Efficacy of GalNAc C3 siRNAs in factor H-deficient mice with C3 glomerulopathy

Complement alternative pathway (AP) dysregulation drives C3 glomerulopathy (C3G), a rare renal disorder characterized by glomerular C3 deposition and glomerular damage, for which no effective treatments are available. Blockade of complement C3 is emerging as a viable therapeutic option. In an earlier study we showed that SLN500, a small interfering RNA targeting liver C3 synthesis, was able to limit AP dysregulation and glomerular C3d deposits in mice with partial factor H (FH) deficiency (Cfh+/- mice). Here, we assessed the pharmacological effects of SLN501 - an optimized SLN500 version - in mice with complete FH deficiency (Cfh-/- mice) that exhibit a more severe C3G phenotype. SLN501 effectively prevented liver C3 synthesis, thus limiting AP dysregulation, glomerular C3d deposits and the development of ultrastructural alterations. These data provide firm evidence of the use of siRNA-mediated liver C3 gene silencing as a potential therapy for treating C3G patients with either partial or complete FH loss of function.

The human factor H protein family - an update

Complement is an ancient and complex network of the immune system and, as such, it plays vital physiological roles, but it is also involved in numerous pathological processes. The proper regulation of the complement system is important to allow its sufficient and targeted activity without deleterious side-effects. Factor H is a major complement regulator, and together with its splice variant factor H-like protein 1 and the five human factor H-related (FHR) proteins, they have been linked to various diseases. The role of factor H in inhibiting complement activation is well studied, but the function of the FHRs is less characterized. Current evidence supports the main role of the FHRs as enhancers of complement activation and opsonization, i.e., counter-balancing the inhibitory effect of factor H. FHRs emerge as soluble pattern recognition molecules and positive regulators of the complement system. In addition, factor H and some of the FHR proteins were shown to modulate the activity of immune cells, a non-canonical function outside the complement cascade. Recent efforts have intensified to study factor H and the FHRs and develop new tools for the distinction, quantification and functional characterization of members of this protein family. Here, we provide an update and overview on the versatile roles of factor H family proteins, what we know about their biological functions in healthy conditions and in diseases.

De novo thrombotic microangiopathy after kidney transplantation in adults: Interplay between complement genetics and multiple endothelial injury

De novo thrombotic microangiopathy (dnTMA), after renal transplantation may significantly alter graft outcomes. However, its pathogenesis and the role of complement alternative pathway dysregulation remain elusive. We studied all consecutive adult patients with a kidney allograft biopsy performed between January 2004 and March 2016 displaying dnTMA. Ninety-two patients were included. The median time of occurrence was 166 (IQR 25-811) days. The majority (82.6 %) had TMA localized only in the graft. Calcineurin inhibitor toxicity and antibody-mediated rejection (ABMR) were the 2 most frequent causes (54.3% and 37.0%, respectively). However, etiological factors were multiple in 37% patients. Interestingly, pathogenic variants in the genes of complement alternative pathway were significantly more frequent in the 42 tested patients than in healthy controls (16.7% vs 3.7% respectively, P < .008). The overall graft survival after biopsy was 66.0% at 5 years and 23.4% at 10 years, significantly worse than a matched cohort without TMA. Moreover, graft survival of patients with TMA and ABMR was worse than a matched cohort with ABMR without TMA. The 2 main prognostic factors were a positive C4d staining and a lower estimated glomerular filtration rate at diagnosis. DnTMA is a severe and multifactorial disease, induced by 1 or several endothelium-insulting conditions, mostly calcineurin inhibitor toxicity and ABMR.

C3 Glomerulopathy With Concurrent Thrombotic Microangiopathy: Clinical and Immunological Features

RATIONALE & OBJECTIVE

C3 glomerulopathy (C3GN) and atypical hemolytic uremic syndrome (aHUS) are 2 distinct rare kidney diseases caused by dysregulation of the alternative complement pathway. Patients with C3GN and concurrent kidney lesions of thrombotic microangiopathy (TMA) have been rarely reported. We characterized the clinical features and underlying immunological abnormalities in these patients.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

Patients with C3GN and concomitant TMA lesions on biopsy registered from 2009 to 2019 in the French National Registry of C3GN.

