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American Journal of Kidney Diseases

Autoimmunity in Anti–Glomerular Basement Membrane Disease: A Review of Mechanisms and Prospects for Immunotherapy

  • Huang Kuang
    Affiliations
    Renal Division, Peking University First Hospital, Beijing, People’s Republic of China

    Institute of Nephrology, Peking University, Beijing, People’s Republic of China

    Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, People’s Republic of China

    Key Laboratory of CKD Prevention and Treatment, Ministry of Education of China, Beijing, People’s Republic of China

    Research Units of Diagnosis and Treatment of Immune-mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, People’s Republic of China
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  • Jing Liu
    Affiliations
    Renal Division, Peking University First Hospital, Beijing, People’s Republic of China

    Institute of Nephrology, Peking University, Beijing, People’s Republic of China

    Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, People’s Republic of China

    Key Laboratory of CKD Prevention and Treatment, Ministry of Education of China, Beijing, People’s Republic of China

    Research Units of Diagnosis and Treatment of Immune-mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, People’s Republic of China
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  • Xiao-yu Jia
    Correspondence
    Address for Correspondence: Xiao-yu Jia, PhD, Renal Division of Peking University First Hospital, No. 8 Xishiku St, Xicheng District, Beijing 100034, People’s Republic of China.
    Affiliations
    Renal Division, Peking University First Hospital, Beijing, People’s Republic of China

    Institute of Nephrology, Peking University, Beijing, People’s Republic of China

    Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, People’s Republic of China

    Key Laboratory of CKD Prevention and Treatment, Ministry of Education of China, Beijing, People’s Republic of China

    Research Units of Diagnosis and Treatment of Immune-mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, People’s Republic of China
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  • Zhao Cui
    Affiliations
    Renal Division, Peking University First Hospital, Beijing, People’s Republic of China

    Institute of Nephrology, Peking University, Beijing, People’s Republic of China

    Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, People’s Republic of China

    Key Laboratory of CKD Prevention and Treatment, Ministry of Education of China, Beijing, People’s Republic of China

    Research Units of Diagnosis and Treatment of Immune-mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, People’s Republic of China
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  • Ming-hui Zhao
    Affiliations
    Renal Division, Peking University First Hospital, Beijing, People’s Republic of China

    Institute of Nephrology, Peking University, Beijing, People’s Republic of China

    Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, People’s Republic of China

    Key Laboratory of CKD Prevention and Treatment, Ministry of Education of China, Beijing, People’s Republic of China

    Research Units of Diagnosis and Treatment of Immune-mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, People’s Republic of China

    Peking-Tsinghua Center for Life Sciences, Beijing, People’s Republic of China
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Published:November 03, 2022DOI:https://doi.org/10.1053/j.ajkd.2022.07.006
      Anti–glomerular basement membrane (anti-GBM) disease is an organ-specific autoimmune disorder characterized by autoantibodies against the glomerular and alveolar basement membranes, leading to rapidly progressive glomerulonephritis and severe alveolar hemorrhage. The noncollagenous domain of the α3 chain of type IV collagen, α3(IV)NC1, contains the main target autoantigen in this disease. Epitope mapping studies of α3(IV)NC1 have identified several nephritogenic epitopes and critical residues that bind to autoantibodies and trigger anti-GBM disease. The discovery of novel target antigens has revealed the heterogeneous nature of this disease. In addition, both epitope spreading and mimicry have been implicated in the pathogenesis of anti-GBM disease. Epitope spreading refers to the development of autoimmunity to new autoepitopes, thus worsening disease progression, whereas epitope mimicry, which occurs via sharing of critical residues with microbial peptides, can initiate autoimmunity. An understanding of these autoimmune responses may open opportunities to explore potential new therapeutic approaches for this disease. We review how current advances in epitope mapping, identification of novel autoantigens, and the phenomena of epitope spreading and mimicry have heightened the understanding of autoimmunity in the pathogenesis of anti-GBM disease, and we discuss prospects for immunotherapy.

      Index Words

      Introduction

      Anti–glomerular basement membrane (anti-GBM) disease is an organ-specific autoimmune disorder characterized by autoimmunity against the basement membrane in kidneys and lungs, resulting in rapidly progressive glomerulonephritis (GN) and an increased risk of pulmonary hemorrhage.
      • Goodpasture E.W.
      The significance of certain pulmonary lesions in relation to the etiology of influenza.
      In those undergoing kidney biopsy it accounts for 1%-5% of GN and 10%-15% of crescentic GN and usually leads to severe kidney injury.
      • Tang W.
      • McDonald S.P.
      • Hawley C.M.
      • et al.
      Anti-glomerular basement membrane antibody disease is an uncommon cause of end-stage renal disease.
      Antibody-mediated autoimmunity has been considered as the major cause of anti-GBM disease, with the target antigen located on a noncollagenous domain of the α3 chain of collagen IV, α3(IV)NC1.
      • Saus J.
      • Wieslander J.
      • Langeveld J.P.
      • Quinones S.
      • Hudson B.G.
      Identification of the Goodpasture antigen as the alpha 3(IV) chain of collagen IV.
      ,
      • Pedchenko V.
      • Bondar O.
      • Fogo A.B.
      • et al.
      Molecular architecture of the Goodpasture autoantigen in anti-GBM nephritis.
      The pathogenic role of anti-GBM antibodies has been confirmed in animal model studies, given that anti-GBM antibodies from the sera of patients with anti-GBM disease induce experimental GN in squirrel monkeys.
      • Lerner R.A.
      • Glassock R.J.
      • Dixon F.J.
      The role of anti-glomerular basement membrane antibody in the pathogenesis of human glomerulonephritis.
      Evidence also supports the role of T-cell–mediated autoimmunity. Animal models have presented direct evidence that T cells are involved in disease initiation
      • Wu J.
      • Hicks J.
      • Borillo J.
      • Glass 2nd, W.F.
      • Lou Y.H.
      CD4+ T cells specific to a glomerular basement membrane antigen mediate glomerulonephritis.
      while autoantigen-specific regulatory T cells confer resistance to anti-GBM GN.
      • Ooi J.D.
      • Petersen J.
      • Tan Y.H.
      • et al.
      Dominant protection from HLA-linked autoimmunity by antigen-specific regulatory T cells.
      Antigenic epitope exposure is the initial trigger for the autoimmune responses. Two generally recognized immunodominant conformational epitopes, EA and EB, have been mapped to residues 17-31 and 127-141 of α3(IV)NC1, respectively (all amino acid numbering used herein has been converted from the original numbering to that used by Pedchenko et al
      • Pedchenko V.
      • Bondar O.
      • Fogo A.B.
      • et al.
      Molecular architecture of the Goodpasture autoantigen in anti-GBM nephritis.
      ).
      • Netzer K.O.
      • Leinonen A.
      • Boutaud A.
      • et al.
      The goodpasture autoantigen: mapping the major conformational epitope(s) of α3(IV) collagen to residues 17-31 and 127-141 of the NC1 domain.
      The identification of EA and EB inspired the application of new techniques to search for related critical residues with nephritogenic effects.
      • Ryan J.J.
      • Mason P.J.
      • Pusey C.D.
      • Turner N.
      Recombinant alpha-chains of type IV collagen demonstrate that the amino terminal of the Goodpasture autoantigen is crucial for antibody recognition.
      ,
      • Gozalbo-Rovira R.
      • Rodríguez-Díaz J.
      • Saus J.
      • Cervera J.
      Precise mapping of the Goodpasture epitope(s) using phage display, site-directed mutagenesis, and surface plasmon resonance.
      Meanwhile, the discovery of novel target antigens emphasized the heterogeneous nature of anti-GBM disease.
      • Shen C.R.
      • Jia X.Y.
      • Luo W.
      • et al.
      Laminin-521 is a novel target of autoantibodies associated with lung hemorrhage in anti-GBM disease.
      • Cui Z.
      • Zhao M.H.
      • Jia X.Y.
      • et al.
      Antibodies to α5 chain of collagen IV are pathogenic in Goodpasture’s disease.
      • McCall A.S.
      • Bhave G.
      • Pedchenko V.
      • et al.
      Inhibitory anti-peroxidasin antibodies in pulmonary-renal syndromes.
      Fine mapping of these epitopes is valuable for better understanding of the pathogenesis of autoimmunity and opens opportunities to explore potential new therapeutic approaches for anti-GBM disease.

