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Thurman JM, Harrison RA. The susceptibility of the kidney to alternative pathway activation-A hypothesis. Immunol Rev 2023; 313:327-338. [PMID: 36369971 DOI: 10.1111/imr.13168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The glomerulus is often the prime target of dysregulated alternative pathway (AP) activation. In particular, AP activation is the key driver of two severe kidney diseases: atypical hemolytic uremic syndrome and C3 glomerulopathy. Both conditions are associated with a variety of predisposing molecular defects in AP regulation, such as genetic variants in complement regulators, autoantibodies targeting AP proteins, or autoantibodies that stabilize the AP convertases (C3- and C5-activating enzymes). It is noteworthy that these are systemic AP defects, yet in both diseases pathologic complement activation primarily affects the kidneys. In particular, AP activation is often limited to the glomerular capillaries. This tropism of AP-mediated inflammation for the glomerulus points to a unique interaction between AP proteins in plasma and this particular anatomic structure. In this review, we discuss the pre-clinical and clinical data linking the molecular causes of aberrant control of the AP with activation in the glomerulus, and the possible causes of this tropism. Based on these data, we propose a model for why the kidney is so uniquely and frequently targeted in patients with AP defects. Finally, we discuss possible strategies for preventing pathologic AP activation in the kidney.
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Affiliation(s)
- Joshua M Thurman
- Department of Medicine, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, Colorado, USA
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Banda NK, Tomlinson S, Scheinman RI, Ho N, Ramirez JR, Mehta G, Wang G, Vu VP, Simberg D, Kulik L, Holers VM. C2 IgM Natural Antibody Enhances Inflammation and Its Use in the Recombinant Single Chain Antibody-Fused Complement Inhibitor C2-Crry to Target Therapeutics to Joints Attenuates Arthritis in Mice. Front Immunol 2020; 11:575154. [PMID: 33178202 PMCID: PMC7596757 DOI: 10.3389/fimmu.2020.575154] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Accepted: 09/08/2020] [Indexed: 01/12/2023] Open
Abstract
Natural IgM antibodies (NAbs) have been shown to recognize injury-associated neoepitopes and to initiate pathogenic complement activation. The NAb termed C2 binds to a subset of phospholipids displayed on injured cells, and its role(s) in arthritis, as well as the potential therapeutic benefit of a C2 NAb-derived ScFv-containing protein fused to a complement inhibitor, complement receptor-related y (Crry), on joint inflammation are unknown. Our first objective was to functionally test mAb C2 binding to apoptotic cells from the joint and also evaluate its inflammation enhancing capacity in collagen antibody-induced arthritis (CAIA). The second objective was to generate and test the complement inhibitory capacity of C2-Crry fusion protein in the collagen-induced arthritis (CIA) model. The third objective was to demonstrate in vivo targeting of C2-Crry to damaged joints in mice with arthritis. The effect of C2-NAb on CAIA in C57BL/6 mice was examined by inducing a suboptimal disease. The inhibitory effect of C2-Crry in DBA/1J mice with CIA was determined by injecting 2x per week with a single dose of 0.250 mg/mouse. Clinical disease activity (CDA) was examined, and knee joints were fixed for analysis of histopathology, C3 deposition, and macrophage infiltration. In mice with suboptimal CAIA, at day 10 there was a significant (p < 0.017) 74% increase in the CDA in mice treated with C2 NAb, compared to mice treated with F632 control NAb. In mice with CIA, at day 35 there was a significant 39% (p < 0.042) decrease in the CDA in mice treated with C2-Crry. Total scores for histopathology were also 50% decreased (p < 0.0005) in CIA mice treated with C2-Crry. C3 deposition was significantly decreased in the synovium (44%; p < 0.026) and on the surface of cartilage (42%; p < 0.008) in mice treated with C2-Crry compared with PBS treated CIA mice. Furthermore, C2-Crry specifically bound to apoptotic fibroblast-like synoviocytes in vitro, and also localized in the knee joints of arthritic mice as analyzed by in vivo imaging. In summary, NAb C2 enhanced arthritis-related injury, and targeted delivery of C2-Crry to inflamed joints demonstrated disease modifying activity in a mouse model of human inflammatory arthritis.
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Affiliation(s)
- Nirmal K Banda
- Division of Rheumatology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Stephen Tomlinson
- Department of Microbiology and Immunology, Medical University of South Carolina, Charleston, SC, United States
| | - Robert I Scheinman
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Nhu Ho
- Division of Rheumatology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States.,Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Joseline Ramos Ramirez
- Division of Rheumatology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Gaurav Mehta
- Division of Rheumatology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Guankui Wang
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Vivian Pham Vu
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Dmitri Simberg
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Liudmila Kulik
- Division of Rheumatology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - V Michael Holers
- Division of Rheumatology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
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Banadakoppa M, Pennington K, Balakrishnan M, Yallampalli C. Complement inhibitor Crry expression in mouse placenta is essential for maintaining normal blood pressure and fetal growth. PLoS One 2020; 15:e0236968. [PMID: 32745140 PMCID: PMC7398533 DOI: 10.1371/journal.pone.0236968] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 07/16/2020] [Indexed: 11/18/2022] Open
Abstract
Many circumstantial evidences from human and animal studies suggest that complement cascade dysregulation may play an important role in pregnancy associated complications including preeclampsia. Deletion of rodent specific complement inhibitor gene, Complement Receptor 1-related Gene/Protein y (Crry) produces embryonic lethal phenotype due to complement activation. It is not clear if decreased expression of Crry during pregnancy produces hypertensive phenotype. We downregulated Crry in placenta by injecting inducible lentivialshRNA vectors into uterine horn of pregnant C57BL/6 mice at the time of blastocyst hatching. Placenta specific downregulation of Crry without significant loss of embryos was achieved upon induction of shRNA using an optimal doxycycline dose at mid gestation. Crry downregulation resulted in placental complement deposition. Late-gestation measurements showed that fetal weights were reduced and blood pressure increased in pregnant mice upon downregulation of Crry suggesting a critical role for Crry in fetal growth and blood pressure regulation.
