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Michels MAHM, Volokhina EB, van de Kar NCAJ, van den Heuvel LPJ. Challenges in diagnostic testing of nephritic factors. Front Immunol 2022; 13:1036136. [PMID: 36451820 PMCID: PMC9702996 DOI: 10.3389/fimmu.2022.1036136] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2022] [Accepted: 10/12/2022] [Indexed: 09/27/2023] Open
Abstract
Nephritic factors (NeFs) are autoantibodies promoting the activity of the central enzymes of the complement cascade, an important first line of defense of our innate immune system. NeFs stabilize the complement convertase complexes and prevent their natural and regulator-mediated decay. They are mostly associated with rare complement-mediated kidney disorders, in particular with C3 glomerulopathy and related diseases. Although these autoantibodies were already described more than 50 years ago, measuring NeFs for diagnostic purposes remains difficult, and this also complicates our understanding of their clinical associations. In this review, we address the multifactorial challenges of NeF diagnostics. We describe the diseases NeFs are associated with, the heterogenic mechanisms of action of different NeF types, the different methods available in laboratories used for their detection, and efforts for standardization. Finally, we discuss the importance of proper NeF diagnostics for understanding the clinical impact of these autoantibodies in disease pathophysiology and for considering future complement-directed therapy.
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Affiliation(s)
- Marloes A. H. M. Michels
- Department of Pediatric Nephrology, Amalia Children’s Hospital, Radboud University Medical Center, Nijmegen, Netherlands
| | - Elena B. Volokhina
- Department of Pediatric Nephrology, Amalia Children’s Hospital, Radboud University Medical Center, Nijmegen, Netherlands
- Innatoss Laboratories, Oss, Netherlands
| | - Nicole C. A. J. van de Kar
- Department of Pediatric Nephrology, Amalia Children’s Hospital, Radboud University Medical Center, Nijmegen, Netherlands
| | - Lambertus P.W. J. van den Heuvel
- Department of Pediatric Nephrology, 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
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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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Hiramatsu M, Tsokos GC. Epstein-Barr virus transformed B cell lines derived from patients with systemic lupus erythematosus produce a nephritic factor of the classical complement pathway. CLINICAL IMMUNOLOGY AND IMMUNOPATHOLOGY 1988; 46:91-9. [PMID: 2826058 DOI: 10.1016/0090-1229(88)90009-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Nephritic factor of the classical complement pathway (C4NeF) is an IgG antibody which stabilizes the C3 convertase (C4b2a) and has been detected in sera from patients with systemic lupus erythematosus (SLE) and acute postinfectious glomerulonephritis. In order to study the production of nephritic factor (NeF), mononuclear cells were isolated from the peripheral blood of patients with SLE and infected with Epstein-Barr virus (EBV) to establish active B lymphocyte cell lines. Supernatants from 15 established B cell lines, as well as from 10 B cell lines established from normal individuals, were investigated for their ability to conserve the classical and the alternative pathway C3 convertases as assessed by EAC3bBb and EAC14b2a stabilizing assays. Supernatants from 2 of 15 B cell lines from patients with SLE, but none from normal individuals, stabilized the classical C3 convertase without having any effect on the alternative pathway C3 convertase. Using anti-human Ig affinity chromatography, we showed that C4NeF activity resided in the IgG fraction; the IgG fraction containing C4NeF activity bound to the C4b2a complex, but not to C4b alone. On gel electrophoresis, following reduction, the heavy chains were slightly heavier than the heavy chains of normal IgG. We were able to isolate C4NeF from the sera of the 2 patients with SLE from whom the positive supernatants were derived, but were unable to detect any C4NeF activity in the sera of the other 13 patients and the 10 normal individuals. Serum and B cell line supernatant-derived C4NeF exhibited comparable characteristics. We conclude that C4NeF produced in vitro by EBV-transformed B cell lines derived from patients with SLE is functionally similar to the conventional C4NeF in serum. These studies confirm the production of autoantibodies by B cells with the ability to stabilize the classical pathway C3 convertase in certain patients with SLE; stabilization of the C4b2a enzyme in these patients is an apparent mechanism for the development of hypocomplementemia. Finally, preparation of homogeneous C4NeF in vitro should improve our understanding of the role of autoantibodies in complement metabolic disturbances in autoimmune diseases.
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Affiliation(s)
- M Hiramatsu
- Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892
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