FINDINGS

Among 278 registered patients with C3GN, 16 (6%) had biopsy-proven glomerular and/or vascular TMA lesions. Their median age at diagnosis was 39 years (range, 7-76), and 59% were female. Fourteen of the 16 patients (88%) had an estimated glomerular filtration rate of<30mL/min/1.73m2 and 3 of 16 (19%) required dialysis. Twelve of the 14 evaluated patients (86%) showed evidence of mechanical hemolysis. Fifty percent of the patients had low C3 levels. Six of the 14 evaluated patients had a rare variant in complement genes, and 4 of the 16 patients (25%) had monoclonal gammopathy. Among the 16 patients, 10 (63%) received eculizumab, 5 (31%) received immunosuppressive therapy, and 4 (25%) received clone-targeted chemotherapy. Median kidney survival was 49 months.

LIMITATIONS

Small retrospective case series with a limited number of biopsies including electron microscopy.

CONCLUSIONS

Concomitant C3GN and TMA is extremely rare and is associated with poor kidney outcomes. Genetic or acquired abnormalities of the alternative complement pathway are common as is the presence of monoclonal gammopathy, which may inform the selection of treatment approaches.

Clinico-Pathogenic Similarities and Differences between Infection-Related Glomerulonephritis and C3 Glomerulopathy

Recently, the comprehensive concept of "infection-related glomerulonephritis (IRGN)" has replaced that of postinfectious glomerulonephritis (PIGN) because of the diverse infection patterns, epidemiology, clinical features, and pathogenesis. In addition to evidence of infection, hypocomplementemia particularly depresses serum complement 3 (C3), with endocapillary proliferative and exudative GN developing into membranoproliferative glomerulonephritis (MPGN); also, C3-dominant or co-dominant glomerular immunofluorescence staining is central for diagnosing IRGN. Moreover, nephritis-associated plasmin receptor (NAPlr), originally isolated from the cytoplasmic fraction of group A Streptococci, is vital as an essential inducer of C3-dominant glomerular injury and is a key diagnostic biomarker for IRGN. Meanwhile, "C3 glomerulopathy (C3G)", also showing a histological pattern of MPGN due to acquired or genetic dysregulation of the complement alternative pathway (AP), mimics C3-dominant IRGN. Initially, C3G was characterized by intensive "isolated C3" deposition on glomeruli. However, updated definitions allow for glomerular deposition of other complement factors or immunoglobulins if C3 positivity is dominant and at least two orders of magnitude greater than any other immunoreactant, which makes it challenging to quickly distinguish pathomorphological findings between IRGN and C3G. As for NAPlr, it was demonstrated to induce complement AP activation directly in vitro, and it aggravates glomerular injury in the development of IRGN. A recent report identified anti-factor B autoantibodies as a contributing factor for complement AP activation in pediatric patients with PIGN. Moreover, C3G with glomerular NAPlr deposition without evidence of infection was reported. Taken together, the clinico-pathogenic features of IRGN overlap considerably with those of C3G. In this review, similarities and differences between the two diseases are highlighted.

Challenges in diagnostic testing of nephritic factors

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.

The potential role of complement alternative pathway activation in hypertensive renal damage

Hypertensive renal damage is a common secondary kidney disease caused by poor control of blood pressure. Recent evidence has revealed abnormal activation of the complement alternative pathway (AP) in hypertensive patients and animal models and that this phenomenon is related to hypertensive renal damage. Conditions in the setting of hypertension, including high renin concentration, reduced binding of factor H to the glomerular basement membrane, and abnormal local synthesis of complement proteins, potentially promote the AP activation in the kidney. The products of the AP activation promote the phenotypic transition of mesangial cells and tubular cells, attack endothelial cells and recruit immunocytes to worsen hypertensive renal damage. The effects of complement inhibition on hypertensive renal damage are contradictory. Although clinical data support the use of C5 monoclonal antibody in malignant hypertension, pharmacological inhibition in hypertensive animals provides little benefit to kidney function. Therefore, the role of the complement AP in the pathogenesis of hypertensive renal damage and the value of complement inhibition in hypertensive renal damage treatment must be further explored.

