Anti-factor H antibody and its role in atypical hemolytic uremic syndrome

Long-Term Outcomes of Anticomplement Factor H Antibody Positive Versus Negative Atypical Hemolytic Uremic Syndrome

Background

Atypical hemolytic uremic syndrome (aHUS) is a severe thrombotic microangiopathy predominantly affecting the kidneys, often associated with complement dysregulation. This study is aimed to analyze the clinical characteristics, treatment outcomes, and long-term implications of aHUS in a resource-limited setting.

Materials and Methods

A retrospective observational study conducted at an institute between January 2016 and December 2022 included all patients with aHUS, excluding secondary causes and renal transplant recipients. Demographic profiles, clinical features, laboratory parameters, treatment modalities (immunosuppression and plasma exchange), and outcomes were collected. Anticomplement Factor H (anti-CFH) antibody, complement levels, and genetic mutation analysis were performed to ascertain etiological factors. The patient and renal outcomes of anti-CFH positive and negative patients on long-term follow-up were compared.

Results

Fifty-seven patients (mean age: 12.5 ± 4.9 years; 63% males) were analyzed. Among them, 33 (57.9%) tested positive for anti-CFH antibodies and eight presented postpartum. Initial remission was achieved in 42 (73.6%) patients, with 13 (22.8%) partial and 29 (50.9%) complete remission. The median follow-up duration was 24 months [interquartile range (IQR) 8.5-84]; 12 (21%) patients died, with two deaths during the index admission, six among nonresponders, and 4 among responders. Dialysis-free renal survival was superior in anti-CFH seropositive patients (81.2%) compared to seronegative counterparts (55.9%), while patient survival was statistically similar between the two groups. Elevated anti-CFH titers (>4000 AU/ml), age ≥16 years, female gender, and seizures predicted nonresponsiveness.

Conclusion

Anti-CFH antibody associated aHUS had better kidney outcomes than the seronegative counterparts. In resource limited settings, a combination of plasma exchange and immunosuppression showed promising results in the short and long term.

Plasma exchange combined with eculizumab in the management of atypical hemolytic uremic in pediatric patients: A case report

RATIONALE

Atypical hemolytic uremic syndrome (aHUS) is a severe rare disease characterized by microvascular hemolytic anemia, thrombocytopenia, and acute renal failure.

PATIENT CONCERNS

A 10-year-old male presented with symptoms of weakness, jaundice, pallor, swollen eyelids, and no significant lower limb swelling. Laboratory investigations revealed critical hemoglobin levels, fragmented red blood cells, thrombocytopenia, and acute kidney injury.

DIAGNOSES

The patient was diagnosed with aHUS based on the clinical trial of microvascular hemolytic anemia, thrombocytopenia, and organ damage due to thrombosis, as well as laboratory findings.

INTERVENTIONS

The patient was treated with a combination of plasma exchange and the drug Eculizumab. Comprehensive nursing care was provided, including the establishment and maintenance of blood purification pipelines, management of complications (such as coagulation, allergic reactions, hypotension, and bleeding), and psychological support for the patient and family.

OUTCOMES

The patient successfully completed a 3-month treatment regimen with Eculizumab and has been followed up for an additional 10 months without any recurrence of the condition, demonstrating favorable treatment outcomes.

LESSONS

The novel approach of combining plasma exchange with Eculizumab in pediatric aHUS presents significant nursing challenges, but the case demonstrates the potential benefits of this combination therapy, particularly in the pediatric population in China where Eculizumab has recently become available. Comprehensive nursing care, including managing complications and providing psychological support, is crucial to the successful treatment of aHUS.

Eculizumab as first-line treatment for patients with severe presentation of complement factor H antibody-mediated hemolytic uremic syndrome

BACKGROUND

Complement factor H (FH) antibody-mediated hemolytic uremic syndrome (HUS) has varying prevalence globally. Plasmapheresis and immunosuppressive drugs are the standard treatment. Recently, eculizumab has been reported as an effective alternative. This study aims to report four children with FH antibody-mediated HUS managed with eculizumab plus immunosuppression as first-line therapy.

METHODS

A retrospective chart review was conducted for children aged ≤ 18 years old with complement-mediated HUS in two referral centers. Patients with FH antibody-mediated HUS treated with eculizumab as first-line therapy were included.