      Autoimmunity and Epitope Mapping

      B-cell Epitope Mapping of α3(IV)NC1

      Collagen IV is the major component of the GBM. There, its 5 α chains (α1-α5) are assembled into a network through the association of α3α4α5 or α1α1α2 chains to form a triple-helical protomer, and further contacts through carboxy-terminal noncollagen (NC1) domains form an NC1 hexamer.
      • Pedchenko V.
      • Bondar O.
      • Fogo A.B.
      • et al.
      Molecular architecture of the Goodpasture autoantigen in anti-GBM nephritis.
      ,
      • Hudson B.G.
      • Tryggvason K.
      • Sundaramoorthy M.
      • Neilson E.G.
      Alport’s syndrome, Goodpasture’s syndrome, and type IV collagen.
      ,
      • Naylor R.W.
      • Morais M.
      • Lennon R.
      Complexities of the glomerular basement membrane.
      The target antigen of anti-GBM disease, α3(IV)NC1, is normally sequestered within the hexamer, where it is stabilized by the formation of sulfilimine crosslinking (S=N) with the participation of chloride and bromine ions.
      • Boudko S.P.
      • Bauer R.
      • Chetyrkin S.V.
      • et al.
      Collagen IV(α345) dysfunction in glomerular basement membrane diseases. II. Crystal structure of the α345 hexamer.
      • McCall A.S.
      • Cummings C.F.
      • Bhave G.
      • Vanacore R.
      • Page-McCaw A.
      • Hudson B.G.
      Bromine is an essential trace element for assembly of collagen IV scaffolds in tissue development and architecture.
      • Pedchenko V.
      • Boudko S.P.
      • Barber M.
      • et al.
      Collagen IV(α345) dysfunction in glomerular basement membrane diseases. III. A functional framework for α345 hexamer assembly.
      However, in the presence of environmental or other factors, it can be exposed and induce an autoimmune response.
      • Pedchenko V.
      • Boudko S.P.
      • Barber M.
      • et al.
      Collagen IV(α345) dysfunction in glomerular basement membrane diseases. III. A functional framework for α345 hexamer assembly.
      • Kalluri R.
      • Cantley L.G.
      • Kerjaschki D.
      • Neilson E.G.
      Reactive oxygen species expose cryptic epitopes associated with autoimmune goodpasture syndrome.
      • Borza D.B.
      • Bondar O.
      • Colon S.
      • et al.
      Goodpasture autoantibodies unmask cryptic epitopes by selectively dissociating autoantigen complexes lacking structural reinforcement: novel mechanisms for immune privilege and autoimmune pathogenesis.
      Epitope mapping of α3(IV)NC1 was established by means of extensive studies of the molecular and immunochemical properties of the NC1 hexamer
      • Saus J.
      • Wieslander J.
      • Langeveld J.P.
      • Quinones S.
      • Hudson B.G.
      Identification of the Goodpasture antigen as the alpha 3(IV) chain of collagen IV.
      (Fig 1). In 1991, using chemically synthesized peptides, Kalluri et al
      • Kalluri R.
      • Gunwar S.
      • Reeders S.T.
      • et al.
      Goodpasture syndrome: localization of the epitope for the autoantibodies to the carboxyl-terminal region of the alpha 3(IV) chain of basement membrane collagen.
      proposed that the dominant epitope for antibody binding likely mapped to the carboxy-terminal region of α3(IV)NC1, namely residues 197-232 (α3197-232). Further experiments employing selective chemical modifications identified lysine and cysteine as the critical amino acids.
      • Kalluri R.
      • Sun M.J.
      • Hudson B.G.
      • Neilson E.G.
      The Goodpasture autoantigen: structural delineation of two immunologically privileged epitopes on alpha3(IV) chain of type IV collagen.
      However, although 7 B-cell epitopes of α3(IV)NC1 were subsequently mapped that could bind with different reactivity to sera of patients with anti-GBM disease, peptides within α3197-232 were not recognized by the antibodies.
      • Levy J.B.
      • Coulthart A.
      • Pusey C.D.
      Mapping B cell epitopes in Goodpasture’s disease.
      Moreover, unlike intact α3(IV)NC1,
      • Kalluri R.
      • Gattone 2nd, V.H.
      • Noelken M.E.
      • Hudson B.G.
      The alpha 3 chain of type IV collagen induces autoimmune Goodpasture syndrome.
      α3197-232 was later found to be unable to induce GN despite an immune response to the epitope itself.
      • Levy J.B.
      • Coulthart A.
      • Pusey C.D.
      Mapping B cell epitopes in Goodpasture’s disease.
      ,
      • Bolton W.K.
      • Luo A.M.
      • Fox P.
      • May W.
      • Fox J.
      Goodpasture’s epitope in development of experimental autoimmune glomerulonephritis in rats.
      Subsequent studies confirmed that the amino-terminal sequence of α3(IV)NC1, but not its carboxy terminus, was recognized by sera from patients with anti-GBM disease.
      • Ryan J.J.
      • Mason P.J.
      • Pusey C.D.
      • Turner N.
      Recombinant alpha-chains of type IV collagen demonstrate that the amino terminal of the Goodpasture autoantigen is crucial for antibody recognition.
      ,
      • Hellmark T.
      • Segelmark M.
      • Unger C.
      • Burkhardt H.
      • Saus J.
      • Wieslander J.
      Identification of a clinically relevant immunodominant region of collagen IV in Goodpasture disease.
      These findings indicated that the amino terminus of α3(IV)NC1 harbors the immunodominant regions for B-cell recognition.
      Figure thumbnail gr1
      Figure 1Time line illustrating key developments in epitope mapping of antigens related to anti-GBM diseases. Abbreviations: GBM, glomerular basement membrane; GN, glomerulonephritis.
      Two fine conformational epitopes were later discovered by Netzer et al
      • Netzer K.O.
      • Leinonen A.
      • Boutaud A.
      • et al.
      The goodpasture autoantigen: mapping the major conformational epitope(s) of α3(IV) collagen to residues 17-31 and 127-141 of the NC1 domain.
      in the amino-terminal regions of α3(IV)NC1, denoted EA and EB. These 2 epitopes in the NC1 hexamer were cryptic, that is, not accessible to anti-GBM antibodies in the absence of dissociation of the hexamers.
      • Borza D.B.
      • Netzer K.O.
      • Leinonen A.
      • et al.
      The goodpasture autoantigen. Identification of multiple cryptic epitopes on the NC1 domain of the alpha3(IV) collagen chain.
      They were reported to be recognized by over 70% of patients with anti-GBM antibodies, with the recognition of EB as an independent risk factor for kidney dysfunction.
      • Chen J.L.
      • Hu S.Y.
      • Jia X.Y.
      • et al.
      Association of epitope spreading of antiglomerular basement membrane antibodies and kidney injury.
      High levels of circulating antibodies against EA and EB in patients with anti-GBM disease were also associated with a worse clinical profile at presentation.
      • Yang R.
      • Hellmark T.
      • Zhao J.
      • et al.
      Levels of epitope-specific autoantibodies correlate with renal damage in anti-GBM disease.
      Another epitope (S2) containing 9 discontinuous amino acids that largely overlap with EA was found later.
      • Hellmark T.
      • Burkhardt H.
      • Wieslander J.
      Goodpasture disease: characterization of a single conformational epitope as the target of pathogenic autoantibodies.
      Further studies using recombinant chimeric proteins confirmed 4 critical residues—alanine18, isoleucine19, valine27, and proline28—were responsible for the recognition of EA by sera from anti-GBM patients.
      • David M.
      • Borza D.B.
      • Leinonen A.
      • Belmont J.M.
      • Hudson B.G.
      Hydrophobic amino acid residues are critical for the immunodominant epitope of the Goodpasture autoantigen: a molecular basis for the cryptic nature of the epitope.
      Notably, the application of new techniques such as phage display disclosed some previously unrecognized critical residues of these 2 regions for antibody binding, including threonine26 and tyrosine30 in EA; threonine127, proline131, histidine134, and lysine141 in EB; and threonine99 and alanine96 outside these regions.
      • Gozalbo-Rovira R.
      • Rodríguez-Díaz J.
      • Saus J.
      • Cervera J.
      Precise mapping of the Goodpasture epitope(s) using phage display, site-directed mutagenesis, and surface plasmon resonance.