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Affiliation(s)
- Manu Banadakoppa
- Department of Obstetrics & Gynecology, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail: (MB); (CY)
| | - Kathleen Pennington
- Department of Obstetrics & Gynecology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Meena Balakrishnan
- Department of Obstetrics & Gynecology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Chandra Yallampalli
- Department of Obstetrics & Gynecology, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail: (MB); (CY)
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Triebwasser MP, Wu X, Bertram P, Hourcade DE, Nelson DM, Atkinson JP. Timing and mechanism of conceptus demise in a complement regulatory membrane protein deficient mouse. Am J Reprod Immunol 2018; 80:e12997. [PMID: 29924462 PMCID: PMC6160323 DOI: 10.1111/aji.12997] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Accepted: 05/24/2018] [Indexed: 01/01/2023] Open
Abstract
PROBLEM Crry is a widely expressed type 1 transmembrane complement regulatory protein in rodents which protects self-tissue by downregulating C3 activation. Crry-/- concepti produced by Crry+/- × Crry+/- matings are attacked by maternal complement system leading to loss before day 10. The membrane attack complex is not the mediator of this death. We hypothesized that the ability of C3b to engage the alternative pathway's feedback loop relatively unchecked on placental membranes induces the lesion yielding the demise of the Crry-/- mouse. METHOD OF STUDY We investigated the basis of Crry-/- conceptus demise by depleting maternal complement with cobra venom factor and blocking antibodies. We monitored their effects primarily by genotyping and histologic analyses. RESULTS We narrowed the critical period of the complement effect from 6.5 to 8.5 days post-coitus (dpc), which is immediately after the conceptus is exposed to maternal blood. Deposition by 5.5 dpc of maternal C3b on the placental vasculature lacking Crry-/- yielded loss of the conceptus by 8.5 dpc. Fusion of the allantois to the chorion during placental assembly did not occur, fetal vessels originating in the allantois did not infiltrate the chorioallantoic placenta, the chorionic plate failed to develop, and the labyrinthine component of the placenta did not mature. CONCLUSION Our data are most consistent with the deposition of C3b being responsible for the failure of the allantois to fuse to the chorion leading to subsequent conceptus demise.
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Affiliation(s)
- Michael P Triebwasser
- Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, MO, USA
| | - Xiaobo Wu
- Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, MO, USA
| | - Paula Bertram
- Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, MO, USA
| | - Dennis E Hourcade
- Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, MO, USA
| | - Donald Michael Nelson
- Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Ultrasound and Genetics, Washington University School of Medicine, St. Louis, MO, USA
| | - John P Atkinson
- Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, MO, USA
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Girardi G. Complement activation, a threat to pregnancy. Semin Immunopathol 2017; 40:103-111. [PMID: 28900713 DOI: 10.1007/s00281-017-0645-x] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Accepted: 08/03/2017] [Indexed: 12/11/2022]
Abstract
Pregnancy poses a challenge for the immune systems of placental mammals. As fetal tissues are semi-allogeneic and alloantibodies that commonly develop in the mother, the fetus and the placenta might be subject to complement-mediated immune attack with the potential risk of adverse pregnancy outcomes. Here, I describe how the use of animal models was pivotal in demonstrating that complement inhibition at the fetomaternal interface is essential for a successful pregnancy. Studies in animals also helped the identification of uncontrolled complement activation as a crucial effector in the pathogenesis of recurrent miscarriages, intrauterine growth restriction, preeclampsia, and preterm birth. Clinical studies employing complement biomarkers in plasma and urine showed an association between dysregulation of the complement system and adverse pregnancy outcomes. A better understanding of the role of the complement system in pregnancy complications will allow a rational approach to manipulate its activation as a potential therapeutic strategy with the goal of protecting pregnancies and improving long-term outcomes for mother and child.
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Affiliation(s)
- Guillermina Girardi
- Pregnancy Laboratory, Department of Women and Children's Health, The Rayne Institute, St Thomas' Hospital, King's College London, London, SE1 7EH, UK.