RESULTS

Four children (aged 6-11 years old) were included. Dialysis was necessary in three patients. Eculizumab was administered 5-23 days after onset. None of them received plasmapheresis. Prednisone and mycophenolate mofetil were added after receiving positive FH antibody results. Hematological signs and kidney function improved after the second eculizumab dose. Eculizumab was discontinued in three patients after 6 months. One patient required rituximab due to persistent high FH antibody titers; discontinuation of eculizumab occurred after 15 months without recurrence. No treatment-related complications were observed. During a mean 12-month follow-up (range 6-24 months), no relapses were recorded and all patients ended with normal GFR.

CONCLUSION

Our data suggest that a short course of 6 months of C5 inhibitor might be sufficient to reverse thrombotic microangiopathy symptoms and improve kidney function in patients with severe FH antibody-mediated HUS. Simultaneously, adding immunosuppressive agents might reduce the risk of relapse and allow cessation of C5 inhibition in a shorter period of time.

Updates in atypical hemolytic syndrome

PURPOSE OF REVIEW

This review aims to summarize how scientific advances in complement biology have not only improved the diagnosis and management of aHUS but also continue to offer insights into the pathophysiology of complement-mediated disease that may be leveraged for future therapeutic developments.

RECENT FINDINGS

Updated information on the clinical and epidemiological features, pathophysiology, diagnosis, management, and potential for future therapeutic advancements in the treatment of aHUS are reviewed.

SUMMARY

aHUS is a rare but potentially life-threatening disease that requires prompt diagnosis and treatment as well as long-term management via a multidisciplinary team providing coordination of primary and specialty care as well as outreach and education for children and families affected by this life-long disease.

Systematic Review of Individual Patient Data COVID-19 Infection and Vaccination-Associated Thrombotic Microangiopathy

Introduction

Sporadic cases of atypical hemolytic uremic syndrome (aHUS) have been described in the literature in association with COVID-19 infection and vaccination in adults and pediatric patients. The exact mechanisms underlying COVID-19-associated thrombotic microangiopathies (TMAs) remain incompletely understood. Herein, we present a detailed meta-analysis of the clinical characteristics, outcomes, and management strategies of COVID-19-associated aHUS and thrombotic thrombocytopenic purpura (TTP).

Methods

This study was performed following the Preferred Reporting Items for Systematic Reviews and Meta-analyses updated guidelines. PubMed was utilized for searching for case reports and series. Adverse outcome at last follow-up was defined as estimated glomerular filtration rate < 30 ml/min per 1.73 m2 (patients with aHUS), no remission with therapy, or patient death. Data were analyzed using Wilcoxon rank and Chi-square tests.

Results

Our analysis cohort included 118 studies reporting on 170 patients. These included 84 cases of aHUS and 86 cases of TTP resulting from COVID-19 infection (n = 92) or vaccination (n = 78). Significantly more cases of aHUS were reported after infection (n = 65) than immunization (n = 19), compared to TTP, where the reverse was true (n = 27 and n = 59, respectively; P < 0.001). In patients with aHUS with stage 3 acute kidney injury (AKI), requirement of kidney replacement therapy (KRT) was seen in three-fourths of the cohort for a median of 15. In patients with TTP, severe COVID-19 infection (P = 0.04) predicted nonremission or death at last follow-up. Administration of i.v., rituximab and caplacizumab were protective (P = 0.03 and P = 0.06, respectively). Immune TTP (iTTP) was reported more often than HUS following mRNA vaccines (81% vs. 58%; P = 0.06).

Conclusion

COVID-19 infection and vaccination are a potential trigger for onset or relapse of aHUS and TTP, especially in patients who are not on maintenance complement inhibitors or immunosuppression.

Exploring the Intersection of Atypical Hemolytic Uremic Syndrome and Substance Use: A Comprehensive Narrative Review

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by hemolytic anemia, renal failure, and thrombocytopenia. While the typical form of HUS is often associated with Shiga toxin-producing Escherichia coli (STEC) infections, atypical hemolytic uremic syndrome (aHUS) is caused by uncontrolled complement system activation, leading to endothelial damage, microthrombi formation, and other complications. Although aHUS is commonly linked to genetic mutations and infections, emerging evidence suggests that certain substances, particularly illicit drugs like heroin, cocaine, and ecstasy, can also trigger this condition, adding complexity to its diagnosis and management. This narrative review examines the mechanisms by which substance use can lead to aHUS, discusses its clinical presentation, and highlights the diagnostic challenges in distinguishing it from other thrombotic microangiopathies, such as thrombotic thrombocytopenic purpura (TTP) and STEC-HUS. A thorough literature search identified relevant case reports, case series, and observational studies, underscoring the need for genetic testing and complement assays to confirm aHUS in substance users. The review also explores the role of complement inhibitors, such as eculizumab and ravulizumab, which target the underlying pathophysiology and have shown promise in improving patient outcomes. However, the management of substance-induced aHUS remains challenging due to limited data, varying clinical presentations, and the need to optimize treatment protocols. Early recognition and tailored therapy are crucial for effective management. Further research is needed to refine diagnostic criteria, develop new therapeutic approaches, and improve care for patients with this under-recognized condition.

