Leukocyte sensing of flow direction
Marie-Pierre Valignat (Laboratoire Adhésion Cellulaire et Inflammation, Marseille)
As they leave the blood stream and travel to lymph nodes or sites of inflammation, leukocytes are captured by the endothelium and migrate along the vascular wall to permissive sites of transmigration. These processes are supposedly orchestrated by chemical signals and take place under the influence of a strong hemodynamic shear stress. The role of flow on leukocyte crawling and extravasation remains generally an unsolved question, however crawling T lymphocytes were recently reported in vivo and in vitro to orient against the direction of flow and to move upstream like salmons in a river. This non-intuitive behavior is manifestly not a passive drift of cells pushed by the flow, and we sought here to clarify the origin, role and mechanism of this upstream flow mechanotaxis behavior.