      T-cell Epitope Mapping of α3(IV)NC1

      T-cell–mediated autoimmunity was also known to be involved in the pathogenesis of anti-GBM disease.
      • Wu J.
      • Hicks J.
      • Borillo J.
      • Glass 2nd, W.F.
      • Lou Y.H.
      CD4+ T cells specific to a glomerular basement membrane antigen mediate glomerulonephritis.
      ,
      • Wu J.
      • Borillo J.
      • Glass W.F.
      • Hicks J.
      • Ou C.N.
      • Lou Y.H.
      T-cell epitope of α3 chain of type IV collagen induces severe glomerulonephritis.
      However, T-cell epitope mapping studies were limited because a large quantity of peripheral blood was required to isolate T cells from patients. In 1996, Merkel et al
      • Merkel F.
      • Kalluri R.
      • Marx M.
      • et al.
      Autoreactive T-cells in Goodpasture’s syndrome recognize the N-terminal NC1 domain on alpha 3 type IV collagen.
      described the first autoreactive T-cell clone derived from a patient with anti-GBM disease and found this clone specifically recognized 1 epitope (glycine-serine-proline-alanine-threonine-tryptophan-threonine-threonine-arginine) on α3(IV)NC1. Similarly, autoreactive HLA-DR15-CD4-positive T cells derived from 6 patients with anti-GBM disease were found later that could proliferate in response to 2 linear T-cell epitopes of α3(IV)NC1, α369-88 and α3129-148.
      • Cairns L.S.
      • Phelps R.G.
      • Bowie L.
      • et al.
      The fine specificity and cytokine profile of T-helper cells responsive to the alpha3 chain of type IV collagen in Goodpasture’s disease.
      Although there are only limited clinical studies of T-cell epitope mapping, evidence from animal models has demonstrated that T-cell–mediated autoimmunity is involved in the pathogenesis of anti-GBM disease. In 2003, a linear T-cell epitope (pCol14-26) from rat α3(IV)NC1 was mapped; it could induce an autoimmune response and severe GN with crescentic lesions in immunized rats.
      • Wu J.
      • Borillo J.
      • Glass W.F.
      • Hicks J.
      • Ou C.N.
      • Lou Y.H.
      T-cell epitope of α3 chain of type IV collagen induces severe glomerulonephritis.
      These findings were later confirmed by subsequent studies.
      • Bolton W.K.
      • Chen L.
      • Hellmark T.
      • Wieslander J.
      • Fox J.W.
      Epitope spreading and autoimmune glomerulonephritis in rats induced by a T cell epitope of Goodpasture’s antigen.
      Further studies of rat α3(IV)NC1 identified a similar nephritogenic linear epitope (pCol10-24) as a mutual B- and T-cell epitope.
      • Reynolds J.
      • Haxby J.
      • Juggapah J.K.
      • Evans D.J.
      • Pusey C.D.
      Identification of a nephritogenic immunodominant B and T cell epitope in experimental autoimmune glomerulonephritis.
      Subsequently, Ooi et al
      • Ooi J.D.
      • Chang J.
      • O’Sullivan K.M.
      • et al.
      The HLA-DRB1∗15:01-restricted Goodpasture’s T cell epitope induces GN.
      identified a T-cell epitope of the murine α-chain of collagen IV (α3136–146) that when used to immunize HLA-DRB1∗15:01 (HLA-DR15) transgenic mice could induce T-cell responses and kidney injury in anti-GBM GN.
      As with most autoimmune diseases, there is a genetic association between anti-GBM disease and HLA alleles, such that HLA-DR15 confers an increased disease susceptibility while HLA-DR1 possesses a protective effect.
      • Ooi J.D.
      • Chang J.
      • O’Sullivan K.M.
      • et al.
      The HLA-DRB1∗15:01-restricted Goodpasture’s T cell epitope induces GN.
      ,
      • Xie L.J.
      • Cui Z.
      • Chen F.J.
      • et al.
      The susceptible HLA class II alleles and their presenting epitope(s) in Goodpasture’s disease.
      Recently, a mechanism accounting for HLA-mediated susceptibility and protection in anti-GBM disease has been proposed, namely that HLA polymorphisms result in structurally important differences in epitope-HLA presentation to T cells. Conventional proinflammatory T cells were generated when α3136–146 was presented by HLA-DR15, and predominantly protective antigen-specific regulatory T cells were generated when the epitope was presented by HLA-DR1.
      • Ooi J.D.
      • Petersen J.
      • Tan Y.H.
      • et al.
      Dominant protection from HLA-linked autoimmunity by antigen-specific regulatory T cells.
      Another similar sequence from human α3(IV)NC1 designated as P14 (α3127-148) could also induce kidney injury and lung hemorrhage in WKY rats.
      • Jia X.Y.
      • Cui Z.
      • Yang R.
      • Hu S.Y.
      • Zhao M.H.
      Antibodies against linear epitopes on the Goodpasture autoantigen and kidney injury.
      ,
      • Hu S.Y.
      • Gu Q.H.
      • Wang J.
      • et al.
      The pathogenicity of T cell epitopes on human Goodpasture antigen and its critical amino acid motif.
      Its nephritogenicity was shown to be dependent on 4 critical residues: tryptophan136, isoleucine137, leucine139, and tryptophan140.
      • Hu S.Y.
      • Gu Q.H.
      • Wang J.
      • et al.
      The pathogenicity of T cell epitopes on human Goodpasture antigen and its critical amino acid motif.

      Autoantibodies Against Other α Chains in Collagen IV

      Human collagen IV comprises a family of 6 proteins, each encoding a different chain (α1-α6), though human GBM lacks α6.
