The clinical and laboratory features of Chinese Han anti-factor H autoantibody-associated hemolytic uremic syndrome

Complement biosensors identify a classical pathway stimulus in complement-mediated thrombotic microangiopathy

ABSTRACT

Complement-mediated thrombotic microangiopathy (CM-TMA) or hemolytic uremic syndrome, previously identified as atypical hemolytic uremic syndrome, is a TMA characterized by germ line variants or acquired antibodies to complement proteins and regulators. Building upon our prior experience with the modified Ham (mHam) assay for ex vivo diagnosis of complementopathies, we have developed an array of cell-based complement "biosensors" by selective removal of complement regulatory proteins (CD55 and CD59, CD46, or a combination thereof) in an autonomously bioluminescent HEK293 cell line. These biosensors can be used as a sensitive method for diagnosing CM-TMA and monitoring therapeutic complement blockade. Using specific complement pathway inhibitors, this model identifies immunoglobulin M (IgM)-driven classical pathway stimulus during both acute disease and in many patients during clinical remission. This provides a potential explanation for ∼50% of patients with CM-TMA who lack an alternative pathway "driving" variant and suggests at least a subset of CM-TMA is characterized by a breakdown of IgM immunologic tolerance.

Complement Biosensors Identify a Classical Pathway Stimulus in Complement-Mediated Hemolytic Uremic Syndrome

Complement-mediated hemolytic uremic syndrome (CM-HUS) is a thrombotic microangiopathy characterized by germline variants or acquired antibodies to complement proteins and regulators. Building upon our prior experience with the modified Ham (mHam) assay for ex vivo diagnosis of complementopathies, we have developed an array of cell-based complement "biosensors'' by selective removal of complement regulatory proteins (CD55 and CD59, CD46, or a combination thereof) in an autonomously bioluminescent HEK293 cell line. These biosensors can be used as a sensitive method for diagnosing CM-HUS and monitoring therapeutic complement blockade. Using specific complement pathway inhibitors, this model identifies IgM-driven classical pathway stimulus during both acute disease and in many patients during clinical remission. This provides a potential explanation for ~50% of CM-HUS patients who lack an alternative pathway "driving" variant and suggests at least a subset of CM-HUS is characterized by a breakdown of IgM immunologic tolerance.

Key Points

CM-HUS has a CP stimulus driven by polyreactive IgM, addressing the mystery of why 40% of CM-HUS lack complement specific variantsComplement biosensors and the bioluminescent mHam can be used to aid in diagnosis of CM-HUS and monitor complement inhibitor therapy.

Variants in complement genes are uncommon in patients with anti-factor H autoantibody-associated atypical hemolytic uremic syndrome

BACKGROUND

Coexisting genetic variants in patients with anti-factor H (FH)-associated atypical hemolytic uremic syndrome (aHUS) have implications for therapy. We estimated the prevalence of complement genetic variants in children with anti-FH aHUS from a prospective nationwide cohort and determined if significant genetic variants impact long-term kidney outcomes.

METHODS

Of 436 patients in the database, 77 consecutive patients, 21 with a relapse and 9 with kidney failure and/or death were included. Targeted sequencing, using a 27-gene panel including CFH, CFI, CFB, C3, CD46, PLG, DGKE, and THBD and multiplex ligation-dependent probe amplification of CFH-CFHR region, was performed. The adverse outcome was eGFR < 30 ml/min/1.73 m2 or death.

RESULTS

Patients had high anti-FH titers 5670 (2177-13,545) AU/ml, relapsing course (42.1%), and adverse outcomes (19.6%). Variants, chiefly of unknown significance, were found in 7 (6.5%; 95% CI 3.1-13.2%); a pathogenic variant was found in one patient. Homozygous deletion of CFHR1 was present in 91.6% compared to 9.8% in 184 healthy controls. Plasma exchanges and immunosuppression showed a trend of improving outcomes, independent of genetic defects (HR 0.32; P = 0.070). Meta-analysis of 18 studies (384 patients) showed that the pooled prevalence of pathogenic and likely pathogenic variants was 3% (95% CI 0-8%). Of 37 total variants in the meta-analysis, 7 (18.9%) each were pathogenic and likely pathogenic; others were variants of unknown significance.

