Autoantibodies to complement components in C3 glomerulopathy and atypical hemolytic uremic syndrome.

The alternative pathway of complement is implicated in the pathogenesis of several renal diseases, such as atypical hemolytic uremic syndrome, dense deposit disease and other forms of C3 glomerulopathy. The underlying complement defects include genetic and/or acquired factors, the latter in the form of autoantibodies. Because the autoimmune forms require a specific treatment, in part different from that of the genetic forms, it is important to detect the autoantibodies as soon as possible and understand their characteristics. In this overview, we summarize the types of anti-complement autoantibodies detected in such diseases, i.e. autoantibodies to factor H, factor I, C3b, factor B and those against the C3 convertases (C3 nephritic factor and C4 nephritic factor). We draw attention to newly described autoantibodies and their characteristics, and highlight similarities and differences in the autoimmune forms of these diseases

The FXII c.-4T > C Polymorphism as a Disease Modifier in Patients With Hereditary Angioedema Due to the FXII p.Thr328Lys Variant

Background: Hereditary angioedema due to the Thr328Lys variant in the coagulation factor XII (HAE-FXII) affects mainly women in whom the symptomatology is dependent on high estrogen levels. Clinical variability and incomplete penetrance are challenging features that hinder the diagnosis and management of HAE-FXII. The c.-4T>C Kozak polymorphism is the only common variation accounting for FXII plasma levels and was previously shown to modify the course of HAE due to C1-Inhibitor deficiency. Objectives: To assess the influence of the c.-4T>C polymorphism on disease expression in 39 Spanish HAE-FXII index patients. Methods: The c.-4T>C polymorphism was sequenced by the standard Sanger method, and HAE severity was calculated according to the score by Cumming et al. (2003) The activation of the contact system was quantified by the kallikrein-like activity of plasma in chromogenic assays upon activation with high-molecular-weight dextran sulfate. Results: The c.-4CC genotype was overrepresented in the studied cohort: 82% were CC-homozygous (expected frequency = 59%) and 18% were CT-heterozygous (expected frequency = 39%) (p = 0.001). Patients with a c.-4CC genotype exhibited higher kallikrein-like activity (0.9659 +/- 0.1136) than those with a c.-4TC genotype (0.7645 +/- 0.1235) (p = 0.024) or healthy donors. Moreover, the polymorphism influenced HAE-FXII severity score (c.-4CC = 4.43 +/- 2.28 vs c.-4TC = 2.0 +/- 1.15; p = 0.006) but not the degree of estrogen dependence or time until remission. Conclusion: The c.-4T>C polymorphism is overrepresented in a Spanish HAE-FXII cohort and significantly influences the degree of contact system activation and the clinical severity of the disease

Heterogeneity but individual constancy of epitopes, isotypes and avidity of factor H autoantibodies in atypical hemolytic uremic syndrome

Factor H (FH) autoantibodies are present in 6-10% of atypical hemolytic uremic syndrome (aHUS) patients, most of whom have homozygous deficiency of the FH-related protein FHR-1. Although the pathogenic role of the autoantibodies is established, little is known about their molecular characteristics and changes over time. Here, we describe the specificity and other immunological features of anti-FH autoantibodies in the Spanish and Hungarian aHUS cohorts. A total of 19 patients were included and serial samples of 14 of them were available. FH autoantibodies from FHR-1 deficient patients (n=13) mainly recognized FH, its SCR19-20 fragment and FHR-1, but autoantibody specificity in patients who are homo- or heterozygous for the CFHR1 gene (n=6) was heterogeneous. No significant changes apart from total antibody titer were observed during follow-up in each patient. Fine epitope mapping with recombinant FH SCR19-20 containing single amino acid mutations showed significantly reduced binding in 6 out of 14 patients. In most cases, autoantibody binding to residues 1183-1189 and 1210-1215 was impaired, revealing a major common autoantibody epitope. Avidities showed variations between patients, but in most cases the avidity index did not change upon time. Most autoantibodies were IgG3, and all but three presented only with kappa or with lambda light chains. Although the pathogenic role of anti-FH autoantibodies in aHUS is well established, this study shows autoantibody heterogeneity among patients, but no significant variation in their characteristics over time in each patient. The presence of a single light chain in 16 out of 19 patients and the limited number of recognized epitopes suggest a restricted autoantibody response in most patients

