Investigation of immune complexes formed by mitochondrial antigens containing a new lipoylated site in sera of primary biliary cholangitis patients

Abstract

Summary Primary biliary cholangitis (PBC) is characterized by the presence of serum anti‐mitochondrial autoantibodies (AMAs). To date, four antigens among the 2‐oxo‐acid dehydrogenase complex family, which commonly have lipoyl domains as an epitope, have been identified as AMA‐corresponding antigens (AMA‐antigens). It has recently been reported that AMAs react more strongly with certain chemically modified mimics than with the native lipoyl domains in AMA‐antigens. Moreover, high concentrations of circulating immune complexes (ICs) in PBC patients have been reported. However, the existence of ICs formed by AMAs and their antigens has not been reported to date. We hypothesized that AMAs and their antigens formed ICs in PBC sera, and analyzed sera of PBC and four autoimmune diseases (Sjögren's syndrome, systemic lupus erythematosus, systemic scleroderma, and rheumatoid arthritis) using immune complexome analysis, in which ICs are separated from serum and are identified by nano‐liquid chromatography‐tandem mass spectrometry. To correctly assign MS/MS spectra to peptide sequences, we used a protein‐search algorithm that including lipoylation and certain xenobiotic modifications. We found three AMA‐antigens, the E2 subunit of the pyruvate dehydrogenase complex (PDC‐E2), the E2 subunit of the 2‐oxo‐glutarate dehydrogenase complex (OGDC‐E2) and dihydrolipoamide dehydrogenase binding protein (E3BP), by detecting peptides containing lipoylation and xenobiotic modifications from PBC sera. Although the lipoylated sites of these peptides were different from the well‐known sites, abnormal lipoylation and xenobiotic modification may lead to production of AMAs and the formation ICs. Further investigation of the lipoylated sites, xenobiotic modifications, and IC formation will lead to deepen our understanding of PBC pathogenesis.

Research experimental design for the construction and identification of the pGEX-BCKD-E4A recombinant point-mutant plasmid

“…At present, the detection of AMAs in human serum is still a very important method for the diagnosis of PBC [32][33][34][35]. However, most current studies target PDC-E2 in mitochondrial autoantigens, and few on BCOADC-E2 [36][37][38]. The effect of the amino acid mutation near the lysine in the active center of the BCOADC-E2 protein on its specific binding to AMA-M2 is completely in the research gap.…”

Interstitial Lung Disease in Primary Biliary Cholangitis: A Cohort Prospective Study

“…Immune complexes containing IgG and complement C1q, but not IgM, were also detected in the pulmonary interstitium in a patient with PBC-associated ILD [ 57 ]. Moreover, immune complexes in PBC may be formed by AMAs and AMA-antigens [ 58 , 59 ]. Further studies could shed light on the role of humoral immunity in PBC-associated ILD pathogenesis.…”

Patterns of interstitial lung disease in primary biliary cholangitis

“…В настоящее время неизвестно, имеет ли IgM ту же антигенную специфичность, что и АМА-М2, у больных ПБХ. Было показано, что иммунные комплексы, циркулирующие в крови больных ПБХ, содержат АМА-М2 и антиген-мишень данных антител [53,54]. При этом по-прежнему окончательно не выяснено, является ли повышенный уровень IgM сыворотки крови при ПБХ лабораторным эпифе-номеном или отражает участие IgM в формировании внепеченочных органных поражений при данном заболевании.…”