Effect of Factor H on Complement Alternative Pathway Activation in Human Serum Remains on Porcine Cells Lacking N-Glycolylneuraminic Acid

Background

Triple knockout (TKO) donor pigs lacking alpha-1,3-galactose (Gal), N-glycolylneuraminic acid (Neu5Gc), and Sd(a) expressions were developed to improve the clinical success of xenotransplantation. Neu5Gc, a sialic acid expressed on cell surfaces, recruits factor H to protect cells from attack by the complement system. Lack of Neu5Gc expression may cause unwanted complement activation, abrogating the potential benefit of gene-modified donor pigs. To investigate whether TKO porcine cells display increased susceptibility to complement activation in human serum, pathway-specific complement activation, apoptosis, and human platelet aggregation by porcine cells were compared between alpha-1,3-galactosyltransferase gene-knockout (GTKO) and TKO porcine cells.

Methods

Primary porcine peripheral blood mononuclear cells (pPBMCs) and endothelial cells (pECs) from GTKO and TKO pigs were used. Cells were incubated in human serum diluted in gelatin veronal buffer (GVB⁺⁺) or Mg⁺⁺-EGTA GVB, and C3 deposition and apoptotic changes in these cells were measured by flow cytometry. C3 deposition levels were also measured after incubating these cells in 10% human serum supplemented with human factor H. Platelet aggregation in human platelet-rich plasma containing GTKO or TKO pECs was analyzed.

Results

The C3 deposition level in GTKO pPBMCs or pECs in GVB⁺⁺ was significantly higher than that of TKO pPBMCs or pECs, respectively, but C3 deposition levels in Mg⁺⁺-EGTA-GVB were comparable between them. The addition of factor H into the porcine cell suspension in 10% serum in Mg⁺⁺ -EGTA-GVB inhibited C3 deposition in a dose-dependent manner, and the extent of inhibition by factor H was similar between GTKO and TKO porcine cells. The percentage of late apoptotic cells in porcine cell suspension in GVB⁺⁺ increased with the addition of human serum, of which the net increase was significantly less in TKO pPBMCs than in GTKO pPBMCs. Finally, the lag time of platelet aggregation in recalcified human plasma was significantly prolonged in the presence of TKO pECs compared to that in the presence of GTKO pECs.

Conclusion

TKO genetic modification protects porcine cells from serum-induced complement activation and apoptotic changes, and delays recalcification-induced human platelet aggregation. It does not hamper factor H recruitment on cell surfaces, allowing the suppression of alternative complement pathway activation.

[The genetic basis of post-bone marrow transplant thrombotic microangiopathy: is this the last piece of the puzzle?]

Transplant-associated thrombotic microangiopathy (TA-TMA) is a complication of hematopoietic stem cell transplantation (HSCT) associated with kidney injury and significant mortality. Recent studies indicate that dysregulation of the alternate complement pathway may be at the basis of the development of TA-TMA. Currently, there are no pre-transplant screening tools to identify patients at risk. To explore the mechanism of TA-TMA, we performed a genetic study that allowed us to identify the deletion of the CFHR3-CFHR1 region in homozygosity. We report the clinical case of a 47-year-old woman who underwent haploidentical HSCT complicated by TA-TMA confirmed by renal biopsy. The patient discontinued treatment with calcineurin inhibitors (potential inducers of TA-TMA) with a brief introduction of prednisone until complete resolution of renal damage and microangiopathy. Identifying genetic variants that affect the mechanism of the alternate complement pathway could help in the stratification of the risk of TA-TMA and in implementing a personalized therapeutic approach.

