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Abstract Background Thrombotic microangiopathy (TMA) syndromes are characterized by the association of hemolytic anemia, thrombocytopenia and organ injury due to arteriolar and capillary thrombosis. Case presentation We report the first case of adult onset cobalamin C (Cbl C) disease associated with anti-factor H antibody-associated hemolytic uremic syndrome (HUS). A 19-year-old woman was admitted to the nephrology department owing to acute kidney failure, proteinuria, and hemolytic anemia with schizocytes. TMA was diagnosed and plasma exchanges were started in emergency. Exhaustive analyses showed 1) circulating anti factor H antibody and 2) hyperhomocysteinemia, hypomethioninemia and high levels of methylmalonic aciduria pointing towards Clb C disease. Cbl C disease has been confirmed by methylmalonic aciduria and homocystinuria type C protein gene sequencing revealing two heterozygous pathogenic variants. The kidney biopsy showed 1) intraglomerular and intravascular thrombi 2) noticeable thickening of the capillary wall with a duplication aspect of the glomerular basement membrane and a glomerular capillary wall IgM associated with Cbl C disease related TMA. We initiated treatment including hydroxycobalamin, folinic acid, betaine and levocarnitine and Eculizumab. Rituximab infusions were performed allowing a high decrease in anti-factor H antibody rate. Six month after the disease onset, Eculizumab was weaning and vitaminotherapy continued. Outcome was favorable with a dramatic improvement in kidney function. Conclusion TMA with renal involvement can have a complex combination of risk factors including anti-FH autoantibody in the presence of cblC deficiency.

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy, related to complement dysregulation, including Factor H deficiency (FH) treated by lifelong eculizumab therapy. Its long-term tolerance is not yet fully described. We report two patients with genetic FH deficiency receiving long-term eculizumab and displaying a peculiar bone phenotype. First case is a 13-year-old girl, presenting with bone pains, arthritis, and deformities, for which X-rays and MRI described multifocal osteochondritis. Bone biopsy revealed an active remodeling bone (many areas of bone formation and resorption) and C3c accumulation on immunohistochemical staining. The second patient is an 11-year-old girl, displaying mechanical bone pains, for which bone scintigraphy found hypofixation of wrists and ankles. These findings could be consistent with a side effect of eculizumab, as C3c accumulation may result from the downstream C5-blockade. Alternatively, bone alterations could be due to the absence of FH, as described in murine models. Further investigations are required to characterize bone disease in aHUS., (© 2024. The Author(s).)

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., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Randomized clinical trials are underway to evaluate the efficacy of novel agents targeting the alternative complement pathway in patients with C3 glomerulopathy (C3G), a rare glomerular disease. The Kidney Health Initiative convened a panel of experts in C3G to ( 1 ) assess the data supporting the use of the prespecified trial end points as measures of clinical benefit and ( 2 ) opine on efficacy findings they would consider compelling as treatment(s) of C3G in native kidneys. Two subpanels of the C3G Trial Endpoints Work Group reviewed the available evidence and uncertainties for the association between the three prespecified end points-( 1 ) proteinuria, ( 2 ) eGFR, and ( 3 ) histopathology-and anticipated outcomes. The full work group provided feedback on the summaries provided by the subpanels and on what potential treatment effects on the proposed end points they would consider compelling to support evidence of an investigational product's effectiveness for treating C3G. Members of the full work group agreed with the characterization of the data, evidence, and uncertainties, supporting the end points. Given the limitations of the available data, the work group was unable to define a minimum threshold for change in any of the end points that might be considered clinically meaningful. The work group concluded that a favorable treatment effect on all three end points would provide convincing evidence of efficacy in the setting of a therapy that targeted the complement pathway. A therapy might be considered effective in the absence of complete alignment in all three end points if there was meaningful lowering of proteinuria and stabilization or improvement in eGFR. The panel unanimously supported efforts to foster data sharing between academic and industry partners to address the gaps in the current knowledge identified by the review of the end points in the aforementioned trials., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Society of Nephrology.)

