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Updated: May 19, 2026
Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells
Published on: January 29, 2014
Sensitive and specific assays for C3 nephritic factors clarify mechanisms underlying complement dysregulation
Danielle Paixão-Cavalcante1, Margarita López-Trascasa, Lillemor Skattum
1Institute of Infection & Immunity, School of Medicine, Cardiff University, Cardiff, UK.
Insights
C3 nephritic factors, autoantibodies linked to kidney disease, were identified and characterized using optimized assays. This study offers a new approach to detect and understand these factors in patients.
Area of Science:
- Immunology
- Complement System Biology
- Renal Pathology
Background:
- C3 nephritic factors (C3NFs) are autoantibodies implicated in renal disease by prolonging C3 convertase activity.
- Their precise role in disease pathogenesis remains debated.
- Current methods for detection and characterization are limited.
Purpose of the Study:
- To optimize and compare a panel of assays for identifying and interrogating C3 nephritic factor activities.
- To characterize the functional impact of C3NFs on complement regulation.
- To provide a rational approach for C3NF detection in patients.
Main Methods:
- Development and comparison of an assay panel for C3NF detection.
- Assessment of autoantibody binding and convertase stabilization in patient samples.
- Evaluation of C3NF effects on complement regulatory proteins (Factor H, DAF, CR1).
- Biacore analysis of purified IgG samples to confirm convertase stabilization and activity.
Main Results:
- 48 out of 101 patients with renal disease tested positive for C3NFs.
- Properdin-dependent C3NF binding and convertase stabilization were detected in 39 and 36 samples, respectively.
- Most C3NFs inhibited convertase decay by Factor H, DAF, and CR1.
- Properdin-independent C3NFs did not affect terminal pathway activity, while properdin-dependent C3NFs enhanced it.
- Purified C3NFs significantly increased C3 convertase half-life and activity, with varying effects based on properdin dependence.
Conclusions:
- The developed assay panel provides a rational and effective approach to detect and characterize C3 nephritic factors.
- C3NFs exhibit distinct functional properties, including properdin dependence/independence, influencing complement activation.
- Characterization of C3NFs is crucial for understanding their role in renal disease pathogenesis.
Abstract:
C3 nephritic factors are autoantibodies that prolong the half-life or prevent regulation of the alternative pathway C3 convertase, resulting in uncontrolled complement activation. They are strongly associated with renal disease but their role in pathogenesis remains controversial. Here we optimized and compared a panel of assays to identify and interrogate nephritic factor activities. Of 101 patients with histologic or clinically evident disease, 48 were positive in some or all assays. In the presence of properdin, binding of autoantibody was detected in 39 samples and convertase stabilization was detected in 36. Forty-two of 48 nephritic factors tested prevented convertase decay by factor H, and most of these by decay accelerating factor (28) and complement receptor 1 (34). Representative properdin-independent nephritic factors had no effect on C5 cleavage and terminal pathway activity, while properdin-dependent nephritic factors enhanced activity. Biacore analysis of four purified IgG samples confirmed resistance to decay and showed that properdin-independent nephritic factors increased convertase half-life over 50-fold, whereas properdin-dependent nephritic factors increased the half-life 10- to 20-fold and also increased activity of the C3 convertase up to 10-fold. Thus, our study provides a rational approach to detect and characterize nephritic factors in patients.
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