Researchers find that activated platelets secrete CCL5, which stimulates megakaryocytes to produce more platelets.
Blood platelets play an important role in many physiological conditions that occur in the body. Their main role is to limit bleeding and blood loss by forming clots at sites where the endothelial layer is disrupted. They are formed from fragments of the cytoplasm of megakaryocytic, large bone marrow progenitor cells that release proplatelets into the bloodstream. When conditions such as infections, inflammation or malignancy occur, there is a transient occurrence of a high platelet count. Their blood levels are important. A low platelet level lead to bleeding and too many can result in blood clots, so understanding how their numbers are regulated is important. However, it is still not clear how this occurs – well, until recently.
Scientists know that in situations of infection or inflammation, there is an abundance of a chemokine, CCL5 that is released in the body. Could CCL5 have an effect on platelet formation and production? A group of researchers from Brigham and Women’s Hospital in Boston have discovered that platelets store large quantities of CCL5 and release it when they get activated under physiological stress. The researchers also found that megakaryocytes express the receptor CCR5, needed for CCL5 function. Upon treating megakaryocytes with CCL5, the researchers managed to increase the generation of proplatelets, with the opposite occurring when the interaction was blocked. In an animal model of colitis, the researchers found a positive correlation between inflammation level and platelet numbers. This confirms the positive feed back loop, in which platelets can ensure their expansion under physiological conditions.1
These findings are important in understanding how to manipulate platelet levels at situations where their numbers need to be corrected. We are excited about this novel evidence and will be following how this will affect diseases where platelet numbers are altered. Here at HemaCare we provide human platelets to study their role in different diseases. You can call us at (877) 397-3087 if you have any questions or would like to place an order.
1 Machlus, K. R. et al., 2015. CCL5 derived from platelets increases megakaryocyte proplatelet formation. Blood 127 (7), DOI 10.1182/blood-2015-05- 644583.