      • Hudson B.G.
      • Tryggvason K.
      • Sundaramoorthy M.
      • Neilson E.G.
      Alport’s syndrome, Goodpasture’s syndrome, and type IV collagen.
      As discussed, anti-GBM autoantibodies mainly target epitopes located on α3(IV)NC1, but autoantibodies against other α chains of collagen IV are present in most patients.
      • Zhao J.
      • Cui Z.
      • Yang R.
      • Jia X.Y.
      • Zhang Y.
      • Zhao M.H.
      Anti-glomerular basement membrane autoantibodies against different target antigens are associated with disease severity.
      Autoantibodies against α5(IV)NC1 represent the second most abundant subset.
      • Zhao J.
      • Cui Z.
      • Yang R.
      • Jia X.Y.
      • Zhang Y.
      • Zhao M.H.
      Anti-glomerular basement membrane autoantibodies against different target antigens are associated with disease severity.
      Interestingly, a unique case of anti-GBM disease with circulating antibodies exclusively against α5(IV)NC1 was reported.
      • Cui Z.
      • Zhao M.H.
      • Jia X.Y.
      • et al.
      Antibodies to α5 chain of collagen IV are pathogenic in Goodpasture’s disease.
      Animal studies indicated that α5(IV)NC1 could induce autoantibodies and cause experimental anti-GBM GN. Mapping studies further demonstrated that α517-31 (α5-EA) and α5127-141 (α5-EB) on α5(IV)NC1 are the regions that react with autoantibodies. The topology of α5-EA and α5-EB is similar to the homologous regions of α3(IV)NC1. Sequence alignment highlights several residues within α5-EA and α5-EB that in the homologous regions of α3(IV)NC1 contribute to the specificity of antibody binding.
      • Cui Z.
      • Zhao M.H.
      • Jia X.Y.
      • et al.
      Antibodies to α5 chain of collagen IV are pathogenic in Goodpasture’s disease.
      In the 5%-10% of patients with Alport syndrome after kidney transplantation who have anti-GBM antibodies,
      • McAdoo S.P.
      • Pusey C.D.
      Anti-glomerular basement membrane disease.
      circulating antibodies do not recognize the classical cryptic EA and EB epitopes of α3(IV)NC1 but instead bind the EA region of α5(IV)NC1 in the intact hexamer.
      • Pedchenko V.
      • Bondar O.
      • Fogo A.B.
      • et al.
      Molecular architecture of the Goodpasture autoantigen in anti-GBM nephritis.
      A peptide consisting of 27 amino acid residues from the carboxy terminus of α4(IV)NC1 was shown to induce anti-GBM GN in WKY rats,
      • Sugihara K.
      • Sado Y.
      • Ninomiya Y.
      • Wada H.
      Experimental anti-GBM glomerulonephritis induced in rats by immunization with synthetic peptides based on six alpha chains of human type IV collagen.
      a result later recapitulated with the full recombinant protein of human α4(IV)NC1.
      • Sado Y.
      • Boutaud A.
      • Kagawa M.
      • Naito I.
      • Ninomiya Y.
      • Hudson B.G.
      Induction of anti-GBM nephritis in rats by recombinant alpha 3(IV)NC1 and alpha 4(IV)NC1 of type IV collagen.
      We found that natural anti-GBM autoantibodies from healthy individuals recognized α4(IV)NC1.
      • Zhao J.
      • Cui Z.
      • Yang R.
      • Jia X.Y.
      • Zhang Y.
      • Zhao M.H.
      Anti-glomerular basement membrane autoantibodies against different target antigens are associated with disease severity.
      Yet, as α4-specific antibodies coexisted with the major pathogenic α3-specific antibodies in most patients and no exclusively circulating autoantibodies against α4(IV)NC1 have been reported in anti-GBM disease, the pathogenicity of α4(IV)NC1 needs to be further elucidated.
      Rarely, anti-GBM disease can be mediated by IgA antibodies. Two studies attempted to characterize the epitopes recognized by IgA, but results were inconsistent. One study found that the epitope was located on the collagenous domain of the α1/α2(IV) collagen network from the GBM
      • Borza D.B.
      • Chedid M.F.
      • Colon S.
      • Lager D.J.
      • Leung N.
      • Fervenza F.C.
      Recurrent Goodpasture’s disease secondary to a monoclonal IgA1-κ antibody autoreactive with the α1/α2 chains of type IV collagen.
      while the other indicated that it was located on the collagenous domain of α1(IV) collagen from human fibroblasts.
      • Antonelou M.
      • Henderson S.R.
      • Bhangal G.
      • et al.
      Binding truths: atypical anti-glomerular basement membrane disease mediated by IgA anti-glomerular basement membrane antibodies targeting the α1 chain of type IV collagen.
      Meanwhile, the pathogenicity of these epitopes remains to be examined. In contrast to α3(IV)NC1, α1(IV) collagen is more abundant in the alveolar basement membrane than the GBM.
      • Shen C.R.
      • Jia X.Y.
      • Luo W.
      • et al.
      Laminin-521 is a novel target of autoantibodies associated with lung hemorrhage in anti-GBM disease.
      Autoantibodies against α1(IV) collagen have been reported in patients with anti-GBM disease combined with lung adenocarcinoma and might be associated with pulmonary hemorrhage.
      • Kalluri R.
      • Petrides S.
      • Wilson C.B.
      • et al.
      Anti-alpha1(IV) collagen autoantibodies associated with lung adenocarcinoma presenting as the Goodpasture syndrome.

