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Abstract
Uncontrolled alternative pathway activation is the primary driver of several diseases, and it contributes to the pathogenesis of many others. Consequently, diagnostic tests to monitor this arm of the complement system are increasingly important. Defects in alternative pathway regulation are strong risk factors for disease, and drugs that specifically block the alternative pathway are entering clinical use. A range of diagnostic tests have been developed to evaluate and monitor the alternative pathway, including assays to measure its function, expression of alternative pathway constituents, and activation fragments. Genetic studies have also revealed many disease-associated variants in alternative pathway genes that predict the risk of disease and prognosis. Newer imaging modalities offer the promise of non-invasively detecting and localizing pathologic complement activation. Together, these various tests help in the diagnosis of disease, provide important prognostic information, and can help guide therapy with complement inhibitory drugs.
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Affiliation(s)
- Joshua M. Thurman
- Department of Medicine, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, CO, USA
| | - Veronique Fremeaux-Bacchi
- Assistance Publique-Hôpitaux de Paris, European Hospital Georges Pompidou, Department of Immunology Biology and INSERM UMRS1138, Centre de Recherche des Cordeliers, Team "Inflammation, Complement and Cancer", Paris, France
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2
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Cortes C, Desler C, Mazzoli A, Chen JY, Ferreira VP. The role of properdin and Factor H in disease. Adv Immunol 2022; 153:1-90. [PMID: 35469595 DOI: 10.1016/bs.ai.2021.12.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The complement system consists of three pathways (alternative, classical, and lectin) that play a fundamental role in immunity and homeostasis. The multifunctional role of the complement system includes direct lysis of pathogens, tagging pathogens for phagocytosis, promotion of inflammatory responses to control infection, regulation of adaptive cellular immune responses, and removal of apoptotic/dead cells and immune complexes from circulation. A tight regulation of the complement system is essential to avoid unwanted complement-mediated damage to the host. This regulation is ensured by a set of proteins called complement regulatory proteins. Deficiencies or malfunction of these regulatory proteins may lead to pro-thrombotic hematological diseases, renal and ocular diseases, and autoimmune diseases, among others. This review focuses on the importance of two complement regulatory proteins of the alternative pathway, Factor H and properdin, and their role in human diseases with an emphasis on: (a) characterizing the main mechanism of action of Factor H and properdin in regulating the complement system and protecting the host from complement-mediated attack, (b) describing the dysregulation of the alternative pathway as a result of deficiencies, or mutations, in Factor H and properdin, (c) outlining the clinical findings, management and treatment of diseases associated with mutations and deficiencies in Factor H, and (d) defining the unwanted and inadequate functioning of properdin in disease, through a discussion of various experimental research findings utilizing in vitro, mouse and human models.
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Affiliation(s)
- Claudio Cortes
- Department of Foundational Medical Studies, Oakland University William Beaumont School of Medicine, Rochester, MI, United States.
| | - Caroline Desler
- Oakland University William Beaumont School of Medicine, Rochester, MI, United States
| | - Amanda Mazzoli
- Oakland University William Beaumont School of Medicine, Rochester, MI, United States
| | - Jin Y Chen
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Viviana P Ferreira
- Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, OH, United States.
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3
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Halting targeted and collateral damage to red blood cells by the complement system. Semin Immunopathol 2021; 43:799-816. [PMID: 34191092 PMCID: PMC8243056 DOI: 10.1007/s00281-021-00859-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 04/18/2021] [Indexed: 12/12/2022]
Abstract
The complement system is an important defense mechanism against pathogens; however, in certain pathologies, the system also attacks human cells, such as red blood cells (RBCs). In paroxysmal nocturnal hemoglobinuria (PNH), RBCs lack certain complement regulators which sensitize them to complement-mediated lysis, while in autoimmune hemolytic anemia (AIHA), antibodies against RBCs may initiate complement-mediated hemolysis. In recent years, complement inhibition has improved treatment prospects for these patients, with eculizumab now the standard of care for PNH patients. Current complement inhibitors are however not sufficient for all patients, and they come with high costs, patient burden, and increased infection risk. This review gives an overview of the underlying pathophysiology of complement-mediated hemolysis in PNH and AIHA, the role of therapeutic complement inhibition nowadays, and the high number of complement inhibitors currently under investigation, as for almost every complement protein, an inhibitor is being developed. The focus lies with novel therapeutics that inhibit complement activity specifically in the pathway that causes pathology or those that reduce costs or patient burden through novel administration routes.
