Exposure to a gradient of ATP inhibits chemokine-directed migration of specific DC types in a dose-dependent fashion. (A) Migration of MoDCs, CD1a⁺ dermal DCs, CD1c⁺ PBDCs, or IL-3R⁺ PDCs to CCL21 in the absence or presence of 100 μM ATP added to the chemokine side of the transwell chambers. Migration to CCL21 in the absence of ATP was normalized to 100% (mean ± SEM; n = 4 for CD1a⁺ dermal DCs; n = 6 for all other DC types). ^*P < .05. (B) Dose-dependent ATP-mediated arrest of migration to CCL21 of MoDCs matured with TNF-α, IFN-α, and PGE₂ for 24 hours (mean ± SEM; n = 4). (C) MoDCs matured with CD40L for 24 hours. (D) Emigrant CD1a⁺ dermal DCs. Representative experiments, each performed in triplicate, are shown (n = 4).