CD177 and polycythemia: CD177 (also known as neutrophil specific antigen B1 [NB1], human neutrophil antigen 2a [HNA-2a], and polycythemia rubra vera 1 [PRV1]) is a 56–64 kDa protein belonging to the Ly-6 family [1, 2], and is expressed exclusively on neutrophils by glycosylphosphatidylinositol (GPI)-linkage [3, 4].