Thrombotic Microangiopathy in Pregnancy: Current Understanding and Management Strategies

Thrombotic microangiopathy (TMA) represents a heterogeneous group of disorders characterized by microvascular thrombosis and end-organ damage. Pregnancy-associated thrombotic microangiopathy (p-TMA) has emerged as a distinct clinical entity with unique diagnostic challenges. Identifying the specific form of p-TMA is critical for appropriate and timely management. This review offers a comprehensive overview of the various forms of thrombotic microangiopathies associated with pregnancy, highlighting our current understanding of their pathophysiology and the evolving landscape of diagnosis and treatment for each.

Recurrent complement-mediated Hemolytic uremic syndrome after kidney transplantation

Hereditary forms of hemolytic uremic syndrome (HUS), formerly known as atypical HUS, typically involve mutations in genes encoding for components of the alternative pathway of complement, therefore they are often referred to as complement-mediated HUS (cHUS). This condition has a high risk of recurrence in the transplanted kidney, leading to accelerated graft loss. The availability of anti-complement component C5 antibody eculizumab has enabled successful transplantation with a notably reduced recurrence rate and improved prognosis. Open questions are related to the potential for complement inhibitor discontinuation, ideal timing of treatment withdrawal, and patient selection based on genetic abnormalities. Our review delves into the pathophysiology, classification, genetic predispositions, and management strategies for cHUS in the native and transplant kidneys.

Anti-factor H Autoantibody-Associated Hemolytic Uremic Syndrome: A Rare Entity in a Pediatric Patient

An 11-year-old patient presented with the primary complaint of hematuria and vomiting. On further investigation and a series of diagnostic tests, including a biopsy and thrombotic microangiopathy (TMA) profile, the patient was diagnosed with thrombotic microangiopathy. TMA is a pathological process involving endothelial cell injury, leading to thrombocytopenia and microangiopathic hemolytic anemia. This case highlights the importance of considering TMA in pediatric patients presenting with nonspecific symptoms, such as loss of appetite. Further research is needed to understand the pathophysiology and optimal management strategies for pediatric TMA. This case adds to the growing body of literature on pediatric TMA and underscores the need for a high index of suspicion in similar clinical scenarios.

Complement dysregulation associated with a genetic variant in factor H-related protein 5 in atypical hemolytic uremic syndrome

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) can be associated with mutations, deletions, or hybrid genes in factor H-related (FHR) proteins.

METHODS

A child with aHUS was investigated. Genetics was assessed by Sanger and next generation sequencing. Serum FHR5 was evaluated by immunoblotting, ELISA, and by induction of rabbit red blood cell hemolysis in the presence/absence of recombinant human rFHR5. Mutagenesis was performed in HEK cells.

RESULTS

A heterozygous genetic variant in factor H-related protein 5 (CFHR5), M514R, was found in the child, who also had a homozygous deletion of CFHR3/CFHR1, and antibodies to factor H, as well as low levels of C3. Patient serum exhibited low levels of FHR5. In the presence of rabbit red blood cells, patient serum induced hemolysis which decreased when rFHR5 was added at physiological concentrations. Similar results were obtained using serum from the father, bearing the CFHR5 variant without factor H antibodies. Patient FHR5 formed normal dimers. The CFHR5 M514R variant was expressed in HEK cells and minimal secretion was detected whereas the protein level was elevated in cell lysates.

CONCLUSIONS

Decreased secretion of the product of the mutant allele could explain the low FHR5 levels in patient serum. Reduced hemolysis when rFHR5 was added to serum suggests a regulatory role regarding complement activation on red blood cells. As such, low levels of FHR5, as demonstrated in the patient, may contribute to complement activation.