CONCLUSIONS

Significant variants in complement regulatory genes are rare in patients with anti-FH-associated aHUS. Irrespective of genetic defects, plasma exchanges and immunosuppression showed a statistical trend to improved outcomes. A higher resolution version of the Graphical abstract is available as Supplementary information.

Clinical features of children with anti-CFH autoantibody-associated hemolytic uremic syndrome: a report of 8 cases

Objective

To explore the clinical characteristics, treatment protocol and prognosis of children with anti-complement factor H (CFH) autoantibody (Ab)-associated hemolytic uremic syndrome (HUS).

Methods

Clinical data of 8 patients with anti-CFH Ab-associated HUS who were admitted to Shandong Provincial Hospital from January 2011 to December 2020 were collected retrospectively.

Results

The age at disease onset ranged between 5.83 and 13.5 years, with a male: female ratio of 1.67:1. The time of onset was distributed from May to June and November to December. Digestive and upper respiratory tract infections were common prodromal infections. Positivity for anti-CFH Ab and reduced C3 levels were observed among all patients. Heterozygous mutation of the CHFR5 gene (c.669del A) and homozygous loss of the CFHR1 gene [loss2(EXON:2-6)] were found in two patients. All patients received early treatment with plasma exchange and corticosteroid therapy. Six patients were given immunosuppressive agents (cyclophosphamide and/or mycophenolate mofetil) for persistent proteinuria. The follow-up period was 12–114 months. Four of 8 patients achieved complete remission, 3 achieved partial remission, and 1 died. Relapse occurred in two patients.

Conclusion

Children with anti-CFH Ab-associated HUS were mainly school-aged and predominantly male, with onset times of summer and winter. Digestive and upper respiratory tract infections were common prodromal infections. Plasma exchange combined with methylprednisolone pulse therapy in the acute phase and cyclophosphamide or mycophenolate mofetil treatment for maintenance can be utilized in children with anti-CFH Ab-associated HUS if eculizumab is not available.

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

Atypical hemolytic uremic syndrome (aHUS) an important form of a thrombotic microangiopathy (TMA) that can frequently lead to acute kidney injury (AKI). An important subset of aHUS is the anti-factor H associated aHUS. This variant of aHUS can occur due to deletion of the complement factor H genes, CFHR1 and CFHR3, along with the presence of anti-factor H antibodies. However, it is a point of interest to note that not all patients with anti-factor H associated aHUS have a CFHR1/R3 deletion. Factor-H has a vital role in the regulation of the complement system, specifically the alternate pathway. Therefore, dysregulation of the complement system can lead to inflammatory or autoimmune diseases. Patients with this disease respond well to treatment with plasma exchange therapy along with Eculizumab and immunosuppressant therapy. Anti-factor H antibody associated aHUS has a certain genetic predilection therefore there is focus on further advancements in the diagnosis and management of this disease. In this article we discuss the baseline characteristics of patients with anti-factor H associated aHUS, their triggers, various treatment modalities and future perspectives.

Anti-Factor H Antibodies in Egyptian Children with Hemolytic Uremic Syndrome

Background

Atypical hemolytic uremic syndrome (aHUS) is an important cause of acute kidney injury in children. It is primarily caused by dysregulation of the complement alternative pathway due to genetic mutations, mainly in complement factor H genes, or due to anti-factor H autoantibodies (anti-FH), leading to uncontrolled overactivation of the complement system. Early diagnosis and treatment of autoimmune HUS (AI-HUS) is essential and leads to a favorable outcome.

Methods

Fifty pediatric HUS patients and 50 age- and sex-matched controls were included in the study. Patients were subjected to full history taking, clinical examination, and laboratory testing. All candidates were subjected to an assessment of anti-FH in serum by a homemade enzyme-linked immunosorbent assay technique.

Results

A high frequency of serum anti-FH was detected in our aHUS patients. The disease onset of AI-HUS was mainly observed in March and April, with significantly higher rates in school-aged males. All patients who started immunosuppressives early together with plasmapheresis upon detection of their anti-FH had complete renal function recovery.

Conclusion

The high frequency of AI-HUS revealed in Egyptian HUS children in our study highlights the importance of implementing anti-FH testing in Egypt to provide early recognition for immediate proper management, including early immunosuppressive therapy, and hence improving patient outcomes.