Combination of a Novel Genetic Variant in CFB Gene and a Pathogenic Variant in COL4A5 Gene in a Sibling Renal Disease: A Case Report

Complement factor B (CFB) variants have been described to play a causative role in auto-immune associated C3 glomerulopathy (C3G) and/or atypical hemolytic uremic syndrome (aHUS) by affecting the dysregulations of alternative pathway activation. However, CFB variant concomitant with COL4A5 variant is scarce. Here, we depict two intriguing cases with concurrent novel heterozygosity for CFB c.2054_2057del (p.Ser687Profs^∗16) variant and a previous reported COL4A5 c.2999G > T (p.Gly1000Val) variant in a pair of siblings. The clinical feature of either paternal CFB variant or maternal COL4A5 variant is just mild microscopic hematuria. Interestingly, their two children with paternal CFB c.2054_2057del (p.Ser687Profs^∗16) variant and maternal COL4A5 c.2999G > T (p.Gly1000Val) variant presented with massive proteinuria, hematuria, and progressive renal failure with poor treatment response. Moreover, complement pathway activation in renal tissue further supports and strengthens the pathogenic role of CFB variant in the development of renal injury in the presence of COL4A5 variant. In conclusion, the rare sibling cases highlight that the extension of genetic analyses in the proband is helpful for the diagnosis and understanding of some family cluster renal diseases.

Quantitative Alterations in Complement Alternative Pathway and Related Genetic Analysis in Severe Phenotype Preeclampsia

Background

Preeclampsia and hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome share many clinical and biologic features with thrombotic microangiopathy syndromes caused by complement abnormalities. Our hypothesis was that similar functional and genetic alterations in the complement alternative pathway (CAP) are present in these disorders of pregnancy.

Methods

We conducted quantitative analysis of proteins involved in CAP using ELISA and nephelometry on prospectively collected blood samples from patients with severe phenotype preeclampsia (defined as delivery ≤34 weeks due to preeclampsia), HELLP syndrome, or eclampsia, and matched normotensive controls (n=25 in each arm) between 2011 and 2016. Sequencing was performed to interrogate 14 genes encoding CAP components.

Results

Both groups were similar in age, gravidity, parity, marital status, and race. The study group had a higher BMI (mean±SD, 32±8 versus 25±4 kg/m²; P=0.002) and earlier gestational age at delivery (32.5±3.6 versus 40.3±1 weeks; P<0.001). Serologic studies demonstrated elevated Bb subunit (median [range], 1.2 [0.5-4.3] versus 0.6 [0.5-1] μg/ml; P<0.001), complement C5 concentration (28 [18-33] versus 24 [15-34] mg/dl; P=0.03), and sMAC (371 [167-761] versus 184 [112-249] ng/ml; P<0.001) concentrations in patients with preeclampsia. Two thirds of patients with preeclampsia had at least one nonsynonymous sequence variant in CAP genes.

Conclusion

Patients with severe phenotype preeclampsia manifest functional alterations in CAP activation. Genetic variants in the CAP genes were detected in several patients, but a larger population study is necessary to fully evaluate genetic risk. Genetic screening and complement-targeted treatment may be useful in risk stratification and novel therapeutic approaches.

IL-1/IL-1R signaling induced by all-trans-retinal contributes to complement alternative pathway activation in retinal pigment epithelium

The underlying mechanisms of complement activation in Stargardt disease type 1 (STGD1) and age-related macular degeneration (AMD) are not fully understood. Overaccumulation of all-trans-retinal (atRAL) has been proposed as the pathogenic factor in both diseases. By incubating retinal pigment epithelium (RPE) cells with atRAL, we showed that C5b-9 membrane attack complexes (MACs) were generated mainly through complement alternative pathway. An increase in complement factor B (CFB) expression as well as downregulation of complement regulatory proteins CD46, CD55, CD59, and CFH were observed in RPE cells after atRAL treatment. Furthermore, interleukin-1β production was provoked in both atRAL-treated RPE cells and microglia/macrophages. Coincubation of RPE cells with interleukin-1 receptor antagonist (IL1Ra) and atRAL ameliorated complement activation and downregulated CFB expression by attenuating both p38 and c-Jun N-terminal kinase (JNK) signaling pathways. Our findings demonstrate that atRAL induces an autocrine/paracrine IL-1/IL-1R signaling to promote complement alternative pathway activation in RPE cells and provide a novel perspective on the pathomechanism of macular degeneration.