The complement system is recognised as a protector against blood-borne pathogens and a controller of immune system and tissue homoeostasis. However, dysregulated complement activity is associated with unwanted or non-resolving immune responses and inflammation, which induce or exacerbate the pathogenesis of a broad range of inflammatory and autoimmune diseases. Although the merit of targeting complement clinically has long been acknowledged, the overall complement drug approval rate has been modest. However, the success of the humanised anti-C5 antibody eculizumab in effectively treating paroxysmal nocturnal haemoglobinuria and atypical haemolytic syndrome has revitalised efforts to target complement therapeutically. Increased understanding of complement biology has led to the identification of novel targets for drug development that, in combination with advances in drug discovery and development technologies, has resulted in a surge of interest in bringing new complement therapeutics into clinical use. The rising number of approved drugs still almost exclusively target rare diseases, but the substantial pipeline of up-and-coming treatment options will possibly provide opportunities to also expand the clinical targeting of complement to common diseases., Competing Interests: Declaration of interests TW has been supported by research grants or contracts from Alsonex Pharmaceuticals, Pfizer, and Takeda Pharmaceuticals (grants and fees paid to the institution); has received ad-hoc consultation fees from Iveric Bio and Visterra, a honorarium from Alexion Pharmaceuticals for conference organisation (paid to institution), and a preclinical complement research reagent from GSK; TW is a non-paid, non-contracted, scientific advisor to Alsonex Pharmaceuticals; and was scientific advisor to Sitala Bio (from May, 2022, to May, 2023; compensation paid to institution). VF-B has received funding for research from Alexion Pharmaceuticals, Apellis Pharmaceuticals, and Novartis (compensation paid to institution); and received consultation compensation and honoraria for lectures and presentations, and financial support for attending meetings from Alexion Pharmaceuticals, Apellis Pharmaceuticals, Novartis, Roche, Samsung, Vifor, and UCB Pharma. CK has been a volunteer member of the Apellis Pharmaceuticals Scientific Advisory Board since 2015; and has a National Institutes of Health (NIH)-approved Collaborative Research and Development Agreement with Apellis Pharmaceuticals (2023–24). CK's research laboratory is supported in part by the Intramural Research Program of the NIH and the National Heart, Lung, and Blood Institute (project number zia/hl006223). EEW declares no competing interests., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Patients with paroxysmal nocturnal hemoglobinuria (PNH) are susceptible to complement-mediated intravascular hemolysis and thrombosis. Factor H (FH) is the main regulator of the complement alternative pathway, which protects cells from unwanted complement-mediated damage. Although FH is not a glycosylphosphatidylinositol-linked molecule, it may play a role in PNH. We sought to determine if rare germline variants in complement factor H (CFH) affect the PNH course, screening 84 patients with PNH treated with eculizumab for rare variants in CFH, CFI, and C3 genes. We compared the allelic frequencies with populational data and a geographically-matched control group, looking for an association between presence of the variants and treatment response (transfusion independence by 6 months). Sixteen patients presented rare variants, 9 in CFH (10.7%). Germline CFH variants were more frequent among patients with PNH than among controls (P = .02) or public data (P < .001) and were more likely to be transfusion-dependent at 6 months after eculizumab initiation (P = .015). With a median follow-up of 5.8 years, 8 of 9 patients with the CFH variant received transfusions, and 2 developed thromboses. None of the patients with the CFH variant had severe aplastic anemia from eculizumab initiation until 6 months. We demonstrated for the first time that rare CFH variants are over-represented among patients with PNH and that germline genetic background may affect the response to eculizumab., (© 2023 by The American Society of Hematology.)

