CD antigen CD177 is also known as Polycythemia rubra vera protein 1 (PRV-1), Human neutrophil alloantigen 2a, NB1 glycoprotein, is a glycosyl-phosphatidylinositol (GPI)-linked N-glycosylated cell surface glycoprotein. CD177 contains two UPAR/Ly6 domains. CD177 is highly expressed in normal bone marrow and weakly expressed in fetal liver. PECAM-1 is a binding partner of CD177.