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Ozawa Y, Uzawa A, Yasuda M, Kojima Y, Oda F, Himuro K, Kawaguchi N, Kuwabara S. Changes in serum complements and their regulators in generalized myasthenia gravis. Eur J Neurol 2020; 28:314-322. [PMID: 32889770 DOI: 10.1111/ene.14500] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 08/19/2020] [Indexed: 01/16/2023]
Abstract
OBJECTIVE To investigate changes in serum complements and their regulators in the pathogenesis of myasthenia gravis (MG). METHODS Forty-four patients with acetylcholine receptor antibody-positive MG, as well as 20 patients with non-inflammatory neurological disorders were enrolled. Serum complements (C3, C4 and soluble C5b-9) and complement regulators (vitronectin, clusterin and properdin) were extensively analysed by enzyme-linked immunosorbent assay and their associations with clinical profiles of MG were examined. RESULTS Serum C3, C4 and clusterin levels were not significantly different between patients with MG and controls. The patients with MG had higher soluble C5b-9 (P = 0.09) and vitronectin (P = 0.001) levels than the controls; moreover, vitronectin levels decreased after treatment (P = 0.09). Serum properdin (P = 0.03) levels were lower in the patients with MG than in the controls, and negatively correlated with the MG Activities of Daily Living score (rs = -0.26, P = 0.09) and with the presence of bulbar palsy (P = 0.04). CONCLUSION Our results show that activation of complements and an altered complement network could contribute to the inflammatory pathogenesis of MG.
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Affiliation(s)
- Y Ozawa
- Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan
| | - A Uzawa
- Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan
| | - M Yasuda
- Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan
| | - Y Kojima
- Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.,Department of Neurology, Kyoto Prefectural University of Medicine, Kyoto, Japan
| | - F Oda
- Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.,Department of Neurology, National Hospital Organization Chiba Medical Center, Chiba, Japan
| | - K Himuro
- Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.,Matsudo Neurology Clinic, Matsudo, Japan
| | - N Kawaguchi
- Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.,Department of Neurology, Neurology Clinic Chiba, Dowa Institute of Clinical Neuroscience, Chiba, Japan
| | - S Kuwabara
- Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan
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Lammerts RGM, Talsma DT, Dam WA, Daha MR, Seelen MAJ, Berger SP, van den Born J. Properdin Pattern Recognition on Proximal Tubular Cells Is Heparan Sulfate/Syndecan-1 but Not C3b Dependent and Can Be Blocked by Tick Protein Salp20. Front Immunol 2020; 11:1643. [PMID: 32849563 PMCID: PMC7426487 DOI: 10.3389/fimmu.2020.01643] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Accepted: 06/19/2020] [Indexed: 11/13/2022] Open
Abstract
Introduction: Proteinuria contributes to progression of renal damage, partly by complement activation on proximal tubular epithelial cells. By pattern recognition, properdin has shown to bind to heparan sulfate proteoglycans on tubular epithelium and can initiate the alternative complement pathway (AP). Properdin however, also binds to C3b(Bb) and properdin binding to tubular cells might be influenced by the presence of C3b(Bb) on tubular cells and/or by variability in properdin proteins in vitro. In this study we carefully evaluated the specificity of the properdin – heparan sulfate interaction and whether this interaction could be exploited in order to block alternative complement activation. Methods: Binding of various properdin preparations to proximal tubular epithelial cells (PTEC) and subsequent AP activation was determined in the presence or absence of C3 inhibitor Compstatin and properdin inhibitor Salp20. Heparan sulfate proteoglycan dependency of the pattern recognition of properdin was evaluated on PTEC knocked down for syndecan-1 by shRNA technology. Solid phase binding assays were used to evaluate the effectivity of heparin(oids) and recombinant Salp20 to block the pattern recognition of properdin. Results: Binding of serum-derived and recombinant properdin preparations to PTECs could be dose-dependently inhibited (P < 0.01) and competed off (P < 0.01) by recombinant Salp20 (IC50: ~125 ng/ml) but not by Compstatin. Subsequent properdin-mediated AP