Background: Cancer-associated thrombotic microangiopathy (TMA) is a rare disease, with a poor prognosis. The classical treatment is urgent chemotherapy. Few data are available on the efficacy of plasma exchange (PE) and eculizumab in these patients., Methods: Cases of cancer-related TMA treated between January 2008 and December 2019 in 12 French treatment centres were retrospectively analysed, excluding cases associated with chemotherapy and stem cell transplantation. Patients were divided into four groups depending on the treatment received: none, PE therapy alone, chemotherapy, with or without PE therapy, or eculizumab, with or without chemotherapy and PE therapy., Results: The data of 59 patients with cancer-associated TMA were analysed. Twenty of these cases were related to a cancer recurrence. The cancer was metastatic in 90% of cases (53/59). Bone marrow invasion was observed in 20/41 biopsies. Some laboratory results, including disseminated intravascular coagulation high ferritin and C-reactive protein, were suggestive of cancer. None of the 16 patients whose alternative complement pathway was assessed had abnormal levels of protein expression or activity. The median survival time was 27 days. Chemotherapy was significantly associated with improved survival, with a 30-day survival rate of 85% (17/20) among patients who received PE and chemotherapy, versus 20% (3/15) among patients who received PE alone. Patients treated with eculizumab in addition to chemotherapy and PE therapy did not have longer overall survival or higher haematological remission rates than those treated with chemotherapy and PE therapy alone. Renal remission rates were non-significantly higher, and times to remission non-significantly shorter, in the eculizumab group., Conclusions: Nephrologists and oncologists should make themselves aware of cancer diagnoses in patients with TMA and bone marrow biopsies should be performed systematically in these cases. All 59 patients had poor survival outcomes, but patients treated with urgent initiation of chemotherapy survived significantly longer than those who were not., (© The Author(s) 2022. Published by Oxford University Press on behalf of the ERA.)

Eculizumab, a recombinant humanized monoclonal antibody (mAb), is used for the treatment of patients (both adults and children) with paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. This mAb binds to complement protein 5 (C5), thereby inhibiting its cleavage. On the other hand, one of the C5 cleavage products, C5a, is a potent anaphylatoxin with proinflammatory properties, involved in antimicrobial surveillance. Administration of eculizumab has been reported to make patients more susceptible to infection by encapsulated bacteria. Here, we are reporting an adult case of disseminated infection due to the encapsulated yeast Cryptococcus neoformans following eculizumab therapy and discuss its pathogenesis., Competing Interests: Potential conflicts of interest. For all the authors, there is no conflict to declare., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Infectious Diseases Society of America.)

Uncontrolled alternative pathway activation is the primary driver of several diseases, and it contributes to the pathogenesis of many others. Consequently, diagnostic tests to monitor this arm of the complement system are increasingly important. Defects in alternative pathway regulation are strong risk factors for disease, and drugs that specifically block the alternative pathway are entering clinical use. A range of diagnostic tests have been developed to evaluate and monitor the alternative pathway, including assays to measure its function, expression of alternative pathway constituents, and activation fragments. Genetic studies have also revealed many disease-associated variants in alternative pathway genes that predict the risk of disease and prognosis. Newer imaging modalities offer the promise of non-invasively detecting and localizing pathologic complement activation. Together, these various tests help in the diagnosis of disease, provide important prognostic information, and can help guide therapy with complement inhibitory drugs., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Rationale & Objective: Hemolytic uremic syndrome (HUS), a thrombotic microangiopathy (TMA) with kidney involvement, is a rare condition in patients with monoclonal gammopathy. In the absence of known causes of TMA, the role of complement activation in endothelial injury in patients with monoclonal gammopathy remains unknown and was the focus of this investigation., Study Design: Case series., Setting & Participants: We studied the 24 patients in the French national registry of HUS between 2000 and 2020 who had monoclonal gammopathy without other causes of secondary TMA. We provide the clinical histories and complement studies of these patients., Findings: Monoclonal gammopathy-associated TMA with kidney involvement is estimated to be 10 times less frequent than adult atypical HUS (aHUS) in the French national registry. It is characterized by severe clinical features, with 17 of 24 patients requiring dialysis at disease onset, and with median renal survival of only 20 months. TMA-mediated extrarenal manifestations, particularly cutaneous and neurological involvement, were common and associated with poor overall prognosis. Complement studies identified low C3, normal C4, and high soluble C5b-9 levels in 33%, 100%, and 77% of tested patients, respectively, indicating a contribution of the alternative and terminal complement pathways in the pathophysiology of the disease. Genetic abnormalities in complement genes known to be associated with aHUS were found in only 3 of 17 (17%) who were tested., Limitations: Retrospective study without comparison group; limited number of patients, limited available blood samples., Conclusions: Within the spectrum of TMA, TMA associated with monoclonal gammopathy represents a distinct subset. Our findings suggest that HUS associated with monoclonal immunoglobulin is a complement-mediated disease akin to aHUS., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Patients with paroxysmal nocturnal hemoglobinuria (PNH) have a clonal population of blood cells deficient in glycosylphosphatidylinositol-anchored (GPI-anchored) proteins, most of the time resulting from a mutation in the X-linked gene PIGA. We report a patient with PNH resulting from a rare biallelic PIGT mutation on chromosome 20., Case Summary: A 47-year-old man was referred to our hospital for febrile pancytopenia. The patient reported a history of recurrent urticaria and arthralgia and he presented during 3 mo recurrent acute dermo-hypodermitis and aseptic meningitidis. Based on clinical cases published with PIGT-PNH, with clinically typical PNH and autoinflammatory symptoms, we treated our patients with repeated infusions of eculizumab to decrease autoinflammatory symptoms and then we performed an allogeneic stem cell transplantation (allo-SCT) with a mismatched unrelated donor. Our patient experienced no acute Graft vs Host disease (GvHD) and a moderate chronic GvHD and is now considered cured at 24 mo after allo-SCT., Conclusion: This case report suggests that allo-SCT should be considered to cure PIGT-PNH patients., Competing Interests: Conflict-of-interest statement: The authors declare no competing financial interests., (©The Author(s) 2022. Published by Baishideng Publishing Group Inc. All rights reserved.)

