Gr-1⁺ PU.1-deficient neutrophils are deficient in CD11b, but not CD18 expression. Short-term cultured (see Materials and Methods) liver-derived hematopoietic cells from normal (panels A and B) or PU.1-null (panels C and D) neonatal mice were assessed by two-color flow cytometry for CD11b (FITC) and Gr-1 (PE) (panels A and C) or CD11b (FITC) and CD18 (PE) (panels B and D) expression. Note the vastly reduced expression of CD11b on PU.1-deficient cells (compare panels A and C) but the presence of CD18 on the majority (86%) of the PU.1-deficient cells (compare panels B and D).