activation on PTECs could be inhibited by Compstatin (P < 0.01) and blocked by recombinant Salp20 (P < 0.05). Syndecan-1 deficiency in PTECs resulted in a ~75% reduction of properdin binding (P = 0.057). In solid-phase binding assays, properdin binding to C3b could be dose-dependently inhibited by recombinant Salp20> heparin(oid) > C3b. Discussion: In this study we showed that all properdin preparations recognize heparan sulfate/syndecan-1 on PTECs with and without Compstatin C3 blocking conditions. In contrast to Compstatin, recombinant Salp20 prevents heparan sulfate pattern recognition by properdin on PTECs. Both complement inhibitors prevented properdin-mediated C3 activation. Binding of properdin to C3b could also be blocked by heparin(oids) and recombinant Salp20. This work indicates that properdin serves as a docking station for AP activation on PTECs and a Salp20 analog or heparinoids may be viable inhibitors in properdin mediated AP activation.
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Affiliation(s)
- Rosa G M Lammerts
- Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Ditmer T Talsma
- Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Wendy A Dam
- Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Mohamed R Daha
- Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Marc A J Seelen
- Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Stefan P Berger
- Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Jacob van den Born
- Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
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Chen JY, Galwankar NS, Emch HN, Menon SS, Cortes C, Thurman JM, Merrill SA, Brodsky RA, Ferreira VP. Properdin Is a Key Player in Lysis of Red Blood Cells and Complement Activation on Endothelial Cells in Hemolytic Anemias Caused by Complement Dysregulation. Front Immunol 2020; 11:1460. [PMID: 32793201 PMCID: PMC7387411 DOI: 10.3389/fimmu.2020.01460] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Accepted: 06/04/2020] [Indexed: 12/18/2022] Open
Abstract
The complement system alternative pathway (AP) can be activated excessively in inflammatory diseases, particularly when there is defective complement regulation. For instance, deficiency in complement regulators CD55 and CD59, leads to paroxysmal nocturnal hemoglobinuria (PNH), whereas Factor H mutations predispose to atypical hemolytic uremic syndrome (aHUS), both causing severe thrombohemolysis. Despite eculizumab being the treatment for these diseases, benefits vary considerably among patients. Understanding the molecular mechanisms involved in complement regulation is essential for developing new treatments. Properdin, the positive AP regulator, is essential for complement amplification by stabilizing enzymatic convertases. In this study, the role of properdin in red blood cell (RBC) lysis and endothelial cell opsonization in these AP-mediated diseases was addressed by developing in vitro assays using PNH patient RBCs and human primary endothelial cells, where the effects of inhibiting properdin, using novel monoclonal antibodies (MoAbs) that we generated and characterized, were compared to other complement inhibitors. In in vitro models of PNH, properdin inhibition prevented hemolysis of patient PNH type II and III RBCs more than inhibition of Factor B, C3, and C5 (>17-fold, or >81-fold, or >12-fold lower molar IC90 values, respectively). When tested in an in vitro aHUS hemolysis model, the anti-properdin MoAbs had 11-fold, and 86-fold lower molar IC90 values than inhibition of Factor B, or C3, respectively (P < 0.0001). When comparing target/inhibitor ratios in all hemolysis assays, inhibiting properdin was at least as efficient as the other complement inhibitors in most cases. In addition, using in vitro endothelial cell assays, the data indicate a critical novel role for properdin in promoting complement activation on human endothelial cells exposed to heme (a hemolysis by-product) and rH19-20 (to inhibit Factor H cell-surface protection), as occurs in aHUS. Inhibition of properdin or C3 in this system significantly reduced C3 fragment deposition by 75%. Altogether, the data indicate properdin is key in promoting RBC lysis and complement activation on human endothelial cells, contributing to the understanding of PNH and aHUS pathogenesis. Further studies to determine therapeutic values of inhibiting properdin in complement-mediated diseases, in particular those that are characterized by AP dysregulation, are warranted.
