [ABSTRACT FROM AUTHOR]

Simple Summary: Pangolins, the only mammals covered in scales, play a crucial role in forest ecosystems as they specialize in myrmecophagy. Unfortunately, all eight pangolin species are critically endangered and susceptible to various pathogenic microorganisms, causing mass mortality, especially in captive Manis pentadactyla. However, information regarding the function of the immune system is lacking, which limits the development of effective rescue methods and subsequently hinders population rejuvenation. This study aimed to investigate the differences in the immunity of Manis javanica and Manis pentadactyla through proteomics and microbiotas conjoint analysis. Our findings revealed that Manis pentadactyla owned more pathogenic bacteria and neutralized through a powerful transferrin system. Manis javanica possessed stronger anti-inflammatory ability, which might be due to the structural deficiency of C5a. This study elucidates the distinct immune factors and microbiomes in Manis javanica compared to Manis pentadactyla, offering a foundational understanding for future immunotherapy research. All eight pangolin species, especially captive Manis pentadactyla, are critically endangered and susceptible to various pathogenic microorganisms, causing mass mortality. They are involved in the complement system, iron transport system, and inflammatory factors. M. pentadactyla exhibited a higher abundance of opportunistic pathogens, Moraxella, which potentially evaded complement-mediated immune response by reducing C5 levels and counteracting detrimental effects through transferrin neutralization. In addition, we found that the major structure of C5a, an important inflammatory factor, was lacking in M. javanica. In brief, this study revealed the differences in immune factors and microbiome between M. javanica and M. pentadactyla, thus providing a theoretical basis for subsequent immunotherapy. [ABSTRACT FROM AUTHOR]

Emerging evidence indicates that activation of complement system leading to the formation of the membrane attack complex (MAC) plays a detrimental role in COVID-19. However, their pathogenic roles have never been experimentally investigated before. We used three knock out mice strains (1. C3−/−; 2. C7−/−; and 3. Cd59ab−/−) to evaluate the role of complement in severe COVID-19 pathogenesis. C3 deficient mice lack a key common component of all three complement activation pathways and are unable to generate C3 and C5 convertases. C7 deficient mice lack a complement protein needed for MAC formation. Cd59ab deficient mice lack an important inhibitor of MAC formation. We also used anti-C5 antibody to block and evaluate the therapeutic potential of inhibiting MAC formation. We demonstrate that inhibition of complement activation (in C3−/−) and MAC formation (in C3−/−. C7−/−, and anti-C5 antibody) attenuates severe COVID-19; whereas enhancement of MAC formation (Cd59ab−/−) accelerates severe COVID-19. The degree of MAC but not C3 deposits in the lungs of C3−/−, C7−/− mice, and Cd59ab−/− mice as compared to their control mice is associated with the attenuation or acceleration of SARS-CoV-2-induced disease. Further, the lack of terminal complement activation for the formation of MAC in C7 deficient mice protects endothelial dysfunction, which is associated with the attenuation of diseases and pathologic changes. Our results demonstrated the causative effect of MAC in severe COVID-19 and indicate a potential avenue for modulating the complement system and MAC formation in the treatment of severe COVID-19. [ABSTRACT FROM AUTHOR]

Background: Glaucoma is a leading cause of blindness, affecting retinal ganglion cells (RGCs) and their axons. By 2040, it is likely to affect 110 million people. Neuroinflammation, specifically through the release of proinflammatory cytokines by M1 microglial cells, plays a crucial role in glaucoma progression. Indeed, in post-mortem human studies, pre-clinical models, and ex-vivo models, RGC degeneration has been consistently shown to be linked to inflammation in response to cell death and tissue damage. Recently, Rho kinase inhibitors (ROCKis) have emerged as potential therapies for neuroinflammatory and neurodegenerative diseases. This study aimed to investigate the potential effects of three ROCKis (Y-27632, Y-33075, and H-1152) on retinal ganglion cell (RGC) loss and retinal neuroinflammation using an ex-vivo retinal explant model. Methods: Rat retinal explants underwent optic nerve axotomy and were treated with Y-27632, Y-33075, or H-1152. The neuroprotective effects on RGCs were evaluated using immunofluorescence and Brn3a-specific markers. Reactive glia and microglial activation were studied by GFAP, CD68, and Iba1 staining. Flow cytometry was used to quantify day ex-vivo 4 (DEV 4) microglial proliferation and M1 activation by measuring the number of CD11b+, CD68+, and CD11b+/CD68+ cells after treatment with control solvent or Y-33075. The modulation of gene expression was measured by RNA-seq analysis on control and Y-33075-treated explants and glial and pro-inflammatory cytokine gene expression was validated by RT-qPCR. Results: Y-27632 and H-1152 did not significantly protect RGCs. By contrast, at DEV 4, 50 µM Y-33075 significantly increased RGC survival. Immunohistology showed a reduced number of Iba1+/CD68+ cells and limited astrogliosis with Y-33075 treatment. Flow cytometry confirmed lower CD11b+, CD68+, and CD11b+/CD68+ cell numbers in the Y-33075 group. RNA-seq showed Y-33075 inhibited the expression of M1 microglial markers (Tnfα, Il-1β, Nos2) and glial markers (Gfap, Itgam, Cd68) and to reduce apoptosis, ferroptosis, inflammasome formation, complement activation, TLR pathway activation, and P2rx7 and Gpr84 gene expression. Conversely, Y-33075 upregulated RGC-specific markers, neurofilament formation, and neurotransmitter regulator expression, consistent with its neuroprotective effects. Conclusion: Y-33075 demonstrates marked neuroprotective and anti-inflammatory effects, surpassing the other tested ROCKis (Y-27632 and H-1152) in preventing RGC death and reducing microglial inflammatory responses. These findings highlight its potential as a therapeutic option for glaucoma. [ABSTRACT FROM AUTHOR]

