NB1, a glycosyl-phosphatidylinositol (GPI)-linked N-glycosylated cell surface glycoprotein, was first described in a case of neonatal alloimmune neutropenia. Highly expressed in normal bone marrow and weakly expressed in fetal liver. Expressed on neutrophils. Expressed in granulocytes of patients with polycythemia vera (PV) and with essential thrombocythemia (ET).