High prevalence of anti-C1q antibodies in biopsy-proven active lupus nephritis

Background. Anti-C1q antibodies (anti-C1q) have been shown to correlate positively with systemic lupus erythematosus (SLE) nephritis. Several clinical studies indicated a high negative predictive value, suggesting that active lupus nephritis is rarely seen in patients with no anti-C1q. However, the true prevalence of anti-C1q at the time of active lupus nephritis has not been well established. The aim of this study was to determine prospectively the prevalence of anti-C1q in proven active lupus nephritis at the time of the renal biopsy. Methods. In this prospective multi-centre study, we investigated adult SLE patients undergoing renal biopsy for suspected active lupus nephritis. Serum samples were taken at the time of the biopsy and analysed for the presence of anti-C1q in a standardized way. The activity of lupus nephritis was classified according to the renal histology. Biopsies were also analysed for the presence of glomerular IgG, C1q and C3 deposition. Results. A total of 38 patients fulfilling at least 4/11 American College of Rheumatology (ACR) criteria for the diagnosis of SLE were included. Out of this, 36 patients had proliferative (class II, III or IV) and two had class V lupus nephritis. All but one patient with proliferative lupus nephritis were positive for anti-C1q (97.2%) compared with the 35% of control SLE patients with inactive lupus nephritis and 25% of SLE patients without lupus nephritis ever. All patients were positive for glomerular C1q (36/36) and 37/38 patients had glomerular IgG deposits. Anti-C1q strongly decreased during successful treatment. Conclusions. Anti-C1q have a very high prevalence in biopsy-proven active lupus nephritis, thus a negative test result almost excludes active nephritis. The data support the hypothesis of a pathogenic role of anti-C1q in lupus nephriti

High prevalence of anti-C1q antibodies in biopsy-proven active lupus nephritis

BACKGROUND: Anti-C1q antibodies (anti-C1q) have been shown to correlate positively with systemic lupus erythematosus (SLE) nephritis. Several clinical studies indicated a high negative predictive value, suggesting that active lupus nephritis is rarely seen in patients with no anti-C1q. However, the true prevalence of anti-C1q at the time of active lupus nephritis has not been well established. The aim of this study was to determine prospectively the prevalence of anti-C1q in proven active lupus nephritis at the time of the renal biopsy. METHODS: In this prospective multi-centre study, we investigated adult SLE patients undergoing renal biopsy for suspected active lupus nephritis. Serum samples were taken at the time of the biopsy and analysed for the presence of anti-C1q in a standardized way. The activity of lupus nephritis was classified according to the renal histology. Biopsies were also analysed for the presence of glomerular IgG, C1q and C3 deposition. RESULTS: A total of 38 patients fulfilling at least 4/11 American College of Rheumatology (ACR) criteria for the diagnosis of SLE were included. Out of this, 36 patients had proliferative (class II, III or IV) and two had class V lupus nephritis. All but one patient with proliferative lupus nephritis were positive for anti-C1q (97.2%) compared with the 35% of control SLE patients with inactive lupus nephritis and 25% of SLE patients without lupus nephritis ever. All patients were positive for glomerular C1q (36/36) and 37/38 patients had glomerular IgG deposits. Anti-C1q strongly decreased during successful treatment. CONCLUSIONS: Anti-C1q have a very high prevalence in biopsy-proven active lupus nephritis, thus a negative test result almost excludes active nephritis. The data support the hypothesis of a pathogenic role of anti-C1q in lupus nephritis

Novel homozygous variants in theSERPING1gene in two Turkish families with hereditary angioedema of recessive inheritance

Lopez Lera, Alberto/0000-0002-9596-6910; GULBAHAR, OKAN/0000-0002-5341-9070; Lopez-Trascasa, Margarita/0000-0001-8594-282XWOS: 000547270600001PubMed: 32445210Hereditary angioedema as a result of deficiency of the C1 inhibitor (HAE-C1INH; MIM# 106100) is a rare autosomal disorder and affected individuals are generally heterozygous for dominant negative variants in theSERPING1gene. Homozygosity forSERPING1pathogenic variants was long considered to be embryonically lethal; however, five nonrelated families with a recessive HAE pattern have been described in the last decade. in this report, we functionally characterized two newly reported nonrelated, consanguineous families with a recessive presentation of HAE attributed toSERPING1variants in the reactive center loop (family D; S438F) and gate (family A; I379T) regions. S438F heterozygotes (family D) showed variable levels of intact 105-kDa and cleaved/inactive 96-kDa isoforms of C1INH, whereas their homozygous relative presented only the 96-kDa band. Functional studies showed that S438F reduced C1INH interaction with target proteases in heterozygous (C1s, 32-38% of controls and FXIIa, 28-35% of controls) and homozygous (C1s, 18-24% of controls and FXIIa, 4-8% of controls) carriers, which is consistent with the more severe presentation of HAE in the family and decreased C1q levels in homozygous patients. By contrast, plasma C1INH from I379T heterozygotes (family A) showed normal C1INH/C1s binding (84-94% of controls) and no significant reduction in C1INH/FXIIa complexes (50-70% of controls). However, the homozygote failed to inhibit both C1s (25-42% of controls) and FXIIa (14-18% of controls). This profile is concordant with the less severe presentation of HAE in the family and the conserved C4 and C1q levels in heterozygous and homozygous patients.[ER19P7AC7541/2019]We thank Dr Alper Ozdemir, Arda Kula, Suat Hopanci and Betul Hopanci for obtaining the patient's serum samples. Alberto Lopez Lera is supported by grant ER19P7AC7541/2019 from Centre for Biomedical Network Research or Rare Diseases (CIBERER)