Myeloid differentiation antigen Gr1 (Ly6G) is a GPI-anchored protein, which is briefly expressed on monocytes in the bone marrow. The level of the Ly6G expression in the bone marrow completely correlates with granulocyte differentiation and maturation. Ly6G ligation on murine neutrophils inhibits neutrophil recruitment, thus providing the first evidence of a function for the Ly6G molecule. Ly6G is seen primarily on neutrophils, also in a subgroup of eosinophils, differentiating pre-monocytes and plasmacytoid dendritic cells.