RA enhances phosphorylation of pRB and increases the expression of cyclin D3. (A-B) CD27⁺ B cells (1 × 10⁶/mL) were stimulated with or without CpG (1 μg/mL) in the presence or absence of RA (100 nM). At indicated time points, total-cell extract was prepared, and protein expression was determined by Western blot analysis. One representative experiment of 3 is shown. (C) CD27⁺ B cells (1 × 10⁶/mL) were cultured as in panels A-B for 24 hours prior to harvesting. Total -cell extracts were subjected to Western blot analysis and examined for the expression of cyclin D3.