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Dias Bastos PA, Vlahou A, Leite-Moreira A, Santos LL, Ferreira R, Vitorino R. Deciphering the disease-related molecular networks using urine proteomics. Trends Analyt Chem 2017. [DOI: 10.1016/j.trac.2017.07.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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C5a/C5aR Pathway Plays a Vital Role in Brain Inflammatory Injury via Initiating Fgl-2 in Intracerebral Hemorrhage. Mol Neurobiol 2016; 54:6187-6197. [PMID: 27709492 DOI: 10.1007/s12035-016-0141-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 09/19/2016] [Indexed: 01/05/2023]
Abstract
Intracerebral hemorrhage (ICH) is a serious emergency with high mortality and morbidity. Up to date, a limited understanding of ICH pathogenesis is difficult to implement effective therapeutic strategy. Much evidence demonstrates that the complement cascade is activated after experimental ICH. However, the exact mechanism has not been well studied in ICH. In the current study, C57BL/6J mice were injected with autologous whole blood. C5a/C5aR levels, microglia infiltration, inflammatory cytokine, and fibrinogen-like protein 2 (Fgl-2) expression in the perihematomal region were analyzed following ICH. In addition, brain water content and neurological dysfunction were detected following ICH. Our data demonstrated that ICH induced complement activation, along with an increase of C5a/C5aR levels, microglia infiltration, and inflammatory cytokine levels. However, C5aR-/- mice exhibited significant attenuation of inflammatory reaction, accompanied by a remarkable reduction of Fgl-2, brain water content, and neurological dysfunction. Furthermore, inhibiting extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 efficiently inhibited C5a-mediated Fgl-2 production following ICH. Taken together, these data suggest that C5a/C5aR plays a vital role in the ICH-induced inflammatory damage via Fgl-2, and ERK1/2 and p38 pathways also are involved in the pathogenesis of ICH. Therefore, inhibition of C5a/C5aR activation might enlarge our insights in ICH therapy.
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Ueda Y, Gullipalli D, Song WC. Modeling complement-driven diseases in transgenic mice: Values and limitations. Immunobiology 2016; 221:1080-90. [PMID: 27371974 DOI: 10.1016/j.imbio.2016.06.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 06/07/2016] [Accepted: 06/09/2016] [Indexed: 12/15/2022]
Abstract
Remarkable advances have been made over past decades in understanding the pathogenesis of complement-mediated diseases. This has led to development of new therapies for, and in some cases re-classification of, complement-driven diseases. This success is due to not only insight from human patients but also studies using transgenic animal models. Animal models that mimic human diseases are useful tools to understand the mechanism of disease and develop new therapies but there are also limitations due to species differences in their complement systems. This review provides a summary of transgenic animal models for three human diseases that are at the forefront of anti-complement therapy, paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). They are discussed here as examples to highlight the values and limitations of animal modeling in complement-driven diseases.
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Affiliation(s)
- Yoshiyasu Ueda
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, United States
| | - Damodar Gullipalli
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, United States
| | - Wen-Chao Song
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, United States.
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Distinct roles for the complement regulators factor H and Crry in protection of the kidney from injury. Kidney Int 2016; 90:109-22. [PMID: 27165610 DOI: 10.1016/j.kint.2016.02.036] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2015] [Revised: 02/23/2016] [Accepted: 02/25/2016] [Indexed: 12/29/2022]
Abstract
Mutations in the complement regulatory proteins are associated with several different diseases. Although these mutations cause dysregulated alternative pathway activation throughout the body, the kidneys are the most common site of injury. The susceptibility of the kidney to alternative pathway-mediated injury may be due to limited expression of complement regulatory proteins on several tissue surfaces within the kidney. To examine the roles of the complement regulatory proteins factor H and Crry in protecting distinct renal surfaces from alternative pathway mediated injury, we generated mice with targeted deletions of the genes for both proteins. Surprisingly, mice with combined genetic deletions of factor H and Crry developed significantly milder renal injury than mice deficient in only factor H. Deficiency of both factor H and Crry was associated with C3 deposition at multiple locations within the kidney, but glomerular C3 deposition was lower than that in factor H alone deficient mice. Thus, factor H and Crry are critical for regulating complement activation at distinct anatomic sites within the kidney. However, widespread activation of the alternative pathway reduces injury by depleting the pool of C3 available at any 1 location.
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Tissue-specific deletion of Crry from mouse proximal tubular epithelial cells increases susceptibility to renal ischemia-reperfusion injury. Kidney Int 2014; 86:726-37. [PMID: 24850152 PMCID: PMC4182132 DOI: 10.1038/ki.2014.103] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 02/05/2014] [Accepted: 02/13/2014] [Indexed: 12/19/2022]
Abstract
The murine cell surface protein Crry (complement receptor 1-related protein/gene y) is a key complement regulator with similar activities to human membrane cofactor protein (MCP) and decay-accelerating factor. MCP has a critical role in preventing complement-mediated tissue injury and its mutation has been implicated in several human kidney diseases. The study of Crry in mice has relevance to understanding MCP activity in human diseases; however, such efforts have been hampered by the embryonic lethality phenotype of Crry gene knockout. Here we used a conditional gene-targeting approach and deleted Crry from the mouse proximal tubular epithelial cells where Crry is prominently expressed. Absence of Crry from proximal tubular epithelial cells resulted in spontaneous C3 deposition on the basolateral surface but no apparent renal disease in unchallenged mice. However, mice deficient in Crry on proximal tubular epithelial cells developed exacerbated renal injury when subjected to renal ischemia-reperfusion, showing increased blood urea nitrogen levels, higher tubular injury scores, more tubular epithelial cell apoptosis, and inflammatory infiltrates. Renal ischemia-reperfusion injury in the Crry conditional knockout mice was prevented by blocking C3 and C5 activation using an anti-properdin or anti-C5 monoclonal antibody (mAb), respectively. Thus, Crry has a critical role in protecting proximal tubular epithelial cells during ischemia-reperfusion challenge. Our results highlight the latent risk for inflammatory kidney injury associated with defects in membrane complement regulators.
