Drivers of thrombopoiesis
Platelets are small cellular particles that circulate in the blood and whose main role is to ensure blood clotting. Platelet numbers can be decreased in certain situations, e.g. following trauma, extensive surgery or in cancer patients. These patients with low platelet counts receive platelet transfusions to prevent bleeding.
Platelets are produced in the bone marrow from ‘parent cells’ called megakaryocytes (MKs) which are derived from bone marrow stem cells. A variety of chemicals and proteins control the production of MKs by stem cells, the main one being thrombopoietin (TPO) which stimulates MK growth. When the platelet count is low, TPO levels in the blood increase which encourages the bone marrow stem cells to produce more MKs. The release of platelets by MKs in the blood stream is a tightly regulated process for which the triggers are still largely unknown.
When blood donors donate platelets by apheresis, their platelet count falls by around 50%. The TPO level in those donors has been shown to rise gradually after 24 hours, peaking 2 days after the donation and then coming back down to baseline level. Previous studies have shown that the total platelet count goes back to baseline level after 7-10 days. This study aims to use samples taken from platelet donors after apheresis to identify the chemical and protein triggers which are responsible for the recovery of platelet count in apheresis donors.