Effects of the RAR antagonist LE540 on growth inhibition and differentiation in NB4 cells induced by ATRA, 9CRA, TT, or 9CTT. The effects of LE540 on growth inhibition (A) and NBT-reducing activity (B) in NB4 cells induced by ATRA (6 × 10⁻⁹ mol/L [○] or 6 × 10⁻⁸ mol/L [•]) or 9CRA (6 × 10⁻⁹ mol/L [▵] or 6 × 10⁻⁸ mol/L [▴]) were examined. Next, the effects of LE540 on growth inhibition (C) and NBT-reducing activity (D) induced by 9CTT at 6 × 10⁻⁶ mol/L (▿) or 9 × 10⁻⁶ mol/L (□) were examined. LE540 alone (•) did not affect growth or NBT reduction. *P < .05, compared with values in the absence of LE540 in (A) through (D). The effects of LE540 on CD11b expression that was induced equally by 3 × 10⁻⁹ mol/L 9CRA and 6 × 10⁻⁶ mol/L 9CTT are shown in (E). *P < .05, compared with 9CRA. Cells (5 × 10⁴ cells/mL) were treated with ATRA, 9CRA, TT, or 9CTT in the absence or presence of LE540 for 4 days. Values represent the means ± SD of three separate experiments.