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Shah TA, Mauriello CT, Hair PS, Sharp JA, Kumar PS, Lattanzio FA, Werner AL, Whitley PH, Maes LA, Cunnion KM, Krishna NK. Complement inhibition significantly decreases red blood cell lysis in a rat model of acute intravascular hemolysis. Transfusion 2014; 54:2892-900. [PMID: 24806146 DOI: 10.1111/trf.12695] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 02/14/2014] [Accepted: 03/02/2014] [Indexed: 11/27/2022]
Abstract
BACKGROUND Prevention of acute hemolytic transfusion reactions is a worldwide concern. The objective of this study was to develop a simple rat model of complement-mediated acute intravascular hemolysis. STUDY DESIGN AND METHODS Human AB red blood cells (RBCs) were incubated with complement-sufficient or complement-deficient Wistar rat serum (WRS) in the presence and absence of human RBC antibody in vitro to elucidate the mechanism of hemolysis. To study the role of complement in acute intravascular hemolysis in vivo, Wistar rats were treated either with or without cobra venom factor (CVF) to deplete complement activity. Human AB RBCs were then injected into both groups of rats, followed by serial blood draws up to 2 hours. Venous blood clearance and lysis of transfused RBCs at each time point were measured by flow cytometry and spectrophotometry. RBC sequestration was determined in the liver, spleen, and kidney by immunohistochemistry. RESULTS In vitro incubation of human RBCs with WRS demonstrated that RBC lysis was mediated via the classical complement pathway and that hemolysis was antibody dependent. Transfusion of human RBCs into rats showed significantly less hemolysis in the CVF group versus untreated group. RBC sequestration in the spleen and liver 2 hours posttransfusion were not quantitatively different between the two groups. CONCLUSIONS Given the much higher degree of similarity for rat and human complement compared to mice, this simple rat model is ideal for testing novel inhibitors of classical pathway activation for the prevention and treatment of acute intravascular hemolysis.
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Affiliation(s)
- Tushar A Shah
- Department of Pediatrics, Eastern Virginia Medical School, Norfolk, Virginia; Children's Specialty Group, Norfolk, Virginia; Children's Hospital of The King's Daughters, Norfolk, Virginia
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Targeting the complement system in systemic lupus erythematosus and other diseases. Clin Immunol 2013; 148:313-21. [DOI: 10.1016/j.clim.2013.02.014] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Revised: 02/22/2013] [Accepted: 02/25/2013] [Indexed: 02/04/2023]
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Barata L, Miwa T, Sato S, Kim D, Mohammed I, Song WC. Deletion of Crry and DAF on murine platelets stimulates thrombopoiesis and increases factor H-dependent resistance of peripheral platelets to complement attack. THE JOURNAL OF IMMUNOLOGY 2013; 190:2886-95. [PMID: 23390291 DOI: 10.4049/jimmunol.1202536] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Complement receptor 1-related gene/protein y (Crry) and decay-accelerating factor (DAF) are two murine membrane C3 complement regulators with overlapping functions. Crry deletion is embryonically lethal whereas DAF-deficient mice are generally healthy. Crry(-/-)DAF(-/-) mice were viable on a C3(-/-) background, but platelets from such mice were rapidly destroyed when transfused into C3-sufficient mice. In this study, we used the cre-lox system to delete platelet Crry in DAF(-/-) mice and studied Crry/DAF-deficient platelet development in vivo. Rather than displaying thrombocytopenia, Pf4-Cre(+)-Crry(flox/flox) mice had normal platelet counts and their peripheral platelets were resistant to complement attack. However, chimera mice generated with Pf4-Cre(+)-Crry(flox/flox) bone marrows showed platelets from C3(-/-) but not C3(+/+) recipients to be sensitive to complement activation, suggesting that circulating platelets in Pf4-Cre(+)-Crry(flox/flox) mice were naturally selected in a complement-sufficient environment. Notably, Pf4-Cre(+)-Crry(flox/flox) mouse platelets became complement susceptible when factor H function was blocked. Examination of Pf4-Cre(+)-Crry(flox/flox) mouse bone marrows revealed exceedingly active thrombopoiesis. Thus, under in vivo conditions, Crry/DAF deficiency on platelets led to abnormal platelet turnover, but peripheral platelet count was compensated for by increased thrombopoiesis. Selective survival of Crry/DAF-deficient platelets aided by factor H protection and compensatory thrombopoiesis demonstrates the cooperation between membrane and fluid phase complement inhibitors and the body's ability to adaptively respond to complement regulator deficiencies.
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Affiliation(s)
- Lidia Barata
- Department of Pharmacology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19401, USA
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Kusner LL, Halperin JA, Kaminski HJ. Cell surface complement regulators moderate experimental myasthenia gravis pathology. Muscle Nerve 2012; 47:33-40. [PMID: 23042232 DOI: 10.1002/mus.23448] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/01/2012] [Indexed: 01/01/2023]
Abstract
INTRODUCTION Intrinsic mouse complement regulators influence the severity of passively induced experimental acquired myasthenia gravis (EAMG). To assess the potential influence of CD59b in the absence of CD59a background, we used the mCD59ab(-/-) mouse model to re-evaluate mCD59 in protecting the neuromuscular junction (NMJ). METHODS EAMG was induced with monoclonal antibody to the acetylcholine receptor (AChR) in Daf1(-/-) , CD59ab(-/-) , Daf1(-/-) CD59ab(-/-) , and wild-type C57Bl/6 mice. Animals were monitored throughout the experiment. Diaphragms were analyzed for NMJ injury. RESULTS Daf1(-/-) CD59ab(-/-) mice required euthanasia 24 hours after disease induction because of severe weakness. Histological assessment demonstrated reduced AChR density, simplification of synaptic folds, and disrupted mitochondria. CD59ab-deficient mice demonstrated mild weakness and reduction in weight after 24 hours. In contrast, Daf1(-/-) had more severe weakness at 60 hours. The NMJ of EAMG-induced Daf1(-/-) and CD59ab(-/-) mice demonstrated similar AChR density. CONCLUSION NMJs of CD59 and DAF mice are protected from complement-mediated injury of passive EAMG.