Background: The prevalence, prognostic role, and diagnostic value of blood pressure in immune-mediated thrombotic thrombocytopenic purpura (iTTP) and other thrombotic microangiopathies (TMAs) remain unclear., Methods: Using a national cohort of iTTP ( n  = 368), Shigatoxin-induced hemolytic uremic syndrome ( n  = 86), atypical hemolytic uremic syndrome ( n  = 84), and hypertension-related thrombotic microangiopathy ( n  = 25), we sought to compare the cohort's blood pressure profile to assess its impact on prognosis and diagnostic performances., Results: Patients with iTTP had lower blood pressure than patients with other TMAs, systolic (130 [interquartile range (IQR) 118-143] vs 161 [IQR 142-180] mmHg) and diastolic (76 [IQR 69-83] vs 92 [IQR 79-105] mmHg, both p  < 0.001). The best threshold for iTTP diagnosis corresponded to a systolic blood pressure <150 mmHg. iTTP patients presenting with hypertension had a significantly poorer survival (hazard ratio 1.80, 95% confidence interval 1.07-3.04), and this effect remained significant after multivariable adjustment (hazard ratio = 1.14, 95% confidence interval 1.00-1.30). Addition of a blood pressure criterion modestly improved the French clinical score to predict a severe A disintegrin and metalloprotease with thrombospondin type 1 deficiency in patients with an intermediate score (i.e., either platelet count <30 × 10 9 /L or serum creatinine <200 µM)., Conclusions: Elevated blood pressure at admission affects the prognosis of iTTP patients and may help discriminate them from other TMA patients. Particular attention should be paid to blood pressure and its management in these patients., (© 2022 The Authors. Research and Practice in Thrombosis and Haemostasis published by Wiley Periodicals LLC on behalf of International Society on Thrombosis and Haemostasis (ISTH).)

As part of the innate immune system, the complement system plays a key role in defense against pathogens and in host cell homeostasis. This enzymatic cascade is rapidly triggered in the presence of activating surfaces. Physiologically, it is tightly regulated on host cells to avoid uncontrolled activation and self-damage. In cases of abnormal complement dysregulation/overactivation, the endothelium is one of the primary targets. Complement has gained momentum as a research interest in the last decade because its dysregulation has been implicated in the pathophysiology of many human diseases. Thus, it appears to be a promising candidate for therapeutic intervention. However, detecting abnormal complement activation is challenging. In many pathological conditions, complement activation occurs locally in tissues. Standard routine exploration of the plasma concentration of the complement components shows values in the normal range. The available tests to demonstrate such dysregulation with diagnostic, prognostic, and therapeutic implications are limited. There is a real need to develop tools to demonstrate the implications of complement in diseases and to explore the complex interplay between complement activation and regulation on human cells. The analysis of complement deposits on cultured endothelial cells incubated with pathologic human serum holds promise as a reference assay. This ex vivo assay most closely resembles the physiological context. It has been used to explore complement activation from sera of patients with atypical hemolytic uremic syndrome, malignant hypertension, elevated liver enzymes low platelet syndrome, sickle cell disease, pre-eclampsia, and others. In some cases, it is used to adjust the therapeutic regimen with a complement-blocking drug. Nevertheless, an international standard is lacking, and the mechanism by which complement is activated in this assay is not fully understood. Moreover, primary cell culture remains difficult to perform, which probably explains why no standardized or commercialized assay has been proposed. Here, we review the diseases for which endothelial assays have been applied. We also compare this test with others currently available to explore complement overactivation. Finally, we discuss the unanswered questions and challenges to overcome for validating the assays as a tool in routine clinical practice., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Meuleman, Duval, Fremeaux-Bacchi, Roumenina and Chauvet.)

