DCs trans-migrate through the endothelium in selected lymphatic sections. The footpad was injected with BMDCs s.c. with 24 h before imaging. (a) Sequential images (timed 0–40 min) demonstrate the typical dynamics of DC transmigration; within 20 min, a DC that adhered to abluminal surface of a lymphatic vessel trans-migrated into the lymphatic lumen and started crawling. (b) Two DCs cross through the same spot on the endothelium, presumably representing a preformed portal (Pflicke and Sixt, 2009).