      Discovery of Novel Target Autoantigens in GBM

      The human GBM contains multiple components other than collagen IV. Laminins are a family of glycoproteins with a set of isoforms composed of α-chains, β-chains, and γ-chains that are expressed in human basement membranes. Several laminin isoforms are well-established autoantigens involved in human autoimmune diseases, such as laminin α5β1γ1 (also known as laminin-511), which is a target antigen in patients with autoimmune pancreatitis.
      • Shiokawa M.
      • Kodama Y.
      • Sekiguchi K.
      • et al.
      Laminin 511 is a target antigen in autoimmune pancreatitis.
      Laminin-521 is the most important constituent of GBM apart from collagen IV.
      • Naylor R.W.
      • Morais M.
      • Lennon R.
      Complexities of the glomerular basement membrane.
      It was recently identified as a novel target autoantigen recognized by sera of more than one-third of patients with anti-GBM disease and possessing disease specificity.
      • Shen C.R.
      • Jia X.Y.
      • Luo W.
      • et al.
      Laminin-521 is a novel target of autoantibodies associated with lung hemorrhage in anti-GBM disease.
      Patients with autoantibodies against laminin-521 had significantly higher prevalence of hemoptysis and pulmonary hemorrhage. These findings imply that anti–laminin-521 autoantibodies may potentially contribute to lung injury in patients with anti-GBM disease, although these patients also were more likely to have a history of smoking.
      Entactin is a bridge molecule that connects laminin-521 to the collagen IV network. The presence of anti-entactin antibodies was observed in a minority of patients with anti-GBM disease, but there was a lack of disease specificity.
      • Saxena R.
      • Bygren P.
      • Butkowski R.
      • Wieslander J.
      Entactin: a possible auto-antigen in the pathogenesis of non-Goodpasture anti-GBM nephritis.
      The quaternary structure of the α3α4α5 hexamer results from the formation of the S=N bond, which is dependent on peroxidasin embedded within GBM. Recently, antiperoxidasin autoantibodies were identified as being present in 46% of a cohort of 24 patients with anti-GBM disease. Examination of sequential serum samples revealed that antiperoxidasin antibodies existed before disease onset. Of note, peroxidasin shows 48% sequence identity with myeloperoxidase (MPO) through the peroxidase domain. The antiperoxidasin antibodies cross-reacted with solid-phase MPO coated on polystyrene plates and were also present in sera from patients with anti-MPO vasculitis.
      • McCall A.S.
      • Bhave G.
      • Pedchenko V.
      • et al.
      Inhibitory anti-peroxidasin antibodies in pulmonary-renal syndromes.
      Our previous study also found that aberrant glycosylated MPO could be recognized by half of the patients with anti-GBM disease without the coexistence of anti-MPO antibodies.
      • Yu J.T.
      • Li J.N.
      • Wang J.
      • Jia X.Y.
      • Cui Z.
      • Zhao M.H.
      Deglycosylation of myeloperoxidase uncovers its novel antigenicity.
      The discovery of these antigenic epitopes may offer insights into the pathogenesis of double-seropositive patients or the mechanisms underlying the production of both anti-MPO and anti-GBM antibodies. A representation of the range of autoantibodies that may be involved in anti-GBM disease is shown in Figure 2.
      Figure thumbnail gr2
      Figure 2Autoantibodies targeting the major GBM components in patients with anti-GBM disease. Briefly, the GBM is mainly composed of a collagen IV α3α4α5 network with LM521 sheets. Pathogenic autoantibodies targeting α3NC1, α5NC1, and LM521 are found in sera of patients with anti-GBM disease. Entactin is a bridge protein that links LM521 to the collagen IV network, and anti-entactin antibodies may be present in the circulation of a minority of patients. PXDN, a hemeperoxidase that shows 48% sequence identity with MPO through the peroxidase domain, is responsible for the formation of the S=N bond via generation of HOBr to stabilize α3α4α5 hexamer; anti-PXDN antibodies are also detected in sera of patients with anti-GBM disease and anti-MPO vasculitis. Of note, half of patients with anti-GBM disease can recognize abnormal glycosylated MPO without the need for concomitant anti-MPO antibodies. Abbreviations: GBM, glomerular basement membrane; HOBr, hypobromous acid; LM521, laminin-521; MPO, myeloperoxidase; PXDN, peroxidasin.
      Increasingly, “atypical” anti-GBM disease is of concern—that is, clinical presentation with undetectable anti-GBM antibodies, less lung involvement, and a diagnosis made only by kidney biopsy.
      • Nasr S.H.
      • Collins A.B.
      • Alexander M.P.
      • et al.
      The clinicopathologic characteristics and outcome of atypical anti-glomerular basement membrane nephritis.
      Ruling out some possible mechanisms for the absence of circulating anti-GBM antibodies (reviewed by Rosales and Colvin
      • Rosales I.A.
      • Colvin R.B.
      Glomerular disease with idiopathic linear immunoglobulin deposition: a rose by any other name would be atypical.
      ), a proportion of these patients might possess antibodies against distinct GBM epitopes. For example, Ho et al
      • Ho J.
      • Gibson I.W.
      • Zacharias J.
      • Fervenza F.
      • Colon S.
      • Borza D.B.
      Antigenic heterogeneity of IgA anti-GBM disease: new renal targets of IgA autoantibodies.
      identified that IgA from serum from a “typical” patient bound to 38- to 48-kDa antigens within the GBM instead NC1 domains of collagen IV. The identification of novel antigens in these patients certainly merits future laboratory work.

