ES/OP9-derived neutrophils contain gelatinase and lactoferrin-positive granules similar to mouse bone marrow–derived PMNs. Bone marrow–derived (A-B) and ES/OP9-derived neutrophils (C-D) were stained for gelatinase (A,C) and lactoferrin (B,D) as described in “Materials and Methods.” Original magnification × 900.