The RAR-specific agonist TTNPB mimics the effects of retinoic acid. Left panel: B cells (1.5 × 10⁶/mL) were stimulated with μ (37 μg/mL) and SAC (0.005%) and harvested at the indicated times after stimulation. Right panel: Cells were stimulated with μ (37 μg/mL) and SAC (0.005%). TTNPB (100 nmol/L) was then added to the cell cultures at each indicated time before harvesting the cells at 32 hours. Total cell lysates were prepared and subjected to Western blot analysis for pRB (top), cyclin E (middle), and p21^Cip1 (bottom). μ, F(ab′)₂ fragment of rabbit antihuman IgM; SAC,Staphylococcus aureus crude cell suspension.