      Autoimmunity and Epitope Spreading

      Autoimmunity can spread to secondary epitopes on the antigen (ie, intramolecular epitope spreading) or to epitopes on other endogenous antigens (intermolecular epitope spreading). Epitope spreading is a well-established mechanism implicated in various autoimmune diseases ranging from systemic lupus erythematosus to diabetes
      • Cornaby C.
      • Gibbons L.
      • Mayhew V.
      • Sloan C.S.
      • Welling A.
      • Poole B.D.
      B cell epitope spreading: mechanisms and contribution to autoimmune diseases.
      and also occurs in anti-GBM disease. In 2004, Wu et al
      • Wu J.
      • Arends J.
      • Borillo J.
      • et al.
      A self T cell epitope induces autoantibody response: mechanism for production of antibodies to diverse glomerular basement membrane antigens.
      observed that a single T-cell epitope of rat α3(IV)NC1 not only induced disease in animal models but also elicited antibodies to multiple B-cell epitopes of native GBM. Their findings tentatively indicated the existence of epitope spreading in anti-GBM disease. The phenomenon of intramolecular epitope spreading in autoimmune GN was proved later by Bolton et al.
      • Bolton W.K.
      • Chen L.
      • Hellmark T.
      • Wieslander J.
      • Fox J.W.
      Epitope spreading and autoimmune glomerulonephritis in rats induced by a T cell epitope of Goodpasture’s antigen.
      They found that serum samples and eluants from kidney tissue from WKY rats immunized with a T-cell epitope of rat α3(IV)NC1 showed reactivity to not only the immunizing epitope but also epitopes of α3(IV)NC1 external to the immunogen itself. Intermolecular epitope spreading was later confirmed with the evidence that samples from WKY rats immunized by a nephritogenic peptide of rat α3(IV)NC1 revealed additional reactivity to human and rat α3(IV)NC1 and to human α4(IV)NC1 domains.
      • Chen L.
      • Hellmark T.
      • Pedchenko V.
      • et al.
      A nephritogenic peptide induces intermolecular epitope spreading on collagen IV in experimental autoimmune glomerulonephritis.
      Furthermore, recent studies have suggested that the pathogenesis of “double-seropositive” patients—namely, those with anti-GBM disease and antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV)—might be explained by intermolecular epitope spreading, with evidence from AAV animal models that proteases released from neutrophils activated by ANCA could lead to exposure of cryptic epitopes on α3(IV)NC1 and thus induction of anti-GBM antibodies.
      • Nishibata Y.
      • Nonokawa M.
      • Tamura Y.
      • et al.
      Possible implication of intermolecular epitope spreading in the production of anti-glomerular basement membrane antibody in anti-neutrophil cytoplasmic antibody-associated vasculitis.
      Concurrent membranous nephropathy (MN) and anti-GBM disease has also been frequently reported but the causal relationships are not clear.
      • Ahmad S.B.
      • Santoriello D.
      • Canetta P.
      • et al.
      Concurrent anti-glomerular basement membrane antibody disease and membranous nephropathy: a case series.
      The antigens of primary MN are mostly expressed on the surface of podocytes, which are spatially compact with GBM containing α3(IV)NC1.
      • Hanset N.
      • Aydin S.
      • Demoulin N.
      • et al.
      Podocyte antigen staining to identify distinct phenotypes and outcomes in membranous nephropathy: a retrospective multicenter cohort study.
      It is reasonable to postulate that intermolecular epitope spreading–induced podocyte injury might initiate autoimmunity against antigens on podocytes, thus linking primary MN and anti-GBM disease. We recently reported that the linear peptide α3141–154 could induce MN lesions in DBA/1 mice, which might offer some clues to the mechanism of MN and anti-GBM disease in combination.
      • Wang J.
      • Wang M.
      • Cui Z.
      • Zhao M.H.
      Epitope mapping of human α3(IV)NC1-induced membranous nephropathy in mice.
      In addition, our previous study suggested that patients with different degrees of kidney injury had antibodies that recognized different α chains, and that patients with more severe injury had a broader range of α chains recognized by their circulating autoantibodies, presenting evidence that intermolecular epitope spreading may be present in patients with anti-GBM disease.
      • Zhao J.
      • Cui Z.
      • Yang R.
      • Jia X.Y.
      • Zhang Y.
      • Zhao M.H.
      Anti-glomerular basement membrane autoantibodies against different target antigens are associated with disease severity.
      Figure 3 presents a hypothesis for how epitope spreading could potentially explain the discovery of different target antigens in patients with anti-GBM disease.
      • Shen C.R.
      • Jia X.Y.
      • Luo W.
      • et al.
      Laminin-521 is a novel target of autoantibodies associated with lung hemorrhage in anti-GBM disease.
      ,
      • McCall A.S.
      • Bhave G.
      • Pedchenko V.
      • et al.
      Inhibitory anti-peroxidasin antibodies in pulmonary-renal syndromes.
      Figure thumbnail gr3
      Figure 3Epitope spreading in the pathogenesis of anti-GBM disease. During the first autoimmune response (middle panel), APCs only present the dominant α3(IV)NC1 epitope by their MHC II, activating autoreactive T cells via the TCR, which causes autoimmunity by the stimulation of humoral and cellular immunity–mediated mechanisms. During intramolecular epitope spreading (top panel), in parallel to presenting the dominant epitope, APCs also present the cryptic epitope on α3(IV)NC1 via MHC II restriction and activate cryptic epitope–specific autoreactive T cells via TCR restriction, triggering a secondary autoimmune response. During intermolecular epitope spreading (bottom panel), APCs present a dominant epitope on an antigen other than α3(IV)NC1. Autoantibodies are not cross-reactive to α3(IV)NC1. Epitope spreading supplies a possible answer to the discovery of autoantibodies against novel antigens in patients with anti-GBM disease. These emerging autoantibodies may be triggered by an ongoing autoimmune response to α3(IV)NC1, likely resulting from exposure of cryptic epitopes due to GBM damage. Therefore, it is reasonable to assume that epitope spreading may play a significant role in worsening the disease. Abbreviations: APC, antigen-presenting cell; GBM, glomerular basement membrane; MHC II, major histocompatibility II; TCR, T-cell receptor.

