How do white blood cells, immune system "soldiers," get to the site of infection or injury? They must crawl swiftly along the lining of the blood vessel, gripping it tightly to avoid being swept away in the blood flow, all the while searching for temporary "road signs" made of special adhesion molecules that let them know where to cross the blood vessel barrier so that they can reach the damaged tissue.

     In research recently published in the journal Immunity, Professor Ronen Alon and his research student Ziv Shulman, of the Weizmann Institute of Science, in Rehovot, Israel, show how white blood cells advance along the length of the endothelial cells lining the blood vessels. Alon's new findings show that the rapid movement of the white blood cells is more like that of millipedes than the current opinion of the movement of inchworms. The cell creates numerous tiny "legs" no more than a micron in length--adhesion points, rich in adhesion molecules that bind to partner adhesion molecules present on the surface of the blood vessels. Numerous tiny legs attach and detach in sequence within seconds--allowing them to move rapidly while keeping a good grip on the vessels' sides.

     The fact that these legs are used in crawling the vessel lining suggests that they may serve as probes to sense exit signals. The present study suggests that shear forces cause their adhesion molecules to enter highly active states. The scientists believe that the tiny legs are trifunctional: used for gripping, moving, and sensing distress signals from the damaged tissue.

     In future studies, the scientists plan to check whether it is possible to regulate aggressive immune reactions (such as in autoimmune diseases) by interrupting the "digging" of immune cell legs into the endothelium. They also plan to investigate whether cancerous blood cells metastasize through the blood stream using similar mechanisms in order to exit the blood vessels and enter different tissues.

--Source: "Scientists Show That White Blood Cells "Crawl," Weizmann Institute of Science, via Newswise, May 6, 2009