Antibodies to α5 chain of collagen IV are pathogenic in Goodpasture's disease

Autoantibody against glomerular basement membrane (GBM) plays a direct role in the initiation and development of Goodpasture's (GP) disease. The principal autoantigen is the non-collagenous domain 1 (NC1) of alpha 3 chain of collagen IV, with two immunodominant epitopes, E-A-alpha 3 and E-B-alpha 3. We recently demonstrated that antibodies targeting alpha 5NC1 are bound to kidneys in GP patients, suggesting their pathogenic relevance. In the present study, we sought to assess the pathogenicity of the alpha 5 autoantibody with clinical and animal studies. Herein, we present a special case of GP disease with circulating auto antibody reactive exclusively to the alpha 5NC1 domain. This autoantibody reacted with conformational epitopes within GBM collagen IV hexamer and produced a linear IgG staining on frozen sections of human kidney. The antibody binds to the two regions within alpha 5NC1 domain, E-A and E-B, and inhibition ELISA indicates that they are targeted by distinct sub-populations of autoantibodies. Sequence analysis highlights five residues that determine specificity of antibody targeting E-A and E-B epitopes of alpha 5NC1 over homologous regions in alpha 3NC1. Furthermore, immunization with recombinant alpha 5NC1 domain induced crescentic glomerulonephritis and alveolar hemorrhage in Wistar-Kyoto rats. Thus, patient data and animal studies together reveal the pathogenicity of alpha 5 antibodies. Given previously documented cases of GP disease with antibodies selectively targeting alpha 3NC1 domain, our data presents a conundrum of why alpha 3-specific antibodies developing in majority of GP patients, with alpha 5-specific antibodies emerged in isolated cases, the answer for which is critical for understanding of etiology and progression of the GP disease. (C) 2016 Elsevier Ltd. All rights reserved.