Author:
Moura Marta Casal,Thompson Gwen E.,Nelson Darlene A.,Fussner Lynn A.,Hummel Amber M.,Jenne Dieter E.,Emerling Daniel,Volkmuth Wayne,Fervenza Fernando C.,Kallenberg Cees G.M.,Langford Carol A.,McCune Joseph W.,Merkel Peter A.,Monach Paul A.,Seo Philip,Spiera Robert F.,St. Clair E. William,Ytterberg Steven R.,Stone John H.,Robinson William H.,Pang Yuan-Ping,Specks Ulrich,
Abstract
AbstractProteinase 3 (PR3) is the major antigen for anti-neutrophil cytoplasmic antibodies (ANCAs) in the systemic autoimmune vasculitis, granulomatosis with polyangiitis (GPA). PR3-targeting ANCAs (PR3-ANCAs) recognize different epitopes on PR3 and are thought to be pathogenic for the development of the necrotizing vasculitis. To identify epitopes recognized by PR3-ANCAs, we pursued a strategy based on human-murine chimeric PR3 mutants. Interestingly, rather than observing reduced binding of PR3-ANCAs to Epitope 5 on a PR3 mutant (iHm5-Val103) with chimeric mutations in Epitope 5, we found substantially increased binding of the majority of PR3-ANCAs to iHm5-Val103 compared with the PR3 mutant (iPR3-Val103) clinically used to detect PR3-ANCAs. More interestingly, using iHm5-Val103 we identified a monoclonal antibody (moANCA518) from a patient with GPA that bound selectively to iHm5-Val103. Inhibition experiments using epitope-specific monoclonal antibodies and their antigen-binding fragments mapped the binding sites of moANCA518 and PR3-ANCAs (from patients displaying preferential binding to iHm5-Val103 over iPR3-Val103) to Epitope 3 on iHm5-Val103, a mutation-free epitope located far from the mutation sites in Epitope 5. These results demonstrate that the selective binding of moANCA518 (and likely the preferential binding of PR3-ANCAs from patients) to iHm5-Val103 is conferred by increased antigenicity of Epitope 3 on iHm5-Val103 caused by distal mutations, indicating that PR3-ANCAs bind to epitopes of a folded antigen conducive to allosteric effects of mutations—a previously unrecognized characteristic with implications for studying antibody-mediated autoimmune diseases and novel treatment approaches.
Publisher
Cold Spring Harbor Laboratory
Cited by
1 articles.
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