Mechanisms that potentially contribute to the development of post-streptococcal glomerulonephritis

Post-streptococcal glomerulonephritis (PSGN) is primarily associated with preceding group A streptococcal skin or throat infections, now mainly observed in economically disadvantaged communities. This condition significantly predisposes individuals to later-life chronic kidney disease and concurrent renal complications, with the elderly experiencing increased severity and less favourable outcomes. Streptococcal pyrogenic exotoxin B and nephritis-associated plasmin receptor are identified nephritogenic antigens (nephritogens). Pathogenesis of PSGN is multifactorial. It can involve the formation of antigen-antibody immune complexes, causing inflammatory damage to renal glomeruli. Deposition of circulating immune complexes or in situ formation of immune complexes in glomeruli, or both, results in glomerulonephritis. Additionally, molecular mimicry is hypothesized as a mechanism, wherein cross-reactivity between anti-streptococcal antibodies and glomerular intrinsic matrix proteins leads to glomerulonephritis. Besides, as observed in clinical studies, streptococcal inhibitor of complement, a streptococcal-secreted protein, can also be associated with PSGN. However, the interplay between these streptococcal antigens in the pathogenesis of PSGN necessitates further investigation. Despite the clinical significance of PSGN, the lack of credible animal models poses challenges in understanding the association between streptococcal antigens and the disease process. This review outlines the postulated mechanisms implicated in the development of PSGN with possible therapeutic approaches.

An integrative framework for clinical diagnosis and knowledge discovery from exome sequencing data

Non-silent single nucleotide genetic variants, like nonsense changes and insertion-deletion variants, that affect protein function and length substantially are prevalent and are frequently misclassified. The low sensitivity and specificity of existing variant effect predictors for nonsense and indel variations restrict their use in clinical applications. We propose the Pathogenic Mutation Prediction (PMPred) method to predict the pathogenicity of single nucleotide variations, which impair protein function by prematurely terminating a protein's elongation during its synthesis. The prediction starts by monitoring functional effects (Gene Ontology annotation changes) of the change in sequence, using an existing ensemble machine learning model (UniGOPred). This, in turn, reveals the mutations that significantly deviate functionally from the wild-type sequence. We have identified novel harmful mutations in patient data and present them as motivating case studies. We also show that our method has increased sensitivity and specificity compared to state-of-the-art, especially in single nucleotide variations that produce large functional changes in the final protein. As further validation, we have done a comparative docking study on such a variation that is misclassified by existing methods and, using the altered binding affinities, show how PMPred can correctly predict the pathogenicity when other tools miss it. PMPred is freely accessible as a web service at https://pmpred.kansil.org/, and the related code is available at https://github.com/kansil/PMPred.

Anti-complement factor H (CFH) autoantibodies could delay pristane-induced lupus nephritis

PURPOSE

Anti-complement factor H (CFH) autoantibodies could be detected in lupus and its significance remained to be elucidated. Herein, we aimed to explore the roles of anti-CFH autoantibodies based on pristane-induced lupus mice.

METHODS

Twenty-four female Balb/c mice were randomly divided into four groups, with one group injected with pristane (pristane group), one group with pristane and then human CFH (hCFH) (pristane-CFH group) 3 times, and the other two as vertical controls, PBS group and PBS-CFH group. Histopathological analysis was performed six months after pristane administration. Levels of hCFH, anti-CFH autoantibodies and anti-dsDNA antibody were detected. Murine IgG (mIgG) were purified and cross-reactivity, epitopes, subclasses and functional analysis were further evaluated in vitro.

RESULTS

Immunization with hCFH and subsequent development of anti-CFH autoantibodies significantly attenuated nephritis of pristane-induced lupus, including lower levels of urinary protein and serum creatinine, decreased levels of serum anti-dsDNA antibody, greatly ameliorated renal histopathologic damage, decreased IgG, complements (C1q, C3) deposits and lower inflammatory factor (IL-6) expression in glomerulus. Furthermore, the purified mIgG (contained anti-CFH autoantibodies) could recognize both hCFH and murine CFH, and the epitopes were predominantly located in hCFH short consensus repeats (SCRs) 1-4, 7 and 11-14. The IgG subclasses were predominant IgG1. The autoantibodies could enhance the binding between hCFH and C3b, and increase factor I mediated-C3b lysis in vitro.

CONCLUSION

Our results suggested that anti-CFH autoantibodies could attenuate pristane-induced lupus nephritis by increasing bio-functions of CFH on regulating complement activation and controlling inflammation.

Inborn Errors of Immunity in Children With Invasive Pneumococcal Disease: A Multicenter Prospective Study

BACKGROUND

In settings with universal conjugate pneumococcal vaccination, invasive pneumococcal disease (IPD) can be a marker of an underlying inborn error of immunity. The aim of this study was to determine the prevalence and characterize the types of immunodeficiencies in children presenting with IPD.