Light chain only variant of proliferative glomerulonephritis with monoclonal immunoglobulin deposits is associated with a high detection rate of the pathogenic plasma cell clone

IgG (mainly IgG3) is the most commonly involved isotype in proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID). Here we describe the first series of PGNMID with deposition of monoclonal immunoglobulin light chain only (PGNMID-light chain). This multicenter cohort of 17 patients presented with nephritic or nephrotic syndrome with underlying hematologic conditions of monoclonal gammopathy of renal significance (71%) or multiple myeloma (29%). Monoclonal immunoglobulin was identified by serum and urine immunofixation in 65% and 73%, respectively, with abnormal serum free light chain in 83%, and a detectable bone marrow plasma cell clone in 88% of patients. Renal biopsy showed a membranoproliferative pattern in most patients. By immunofluorescence, deposits were restricted to glomeruli and composed of restricted light chain (kappa in 71%) and C3, with granular appearance and subendothelial, mesangial and subepithelial distribution by electron microscopy. Proteomic analysis in four cases of kappa PGNMID-light chain revealed spectra for kappa constant and variable domains, without evidence of Ig heavy chains; spectra for proteins of the alternative pathway of complement and terminal complex were detected in three. The classical pathway was not detected in three cases. After median follow up of 70 months, the renal response was dependent on a hematologic response and occurred in six of ten patients treated with plasma cell-directed chemotherapy but none of five patients receiving other therapies. Thus, PGNMID-light chain differs from PGNMID-IgG by higher frequency of a detectable pathogenic plasma cell clone. Hence, proper recognition is crucial as anti-myeloma agents may improve renal prognosis. Activation of an alternative pathway of complement by monoclonal immunoglobulin light chain likely plays a role in its pathogenesis.

Complement alternative pathway activation associated with pulmonary hypertension in lupus nephritis patients

Pulmonary hypertension occurs in systemic lupus erythematosus (SLE) for several reasons, such as vasculopathy. Previous studies have indicated that the excessive activation of the complement alternative pathway might be involved in the pathogenesis of lupus nephritis, especially in the absence of factor H or its functional impairment. However, the clinical and pathological significance of the alternative complement activation in lupus nephritis patients with pulmonary hypertension remains elusive. The data on patients with pulmonary hypertension and non-pulmonary hypertension lupus nephritis were retrospectively analyzed in our centre. Major plasma levels of complement components were evaluated. The depositions of Bb, C3d and C5b-9 in the lung specimens of pulmonary hypertension combined with SLE patients were detected by immunofluorescence staining. Among 352 lupus nephritis cases, 24 were diagnosed with pulmonary hypertension and 328 with non-pulmonary hypertension. Higher levels of Bb and lower levels of factor H were detected in the pulmonary hypertension group in comparison with the negative group (P = 0.049, P = 0.024, respectively). Pulmonary hypertension was a risk factor for renal outcome as deduced by the log-rank and Cox test for survival analysis. C3d, C5b-9 and Bb were found to be positive in lung specimens of lupus nephritis patients with pulmonary hypertension. We concluded that activation of the complement alternative pathway may be involved in the pathogenesis of pulmonary hypertension in lupus nephritis.

An Ex Vivo Test of Complement Activation on Endothelium for Individualized Eculizumab Therapy in Hemolytic Uremic Syndrome

RATIONALE & OBJECTIVE

Although primary atypical hemolytic uremic syndrome (aHUS) is associated with abnormalities in complement genes and antibodies to complement factor H, the role of complement in secondary aHUS remains debatable. We evaluated the usefulness of an ex vivo test to: (1) detect complement activation within the endothelium in primary and secondary aHUS, (2) differentiate active disease from remission, (3) monitor the effectiveness of eculizumab therapy, and (4) identify relapses during eculizumab dosage tapering and after discontinuation of treatment.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

121 patients with primary aHUS and 28 with secondary aHUS. Serum samples were collected during acute episodes, following remission, and during eculizumab treatment and were assessed using a serum-induced ex vivo C5b-9 endothelial deposition test.

