The detection of IL-24–positive cells in follicular B cells on OCT-embedded frozen sections. (Top left) Section was stained with anti-CD20cy MAb followed by a secondary Alexa 594 F(ab)′2-goat anti–mouse Ab, and DAPI-containing mounting medium. (Middle) Goat anti–human IL-24 Ab was followed by biotinylated rabbit anti–goat Ab and streptavidin–Alexa 488. (Right) Section was stained sequentially with anti–IL-24 then with anti-CD20 Abs. (Bottom panels from left to right) Controls are in order: DAPI, goat IgG + biotin–anti-goat + SA–Alexa 488, mouse IgG2a + Alexa 594 goat anti–mouse Ab.