      Autoimmunity and Epitope Mimicry

      Another potential mechanism proposed to account for the development of autoimmunity is epitope (molecular) mimicry. Molecular mimicry refers to immunological cross-reactivity between host antigens and bacterial antigens when there is similarity in their amino acid sequences or structures. It is well known that protection against autoimmunity depends on the negative selection of self-reactive T cells in the thymus and later induction of tolerance in the periphery.
      • Albert L.J.
      • Inman R.D.
      Molecular mimicry and autoimmunity.
      Yet some T cells are not depleted because they are not exposed to autoantigen during this process, or due to antigen levels being too low to activate T cells. These cells are called “ignorant” T cells, and the antigens they recognize are regarded as “cryptic.”
      • Goodnow C.C.
      Balancing immunity and tolerance: deleting and tuning lymphocyte repertoires.
      A similar mechanism occurs during B-cell maturation.
      • Nemazee D.
      Mechanisms of central tolerance for B cells.
      Actually, both α3(IV)NC1-specific T cells and natural anti-GBM antibodies are present in the sera of healthy individuals.
      • Cui Z.
      • Wang H.Y.
      • Zhao M.H.
      Natural autoantibodies against glomerular basement membrane exist in normal human sera.
      ,
      • Zou J.
      • Hannier S.
      • Cairns L.S.
      • et al.
      Healthy individuals have Goodpasture autoantigen-reactive T cells.
      Molecular mimicry might provide a stimulus for the breakdown of immune tolerance and initiation of autoimmunity through the activation of autoreactive T and B cells.
      The prevalence of prodromal infections in patients with anti-GBM disease is as high as 80%.
      • Gu Q.H.
      • Xie L.J.
      • Jia X.Y.
      • et al.
      Fever and prodromal infections in anti-glomerular basement membrane disease.
      These findings suggest that infections could serve as one of the triggers of disease pathogenesis through molecular mimicry. The identification of critical residues by epitope mapping of α3(IV)NC1 underlies the investigation of molecular mimicry in disease pathogenesis. Accordingly, lung hemorrhage and GN were induced in rats by a peptide from Clostridium botulinum mimicking a T-cell epitope of rat α3(IV)NC1.
      • Arends J.
      • Wu J.
      • Borillo J.
      • et al.
      T cell epitope mimicry in antiglomerular basement membrane disease.
      However, the T-cell epitope used in this study is not identical in sequence to human α3(IV)NC1 counterparts and Clostridium botulinum–associated infections in patients with anti-GBM disease have not been reported. A few microbial peptides sharing critical residues of human α3(IV)NC1 identified using bioinformatic tools have been shown to be recognized by the sera of patients with anti-GBM disease.
      • Hu S.Y.
      • Gu Q.H.
      • Wang J.
      • et al.
      The pathogenicity of T cell epitopes on human Goodpasture antigen and its critical amino acid motif.
      ,
      • Jia X.Y.
      • Cui Z.
      • Li J.N.
      • Hu S.Y.
      • Zhao M.H.
      Identification of critical residues of linear B cell epitope on Goodpasture autoantigen.
      • Li J.N.
      • Jia X.
      • Wang Y.
      • et al.
      Plasma from patients with anti-glomerular basement membrane disease could recognize microbial peptides.
      • Gu Q.H.
      • Huynh M.
      • Shi Y.
      • et al.
      Experimental antiglomerular basement membrane GN induced by a peptide from actinomyces.
      Among them, a peptide from Actinomyces could induce experimental anti-GBM GN by activating autoreactive T and B cells. These findings provide support for the infection-mediated disease initiation hypothesis (Fig 4).
      Figure thumbnail gr4
      Figure 4Epitope mimicry in the pathogenesis of anti-GBM disease. In epitope mimicry, APCs present, via MCH II, an epitope from an infectious microbe, activating the microbial-specific T cell via TCR, leading to GBM injury through proinflammatory responses. Due to sequence similarity with a microbial epitope, an autoepitope on GBM can be cross-recognized by the autoreactive T cells, which causes autoimmunity by the stimulation of humoral and cellular immunity–mediated mechanisms. Abbreviations: APC, antigen-presenting cell; GBM, glomerular basement membrane; MHC II, major histocompatibility II; TCR, T-cell receptor.
      Of note, beyond molecular mimicry, there are other pathways such as the bystander effect and superantigen activation that may be involved in the pathogenesis of autoimmune diseases.
      • Pacheco Y.
      • Acosta-Ampudia Y.
      • Monsalve D.M.
      • Chang C.
      • Gershwin M.E.
      • Anaya J.M.
      Bystander activation and autoimmunity.
      Further investigations are needed to clarify these pathways and their potential implications for therapeutic strategies for anti-GBM disease.