The complement system plays a complex role in cancer. In clear cell renal cell carcinoma (ccRCC), local production of complement proteins drives tumor progression, but the mechanisms by which they do this are poorly understood. We found that complement activation, as reflected by high plasma C4d or as C4d deposits at the tumor site, was associated with poor prognosis in two cohorts of patients with ccRCC. High expression of the C4-activating enzyme C1s by tumor cells was associated with poor prognosis in three cohorts. Multivariate Cox analysis revealed that the prognostic value of C1s was independent from complement deposits, suggesting the possibility of complement cascade-unrelated, protumoral functions for C1s. Silencing of C1s in cancer cell lines resulted in decreased proliferation and viability of the cells and in increased activation of T cells in in vitro cocultures. Tumors expressing high levels of C1s showed high infiltration of macrophages and T cells. Modification of the tumor cell phenotype and T-cell activation were independent of extracellular C1s levels, suggesting that C1s was acting in an intracellular, noncanonical manner. In conclusion, our data point to C1s playing a dual role in promoting ccRCC progression by triggering complement activation and by modulating the tumor cell phenotype and tumor microenvironment in a complement cascade-independent, noncanonical manner. Overexpression of C1s by tumor cells could be a new escape mechanism to promote tumor progression. See related Spotlight by Magrini and Garlanda, p. 855. See article by Daugan et al., p. 909 (40)., (©2021 American Association for Cancer Research.)

Background: Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection causes direct lung damage, overwhelming endothelial activation, and inflammatory reaction, leading to acute respiratory failure and multi-organ dysfunction. Ongoing clinical trials are evaluating targeted therapies to hinder this exaggerated inflammatory response. Critically ill coronavirus disease 2019 (COVID-19) patients have shown heterogeneous severity trajectories, suggesting that response to therapies is likely to vary across patients., Research Question: Are critically ill COVID-19 patients biologically and immunologically dissociable based on profiling of currently evaluated therapeutic targets?, Study Design and Methods: We did a single-center, prospective study in an ICU department in France. Ninety-six critically ill adult patients admitted with a documented SARS-CoV-2 infection were enrolled. We conducted principal components analysis and hierarchical clustering on a vast array of immunologic variables measured on the day of ICU admission., Results: We found that patients were distributed in three clusters bearing distinct immunologic features and associated with different ICU outcomes. Cluster 1 had a "humoral immunodeficiency" phenotype with predominant B-lymphocyte defect, relative hypogammaglobulinemia, and moderate inflammation. Cluster 2 had a "hyperinflammatory" phenotype, with high cytokine levels (IL-6, IL-1β, IL-8, tumor necrosis factor-alpha [TNF⍺]) associated with CD4+ and CD8+ T-lymphocyte defects. Cluster 3 had a "complement-dependent" phenotype with terminal complement activation markers (elevated C3 and sC5b-9)., Interpretation: Patients with severe COVID-19 exhibiting cytokine release marks, complement activation, or B-lymphocyte defects are distinct from each other. Such immunologic variability argues in favor of targeting different mediators in different groups of patients and could serve as a basis for patient identification and clinical trial eligibility., (Copyright © 2020 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.)