RESULTS

Serum-induced C5b-9 deposition on cultured microvascular endothelium was quantified by calculating the endothelial area covered by C5b-9 staining; values were expressed as percentage of C5b-9 deposits induced by a serum pool from healthy controls. Testing with adenosine diphosphate-activated endothelium demonstrated elevated C5b-9 deposits for all untreated patients with aHUS independent of disease activity, while testing with unstimulated endothelium demonstrated deposits only in active disease. Similar findings were observed in secondary aHUS. Serum-induced C5b-9 deposits on activated and unstimulated endothelium normalized during eculizumab treatment. 96% (22/23) of patients receiving eculizumab at extended 3- or 4-week dosing intervals demonstrated normal C5b-9 deposits on activated endothelium, despite most patients having CH50Eq (serum complement activity) > 20 UEq/mL, indicating that adequate complement control was achieved even with incomplete blockade of circulating C5. During eculizumab dosage tapering or after treatment discontinuation, all patients experiencing relapses versus only 6% (1/17) of those in stable remission had elevated C5b-9 deposits on unstimulated endothelium.

LIMITATIONS

The C5b-9 endothelial deposition test can be performed in only specialized laboratories. Findings on eculizumab dosage tapering need to be confirmed with longitudinal monitoring of C5b-9 deposition.

CONCLUSIONS

The C5b-9 endothelial deposition assay may represent an advance in our ability to monitor aHUS activity and individualize therapy.

Complement Activation Contributes to the Pathophysiology of Shiga Toxin-Associated Hemolytic Uremic Syndrome

Shiga toxin (Stx)-producing Escherichia coli (STEC) infections have become a threat to public health globally because of the severe illnesses that they can trigger, such as hemorrhagic colitis and the post-diarrheal hemolytic uremic syndrome (HUS), characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney failure. Glomerular endothelial cells are primary targets of Stx which, after binding to its specific receptor globotriaosylceramide, upregulates proinflammatory proteins involved both in the recruitment and adhesion of leukocytes and thrombus formation at the site of endothelial injury. In this review, we discuss the role of complement activation in promoting glomerular microvascular dysfunction, providing evidence from experimental models and patients with STEC-HUS. Within the glomerulus, an important target for Stx-induced complement activation is the podocyte, a cell type that is in close contact with endothelial cells and participates in maintaining the filtration barrier. Recently, podocyte injury and loss have been indicated as potential risk factors for long-term renal sequelae in patients with STEC-HUS. Therapeutic approaches targeting the complement system, that may be useful options for patients with STEC-HUS, will also be discussed.

Unraveling the Molecular Mechanisms Underlying Complement Dysregulation by Nephritic Factors in C3G and IC-MPGN