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Affiliation(s)
- Jin Y Chen
- Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, OH, United States
| | - Neeti S Galwankar
- Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, OH, United States
| | - Heather N Emch
- Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, OH, United States
| | - Smrithi S Menon
- Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, OH, United States
| | - Claudio Cortes
- Department of Foundational Medical Studies, Oakland University William Beaumont School of Medicine, Rochester, MI, United States
| | - Joshua M Thurman
- Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Samuel A Merrill
- Section of Hematology/Oncology, Department of Medicine, West Virginia University School of Medicine, Morgantown, WV, United States
| | - Robert A Brodsky
- Division of Hematology, Department of Medicine, John Hopkins University School of Medicine, Baltimore, MD, United States
| | - Viviana P Ferreira
- Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, OH, United States
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Hair P, Goldman DW, Li J, Petri M, Krishna N, Cunnion K. Classical complement activation on human erythrocytes in subjects with systemic lupus erythematosus and a history of autoimmune hemolytic anemia. Lupus 2020; 29:1179-1188. [PMID: 32659155 DOI: 10.1177/0961203320936347] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
INTRODUCTION Autoimmune hemolytic anemia (AIHA) is a serious manifestation of systemic lupus erythematosus (SLE) associated with significant morbidity and mortality. In order to more fully understand the causative pathways, we utilized sera from subjects with SLE and active AIHA, or a history of AIHA, to evaluate the classical complement pathway, anti-erythrocyte antibodies, and immune complexes. METHODS To evaluate antibody-mediated complement activation on the surface of erythrocytes, as occurs in AIHA, blood type O erythrocytes were incubated with sera from 19 subjects with SLE and a history of AIHA. Circulating anti-erythrocyte antibodies and immune complexes were measured with ELISA-based assays. RESULTS In total, 90% of subjects with SLE and a history of AIHA, but not active clinical hemolysis, had measurable anti-erythrocyte antibodies. Of those with anti-erythrocyte antibody, 53% demonstrated complement opsonization on the erythrocyte surface >twofold above negative control and 29% generated the anaphylatoxin C5a. CONCLUSIONS For subjects with SLE and a history of AIHA, the persistence of circulating anti-erythrocyte antibodies and resultant erythrocyte complement opsonization and anaphylatoxin generation suggests the possibility that these complement effectors contribute to chronic morbidity and risk of AIHA relapse.
