Topical application of PMA activates only local MCs, allowing visualization of trafficked granules in the DLN. (A–C) Toludine blue–stained sections of DLN tissue 2 h after injection with 32 µg of compound 48/80 (A), topical application of vehicle alone (B), or topical application of 10 µg PMA (C). (D and E) Free metachromatic granules could be visualized within the DLNs of PMA-treated footpads. E is the magnified view of the white box in D. All panels show results that are representative of three independent experiments using groups of 2–3 mice each. Bars: (A–D) 50 µm; (E) 20 µm.