Membranoproliferative glomerulonephritis (MPGN) was recently classified as C3 glomerulopathies (C3G), and immune-complex (IC) mediated MPGN. Dysregulation of the complement alternative pathway, driven by acquired and/or genetic defects, plays a pathogenetic role in C3G. However, alternative pathway abnormalities were also found in IC-MPGN. The most common acquired drivers are the C3 nephritic factors (C3NeFs), heterogeneous autoantibodies that stabilize the C3 convertase, C3bBb. C3NeFs are traditionally detected by hemolytic assays based on sheep erythrocyte lysis, which however do not provide a direct molecular estimation of C3bBb formation and decay. We set up a microplate/western blot assay that specifically detects and quantifies C3bBb, and its precursor, the C3 proconvertase C3bB, to investigate the complex mechanistic effects of C3NeFs from patients with primary IC-MPGN (n = 13) and C3G (n = 13). In the absence of properdin, 9/26 patients had C3NeF IgGs stabilizing C3bBb against spontaneous and FH-accelerated decay. In the presence of properdin the IgGs of all but one patient had C3bBb-stabilizing activity. Properdin-independent C3NeFs were identified mostly in DDD patients, while properdin-dependent C3NeFs associated with either C3GN or IC-MPGN and with higher incidence of nephrotic syndrome. When we grouped patients based on our recent cluster analysis, patients in cluster 3, with highly electron-dense intramembranous deposits, low C3, and mostly normal sC5b-9 levels, had a higher prevalence of properdin-independent C3NeFs than patients in clusters 1 and 2. Conversely, about 70% of cluster 1 and 2 patients, with subendothelial, subepithelial, and mesangial deposits, low C3 levels and high sC5b-9 levels, had properdin-dependent C3NeFs. The flexibility of the assay allowed us to get deep insights into C3NeF mechanisms of action, showing that: (1) most C3NeFs bind strongly and irreversibly to C3 convertase; (2) C3NeFs and FH recognize different epitopes in C3 convertase; (3) C3NeFs bind rapidly to C3 convertase and antagonize the decay accelerating activity of FH on newly formed complexes; (4) C3NeFs do not affect formation and stability of the C3 proconvertase. Thus, our study provides a molecular approach to detecting and characterizing C3NeFs. The results highlight different mechanisms of complement dysregulation resulting in different complement profiles and patterns of glomerular injury, and this may have therapeutic implications.

Different types of glomerulonephritis associated with the dysregulation of the complement alternative pathway in 2 brothers: A case report

RATIONALE

C3 glomerulonephritis (C3GN) and complement-mediated hemolytic uremic syndrome (HUS) both result from the abnormal regulation of the complement system. A significant number of patients with C3GN or complement-mediated HUS have mutations of more than 1 complement protein. This discovery has had a major impact on identifying the underlying cause of familial C3GN or complement-mediated HUS.

PATIENT CONCERNS

We report the cases of 2 brothers (herein referred to as patient II-1 and patient II-9), both with complement disorders that differed in their clinical and genetic features.

DIAGNOSES

Patient II-1 clinically presented with nephrotic syndrome and acute kidney injury and pathologically presented with C3GN combined with thrombotic microangiopathy (TMA) and subacute tubulointerstitial nephritis. Meanwhile, patient II-9 clinically presented with HUS and pathologically presented with TMA combined with acute severe tubular injury.

INTERVENTIONS

Screenings for genetic mutations contributed to complement system dysregulation were performed on patient II-1.

OUTCOMES

The genome sequencing identified that patient II-1 had a heterozygous mutation in the C3 gene (c.C1774T/p.R592W). Nine other relatives of the brothers were checked for this C3 mutation and only the daughter of patient II-1 (herein referred to as patient III-2) carried it, but so far, she does not have any clinical manifestations of kidney disease.

LESSIONS

Family members with a dysregulation of the complement alternative pathway may differ in its clinical and genetic features.

C3 glomerulopathy associated to multiple myeloma successfully treated by autologous stem cell transplant

A 32-year-old male presented with advanced renal failure and nephrotic proteinuria due to lambda light chain multiple myeloma. Renal biopsy showed a proliferative glomerulonephritis with isolated C3 deposits. Renal recovery was obtained after chemotherapy and autologous stem cell transplant. We review previously described cases of C3 glomerulopathy associated with monoclonal gammopathy.

Retinal disease in the C3 glomerulopathies and the risk of impaired vision

BACKGROUND

Dense deposit disease and atypical hemolytic uremic syndrome are often caused by Complement Factor H (CFH) mutations. This study describes the retinal abnormalities in dense deposit disease and, for the first time, atypical haemolytic uremic syndrome. It also reviews our understanding of drusen pathogenesis and their relevance for glomerular disease.

METHODS

Six individuals with dense deposit disease and one with atypical haemolytic uremic syndrome were studied from 2 to 40 years after presentation. Five had renal transplants. All four who had genetic testing had CFH mutations. Individuals underwent ophthalmological review and retinal photography, and in some cases, optical coherence tomography, and further tests of retinal function.