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Affiliation(s)
- Linda L Kusner
- Department of Pharmacology and Physiology, George Washington University, Washington, DC, USA.
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Soltys J, Wu X. Complement regulatory protein Crry deficiency contributes to the antigen specific recall response in experimental autoimmune myasthenia gravis. JOURNAL OF INFLAMMATION-LONDON 2012; 9:20. [PMID: 22642809 PMCID: PMC3524051 DOI: 10.1186/1476-9255-9-20] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Accepted: 04/18/2012] [Indexed: 12/20/2022]
Abstract
UNLABELLED BACKGROUND Myasthenia gravis (MG) and animal model of experimental autoimmune myasthenia gravis (EAMG) is the most common autoimmune disorder of neuromuscular transmission. The disease is caused by the breakdown of the acetylcholine receptor (AChR) which is largely due to complement activation at the neuromuscular junction (NMJ). Limited knowledge exists to the extent that complement receptor 1-related gene/protein y deficiency (Crry -/-) modulates the adaptive immune response and EAMG outcome. METHODS Mouse EAMG was induced by s.c. administrations of purified acetylcholine receptor (AChR) to Crry -/- and age- matched WT (C57BL/6) mice. Disease severity was assessed by clinical score assessment and muscle grip strength measurements. Serum complement activity was determined by hemolytic assay. ELISA was used to detect the level of AChR specific antibodies. Splenic cells were analyzed for T and B cells subsets distribution, release of cytokines and AChR specific recall responses. Deposition of complement components at the NMJ was assessed by immunofluorescence staining. RESULTS In comparison to WT EAMG, Crry -/- EAMG mice showed signs of augmented muscle weakness but differences, except for one time point, were not statistically significant. Serum complement activity was reduced in Crry -/- EAMG mice and no substantial changes in deposition of C3, C3b/iC3b and C5b-9 (MAC) at the NMJ between WT EAMG and Crry -/- EAMG mice were detected. Lack of Crry affected adaptive immune response. Crry -/- EAMG mice showed increases in the number of AChR specific splenic T-cells secreting IFN-γ and IL-4. Production of complement fixing antibodies (IgG2b, IgG2c) was also augmented. More Th1, Th2 and Th17 cytokines were released into the bloodstream of Crry -/- EAMG mice. CONCLUSIONS Data suggest that Crry deficiency modulates the adaptive immune response in EAMG, but its effect on disease outcome is limited. This was due to the generally lower serum complement level caused by increased C3 turnover. Modulation of complement activity with soluble or membrane bound regulators of complement activity represents a potentially effective approach to modify autoimmune processes in MG and EAMG.
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Affiliation(s)
- Jindrich Soltys
- Department of Neurology & Psychiatry, 1438 South Grand Boulevard, Saint Louis University School of Medicine, Saint Louis, MO, 63104, USA.
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C3-dependent mechanism of microglial priming relevant to multiple sclerosis. Proc Natl Acad Sci U S A 2012; 109:965-70. [PMID: 22219359 DOI: 10.1073/pnas.1111924109] [Citation(s) in RCA: 111] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Microglial priming predisposes the brain to neurodegeneration and affects disease progression. The signal to switch from the quiescent to the primed state is unknown. We show that deleting the C3 convertase regulator complement receptor 1-related protein y (Crry) induces microglial priming. Mice that were double-knockout for Crry and either C3 or factor B did not show priming, demonstrating dependence on alternative pathway activation. Colocalization of C3b/iC3b and CR3 implicated the CR3/iC3b interaction in priming. Systemic lipopolysaccharide challenge overactivated primed microglia with florid expression of proinflammatory molecules, which were blocked by complement inhibition. Relevance for neurodegenerative disease is exemplified by human multiple sclerosis (MS) and by experimental autoimmune encephalomyelitis (EAE), a model of MS. In human MS, microglial priming was evident in perilesional white matter, in close proximity to C3b/iC3b deposits. EAE was accelerated and exacerbated in Crry-deficient mice, and was dependent on C activation. In summary, C3-dependent microglial priming confers susceptibility to other challenges. Our observations are relevant to progression in MS and other neurological diseases exacerbated by acute insults.
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Too Much of a Good Thing at the Site of Tissue Injury: The Instructive Example of the Complement System Predisposing to Thrombotic Microangiopathy. Hematology 2011; 2011:9-14. [DOI: 10.1182/asheducation-2011.1.9] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Abstract
The interplay between the complement and coagulation systems is just beginning to be explored and characterized. This interaction, however, is ancient. For example, if endotoxin is added to the hemolymph of the horseshoe crab, a protease is activated that triggers both the coagulation and complement systems. However, in extant mammals, these 2 cascades have diverged. These infamous “terrible C's” are the scourge of many a medical student (and possibly even a few hematologists). They also are intimately involved in the pathophysiology of thrombomicroangiopathies (TMAs). The complement system generates a procoagulant microenvironment and the coagulation system forms a clot in the renal microvasculature, and thus the 2 systems are partners in mediating multiple pathophysiological conditions.
