Analysis of the kinetics of TPO uptake during platelet transfusion

BACKGROUND: It has been shown in several studies that platelets play a role in the removal of TPO from the circulation. For instance, in vitro studies have shown that platelets can bind and internalize TPO, and transfusion studies have shown that the concentration of circulating TPO decreased after platelet transfusion. In the current study, the in vivo kinetics of plasma TPO levels and TPO uptake by transfused platelets is analyzed in more detail. STUDY DESIGN AND METHODS: Serial blood samples from patients who received a platelet transfusion were analyzed with respect to platelet count, plasma TPO concentration, and TPO content per platelet. In addition, the capacity of transfused platelets to bind TPO in vitro was assessed. RESULTS: Platelet counts increased immediately after transfusion, but subsequently started to decrease. Conversely, TPO levels decreased significantly but then returned to baseline level by 44 hours after transfusion. Platelet count and plasma TPO concentration were inversely correlated (r(p) = -0.9; p <0.05). The decrease in TPO concentration upon transfusion was accompanied by a significant increase in the platelet-associated TPO concentration. After transfusion, platelets isolated from the patient still displayed functional TPO receptors, as indicated by their intact capacity to bind TPO in vitro. CONCLUSION: The decrease in plasma TPO followed by the increase in platelet TPO provides evidence that platelets are responsible for the clearance of TPO in circulation. In vivo, platelets can bind and may degrade TPO upon platelet transfusion.