For the last 10 years the research project has focused on a specific type of leukocyte called neutrophils, which are the first of the white blood cells to show up at the site of an injury or infection. The project team discovered that while many neutrophils attracted to the injured tissue roll along the surface of the blood vessel, only some are "captured" while flowing by, and fewer still actually enter the tissue. Adhesion molecules are expressed in high concentrations at the site of the injury, which makes the surface of the blood vessel stickier and causes many neutrophils to slow down or stop for a few minutes. Waugh likens the situation to fuzz balls rolling along a Velcro surface. The fuzz balls may or may not come to a stop, but they will certainly move more slowly as they remain in contact with the surface. Ultimately, most of the neutrophils will resume their flow through the blood vessel, while others will enter the tissue through specific locations that Waugh refers to as "hot spots."
The neutrophil does more than simply sit there after it comes to a stop. The cell, which has a wrinkled surface, flattens out, allowing more of its receptors to come in contact with the lining of the blood vessel, thereby increasing the level of communication between the neutrophil and the blood vessel wall. If the cell does not flatten out, it won't get enough information and will simply move on.
"We know there are preferred sites for egress and that the cells use some kind of tactile cues to find their way into the tissue space," said Waugh. "But we don't quite know what determines the existence of hot spots. That's one thing we're working to understand."
|Contact: Peter Iglinski|
University of Rochester