Your Blood Cells Are Crawling Inside You

LiveScience Staff

Date: 11 May 2009 Time: 06:52 AM ET

When a cell undergoes apoptosis, white blood cells called macrophages consume cell debris.
CREDIT: U.S. National Library of Medicine

White blood cells, the immune system's "soldiers" for your body, actually crawl along your blood vessels to find their way to infection and injury sites, new research shows.

The cells move like millipedes, creating many minute legs that adhere to the endothelial cells lining blood vessel walls, said researcher Ronen Alon of the Weizmann Institute of Science in Israel. Scientists had previously thought that these cells moved like inchworms, forming attachments at their front and back, then folding in the middle and pushing forward.

Instead, the cells' tiny legs rapidly attach and detach themselves, allowing the cells to quickly migrate to their destination.

When the scientists looked closely at these limb-like protrusions, using an electron microscope, they saw that the legs actually "dig" into the endothelium.

The white blood cells may use the protrusions for more than just gripping and moving. The legs might also sense signals that let the cells know when to exit from the blood vessel and migrate to damaged tissue, Alon said.

Before this study, scientists thought the legs only appeared after the cells left blood vessels. But since the protrusions are also used for crawling, they might help the cells probe for cues that indicate to move across the endothelial barrier and leave the blood vessels, Alon said.

This work, funded by the De Benedetti Foundation, was published in the March 20 issue of the journal Immunity.