Ly-6G, formerly known as the myeloid differentiation antigen Gr-1, is a GPI-anchored protein.1 In the bone marrow, the level of antigen expression is directly correlated with granulocyte differentiation and maturation. It is also transiently expressed on monocytes in the bone marrow.2 In the periphery, Ly-6G is expressed predominantly on neutrophils.3, 4