BCR and CD40 stimulation are the optimal inducers of IL-24 mRNA expression. (A) GC B cells were cultured with medium only, F(ab)′2 anti-IgM, anti-IgM + CD40L, LPS, control CpG/ODN, or CpG/ODN for 2 and 5 days before RNA was extracted, reverse-transcribed, and analyzed by qPCR (n = 5). (B) CD44⁺IgD⁻ centrocytes were sorted and restimulated or not with anti-IgM or anti-IgM + CD40L for 5 days and qPCR was performed (n = 3). (C) Intracellular expression of IL-24 was analyzed by FACS on fresh (day 0) or stimulated with anti-IgM + CD40-L for 4 days (day 4), purified tonsil B cells. Cells were fixed, permeabilized, and stained with biotinylated goat control IgG or goat anti–IL-24 Abs followed by SA-FITC as shown by black (day 0) or gray (day 4) histograms.