New function of platelets
Scientists at the Robert Koch Institute have discovered that in the event of an injury to the vascular system, thrombocytes not only help to stop the bleeding, but also trigger inflammation in the vascular wall and in this way initiate the repair of the vessel. The discovered mechanism improves the understanding of normal wound healing, but also of the pathological vascular wall processes that lead to arteriosclerosis and heart attacks. The working group headed by Richard Kroczek at the Robert Koch Institute (RKI) discovered that platelets constantly carry a special protein with them. This protein, known as TRAP (TNF-related activation protein) because of its relationship to the inflammatory messenger TNF, but also known as CD40 ligand, is normally hidden inside the platelets. If a vessel wall is injured, platelets clump together to stop the bleeding and simultaneously transfer their TRAP molecules to the cell surface within seconds.
In cooperation with the laboratories of Gert Müller-Berghaus at the Kerckhoff Clinic of the Max Planck Society in Bad Nauheim and Michael Graefe at the German Heart Center in Berlin, the RKI working group was able to show that the TRAP molecules on the surface of platelets bind to appropriate receptors on endothelial cells lining the vasculature. This stimulates the endothelial cells to release messenger substances and form adhesion molecules on the surface (Nature, Vol. 391, pp. 591-594). The released messenger substances attract inflammatory cells (granulocytes, monocytes), while the adhesion molecules hold the cells attracted in this way to the damaged endothelium. This leads to an accumulation of inflammatory cells at the site of vascular damage within a short period of time - the first step in repairing the vessel.
The new findings expand our understanding of the function of platelets, which until now have been considered exclusively as vascular-sealing cells. "We were able to show," says the immunologist Richard Kroczek, "that the blood platelets also act as inflammatory cells in blood clotting. The inflammatory response initiated by platelets is essential for the repair of the damaged inner wall of the vessel and the affected surrounding tissue.”
The work of the RKI working group leads to a better understanding of normal wound healing. At the same time, they shed new light on the mechanism by which arteriosclerosis develops, which often leads to heart attacks or cerebral infarctions. In the case of arteriosclerosis, it is known that thrombocytes and certain inflammatory cells (monocytes) play a key role in the progression of the disease. New diagnostic and therapeutic approaches could result from a better understanding of the disease process that leads to arteriosclerosis.