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Roversi P, Johnson S, Caesar JJE, McLean F, Leath KJ, Tsiftsoglou SA, Morgan BP, Harris CL, Sim RB, Lea SM. Structures of the rat complement regulator CrrY. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011; 67:739-43. [PMID: 21795784 PMCID: PMC3144786 DOI: 10.1107/s1744309111016551] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 05/02/2011] [Indexed: 11/26/2022]
Abstract
Complement receptor 1-related protein Y (CrrY) is an important cell-surface regulator of complement that is unique to rodent species. The structure of rat CrrY domains 1-4 has been determined in two distinct crystal forms and reveals a 70° bend between domains 3 and 4. Comparisons of this structure with those of other complement regulators suggests that rearrangement of this interface may occur on forming the regulatory complex with C3b.
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Affiliation(s)
- Pietro Roversi
- Sir William Dunn School of Pathology, Oxford University, South Parks Road, Oxford OX4 3RE, England
| | - Steven Johnson
- Sir William Dunn School of Pathology, Oxford University, South Parks Road, Oxford OX4 3RE, England
| | - Joseph J. E. Caesar
- Sir William Dunn School of Pathology, Oxford University, South Parks Road, Oxford OX4 3RE, England
| | - Florence McLean
- Sir William Dunn School of Pathology, Oxford University, South Parks Road, Oxford OX4 3RE, England
| | - Kirstin J. Leath
- Sir William Dunn School of Pathology, Oxford University, South Parks Road, Oxford OX4 3RE, England
| | | | - B. Paul Morgan
- Department of Infection, Immunity and Biochemistry, Cardiff University, Cardiff CF14 4XN, Wales
| | - Claire L. Harris
- Department of Infection, Immunity and Biochemistry, Cardiff University, Cardiff CF14 4XN, Wales
| | - Robert B. Sim
- Department of Biochemistry, Oxford University, South Parks Road, Oxford OX1 3QU, England
| | - Susan M. Lea
- Department of Biochemistry, Oxford University, South Parks Road, Oxford OX1 3QU, England
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Properdin homeostasis requires turnover of the alternative complement pathway. Proc Natl Acad Sci U S A 2010; 107:19444-8. [PMID: 20974943 DOI: 10.1073/pnas.1006608107] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Properdin is a plasma protein and is also released from neutrophil granules following stimulation. At inflammatory sites it can bind bacteria and apoptotic bodies to trigger alternative pathway (AP) activation. Principles governing properdin homeostasis are unknown. We monitored properdin during AP activation and in complement-deficient mice. There was a >90% reduction of properdin in the Crry single-knockout mice (Crry SKO). These membrane complement regulatory protein-deficient mice feature accelerated AP turnover, leading to reduced C3 and fB. Injecting cobra venom factor into wild-type mice activated the AP and led to the consumption of C3, fB, and properdin. However, and unexpectedly, properdin was also deficient in C3(-/-), fB(-/-), and fD(-/-) mice. It was present in C1q(-/-), C4(-/-), and C5(-/-) mice. These findings implicate AP turnover in the maintenance of basal levels of properdin in the blood. To explore the mechanism, classical pathway-activating immune complexes were infused. Within 10 min, properdin was partially restored in fB(-/-) but not in C3(-/-) mice. Markedly reduced properdin in mice deficient in an AP component and its partial restoration by activating C3 suggest a requirement for continuous C3 activation via AP tickover to maintain properdin homeostasis. The mechanism underlying this C3-dependent process was not identified. Engagement of C3a and C5a receptors was ruled out. These findings represent an instructive example of how a positive regulator of an innate immune recognition and effector pathway is controlled. A rationale for such a means to supply properdin for immune reactions is proposed.
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Moulton EA, Bertram P, Chen N, Buller RML, Atkinson JP. Ectromelia virus inhibitor of complement enzymes protects intracellular mature virus and infected cells from mouse complement. J Virol 2010; 84:9128-39. [PMID: 20610727 PMCID: PMC2937632 DOI: 10.1128/jvi.02677-09] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2009] [Accepted: 06/27/2010] [Indexed: 11/20/2022] Open
Abstract
Poxviruses produce complement regulatory proteins to subvert the host's immune response. Similar to the human pathogen variola virus, ectromelia virus has a limited host range and provides a mouse model where the virus and the host's immune response have coevolved. We previously demonstrated that multiple components (C3, C4, and factor B) of the classical and alternative pathways are required to survive ectromelia virus infection. Complement's role in the innate and adaptive immune responses likely drove the evolution of a virus-encoded virulence factor that regulates complement activation. In this study, we characterized the ectromelia virus inhibitor of complement enzymes (EMICE). Recombinant EMICE regulated complement activation on the surface of CHO cells, and it protected complement-sensitive intracellular mature virions (IMV) from neutralization in vitro. It accomplished this by serving as a cofactor for the inactivation of C3b and C4b and by dissociating the catalytic domain of the classical pathway C3 convertase. Infected murine cells initiated synthesis of EMICE within 4 to 6 h postinoculation. The levels were sufficient in the supernatant to protect the IMV, upon release, from complement-mediated neutralization. EMICE on the surface of infected murine cells also reduced complement activation by the alternative pathway. In contrast, classical pathway activation by high-titer antibody overwhelmed EMICE's regulatory capacity. These results suggest that EMICE's role is early during infection when it counteracts the innate immune response. In summary, ectromelia virus produced EMICE within a few hours of an infection, and EMICE in turn decreased complement activation on IMV and infected cells.
