Genetic regulation of CD177 and the role of CD177-proteinase-3 interactions in ANCA-associated vasculitis.

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Proteinase 3 (PR3) and myeloperoxidase (MPO) are the major antigens in anti-neutrophil cytoplasmic autoantibody (ANCA)-mediated vasculitis and necrotizing crescentic glomerulonephritis (NCGN). PR3 is harbored by the entire neutrophil population but is bimodally presented on the neutrophil membrane yielding membrane PR3 (mPR3)low and (mPR3)high subsets. The larger the mPR3high subset the stronger the neutrophil activation by PR3-ANCA in vitro and the worse the clinical disease course in patients with PR3-ANCA-induced vasculitis. We described neutrophil-specific CD177 previously as a membrane receptor for PR3. CD177 receptor protein and full-length mRNA are expressed by the CD177positive/mPR3high population, but not by the CD177negative/mPR3low population of neutrophils. Our proposal has two tightly related experimental aspects focusing on the CD177-PR3 interaction, namely (1) the regulation of the CD177 expression and (2) the significance of the CD177-PR3 interaction for PR3-ANCA-induced vasculitis. To (1) establish the genetic or epigenetic basis for a restricted CD177 gene expression, we will perform DNA and cDNA analysis of the CD177 gene and genome-wide, copy-number variation analysis, haplotype studies in trios, studies on methylation, histone modifications, and non-coding RNAs. We will assess blood- and stem cell-derived human neutrophils. Whereas others and we established mouse models for anti-MPO antibody-mediated vasculitis, no murine model for anti-PR3 antibodies exists. Murine CD177 and PR3 differ substantially from their human orthologs and were predicted incapable of physical interaction. We hypothesize that (2) mice expressing both human CD177 and PR3 under the myeloid-related protein 8 (MRP8) promoter will present human PR3 on the neutrophil surface and develop vasculitis and NCGN when challenged with PR3-ANCA from patients. These studies will clarify the role of CD177-PR3 interaction for PR3-ANCA induced vasculitis and possibly establish the CD177-PR3 complex as a novel treatment target.