Wright-Giemsa morphology and CAE staining characteristics of PU.1-deficient neutrophils are similar to neutrophils from normal individuals. Neutrophils cultured from normal neonates as described in Materials and Methods are shown (A). Cells cultured from neonatal PU.1-null mice after 12 days (B) and >6 months (C) have similar polymorphonuclear morphology. Note presence of mitotic cells in PU.1-deficient cultures (B and F). Abundant CAE activity as indicated by red granules in PU.1-deficient cells (E and F) is also evident, as in normal neutrophils (D).