Competitively disrupting the neutrophil-specific receptor-autoantigen CD177:proteinase 3 membrane complex reduces anti-PR3 antibody-induced neutrophil activation

CD177 is a neutrophil-specific receptor presenting the proteinase 3 (PR3) autoantigen on the neutrophil surface. CD177 expression is restricted to a neutrophil subset, resulting in CD177(pos)/mPR3(high) and CD177(neg)/mPR3(low) populations. The CD177(pos)/mPR3(high) subset has implications for anti-neutrophil cytoplasmic autoantibody (ANCA)-associated autoimmune vasculitis (AAV), wherein patients harbor PR3-specific ANCAs that activate neutrophils for degranulation. Here we generated high-affinity anti-CD177 monoclonal antibodies, some of which interfered with PR3 binding to CD177 (PR3 "blockers") as determined by surface plasmon resonance spectroscopy, and used them to test the effect of competing PR3 from the surface of CD177(pos) neutrophils. Because intact anti-CD177 antibodies also caused neutrophil activation, we prepared non-activating Fab fragments of a PR3 blocker and non-blocker that bound specifically to CD177(pos) neutrophils. We observed that Fab blocker clone 40, but not non-blocker clone 80, dose-dependently reduced anti-PR3 antibody binding to CD177(pos) neutrophils. Importantly, preincubation with clone 40 significantly reduced respiratory burst in primed neutrophils challenged with either monoclonal antibodies to PR3 or PR3-ANCA IgG from AAV patients. After separating the two CD177/mPR3 neutrophil subsets from individual donors by magnetic sorting, we found that PR3-ANCAs provoked significantly more superoxide production in CD177(pos)/mPR3(high) than in CD177(neg)/mPR3(low) neutrophils, and that anti-CD177 Fab clone 40 reduced the superoxide production of CD177(pos) cells to the level of the CD177(neg) cells. Our data demonstrate the importance of the CD177:PR3 membrane complex in maintaining a high ANCA epitope density and thereby underscore the contribution of CD177 to the severity of PR3-ANCA diseases.