Human C-reactive protein (CRP) is a pentameric complex involved in immune defense and regulation of autoimmunity. CRP is also a therapeutic target, with both administration and depletion of serum CRP being pursued as a possible treatment for autoimmune and cardiovascular diseases, among others. CRP binds to phosphocholine (PC) moieties on membranes to activate the complement system via the C1 complex, but it is unknown how CRP, or any pentraxin, binds to C1. Here, we present a cryoelectron tomography (cryoET)-derived structure of CRP bound to PC ligands and the C1 complex. To gain control of CRP binding, a synthetic mimotope of PC was synthesized and used to decorate cell-mimetic liposome surfaces. Structure-guided mutagenesis of CRP yielded a fully active complex able to bind PC-coated liposomes that was ideal for cryoET and subtomogram averaging. In contrast to antibodies, which form Fc-mediated hexameric platforms to bind and activate the C1 complex, CRP formed rectangular platforms assembled from four laterally associated CRP pentamers that bind only four of the six available globular C1 head groups. Potential residues mediating lateral association of CRP were identified from interactions between unit cells in existing crystal structures, which rationalized previously unexplained mutagenesis data regarding CRP-mediated complement activation. The structure also enabled interpretation of existing biochemical data regarding interactions mediating C1 binding and identified additional residues for further mutagenesis studies. These structural data therefore provide a possible mechanism for regulation of complement by CRP, which limits complement progression and has consequences for how the innate immune system influences autoimmunity. [ABSTRACT FROM AUTHOR]

Aim: The availability of disease-modifying therapies and newborn screening programs for spinal muscular atrophy (SMA) has generated an urgent need for reliable prognostic biomarkers to classify patients according to disease severity. We aim to identify cerebrospinal fluid (CSF) prognostic protein biomarkers in CSF samples of SMA patients collected at baseline (T0), and to describe proteomic profile changes and biological pathways influenced by nusinersen before the sixth nusinersen infusion (T302). Methods: In this multicenter retrospective longitudinal study, we employed an untargeted liquid chromatography mass spectrometry (LC-MS)-based proteomic approach on CSF samples collected from 61 SMA patients treated with nusinersen (SMA1 n=19, SMA2 n=19, SMA3 n=23) at T0 at T302. The Random Forest (RF) machine learning algorithm and pathway enrichment analysis were applied for analysis. Results: The RF algorithm, applied to the protein expression profile of naïve patients, revealed several proteins that could classify the different types of SMA according to their differential abundance at T0. Analysis of changes in proteomic profiles identified a total of 147 differentially expressed proteins after nusinersen treatment in SMA1, 135 in SMA2, and 289 in SMA3. Overall, nusinersen-induced changes on proteomic profile were consistent with i) common effects observed in allSMA types (i.e. regulation of axonogenesis), and ii) disease severity-specific changes, namely regulation of glucose metabolism in SMA1, of coagulation processes in SMA2, and of complement cascade in SMA3. Conclusions: This untargeted LC-MS proteomic profiling in the CSF of SMA patients revealed differences in protein expression in naïve patients and showed nusinersen-related modulation in several biological processes after 10 months of treatment. Further confirmatory studies are needed to validate these results in larger number of patients and over abroader timeframe. [ABSTRACT FROM AUTHOR]

C-reactive protein (CRP) plays a crucial role in the diagnosis and monitoring of the non-specific acute phase response in humans. In contrast, rat CRP (rCRP) is an atypical acute-phase protein that possesses unique features, such as a possible incapacity to trigger the complement system and markedly elevated baseline plasma concentrations. To facilitate in vitro studies on these unique characteristics, obtaining high-quality pure rCRP is essential. Here we explored various strategies for rCRP purification, including direct isolation from rat plasma and recombinant expression in both prokaryotic and eukaryotic systems. Our study optimized the recombinant expression system to enhance the secretion and purification efficiency of rCRP. Compared to traditional purification methods, we present a streamlined and effective approach for the expression and purification of rCRP in the Pichia pastoris system. This refined methodology offers significant improvements in the efficiency and effectiveness of rCRP purification, thereby facilitating further structural and functional studies on rCRP. [ABSTRACT FROM AUTHOR]

Background: Complement activation in atypical hemolytic uremic syndrome (aHUS), C3 glomerulonephropathy (C3G) and immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) may be associated with rare genetic variants. Here we describe gene variants in the Swedish and Norwegian populations. Methods: Patients with these diagnoses (N=141) were referred for genetic screening. Sanger or next-generation sequencing were performed to identify genetic variants in 16 genes associated with these conditions. Nonsynonymous genetic variants are described when they have a minor allele frequency of <1% or were previously reported as being disease-associated. Results: In patients with aHUS (n=94, one also had IC-MPGN) 68 different genetic variants or deletions were identified in 60 patients, of which 18 were novel. Thirty-two patients had more than one genetic variant. In patients with C3G (n=40) 29 genetic variants, deletions or duplications were identified in 15 patients, of which 9 were novel. Eight patients had more than one variant. In patients with IC-MPGN (n=7) five genetic variants were identified in five patients. Factor H variants were the most frequent in aHUS and C3 variants in C3G. Seventeen variants occurred in more than one condition. Conclusion: Genetic screening of patients with aHUS, C3G and IC-MPGN is of paramount importance for diagnostics and treatment. In this study, we describe genetic assessment of Nordic patients in which 26 novel variants were found. [ABSTRACT FROM AUTHOR]