Experimental Antiglomerular Basement Membrane GN Induced by a Peptide from Actinomyces

Significance Statement Antiglomerular basement membrane (anti-GBM) disease is associated with HLA-DRB1*1501 (the major predisposing genetic factor in the disease), with ?3(127?148) as a nephritogenic T and B cell epitope. Association of infections with anti-GBM disease has been long suspected. In this study, the authors used bioinformatic tools to search for peptides from microbes mimicking the critical motif of a pathogenic epitope for Goodpasture disease (?3(127?148)). They identified a pathogenic peptide derived from Actinomyces, which was recognized by sera from patients with anti-GBM disease and that induced proteinuria, linear IgG deposition on GBM, and crescent formation in both WKY rats and humanized HLA-DR15 transgenic mice via crossreactivity of lymphocytes. These findings implicate a role for infection and molecular mimicry in the pathogenesis of anti-GBM disease. Background Antiglomerular basement membrane (anti-GBM) disease is associated with HLA-DRB1*1501 (the major predisposing genetic factor in the disease), with ?3(127?148) as a nephritogenic T and B cell epitope. Although the cause of disease remains unclear, the association of infections with anti-GBM disease has been long suspected. Methods To investigate whether microbes might activate autoreactive T and B lymphocytes via molecular mimicry in anti-GBM disease, we used bioinformatic tools, including BLAST, SYFPEITHI, and ABCpred, for peptide searching and epitope prediction. We used sera from patients with anti-GBM disease to assess peptides recognized by antibodies, and immunized WKY rats and a humanized mouse model (HLA-DR15 transgenic mice) with each of the peptide candidates to assess pathogenicity. Results On the basis of the critical motif, the bioinformatic approach identified 36 microbial peptides that mimic human ?3(127?148). Circulating antibodies in sera from patients with anti-GBM recognized nine of them. One peptide, B7, derived from Actinomyces species, induced proteinuria, linear IgG deposition on the GBM, and crescent formation when injected into WKY rats. The antibodies to B7 also targeted human and rat ?3(127?148). B7 induced T cell activation from human ?3(127?148)-immunized rats. T cell responses to B7 were detected in rats immunized by Actinomyces lysate proteins or recombinant proteins. We confirmed B7?s pathogenicity in HLA-DR15 transgenic mice that developed kidney injury similar to that observed in ?3(135?145)-immunized mice. Conclusions Sera from patients with anti-GBM disease recognized microbial peptides identified through a bioinformatic approach, and a peptide from Actinomyces induced experimental anti-GBM GN by T and B cell crossreactivity. These studies demonstrate that anti-GBM disease may be initiated by immunization with a microbial peptide.