Patient-specific iPSC-derived endothelial cells reveal aberrant p38 MAPK signaling in atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is a rare disease associated with high morbidity and mortality. Existing evidence suggests that the central pathogenesis to aHUS might be endothelial cell damage. Nevertheless, the role of endothelial cell alterations in aHUS has not been well characterized and the underlying mechanisms remain unclear. Utilizing an induced pluripotent stem cell-derived endothelial cell (iPSC-EC) model, we showed that anti-complement factor H autoantibody-associated aHUS patient-specific iPSC-ECs exhibited an intrinsic defect in endothelial functions. Stimulation using aHUS serums exacerbated endothelial dysfunctions, leading to cell apoptosis in iPSC-ECs. Importantly, we identified p38 as a novel signaling pathway contributing to endothelial dysfunctions in aHUS. These results illustrate that iPSC-ECs can be a reliable model to recapitulate EC pathological features, thus providing a unique platform for gaining mechanistic insights into EC injury in aHUS. Our findings highlight that the p38 MAPK signaling pathway can be a therapeutic target for treatment of aHUS.

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aHUS patient-specific iPSC-ECs exhibit intrinsic defect in endothelial functions

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Stimulation using aHUS serums exacerbates EC dysfunctions and causes EC apoptosis

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p38 signaling contributes to EC dysfunctions in anti-CFH Ab-associated aHUS

IgM Autoantibodies to Complement Factor H in Atypical Hemolytic Uremic Syndrome

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS), a severe thrombotic microangiopathy, is often related to complement dysregulation, but the pathomechanisms remain unknown in at least 30% of patients. Researchers have described autoantibodies to complement factor H of the IgG class in 10% of patients with aHUS but have not reported anti-factor H autoantibodies of the IgM class.

METHODS

In 186 patients with thrombotic microangiopathy clinically presented as aHUS, we searched for anti-factor H autoantibodies of the IgM class and those of the IgG and IgA classes. We used immunochromatography to purify anti-factor H IgM autoantibodies and immunoenzymatic methods and a competition assay with mapping mAbs to characterize interaction with the target protein.

RESULTS

We detected anti-factor H autoantibodies of the IgM class in seven of 186 (3.8%) patients with thrombotic microangiopathy presented as aHUS. No association was observed between anti-factor H IgM and homozygous deletions involving CFHR3-CFHR1. A significantly higher proportion of patients with bone marrow transplant-related thrombotic microangiopathy had anti-factor H IgM autoantibodies versus other patients with aHUS: three of 20 (15%) versus four of 166 (2.4%), respectively. The identified IgM autoantibodies recognize the SCR domain 19 of factor H molecule in all patients and interact with the factor H molecule, inhibiting its binding to C3b.

CONCLUSIONS

Detectable autoantibodies to factor H of the IgM class may be present in patients with aHUS, and their frequency is six-fold higher in thrombotic microangiopathy forms associated with bone marrow transplant. The autoantibody interaction with factor H's active site may support an autoimmune mechanism in some cases previously considered to be of unknown origin.

Clinical and Genetic Characteristics of Atypical Hemolytic Uremic Syndrome in Children: A Chinese Cohort Study

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is a rare but critical illness. To this date, few studies have reported on the disease in Chinese children.

METHODS

We studied a Chinese pediatric cohort to delineate the clinical characteristics, genotypes, and prognosis. Ninety-one patients with aHUS were enrolled in this study.

RESULTS

Fifty-nine children (64.8%) had anti-complement-factor-H autoantibody-associated aHUS (anti-CFH aHUS). Of these children, 21 (46.7%) had complement factor-H-related protein 1 (CFHR1) homozygous deletion, and most patients with CFHR1 homozygous deletion also had complement factor-H-related protein 3 (CFHR3) homozygous deletions (76.2%). Using gene sequencing of 15 candidate genes, we identified 14 genetic variants in 46 aHUS patients, including 5 pathogenic or like pathogenic variants and 9 variants of uncertain significance. The average follow-up time was 46.1 ± 28 months. Among patients with anti-CFH aHUS, there was a correlation between CFHR1 homozygous deletion and patients with persistent proteinuria (odds ratio [OR] 6.954, 95% confidence interval [CI] 1.033-46.821, p = 0.046). As of the last follow-up, ESRD or deaths occurred in 3.6% of the children with anti-CFH aHUS and 26.7% of children with aHUS who were negative for anti-CFH.

