Goodpasture autoantibodies unmask cryptic epitopes by selectively dissociating autoantigen complexes lacking structural reinforcement: novel mechanisms for immune privilege and autoimmune pathogenesis.
Rapidly progressive glomerulonephritis in Goodpasture disease is mediated by autoantibodies binding to the non-collagenous NC1 domain of alpha3(IV) collagen in the glomerular basement membrane. Goodpasture epitopes in the native autoantigen are cryptic (sequestered) within the NC1 hexamers of the alpha3alpha4alpha5(IV) collagen network. The biochemical mechanism for crypticity and exposure for autoantibody binding is not known. We now report that crypticity is a feature of the quaternary structure of two distinct subsets of alpha3alpha4alpha5(IV) NC1 hexamers: autoantibody-reactive M-hexamers containing only monomer subunits and autoantibody-impenetrable D-hexamers composed of both dimer and monomer subunits. Goodpasture antibodies only breach the quaternary structure of M-hexamers, unmasking the cryptic epitopes, whereas D-hexamers are resistant to autoantibodies under native conditions. The epitopes of D-hexamers are structurally sequestered by dimer reinforcement of the quaternary complex, which represents a new molecular solution for conferring immunologic privilege to a potential autoantigen. Dissociation of non-reinforced M-alpha3alpha4alpha5(IV) hexamers by Goodpasture antibodies is a novel mechanism whereby pathogenic autoantibodies gain access to cryptic B cell epitopes. These findings provide fundamental new insights into immune privilege and the molecular mechanisms underlying the pathogenesis of human autoimmune Goodpasture disease.
Borza
Dorin-Bogdan
DB
Division of Nephrology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, 37232, USA. Dorin-Bogdan.Borza@vanderbilt.edu
Bondar
Olga
O
Colon
Selene
S
Todd
Parvin
P
Sado
Yoshikazu
Y
Neilson
Eric G
EG
Hudson
Billy G
BG
D019867:Anti-Glomerular Basement Membrane Disease / Q000150:complications / Q000276:immunology*; D000937:Antigen-Antibody Reactions; D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology*; D001327:Autoimmune Diseases / Q000209:etiology*; D002460:Cell Line; D024141:Collagen Type IV / Q000737:chemistry / Q000276:immunology; D019281:Dimerization; D000939:Epitopes / Q000378:metabolism; D006801:Humans; D007118:Immunoassay; D011489:Protein Denaturation / Q000276:immunology; D020836:Protein Structure, Quaternary; D014162:Transfection
D001323:Autoantibodies; D001324:Autoantigens; D024141:Collagen Type IV; D000939:Epitopes; C057112:type IV collagen alpha3 chain