The spectrum of human diseases with complement contribution is ever increasing. Tools to study the complement contribution and the potential interest of novel complement inhibitors in clinical practice are lacking. Here we discuss a functional ex vivo assay to monitor complement activation on endothelial cells, which can answer to this need., Competing Interests: Declaration of Interests The authors declare no conflict of interest., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Rhabdomyolysis is a life-threatening condition caused by skeletal muscle damage with acute kidney injury being the main complication dramatically worsening the prognosis. Specific treatment for rhabdomyolysis-induced acute kidney injury is lacking and the mechanisms of the injury are unclear. To clarify this, we studied intra-kidney complement activation (C3d and C5b-9 deposits) in tubules and vessels of patients and mice with rhabdomyolysis-induced acute kidney injury. The lectin complement pathway was found to be activated in the kidney, likely via an abnormal pattern of Fut2-dependent cell fucosylation, recognized by the pattern recognition molecule collectin-11 and this proceeded in a C4-independent, bypass manner. Concomitantly, myoglobin-derived heme activated the alternative pathway. Complement deposition and acute kidney injury were attenuated by pre-treatment with the heme scavenger hemopexin. This indicates that complement was activated in a unique double-trigger mechanism, via the alternative and lectin pathways. The direct pathological role of complement was demonstrated by the preservation of kidney function in C3 knockout mice after the induction of rhabdomyolysis. The transcriptomic signature for rhabdomyolysis-induced acute kidney injury included a strong inflammatory and apoptotic component, which were C3/complement-dependent, as they were normalized in C3 knockout mice. The intra-kidney macrophage population expressed a complement-sensitive phenotype, overexpressing CD11b and C5aR1. Thus, our results demonstrate a direct pathological role of heme and complement in rhabdomyolysis-induced acute kidney injury. Hence, heme scavenging and complement inhibition represent promising therapeutic strategies., (Copyright © 2020 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Introduction: Connective tissue diseases, including systemic sclerosis and idiopathic inflammatory myopathies (IIMs), are a very rare cause of thrombotic microangiopathies (TMAs). Whether dysregulation of the complement pathways underlies these secondary forms of TMA and may be targeted by complement blocking agents remains elusive., Methods: Kidney pathology and outcomes of 18 critically ill patients with TMA related to inflammatory myopathy flare-up (IIM, n =7) or scleroderma renal crisis (SRC, n =11; biopsy n =9) are assessed., Results: IIM-TMA is characterized by acute thrombotic lesions only, whereas SRC-TMA patients also harbored chronic vascular lesions and more interstitial fibrosis. C5b9 deposits, a marker of complement component 5 (C5) cleavage, were observed in the 2 subgroups at the junction of media and intima of arterioles, colocalizing with subendothelial edema. Thus, kidney biopsy distinguished between acute and chronic renal phenotypes that may help to individualize treatment. Treatment of IIM-TMA patients with combined full-code organ support, corticosteroids, B-cell depletion, and complement C5 blocking led to 1-year survival of 72%, compared with 19% in historical cohorts. Treatment of SRC-TMA was more heterogenous and relied on conversion enzyme inhibitor only or with eculizumab ( n =6) and immunosuppressor ( n =5). One-year survival of SRC-TMA patients was 52%, a result similar to historical cohorts. Eculizumab was followed by a rapid dramatic improvement of TMA in all the treated patients., Conclusion: C5 blocking may reverse hematologic abnormalities in IIM- and SRC-TMA, and adding an early and aggressive immunosuppressive regimen may improve the survival of IIM-TMA. Underlying chronic vascular and interstitial lesions mitigate renal response in SRC-TMA., (© 2021 International Society of Nephrology. Published by Elsevier Inc.)