CONCLUSIONS

Anti-complement-factor-H antibody positivity is the main cause of morbidity in Chinese children with aHUS. There may be a correlation between CFHR1 homozygous deletion and persistent proteinuria. Comprehensive assessment of anti-CFH antibodies and genetic variants is essential for the management of aHUS children.

Early relapse rate determines further relapse risk: results of a 5-year follow-up study on pediatric CFH-Ab HUS

BACKGROUND

The complement factor H antibody (CFH-Ab)-associated hemolytic uremic syndrome (HUS) forms a distinct subgroup within the complement-mediated HUS disease spectrum. The autoimmune nature of this HUS subgroup implies the potential benefit of a targeted immunosuppressive therapy. Data on long-term outcome are scarce.

METHODS

This observational study evaluates the clinical outcome of 19 pediatric CFH-Ab HUS patients from disease onset until their 5-year follow-up.

RESULTS

All but one relapse occurred during the first 2 years, and patients who had no relapse within the first 6 months were relapse-free until the end of the observation period. Kidney function at disease onset determines long-term kidney function: all individuals with normal kidney function at disease onset had normal kidney function after 5 years, and all patients with reduced kidney function at onset had impaired kidney function at the last follow-up. Level of CFH-Ab titer at disease onset was not correlated with a higher risk of recurrences or worse long-term outcome after 5 years. Resolution of CFH-Ab titers after 5 years was common.

CONCLUSIONS

CFH-Ab HUS patients have a varied overall long-term course. Early relapses are common, making close surveillance during the first years essential, regardless of the initial CFH-Ab titer.

Association between thrombotic microangiopathy and activated alternative complement pathway in malignant nephrosclerosis

BACKGROUND

Malignant nephrosclerosis, defined as renal microangiopathy in the setting of severe hypertension, remains a critical renal emergency leading to end-stage renal disease despite aggressive anti-hypertensive treatment. Recently, activation of the complement alternative pathway (AP) has been reported to play a prominent role in the pathogenesis of malignant nephrosclerosis. However, subsequent study failed to recapitulate the findings of genetic complement abnormalities in the disease. This study aimed to determine the presence of AP activation and genetic complement defects and establish their correlations to renal microangiopathy lesions, clinical features and prognosis in patients with malignant nephrosclerosis.

METHODS

Fifty patients with malignant hypertension and concomitant thrombotic microangiopathy (TMA) proven by renal biopsy were investigated; 25 cases of kidney donors who received zero-hour allograft biopsies were used as normal controls. Various renal TMA lesions in patients with malignant nephrosclerosis were reviewed and evaluated using a semi-quantitative scoring system. Deposition of C5b-9, C3a, C5a, C4d and mannose-binding lectin was assessed by immunohistochemistry. Co-localization of C5b-9 and CD34 was detected by confocal microscopy. Complement factor B (FB), factor P (FP; properdin), factor D (FD), factor H (FH), C3a and C5a levels were quantified by enzyme-linked immonosorbent assay in plasma and urine samples of patients with malignant nephrosclerosis and controls. Genetic abnormalities of complement components were analysed by whole-exome sequencing.

RESULTS

Renal biopsies of malignant nephrosclerosis showed identical histopathological and ultrastructural features to atypical haemolytic uraemic syndrome. C5b-9, C3a and C5a deposits were found along the walls of arteries/arterioles and glomerular capillaries and localized in the endothelial cells. Elevated plasma and urinary levels of FB, FP, FD, C3a and C5a as well as decreased FH levels were observed in patients with malignant nephrosclerosis compared with normal controls. The urinary levels of complement AP components, but not the plasma levels, were correlated with renal functions, prognosis and active TMA lesions except for arteriolar thrombi. Finally, mutations of the MCP, CFB, CFH and CFHR5 genes were identified in 8 of 20 patients with malignant nephrosclerosis.

CONCLUSIONS

Aberrant complement AP dysregulation was demonstrated and associated with the activity, severity and renal outcomes of malignant nephrosclerosis. This observation warrants screening for complement defects in patients with malignant nephrosclerosis for the potential use of complement regulators and also highlights the need for further investigation of the precise role of AP in the pathogenesis of the disease.

