In Dr. McEver's lab they study how circulating blood cells attach to blood vessel surfaces at sites of tissue injury or infection. Substances released at these sites direct the endothelial cells that line blood vessels to display â??adhesion molecules.â? These molecules enable circulating white blood cells, or leukocytes, to roll along the vessel surface. The rolling cells then slow to a stop and then crawl between the endothelial cells into the tissues, where they destroy invading microbes. This process is known as inflammation. Similarly, circulating platelets use adhesion molecules to roll along tissues that are exposed when blood vessels are disrupted. The platelets then stop and form clumps to slow hemorrhage and promote blood clotting. Inflammation and blood clotting are often linked. Indeed, leukocytes sometimes roll on and then stick to blood platelets. Excessive inflammation and blood clotting contribute towards many diseases, including heart attacks, stroke, dysfunction of transplanted organs, deep vein thrombosis, and sickle cell crisis.