Induction of differentiation of NB4 cells. (A) Expression of CD11b antigens on NB4 cells. NB4 cells were treated for 3 days with several concentrations (10⁻¹⁰ to 10⁻⁷mol/L) of either 1,25D₃ or Ro-25 9716, and then analyzed by FACS. (□), 1,25D₃; (⌾), Ro 25-9716. (B) Combination of ATRA plus either 1,25D₃ or Ro 25-9716 on differentiation of NB4 cells. NB4 cells were treated with 1,25D₃ alone (10⁻⁹ to 10⁻¹⁰ mol/L, □), Ro 25-9716 alone (10⁻⁹ to 10⁻¹⁰ mol/L, ⌾), the combination of either ATRA (10⁻⁷ mol/L) plus 1,25D₃ (10⁻⁹ to 10⁻¹⁰ mol/L, X), or ATRA (10⁻⁷ mol/L) plus Ro 25-9716 (10⁻⁹ to 10⁻¹⁰ mol/L, □), and differentiation was determined by NBT reduction. Results represent the mean of three experiments with triplicate dishes.