| CD177, also known as neutrophil antigen NB1 or polycythemia rubra vera‑1, is a glycosylphosphatidylinositol‑anchored Ly6/uPAR‑family glycoprotein predominantly expressed on a subset of human neutrophils and neutrophilic precursors, where it acts as a neutrophil-specific receptor and organizer of surface protease and adhesion signaling relevant to inflammation and vasculitis. The extracellular region comprises multiple LU domains that form a globular head connected to downstream segments by a flexible linker, providing a structured interface for binding partners including proteinase 3 (PR3) and endothelial adhesion receptors. CD177 acts as the high-affinity receptor for mature PR3, capturing the protease at the neutrophil surface so that most membrane-bound PR3 resides in CD177:PR3 complexes; a mainly hydrophobic binding interface involving the first two LU domains of CD177 defines the CD177-binding surface of PR3 as a dominant ANCA epitope targeted in granulomatosis with polyangiitis. CD177 expression stratifies neutrophils into CD177pos/mPR3high and CD177neg/mPR3low populations, and elevated CD177 and membrane PR3 expression are linked to ANCA-associated systemic vasculitis and systemic lupus erythematosus, where PR3-ANCA binding triggers oxidative burst and degranulation. Structure-guided mutation of the CD177-binding site on PR3 reduces ANCA binding, highlighting the functional importance of the CD177–PR3 interface in autoantibody recognition and effector activation. CD177 also serves as a heterophilic adhesion receptor by binding platelet endothelial cell adhesion molecule-1 (PECAM‑1) on endothelial cells and associating with β2 integrins such as Mac‑1 (ITGAM/ITGB2); these interactions modulate neutrophil transendothelial migration, degranulation and superoxide production, and by preventing β2 integrin internalization and attenuating chemokine signaling, CD177 can bias neutrophils toward adhesion rather than migration in defined inflammatory contexts. Under inflammatory conditions, CD177 expression is upregulated, and CD177+ neutrophils accumulate at inflamed mucosal and vascular sites, where they regulate the release of inflammatory mediators, form neutrophil extracellular traps and influence barrier integrity and tissue damage in diseases such as inflammatory bowel disease, acute respiratory distress syndrome and vascular inflammation. CD177 expression on epithelial cells and tumor-infiltrating regulatory T cells has been associated with tumor invasion, disease stage, and patient survival in several solid cancers, suggesting additional roles in tumor microenvironment signaling and immune modulation. Genetic variants in CD177 affect its expression and IgG-mediated functions, and recent work identifies CD177 as a novel IgG Fc receptor that contributes to antibody-dependent effector mechanisms, adding another layer to its role in autoimmunity and host defense. |
