CD81 is important for chemotaxis of DCs on 2-dimensional substrates. Transwell migration assays of LPS-stimulated (200 ng/mL) CD81 RNAi knockdown BM-DCs (A) and CD81 RNAi knockdown Mo-DCs (E) toward CCL19 (200 ng/mL). Chemotactic migration of BM-DCs (B-D) and Mo-DCs (F-H) in response to a stable CCL19 gradient (200 ng/mL) on 2-dimensional fibronectin-coated (50 μg/mL) commercial chemotaxis chambers. Migration plots of 40 cells/sample monitored by time-lapse videomicroscopy over a period of 1 hour by capturing digital images every minute from 1 representative experiment of 3 are depicted (B,F). Quantification of average migratory speed (velocity; C,G), y-forward migration index (y-FMI, which means directional persistence toward the chemokine; D), and accumulated (Acc.) distance of migrating DCs (H) after manual tracking of motile cells are representative for 1 experiment of 3. Error bars indicate ± SD. **P ≤ .01, ***P ≤ .001.