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Michels MAHM, Maas RJF, van der Velden TJAM, van de Kar NCAJ, van den Heuvel LPWJ, Volokhina EB. The Role of Properdin in C5 Convertase Activity and C5b-9 Formation in the Complement Alternative Pathway. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2021; 207:2465-2472. [PMID: 34635587 DOI: 10.4049/jimmunol.2100238] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 09/03/2021] [Indexed: 12/30/2022]
Abstract
The complement system is an important part of innate immunity. Complement activation leads to formation of convertase enzymes, switch of their specificity from C3 to C5 cleavage, and generation of lytic membrane attack complexes (C5b-9) on surfaces of pathogens. Most C5 cleavage occurs via the complement alternative pathway (AP). The regulator properdin promotes generation and stabilization of AP convertases. However, its role in C5 activation is not yet understood. In this work, we showed that serum properdin is essential for LPS- and zymosan-induced C5b-9 generation and C5b-9-mediated lysis of rabbit erythrocytes. Furthermore, we demonstrated its essential role in C5 cleavage by AP convertases. To this end, we developed a hemolytic assay in which AP convertases were generated on rabbit erythrocytes by using properdin-depleted serum in the presence of C5 inhibitor (step 1), followed by washing and addition of purified C5-C9 components to allow C5b-9 formation (step 2). In this assay, addition of purified properdin to properdin-depleted serum during convertase formation (step 1) was required to restore C5 cleavage and C5b-9-mediated hemolysis. Importantly, C5 convertase activity was also fully restored when properdin was added together with C5b-9 components (step 2), thus after convertase formation. Moreover, with C3-depleted serum, not capable of forming new convertases but containing properdin, in step 2 of the assay, again full C5b-9 formation was observed and blocked by addition of properdin inhibitor Salp20. Thus, properdin is essential for the convertase specificity switch toward C5, and this function is independent of properdin's role in new convertase formation.
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Affiliation(s)
- Marloes A H M Michels
- Radboud Institute for Molecular Life Sciences, Department of Pediatric Nephrology, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, the Netherlands;
| | - Rianne J F Maas
- Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Thea J A M van der Velden
- Radboud Institute for Molecular Life Sciences, Department of Pediatric Nephrology, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Nicole C A J van de Kar
- Radboud Institute for Molecular Life Sciences, Department of Pediatric Nephrology, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Lambertus P W J van den Heuvel
- Radboud Institute for Molecular Life Sciences, Department of Pediatric Nephrology, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, the Netherlands.,Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen, the Netherlands.,Department of Pediatrics/Pediatric Nephrology, University Hospitals Leuven, Leuven, Belgium; and.,Department of Development and Regeneration, University Hospitals Leuven, Leuven, Belgium
| | - Elena B Volokhina
- Radboud Institute for Molecular Life Sciences, Department of Pediatric Nephrology, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, the Netherlands.,Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen, the Netherlands
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Michels MAHM, van de Kar NCAJ, van Kraaij SAW, Sarlea SA, Gracchi V, Engels FAPT, Dorresteijn EM, van der Deure J, Duineveld C, Wetzels JFM, van den Heuvel LPWJ, Volokhina EB. Different Aspects of Classical Pathway Overactivation in Patients With C3 Glomerulopathy and Immune Complex-Mediated Membranoproliferative Glomerulonephritis. Front Immunol 2021; 12:715704. [PMID: 34456924 PMCID: PMC8386118 DOI: 10.3389/fimmu.2021.715704] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Accepted: 07/20/2021] [Indexed: 11/13/2022] Open
Abstract
The rare and heterogeneous kidney disorder C3 glomerulopathy (C3G) is characterized by dysregulation of the alternative pathway (AP) of the complement system. C3G is often associated with autoantibodies stabilizing the AP C3 convertase named C3 nephritic factors (C3NeF). The role of classical pathway (CP) convertase stabilization in C3G and related diseases such as immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) remains largely unknown. Here, we investigated the CP convertase activity in patients with C3G and IC-MPGN. Using a refined two-step hemolytic assay, we measured the stability of CP convertases directly in the serum of 52 patients and 17 healthy controls. In four patients, CP convertase activity was prolonged compared to healthy controls, i.e. the enzymatic complex was stabilized. In three patients (2 C3G, 1 IC-MPGN) the convertase stabilization was caused by immunoglobulins, indicating the presence of autoantibodies named C4 nephritic factors (C4NeFs). Importantly, the assay also enabled detection of non-immunoglobulin-mediated stabilization of the CP convertase in one patient with C3G. Prolonged CP convertase activity coincided with C3NeF activity in all patients and for up to 70 months of observation. Crucially, experiments with C3-depleted serum showed that C4NeFs stabilized the CP C3 convertase (C4bC2a), that does not contain C3NeF epitopes. All patients with prolonged CP convertase activity showed clear signs of complement activation, i.e. lowered C3 and C5 levels and elevated levels of C3d, C3bc, C3bBbP, and C5b-9. In conclusion, this work provides new insights into the diverse aspects and (non-)immunoglobulin nature of factors causing CP convertase overactivity in C3G/IC-MPGN.
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Affiliation(s)
- Marloes A H M Michels
- Department of Pediatric Nephrology, Radboud Institute for Molecular Life Sciences, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, Netherlands
| | - Nicole C A J van de Kar
- Department of Pediatric Nephrology, Radboud Institute for Molecular Life Sciences, Amalia Children's Hospital, Radboud University Medical Center, 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 Institute for Molecular Life Sciences, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, Netherlands
| | - Valentina Gracchi
- Department of Pediatric Nephrology, Beatrix Children's Hospital, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Flore A P T Engels
- Department of Pediatric Nephrology, Maastricht University Medical Center+, Maastricht, Netherlands
| | - Eiske M Dorresteijn
- Department of Pediatric Nephrology, Sophia Children's Hospital, Erasmus Medical Center, Rotterdam, Netherlands
| | | | - Caroline Duineveld
- Department of Nephrology, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, Netherlands
| | - Jack F M Wetzels
- Department of Nephrology, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, Netherlands
| | - Lambertus P W J van den Heuvel
- Department of Pediatric Nephrology, Radboud Institute for Molecular Life Sciences, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, Netherlands.,Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen, Netherlands.,Department of Pediatrics/Pediatric Nephrology, University Hospitals Leuven, Leuven, Belgium.,Department of Development and Regeneration, University Hospitals Leuven, Leuven, Belgium
| | - Elena B Volokhina
- Department of Pediatric Nephrology, Radboud Institute for Molecular Life Sciences, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, Netherlands.,Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen, Netherlands
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