title: Sensitive and specific assays for C3 nephritic factors clarify mechanisms underlying complement dysregulation.
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.
authors.affiliation: Institute of Infection & Immunity, School of Medicine, Cardiff University, Cardiff, UK.
authors.forename: Danielle
authors.initials: D
authors.lastname: Paixão-Cavalcante
authors.forename: Margarita
authors.initials: M
authors.lastname: López-Trascasa
authors.forename: Lillemor
authors.initials: L
authors.lastname: Skattum
authors.forename: Patricia C
authors.initials: PC
authors.lastname: Giclas
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Goodship
authors.forename: Santiago Rodríguez
authors.initials: SR
authors.lastname: de Córdoba
authors.forename: Lennart
authors.initials: L
authors.lastname: Truedsson
authors.forename: B Paul
authors.initials: BP
authors.lastname: Morgan
authors.forename: Claire L
authors.initials: CL
authors.lastname: Harris
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000097:blood; D018958:CD55 Antigens / Q000378:metabolism; D016022:Case-Control Studies; D003167:Complement Activation; D003176:Complement C3 / Q000378:metabolism; D003178:Complement C3 Nephritic Factor / Q000378:metabolism*; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D011416:Complement Factor D / Q000378:metabolism; D017242:Complement Factor H / Q000378:metabolism; D015941:Complement Hemolytic Activity Assay; D004797:Enzyme-Linked Immunosorbent Assay; D015432:Glomerulonephritis, Membranoproliferative / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D006801:Humans; D007118:Immunoassay / Q000379:methods; D011237:Predictive Value of Tests; D011414:Properdin / Q000378:metabolism; D011485:Protein Binding; D011951:Receptors, Complement / Q000378:metabolism; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012756:Sheep; D013997:Time Factors
chemical_list: D015415:Biomarkers; D018958:CD55 Antigens; C493495:CFH protein, human; D003176:Complement C3; D003178:Complement C3 Nephritic Factor; D011951:Receptors, Complement; D011414:Properdin; D017242:Complement Factor H; D050577:Complement C3-C5 Convertases; C493488:CFD protein, human; D011416:Complement Factor D