METHODS

Multicenter prospective audit following the introduction of routinely recommended immunological screening in children presenting with IPD. The minimum immunological evaluation comprised a full blood examination and film, serum immunoglobulins (IgG, IgA and IgM), complement levels and function. Included participants were children in whom Streptococcus pneumoniae was isolated from a normally sterile site (cerebrospinal fluid, pleura, peritoneum and synovium). If isolated from blood, features of sepsis needed to be present. Children with predisposing factors for IPD (nephrotic syndrome, anatomical defect or malignancy) were excluded.

RESULTS

Overall, there were 379 episodes of IPD of which 313 (83%) were eligible for inclusion and 143/313 (46%) had an immunologic evaluation. Of these, 17/143 (12%) were diagnosed with a clinically significant abnormality: hypogammaglobulinemia (n = 4), IgA deficiency (n = 3), common variable immunodeficiency (n = 2), asplenia (n = 2), specific antibody deficiency (n = 2), incontinentia pigmenti with immunologic dysfunction (n = 1), alternative complement deficiency (n = 1), complement factor H deficiency (n = 1) and congenital disorder of glycosylation (n = 1). The number needed to investigate to identify 1 child presenting with IPD with an immunologic abnormality was 7 for children under 2 years and 9 for those 2 years old and over.

CONCLUSIONS

This study supports the routine immune evaluation of children presenting with IPD of any age, with consideration of referral to a pediatric immunologist.

HUS and TTP: traversing the disease and the age spectrum

Hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenia purpura (TTP) are rare diseases sharing a common pathological feature, thrombotic microangiopathy (TMA). TMA is characterized by microvascular thrombosis with consequent thrombocytopenia, microangiopathic hemolytic anemia and/or multiorgan dysfunction. In the past, the distinction between HUS and TTP was predominantly based on clinical grounds. However, clinical presentation of the two syndromes often overlaps and, the differential diagnosis is broad. Identification of underlying pathogenic mechanisms has enabled the classification of these syndromes on a molecular basis: typical HUS caused by Shiga toxin-producing Escherichia coli (STEC-HUS); atypical HUS or complement-mediated TMA (aHUS/CM-TMA) associated with genetic or acquired defects leading to dysregulation of the alternative pathway (AP) of complement; and TTP that results from a severe deficiency of the von Willebrand Factor (VWF)-cleaving protease, ADAMTS13. The etiology of TMA differs between pediatric and adult patients. Childhood TMA is chiefly caused by STEC-HUS, followed by CM-TMA and pneumococcal HUS (Sp-HUS). Rare conditions such as congenital TTP (cTTP), vitamin B12 metabolism defects, and coagulation disorders (diacylglycerol epsilon mutation) present as TMA chiefly in children under 2 years of age. In contrast secondary causes and acquired ADAMT13 deficiency are more common in adults. In adults, compared to children, diagnostic delays are more frequent due to the wide range of differential diagnoses. In this review we focus on the three major forms of TMA, STEC-HUS, aHUS and TTP, outlining the clinical presentation, diagnosis and management of the affected patients, to help highlight the salient features and the differences between adult and pediatric patients which are relevant for management.

Kidney diseases

Dysregulation and accelerated activation of the alternative pathway (AP) of complement is known to cause or accentuate several pathologic conditions in which kidney injury leads to the appearance of hematuria and proteinuria and ultimately to the development of chronic renal failure. Multiple genetic and acquired defects involving plasma- and membrane-associated proteins are probably necessary to impair the protection of host tissues and to confer a significant predisposition to AP-mediated kidney diseases. This review aims to explore how our current understanding will make it possible to identify the mechanisms that underlie AP-mediated kidney diseases and to discuss the available clinical evidence that supports complement-directed therapies. Although the value of limiting uncontrolled complement activation has long been recognized, incorporating complement-targeted treatments into clinical use has proved challenging. Availability of anti-complement therapy has dramatically transformed the outcome of atypical hemolytic uremic syndrome, one of the most severe kidney diseases. Innovative drugs that directly counteract AP dysregulation have also opened new perspectives for the management of other kidney diseases in which complement activation is involved. However, gained experience indicates that the choice of drug should be tailored to each patient's characteristics, including clinical, histologic, genetic, and biochemical parameters. Successfully treating patients requires further research in the field and close collaboration between clinicians and researchers who have special expertise in the complement system.