This gene encodes a glycosyl-phosphatidylinositol (GPI)-linked cell surface glycoprotein that plays a role in neutrophil activation. The protein can bind platelet endothelial cell adhesion molecule-1 and function in neutrophil transmigration. Mutations in this gene are associated with myeloproliferative diseases. Over-expression of this gene has been found in patients with polycythemia rubra vera. Autoantibodies against the protein may result in pulmonary transfusion reactions, and it may be