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 involved in Wegener's granulomatosis. A related pseudogene, which is adjacent to this gene on chromosome 19, has been identified.