RESULTS

All subjects with dense deposit disease had impaired night vision and retinal drusen or whitish-yellow deposits. Retinal atrophy, pigmentation, and hemorrhage were common. In late disease, peripheral vision was restricted, central vision was distorted, and there were scotoma from sub-retinal choroidal neovascular membranes and atypical serous retinopathy. Drusen were present but less prominent in the young person with atypical uremic syndrome due to a heterozygous CFH mutation.

CONCLUSIONS

Drusen are common in forms of C3 glomerulopathy caused by compound heterozygous or heterozygous CFH mutations. They are useful diagnostically but also impair vision. Drusen have an identical composition to glomerular deposits. They are also identical to the drusen of age-related macular degeneration, and may respond to the same treatments. Individuals with a C3 glomerulopathy should be assessed ophthalmologically at diagnosis, and monitored regularly for vision-threatening complications.

Eculizumab for treatment of rapidly progressive C3 glomerulopathy

C3 glomerulopathy (C3G) is a prototypic complement-mediated kidney disease. Rapidly progressive forms of C3G usually respond poorly to conventional treatments. We report on the efficacy of the terminal complement inhibitor eculizumab in 3 adult patients with rapidly progressive C3G. In all 3 patients, serum creatinine levels had increased by >50% in the 2 months preceding initiation of eculizumab treatment despite the use of conventional immunosuppressive drugs and/or plasma exchanges in 2 of these individuals. Of note, 2 patients had long-standing nephrotic syndrome. Kidney biopsy performed prior to eculizumab treatment disclosed marked glomerular inflammatory changes and increased C5b-9 deposition in all patients. Eculizumab use was associated with significant improvement in kidney function, with estimated glomerular filtration rates of patients increasing 22 to 38 mL/min/1.73 m(2). Eculizumab use also was associated with remission of nephrotic syndrome in the 2 affected patients, an effect observed as early as one week after treatment initiation. Repeat kidney biopsy disclosed regression of glomerular inflammatory changes and decreases in glomerular staining for C5b-9 in all patients. These results warrant further assessment of eculizumab for treatment of rapidly progressive forms of C3G with markedly increased glomerular C5b-9 deposits.

Anti-Complement Treatment in Paroxysmal Nocturnal Hemoglobinuria: Where we Stand and Where we are Going

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal, non-malignant, hematological disorder characterized by the expansion of hematopoietic stem cells and progeny mature blood cells which are deficient in some surface proteins, including the two complement regulators CD55 and CD59. PNH is the paradigm of diseases implying complement dysregulation as main pathogenic mechanism; in fact, PNH erythrocytes are uncapable to modulate on their surface physiologic complement activation, which eventually leads to the typical clinical hallmark of PNH - the chronic complement-mediated intravascular anemia. Indeed, due to the lack of CD55 complement is continuously activated on erythrocyte surface, which subsequently enables the terminal lytic complement because of the lack of CD59, finally resulting in erythrocyte lysis. The availability of eculizumab as the first complement inhibitor for clinical use renewed the interest for this rare hematological disease. Indeed, in the last decad the anti-C5 monoclonal antibody has proven effective for the treatment of PNH, resulting in a sustained control of complement-mediated intravascular hemolysis, with a remarkable clinical benefit. Anti-complement treatment allowed transfusion independence in at least half of PNH patients receiving eculizumab, with adequate control of all hemolysis-associated symptoms even in almost all remaining patients. In addition, the risk of thromboembolic events - an other clinical hallmark of PNH, which significantly affects prognosis and survival - seems substantially reduced on eculizumab treatment, apparently resulting in improved survival. Even with all these remarkable effects, eculizumab treatment does not result in hemoglobin normalization, and most patients remain anemic. It has been demonstrated that this is due to persistent activation of the early phases of complement activation (upstream the C5), leading to complement-mediated extravascular hemolysis. Ongoing researches are focusing on possible strategies to improve current anti-complement therapies, aiming to develop second-generation complement therapeutics. Here we review PNH and its complement-mediated pathophysiology, summarizing available data on anti-complement treatment; we'll also discuss recent pathogenic insights which drive the development of novel strategies of complement inhibition.