Alport alloantibodies but not Goodpasture autoantibodies induce murine glomerulonephritis: Protection by quinary crosslinks locking cryptic α3(IV) collagen autoepitopes in vivo

摘要

The noncollagenous (NC1) domains of α3α4α5(IV) collagen in the glomerular basement membrane (GBM) are targets of Goodpasture autoantibodies or Alport post-transplant nephritis alloantibodies mediating rapidly progressive glomerulonephritis. Because the autoepitopes but not the alloepitopes become cryptic upon assembly of α3α4α5NC1 hexamers, we investigated how the accessibility of B cell epitopes in vivo influences the development of glomerulonephritis in mice passively immunized with human anti-GBM antibodies. Alport alloantibodies, which bound to native murine α3α4α5NC1 hexamers in vitro, deposited linearly along the mouse GBM in vivo, eliciting crescentic glomerulonephritis in Fcgr2b−/− mice susceptible to antibody-mediated inflammation. Goodpasture autoantibodies, which bound to murine α3NC1 monomer and dimer subunits but not to native α3α4α5NC1 hexamers in vitro, neither bound to the mouse GBM in vivo nor induced experimental glomerulonephritis. This was due to quinary NC1 cross-links, recently identified as sulfilimine bonds, which comprehensively locked the cryptic Goodpasture autoepitopes in the mouse GBM. In contrast, non-crosslinked α3NC1 subunits were identified as a native target of Goodpasture autoantibodies in the GBM of squirrel monkeys—a species susceptible to Goodpasture autoantibody-mediated nephritis. Thus, crypticity of B cell autoepitopes in tissues uncouples potentially pathogenic autoantibodies from autoimmune disease. Crosslinking of α3α4α5NC1 hexamers represents a novel mechanism averting autoantibody binding and subsequent tissue injury by post-translational modifications of an autoantigen.