Clinical and Immunological Profile of Anti-factor H Antibody Associated Atypical Hemolytic Uremic Syndrome: A Nationwide Database

Background: Atypical hemolytic uremic syndrome (aHUS), an important cause of acute kidney injury (AKI), is characterized by dysregulation of the alternative complement pathway. Autoantibodies to factor H (FH), a chief regulator of this pathway, account for a distinct subgroup. While high anti-FH titers predict relapse, they do not correlate well with disease activity and their functional characterization is required.

Methods: Of 781 patients <18-year-old of aHUS in the nationwide database from 2007 to 2018, 436 (55.8%) had anti-FH antibodies. Clinical features and outcome of patients managed in the last 6-year (n = 317) were compared to before (n = 119). In plasma samples of 44 patients, levels of serial circulating FH immune complexes (CIC), free FH, soluble terminal complement complex (sC5b-9), sheep red blood cell (SRBC) lysis and epitope specificity (n = 8) were examined. Functional renal reserve, ambulatory hypertension, left ventricular hypertrophy (LVH), and proteinuria were evaluated in a subset.

Results: Patients presented with markedly elevated anti-FH titers (10,633.2 ± 998.5 AU/ml). Management varied by center, comprising plasma exchange (PEX; 77.5%) and immunosuppression (73.9%). Patients managed in the last 6-year showed better renal survival at mean 28.5 ± 27.3 months (log rank P = 0.022). Mean anti-FH titers stayed 700–1,164 AU/ml during prolonged follow-up, correlating with CIC. Patients with relapse had lower free-FH during remission [Generalized estimating equations (GEE), P = 0.001]; anti-FH levels ≥1,330 AU/ml and free FH ≤440 mg/l predicted relapse (hazards ratio, HR 6.3; P = 0.018). Epitope specificity was similar during onset, remission and relapse. Antibody titer ≥8,000 AU/ml (HR 2.23; P = 0.024), time to PEX ≥14 days (HR 2.09; P = 0.071) and PEX for <14 days (HR 2.60; P = 0.017) predicted adverse renal outcomes. Combined PEX and immunosuppression improved long-term outcomes (HR 0.37; P = 0.026); maintenance therapy reduced risk of relapses (HR 0.11; P < 0.001). At 4.4±2.5 year, median renal reserve was 15.9%; severe ambulatory, masked and pre-hypertension were found in 38, 30, and 18%, respectively. Proteinuria and LVH occurred in 58 and 28% patients, respectively.

Conclusion: Prompt recognition and therapy with PEX and immunosuppression, is associated with satisfactory outcomes. Free-FH predicts early relapses in patients with high anti-FH titers. A significant proportion of impaired functional reserve, ambulatory hypertension, proteinuria and LVH highlight the need for vigilant long-term follow-up.

Immunological features and functional analysis of anti-CFH autoantibodies in patients with atypical hemolytic uremic syndrome

OBJECTIVE

Atypical hemolytic uremic syndrome (aHUS) is associated with defective complement regulation. Anti-complement factor H (CFH) antibodies were thought to participate in the pathogenesis of aHUS. The aim of this study was to address the functions and properties of CFH autoantibodies in a Chinese Han cohort of aHUS patients.

METHODS

Thirty-six anti-CFH antibody-positive aHUS patients at the acute phase of the disease were involved in this study. Clinical data of the patients were collected. Anti-CFH immunoglobulin G (IgG) subclasses and antibody isotypes were detected by ELISA. Epitope mapping was performed using recombinant CFH fragments (SCRs 1-4, SCR 7, SCRs 11-14, and SCRs 19-20). Purified IgG from plasma from seven patients were used for functional analyses.

RESULTS

All patients presented with the classic triad of HUS. The anti-CFH autoantibodies mostly bound to the SCRs 19-20 domains of CFH but not the SCRs 1-4 domains. CFI cofactor activity was not disturbed by the anti-CFH antibody in any of the seven patients. Purified IgG interfered with the binding of CFH to C3b and CFH-mediated sheep erythrocyte protection in all seven patients. IgG from 4/5 (80%) patients tested inhibited the binding of CFH to glomerular endothelial cells.

CONCLUSIONS

Our study suggests that the properties of CFH antibodies from patients with aHUS, including the recognition of SCRs and IgG subclasses, can influence and impair the biological role of CFH and therefore contribute to aHUS susceptibility.