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Affiliation(s)
- Pamela Hair
- Eastern Virginia Medical School Pediatric Research, Department of Pediatrics, Norfolk, VA
| | - Daniel W Goldman
- Johns Hopkins University School of Medicine, Division of Rheumatology, Baltimore, MD
| | - Jessica Li
- Johns Hopkins University School of Medicine, Division of Rheumatology, Baltimore, MD
| | - Michelle Petri
- Johns Hopkins University School of Medicine, Division of Rheumatology, Baltimore, MD
| | - Neel Krishna
- Eastern Virginia Medical School, Department of Microbiology and Molecular Cell Biology, Norfolk, VA
| | - Kenji Cunnion
- Eastern Virginia Medical School Pediatric Research, Department of Pediatrics, Norfolk, VA
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Pedersen DV, Gadeberg TAF, Thomas C, Wang Y, Joram N, Jensen RK, Mazarakis SMM, Revel M, El Sissy C, Petersen SV, Lindorff-Larsen K, Thiel S, Laursen NS, Fremeaux-Bacchi V, Andersen GR. Structural Basis for Properdin Oligomerization and Convertase Stimulation in the Human Complement System. Front Immunol 2019; 10:2007. [PMID: 31507604 PMCID: PMC6713926 DOI: 10.3389/fimmu.2019.02007] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Accepted: 08/07/2019] [Indexed: 12/05/2022] Open
Abstract
Properdin (FP) is a positive regulator of the immune system stimulating the activity of the proteolytically active C3 convertase C3bBb in the alternative pathway of the complement system. Here we present two crystal structures of FP and two structures of convertase bound FP. A structural core formed by three thrombospondin repeats (TSRs) and a TB domain harbors the convertase binding site in FP that mainly interacts with C3b. Stabilization of the interaction between the C3b C-terminus and the MIDAS bound Mg2+ in the Bb protease by FP TSR5 is proposed to underlie FP convertase stabilization. Intermolecular contacts between FP and the convertase subunits suggested by the structure were confirmed by binding experiments. FP is shown to inhibit C3b degradation by FI due to a direct competition for a common binding site on C3b. FP oligomers are held together by two sets of intermolecular contacts, where the first is formed by the TB domain from one FP molecule and TSR4 from another. The second and largest interface is formed by TSR1 and TSR6 from the same two FP molecules. Flexibility at four hinges between thrombospondin repeats is suggested to enable the oligomeric, polydisperse, and extended architecture of FP. Our structures rationalize the effects of mutations associated with FP deficiencies and provide a structural basis for the analysis of FP function in convertases and its possible role in pattern recognition.
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Affiliation(s)
- Dennis V. Pedersen
- Department of Molecular Biology and Genetics, Center for Structural Biology, Aarhus University, Aarhus, Denmark
| | - Trine A. F. Gadeberg
- Department of Molecular Biology and Genetics, Center for Structural Biology, Aarhus University, Aarhus, Denmark
| | - Caroline Thomas
- Service d'Oncologie Pédiatrique, CHU Nantes, Hôpital Mère Enfant, Nantes, France
| | - Yong Wang
- Department of Biology, Linderstrøm-Lang Centre for Protein Science, University of Copenhagen, Copenhagen, Denmark
| | - Nicolas Joram
- Service de Réanimation Pédiatrique, CHU Nantes, Nantes, France
| | - Rasmus K. Jensen
- Department of Molecular Biology and Genetics, Center for Structural Biology, Aarhus University, Aarhus, Denmark
| | - Sofia M. M. Mazarakis
- Department of Molecular Biology and Genetics, Center for Structural Biology, Aarhus University, Aarhus, Denmark
| | - Margot Revel
- Centre de Recherche des Cordeliers, INSERM, Sorbonne Université, USPC, Université Paris Descartes, Université Paris Diderot, Paris, France
| | - Carine El Sissy
- Service d'Immunologie Biologique, Assistance Publique – Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Paris, France
| | | | - Kresten Lindorff-Larsen
- Department of Biology, Linderstrøm-Lang Centre for Protein Science, University of Copenhagen, Copenhagen, Denmark
| | - Steffen Thiel
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Nick S. Laursen
- Department of Molecular Biology and Genetics, Center for Structural Biology, Aarhus University, Aarhus, Denmark
| | - Véronique Fremeaux-Bacchi
- Service d'Immunologie Biologique, Assistance Publique – Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Paris, France
| | - Gregers R. Andersen
- Department of Molecular Biology and Genetics, Center for Structural Biology, Aarhus University, Aarhus, Denmark