      Immunotherapies

      Currently, the standard treatment for anti-GBM disease includes immunosuppressive therapy plus plasma exchange to remove circulating pathogenic antibodies. Although patient outcomes have greatly improved in recent decades, kidney recovery remains suboptimal.
      • McAdoo S.P.
      • Pusey C.D.
      Anti-glomerular basement membrane disease.
      Exploring potential immunotherapeutic strategies that could act at the onset of autoimmunity seems a promising approach. In fact, in animal models, targeting either T-cell– or B-cell–mediated autoimmunity can attenuate the development of anti-GBM GN.
      • Reynolds J.
      • Tam F.W.
      • Chandraker A.
      • et al.
      CD28-B7 blockade prevents the development of experimental autoimmune glomerulonephritis.
      • Reynolds J.
      • Khan S.B.
      • Allen A.R.
      • Benjamin C.D.
      • Pusey C.D.
      Blockade of the CD154-CD40 costimulatory pathway prevents the development of experimental autoimmune glomerulonephritis.
      • Reynolds J.
      • Norgan V.A.
      • Bhambra U.
      • Smith J.
      • Cook H.T.
      • Pusey C.D.
      Anti-CD8 monoclonal antibody therapy is effective in the prevention and treatment of experimental autoimmune glomerulonephritis.
      • McAdoo S.P.
      • Reynolds J.
      • Bhangal G.
      • et al.
      Spleen tyrosine kinase inhibition attenuates autoantibody production and reverses experimental autoimmune GN.
      Moreover, T-cell immune tolerance can be established in rats by oral or nasal administration of GBM antigen before disease induction and can prevent anti-GBM GN.
      • Reynolds J.
      • Pusey C.D.
      Oral administration of glomerular basement membrane prevents the development of experimental autoimmune glomerulonephritis in the WKY rat.
      ,
      • Reynolds J.
      • Prodromidi E.I.
      • Juggapah J.K.
      • et al.
      Nasal administration of recombinant rat alpha3(IV)NC1 prevents the development of experimental autoimmune glomerulonephritis in the WKY rat.
      Unraveling the mechanism of HLA-mediated autoimmunity might lead to more immunotherapies tailored to patients with anti-GBM disease.
      • Ooi J.D.
      • Petersen J.
      • Tan Y.H.
      • et al.
      Dominant protection from HLA-linked autoimmunity by antigen-specific regulatory T cells.
      Huynh et al
      • Huynh M.
      • Eggenhuizen P.J.
      • Olson G.L.
      • et al.
      HLA-DR15-specific inhibition attenuates autoreactivity to the Goodpasture antigen.
      demonstrated the potency of HLA-DR15 inhibition to alleviate α3136-146–immunized anti-GBM GN by administering HLA-DR15 transgenic mice with PV-267 (an HLA-DR15–specific inhibitor). PV-267 administration limited α3136-146–specific proinflammatory responses and attenuated kidney injury in animal models.
      A modified peptide derived from the nephritogenic T-cell epitope P14 of human α3(IV)NC1 by substituting in one critical amino acid from α1(IV)NC1 could alleviate the kidney injury associated with experimental anti-GBM GN in WKY rats.
      • Shi Y.
      • Jia X.Y.
      • Gu Q.H.
      • Wang M.
      • Cui Z.
      • Zhao M.H.
      A modified peptide derived from goodpasture autoantigen arrested and attenuated kidney injuries in a rat model of anti-GBM glomerulonephritis.
      It exerted its therapeutic effect by modulating T-cell differentiation toward an anti-inflammatory profile, including fewer T-helper 17 (TH17) cells and an increased ratio of regulatory T cells to TH17 cells, as well as via inhibitory binding of the pathogenic antibodies (Fig 5). This study demonstrated the validity of epitope-specific immunotherapy in anti-GBM disease and may offer new insights into immunotherapy for other autoimmune kidney diseases in the future.
      Figure thumbnail gr5
      Figure 5Potential mechanisms for epitope-specific immunotherapy. Application of a modified epitope that replaces critical amino acids of a nephritogenic autoepitope could alleviate anti-GBM GN, possibly through mechanisms that inhibit the presentation process of the autoepitope, thereby arresting autoreactive T-cell activation, modulating T-cell differentiation, and inhibiting antibody binding to the autoepitope. Abbreviations: APC, antigen-presenting cell; GBM, glomerular basement membrane; GN, glomerulonephritis.
      As discussed previously, the major epitopes of anti-GBM disease are EA and EB, which are normally cryptic in the α3α4α5 hexamer. Interestingly, details of the assembly and crystal structure of the α3α4α5 hexamer were recently revealed, with the important finding that the apexes of the α3 monomer feature loop-crevice-loop (LCL) bioactive sites that contain the cryptic epitopes involved in anti-GBM disease.
      • Boudko S.P.
      • Bauer R.
      • Chetyrkin S.V.
      • et al.
      Collagen IV(α345) dysfunction in glomerular basement membrane diseases. II. Crystal structure of the α345 hexamer.
      ,
      • Pedchenko V.
      • Boudko S.P.
      • Barber M.
      • et al.
      Collagen IV(α345) dysfunction in glomerular basement membrane diseases. III. A functional framework for α345 hexamer assembly.
      It also revealed a chloride-dependent mechanism for the exposure of EA and EB epitopes within the LCL site due to the discovery of a ring of chloride ions at the trimer-trimer interface that stabilized hexamer assembly with sulfilimine crosslinks. This group also proposed that α3α4α5 hexamer variants could alter the conformation of LCL sites, together with other endogenous and exogenous triggers, to expose autoepitopes of anti-GBM autoantibodies.
      • Pokidysheva E.N.
      • Seeger H.
      • Pedchenko V.
      • et al.
      Collagen IV(α345) dysfunction in glomerular basement membrane diseases. I. Discovery of a COL4A3 variant in familial Goodpasture’s and Alport diseases.
      Collectively, these findings suggest that these LCL sites could be therapeutic targets in anti-GBM disease.

      Conclusions

      In summary, both T-cell and B-cell epitope mapping are essential for the understanding of autoimmune responses in anti-GBM disease. A more detailed view of the pathogenesis of anti-GBM disease, in turn, confers greater feasibility to the prospect of developing effective immunotherapies.

      Article Information

      Authors’ Full Names and Academic Degrees

      Huang Kuang, BA, Jing Liu, BA, Xiao-yu Jia, PhD, Zhao Cui, MD, and Ming-hui Zhao, MD, PhD.

      Support

      This work was supported by the National Natural Science Foundation of China (82090020 to Ming-hui Zhao) and Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences (2019-I2M-5-046). The funding sources did not have any role in the preparation, review, or approval of the manuscript.

      Financial Disclosure

      The authors declare that they have no relevant financial interests.

      Peer Review

      Received April 28, 2022. Evaluated by 2 external peer reviewers, with direct editorial input from an Associate Editor and a Deputy Editor. Accepted in revised form July 10, 2022.

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