Characterization of genetic predisposition and autoantibody profile in atypical haemolytic–uraemic syndrome

Abstract

We previously reported that Indian paediatric patients with atypical haemolytic-uraemic syndrome (aHUS) showed high frequencies of anti-complement factor H (FH) autoantibodies that are correlated with homozygous deletion of the genes for FH-related proteins 1 and 3 (FHR1 and FHR3) (FHR1/3 ). We now report that Indian paediatric aHUS patients without anti-FH autoantibodies also showed modestly higher frequencies of the FHR1/3 genotype. Further, when we characterized epitope specificities and binding avidities of anti-FH autoantibodies in aHUS patients, most anti-FH autoantibodies were directed towards the FH cell-surface anchoring polyanionic binding site-containing C-terminal short conservative regions (SCRs) 17-20 with higher binding avidities than for native FH. FH SCR17-20-binding anti-FH autoantibodies also bound the other cell-surface anchoring polyanionic binding site-containing region FH SCR5-8, at lower binding avidities. Anti-FH autoantibody avidities correlated with antibody titres. These anti-FH autoantibody characteristics did not differ between aHUS patients with or without the FHR1/3 genotype. Our data suggest a complex matrix of interactions between FHR1-FHR3 deletion, immunomodulation and anti-FH autoantibodies in the aetiopathogenesis of aHUS.

Deficiency of Mouse FHR-1 Homolog, FHR-E, Accelerates Sepsis, and Acute Kidney Injury Through Enhancing the LPS-Induced Alternative Complement Pathway

“…It was believed that aHUS may result from the blocking of FH function by FH auto-antibody. However, this cannot explain those aHUS patients with CFHR1 deletion without FH auto-antibody (59). Our results suggest that FHR-E deficiency promotes infection-induced damage through enhancing AP activation.…”

Factor H Autoantibodies and Complement-Mediated Diseases

“…The deletion of 79.4 kb on chromosome 1 (gnomAD ID: MCNV_1_81) that includes two CFH -related genes, CFHR3 and CFHR1 , is a common CNV in the human genome with homozygous deletion of both copies of the CFHR3-CFHR1 genes present in 4.1% of Europeans, 16.2% of Africans, 1.9% of Latinos and 0.3% of East Asians (data based on the reported non-diploid CN frequency in the gnomAD). In fact, FHR1 deficiency has been reported in FHAA- negative aHUS patients at a frequency that is higher than that in an ethnically matched control population ( 32 ).…”

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

“…Using FH fragments that were generated in E. coli and purified by gel filtration, Gurjar et al used inhibition ELISA to determine epitope specificity in 21 patients of this cohort with anti-FH associated HUS (16). Antibodies showed strong binding to SCR 17–20; binding with lower affinity was present to SCR 5–8 (16). We extended this work to examine whether there was altered epitope specificity to FH at onset of the illness, remission and during relapse in eight more patients.…”

“…The small number of patients studied limits conclusions regarding epitope specificity. Table 5 summarizes findings from various reports on epitope specificity of anti-FH antibodies, emphasizing predominant binding to the C-terminal, and also other domains on FH (5, 11, 13, 14, 16, 25, 38–40).…”

“…Short consensus repeats (SCR) 1–4, 5–8, 9–12, 13–16, and 17–20 were PCR amplified with specific primers from the FH cDNA (OriGene, Rockville, MD) and cloned in pET28 and pET29 expression vectors (16). The clones were verified by DNA sequencing (ABI 3730 DNA analyzer; Applied Biosystems), products were transformed in E. coli BL21 and expressed in inclusion bodies generated after induction with 1 mM isopropyl-1-thio-b-D-galactopyranoside and purified using Ni-NTA resin.…”