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Michels MAHM, van de Kar NCAJ, van den Bos RM, van der Velden TJAM, van Kraaij SAW, Sarlea SA, Gracchi V, Oosterveld MJS, Volokhina EB, van den Heuvel LPWJ. Novel Assays to Distinguish Between Properdin-Dependent and Properdin-Independent C3 Nephritic Factors Provide Insight Into Properdin-Inhibiting Therapy. Front Immunol 2019; 10:1350. [PMID: 31263464 PMCID: PMC6590259 DOI: 10.3389/fimmu.2019.01350] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 05/28/2019] [Indexed: 01/01/2023] Open
Abstract
C3 glomerulopathy (C3G) is an umbrella classification for severe renal diseases characterized by predominant staining for complement component C3 in the glomeruli. The disease is caused by a dysregulation of the alternative pathway (AP) of the complement system. In more than half of C3G patients C3 nephritic factors (C3NeFs) are found. These autoantibodies bind to the AP C3 convertase, prolonging its activity. C3NeFs can be dependent or independent of the complement regulator properdin for their convertase-stabilizing function. However, studies to determine the properdin-dependency of C3NeFs are rare and not part of routine patient workup. Until recently, only supportive treatments for C3G were available. Complement-directed therapies are now being investigated. We hypothesized that patients with properdin-dependent C3NeFs may benefit from properdin-inhibiting therapy to normalize convertase activity. Therefore, in this study we validated two methods to distinguish between properdin-dependent and properdin-independent C3NeFs. These methods are hemolytic assays for measuring convertase activity and stability in absence of properdin. The first assay assesses convertase stabilization by patient immunoglobulins in properdin-depleted serum. The second assay measures convertase stabilization directly in patient serum supplemented with the properdin-blocking agent Salp20. Blood samples from 13 C3NeF-positive C3G patients were tested. Three patients were found to have properdin-dependent C3NeFs, whereas the C3NeF activity of the other ten patients was independent of properdin. The convertase-stabilizing activity in the samples of the patients with properdin-dependent C3NeFs disappeared in absence of properdin. These data indicate that inhibition of properdin in patients with properdin-dependent C3NeFs can normalize convertase activity and could represent a novel therapy for normalizing AP hyperactivity. Our assays provide a tool for identifying C3G patients who may benefit from properdin-inhibiting therapy and can be incorporated into standard C3G laboratory investigations.
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Affiliation(s)
- Marloes A H M Michels
- Department of Pediatric Nephrology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, Amalia Children's Hospital, Nijmegen, Netherlands
| | - Nicole C A J van de Kar
- Department of Pediatric Nephrology, Radboud University Medical Center, Amalia Children's Hospital, Nijmegen, Netherlands
| | - Ramon M van den Bos
- Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Department of Chemistry, Faculty of Science, Utrecht University, Utrecht, Netherlands
| | - Thea J A M van der Velden
- Department of Pediatric Nephrology, Radboud University Medical Center, Amalia Children's Hospital, Nijmegen, Netherlands
| | - Sanne A W van Kraaij
- Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen, Netherlands
| | - Sebastian A Sarlea
- Department of Pediatric Nephrology, Radboud University Medical Center, Amalia Children's Hospital, Nijmegen, Netherlands
| | - Valentina Gracchi
- Department of Pediatric Nephrology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Michiel J S Oosterveld
- Department of Pediatric Nephrology, Emma Children's Hospital, Amsterdam University Medical Center, Amsterdam, Netherlands
| | - Elena B Volokhina
- Department of Pediatric Nephrology, Radboud University Medical Center, Amalia Children's Hospital, Nijmegen, Netherlands.,Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen, Netherlands
| | - Lambertus P W J van den Heuvel
- Department of Pediatric Nephrology, Radboud University Medical Center, Amalia Children's Hospital, Nijmegen, Netherlands.,Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen, Netherlands.,Department of Pediatrics/Pediatric Nephrology and Department of Development and Regeneration, University Hospitals Leuven, Leuven, Belgium
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