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Affiliation(s)
- Elizabeth A. Moulton
- Division of Rheumatology, Department of Medicine, Washington University School of Medicine, Saint Louis, Missouri 63110, Department of Molecular Microbiology and Immunology, Saint Louis University Health Sciences Center, Saint Louis, Missouri 63104
| | - Paula Bertram
- Division of Rheumatology, Department of Medicine, Washington University School of Medicine, Saint Louis, Missouri 63110, Department of Molecular Microbiology and Immunology, Saint Louis University Health Sciences Center, Saint Louis, Missouri 63104
| | - Nanhai Chen
- Division of Rheumatology, Department of Medicine, Washington University School of Medicine, Saint Louis, Missouri 63110, Department of Molecular Microbiology and Immunology, Saint Louis University Health Sciences Center, Saint Louis, Missouri 63104
| | - R. Mark L. Buller
- Division of Rheumatology, Department of Medicine, Washington University School of Medicine, Saint Louis, Missouri 63110, Department of Molecular Microbiology and Immunology, Saint Louis University Health Sciences Center, Saint Louis, Missouri 63104
| | - John P. Atkinson
- Division of Rheumatology, Department of Medicine, Washington University School of Medicine, Saint Louis, Missouri 63110, Department of Molecular Microbiology and Immunology, Saint Louis University Health Sciences Center, Saint Louis, Missouri 63104
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21
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Renner B, Coleman K, Goldberg R, Amura C, Holland-Neidermyer A, Pierce K, Orth HN, Molina H, Ferreira VP, Cortes C, Pangburn MK, Holers VM, Thurman JM. The complement inhibitors Crry and factor H are critical for preventing autologous complement activation on renal tubular epithelial cells. THE JOURNAL OF IMMUNOLOGY 2010; 185:3086-94. [PMID: 20675597 DOI: 10.4049/jimmunol.1000111] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Congenital and acquired deficiencies of complement regulatory proteins are associated with pathologic complement activation in several renal diseases. To elucidate the mechanisms by which renal tubular epithelial cells (TECs) control the complement system, we examined the expression of complement regulatory proteins by the cells. We found that Crry is the only membrane-bound complement regulator expressed by murine TECs, and its expression is concentrated on the basolateral surface. Consistent with the polarized localization of Crry, less complement activation was observed when the basolateral surface of TECs was exposed to serum than when the apical surface was exposed. Furthermore, greater complement activation occurred when the basolateral surface of TECs from Crry(-/-)fB(-/-) mice was exposed to normal serum compared with TECs from wild-type mice. Complement activation on the apical and basolateral surfaces was also greater when factor H, an alternative pathway regulatory protein found in serum, was blocked from interacting with the cells. Finally, we injected Crry(-/-)fB(-/-) and Crry(+/+)fB(-/-) mice with purified factor B (an essential protein of the alternative pathway). Spontaneous complement activation was seen on the tubules of Crry(-/-)fB(-/-) mice after injection with factor B, and the mice developed acute tubular injury. These studies indicate that factor H and Crry regulate complement activation on the basolateral surface of TECs and that factor H regulates complement activation on the apical surface. However, congenital deficiency of Crry or reduced expression of the protein on the basolateral surface of injured cells permits spontaneous complement activation and tubular injury.
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Affiliation(s)
- Brandon Renner
- Department of Medicine, University of Colorado Denver School of Medicine, Denver, CO 80045, USA
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Fakhouri F, Roumenina L, Provot F, Sallée M, Caillard S, Couzi L, Essig M, Ribes D, Dragon-Durey MA, Bridoux F, Rondeau E, Frémeaux-Bacchi V. Pregnancy-associated hemolytic uremic syndrome revisited in the era of complement gene mutations. J Am Soc Nephrol 2010; 21:859-67. [PMID: 20203157 DOI: 10.1681/asn.2009070706] [Citation(s) in RCA: 281] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In contrast to pregnancy-associated thrombotic thrombocytopenic purpura, the pathogenesis and presentation of pregnancy-associated atypical hemolytic uremic syndrome (P-aHUS) remain ill-defined. We conducted a retrospective study to assess the presentation and outcomes of patients presenting with P-aHUS and the prevalence of alternative C3 convertase dysregulation. P-aHUS occurred in 21 of the 100 adult female patients with atypical HUS, with 79% presenting postpartum. We detected complement abnormalities in 18 of the 21 patients. The outcomes were poor: 62% reached ESRD by 1 month and 76% by last follow-up. The risk for P-aHUS was highest during a second pregnancy. Thirty-five women, 26 (74%) of whom had complement abnormalities, had at least one pregnancy before the onset of a non-pregnancy-related aHUS. Outcomes did not differ between patients with pregnancy-related and non-pregnancy-related aHUS. Mutations in the SCR19-20 domains of factor H were less frequent in P-aHUS patients compared with non-pregnancy-related aHUS. Pregnancies in female patients with complement abnormalities (n = 44) were complicated by fetal loss and preeclampsia in 4.8% and 7.7%, respectively. Better understanding of complement dysregulation in pregnancy complications is essential, especially to guide development of pharmacologic agents to modulate this system.
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Affiliation(s)
- Fadi Fakhouri
- Department of Nephrology and UMR 643, CHU de Nantes, Paris, France
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Wilson RA, Coulson PS. Immune effector mechanisms against schistosomiasis: looking for a chink in the parasite's armour. Trends Parasitol 2009; 25:423-31. [PMID: 19717340 DOI: 10.1016/j.pt.2009.05.011] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Revised: 05/15/2009] [Accepted: 05/22/2009] [Indexed: 11/19/2022]
Abstract
A recombinant antigen vaccine against Schistosoma mansoni remains elusive, in part because the parasite deploys complex defensive and offensive strategies to combat immune attack. Nevertheless, research on rodent and primate models has shown that schistosomes can be defeated when appropriate responses are elicited. Acquired protection appears to involve protracted inhibition of larval migration or key molecular processes at the adult surfaces, not rapid cytolytic killing mechanisms. A successful vaccine will likely require a cocktail of antigens rather than a single recombinant protein. In addition, ways need to be found of keeping the immune system on permanent alert, either to achieve adequate inhibition of protein function in adults, or because a trickle of incoming parasites does not amplify the secondary response.