Intravascular hemolysis of any cause can induce acute kidney injury (AKI). Hemolysis-derived product heme activates the innate immune complement system and contributes to renal damage. Therefore, we explored the role of the master complement regulator Factor H (FH) in the kidney's resistance to hemolysis-mediated AKI. Acute systemic hemolysis was induced in mice lacking liver expression of FH (hepatoFH -/- , ~20% residual FH) and in WT controls, by phenylhydrazine injection. The impaired complement regulation in hepatoFH -/- mice resulted in a delayed but aggravated phenotype of hemolysis-related kidney injuries. Plasma urea as well as markers for tubular (NGAL, Kim-1) and vascular aggression peaked at day 1 in WT mice and normalized at day 2, while they increased more in hepatoFH -/- compared to the WT and still persisted at day 4. These were accompanied by exacerbated tubular dilatation and the appearance of tubular casts in the kidneys of hemolytic hepatoFH -/- mice. Complement activation in hemolytic mice occurred in the circulation and C3b/iC3b was deposited in glomeruli in both strains. Both genotypes presented with positive staining of FH in the glomeruli, but hepatoFH -/- mice had reduced staining in the tubular compartment. Despite the clear phenotype of tubular injury, no complement activation was detected in the tubulointerstitium of the phenylhydrazin-injected mice irrespective of the genotype. Nevertheless, phenylhydrazin triggered overexpression of C5aR1 in tubules, predominantly in hepatoFH -/- mice. Moreover, C5b-9 was deposited only in the glomeruli of the hemolytic hepatoFH -/- mice. Therefore, we hypothesize that C5a, generated in the glomeruli, could be filtered into the tubulointerstitium to activate C5aR1 expressed by tubular cells injured by hemolysis-derived products and will aggravate the tissue injury. Plasma-derived FH is critical for the tubular protection, since pre-treatment of the hemolytic hepatoFH -/- mice with purified FH attenuated the tubular injury. Worsening of acute tubular necrosis in the hepatoFH -/- mice was trigger-dependent, as it was also observed in LPS-induced septic AKI model but not in chemotherapy-induced AKI upon cisplatin injection. In conclusion, plasma FH plays a key role in protecting the kidneys, especially the tubules, against hemolysis-mediated injury. Thus, FH-based molecules might be explored as promising therapeutic agents in a context of AKI., (Copyright © 2020 Merle, Leon, Poillerat, Grunenwald, Boudhabhay, Knockaert, Robe-Rybkine, Torset, Pickering, Chauvet, Fremeaux-Bacchi and Roumenina.)

Background: Different types of in silico approaches can be used to predict the phenotypic consequence of missense variants. Such algorithms are often categorized as sequence based or structure based, when they necessitate 3D structural information. In addition, many other in silico tools, not dedicated to the analysis of variants, can be used to gain additional insights about the possible mechanisms at play., Methods: Here we applied different computational approaches to a set of 20 known missense variants present on different proteins (CYP, complement factor B, antithrombin and blood coagulation factor VIII). The tools that were used include fast computational approaches and web servers such as PolyPhen-2, PopMusic, DUET, MaestroWeb, SAAFEC, Missense3D, VarSite, FlexPred, PredyFlexy, Clustal Omega, meta-PPISP, FTMap, ClusPro, pyDock, PPM, RING, Cytoscape, and ChannelsDB., Results: We observe some conflicting results among the methods but, most of the time, the combination of several engines helped to clarify the potential impacts of the amino acid substitutions., Conclusion: Combining different computational approaches including some that were not developed to investigate missense variants help to predict the possible impact of the amino acid substitutions. Yet, when the modified residues are involved in a salt-bridge, the tools tend to fail, even when the analysis is performed in 3D. Thus, interactive structural analysis with molecular graphics packages such as Chimera or PyMol or others are still needed to clarify automatic prediction., (© 2020 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc.)

Properdin (FP) is a positive regulator of the immune system stimulating the activity of the proteolytically active C3 convertase C3bBb in the alternative pathway of the complement system. Here we present two crystal structures of FP and two structures of convertase bound FP. A structural core formed by three thrombospondin repeats (TSRs) and a TB domain harbors the convertase binding site in FP that mainly interacts with C3b. Stabilization of the interaction between the C3b C-terminus and the MIDAS bound Mg 2+ in the Bb protease by FP TSR5 is proposed to underlie FP convertase stabilization. Intermolecular contacts between FP and the convertase subunits suggested by the structure were confirmed by binding experiments. FP is shown to inhibit C3b degradation by FI due to a direct competition for a common binding site on C3b. FP oligomers are held together by two sets of intermolecular contacts, where the first is formed by the TB domain from one FP molecule and TSR4 from another. The second and largest interface is formed by TSR1 and TSR6 from the same two FP molecules. Flexibility at four hinges between thrombospondin repeats is suggested to enable the oligomeric, polydisperse, and extended architecture of FP. Our structures rationalize the effects of mutations associated with FP deficiencies and provide a structural basis for the analysis of FP function in convertases and its possible role in pattern recognition.