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Affiliation(s)
- R Alan Wilson
- Department of Biology, University of York, PO Box 373,York YO10 5YW, UK.
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Bao L, Wang Y, Chen P, Sarav M, Haas M, Minto AW, Petkova M, Quigg RJ. Mesangial cell complement receptor 1-related protein y limits complement-dependent neutrophil accumulation in immune complex glomerulonephritis. Immunology 2009; 128:e895-904. [PMID: 19740350 DOI: 10.1111/j.1365-2567.2009.03102.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The absence of complement receptor 1 (CR1) related gene/protein y (Crry) leads to embryonic lethality as a result of unrestricted complement activation and concomitant neutrophil infiltration. Here we used Crry(-/-)C3(+/-) mice to investigate the role of Crry in the pathogenesis of immune complex glomerulonephritis (GN). After 3 weeks of immunization with horse spleen apoferritin, six of nine Crry(-/-) C3(+/-) mice and none of the six control C3(+/-) mice developed proliferative GN (P = 0.010). After 5 weeks of immunization, GN scores in Crry(-/-) C3(+/-) mice were 0.67 +/- 0.22 mean +/- standard error of the mean (SEM), compared with 0.32 +/- 0.16 in C3(+/-) mice. Glomerular hypercellularity was attributable to neutrophil infiltration in mice with GN (1.7 +/- 0.3/glomerulus) compared with those without GN (0.4 +/- 0.1/glomerulus) (P = 0.001). Absent staining for alpha-smooth muscle actin and proliferating cell nuclear antigen suggested that mesangial cell proliferation did not play a significant role in this model. Serum C3 levels in Crry(-/-) C3(+/-) mice were approximately 20% and 30% those of wild-type mice and C3(+/-) mice, respectively. To determine whether this acquired hypocomplementaemia was relevant to this GN model system, Crry(-/-) C3(+/-) mouse kidneys were transplanted into wild-type mice followed by immunization with apoferritin for 1 or 2 weeks. Surprisingly, none of the Crry(-/-) C3(+/-) mouse kidneys developed GN at these early time-points, indicating that increasing circulating C3 levels several-fold did not increase susceptibility to GN. Renal expression of decay-accelerating factor was not different among any of the groups studied. Thus, our data indicate that mesangial cell Crry limits complement activation and subsequent neutrophil recruitment in the setting of local immune complex deposition.
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Affiliation(s)
- Lihua Bao
- The University of Chicago, Chicago, IL 60637, USA.
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Surviving mousepox infection requires the complement system. PLoS Pathog 2008; 4:e1000249. [PMID: 19112490 PMCID: PMC2597719 DOI: 10.1371/journal.ppat.1000249] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2008] [Accepted: 11/26/2008] [Indexed: 11/19/2022] Open
Abstract
Poxviruses subvert the host immune response by producing immunomodulatory proteins, including a complement regulatory protein. Ectromelia virus provides a mouse model for smallpox where the virus and the host's immune response have co-evolved. Using this model, our study investigated the role of the complement system during a poxvirus infection. By multiple inoculation routes, ectromelia virus caused increased mortality by 7 to 10 days post-infection in C57BL/6 mice that lack C3, the central component of the complement cascade. In C3−/− mice, ectromelia virus disseminated earlier to target organs and generated higher peak titers compared to the congenic controls. Also, increased hepatic inflammation and necrosis correlated with these higher tissue titers and likely contributed to the morbidity in the C3−/− mice. In vitro, the complement system in naïve C57BL/6 mouse sera neutralized ectromelia virus, primarily through the recognition of the virion by natural antibody and activation of the classical and alternative pathways. Sera deficient in classical or alternative pathway components or antibody had reduced ability to neutralize viral particles, which likely contributed to increased viral dissemination and disease severity in vivo. The increased mortality of C4−/− or Factor B−/− mice also indicates that these two pathways of complement activation are required for survival. In summary, the complement system acts in the first few minutes, hours, and days to control this poxviral infection until the adaptive immune response can react, and loss of this system results in lethal infection. As one of the most successful pathogens ever, smallpox caused death and disfigurement worldwide until its eradication in the 1970s. The complement system, an essential part of the innate immune response, protects against many pathogens; however, its role during smallpox infection is unclear. In this study, we investigated the importance of the complement system in mousepox infection as a model for human smallpox disease. We compared mice with and without genetic deficiencies in complement following infection by multiple routes with ectromelia virus, the causative agent of mousepox. Deficiencies in several complement proteins reduced survival of ectromelia infection. Sera from these same complement-deficient mice also have reduced ability to neutralize ectromelia virus in vitro. In complement-deficient mice, ectromelia virus disseminated from the inoculation site earlier and produced higher levels of virus in the bloodstream, spleen, and liver. The increased infection in the liver resulted in greater tissue damage. We hypothesize that the complement-deficient mice's reduced ability to neutralize ectromelia virus at the inoculation site resulted in earlier dissemination and more severe disease. We have demonstrated that surviving ectromelia virus infection requires the complement system, which suggests that this system may also protect against smallpox infection.
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