Impaired surface receptor expression on immature platelets in bleeding patients with abnormal light transmission aggregometry

BACKGROUND: A platelet function defect (PFD) is diagnosed in patients with mild to moderate bleeding disorders and abnormalities in light transmission aggregometry. The influence of platelet aging on platelet function in PFD remains unclear. OBJECTIVES: We aimed to assess surface receptor profiles of mature and immature platelets in patients with suspected PFD and their relation to hemostatic function. METHODS: Twenty-two patients with light transmission aggregometry alterations from the Vienna Bleeding Biobank were compared with 19 age- and biological sex-matched healthy controls. Blood samples were immediately analyzed using platelet function analyzer-100 system (Dade Behring Inc) with epinephrine cartridges. Platelet subtypes were characterized via surface receptor profiling of CD9, CD31, CD36, CD40L, CD42b, CD62P, CD63, CD107, and Toll-like receptors (TLRs) 2, 4, and 9, and immature (RNA-rich) platelets were quantified. RESULTS: Platelet counts, immature platelet fraction, and mean platelet volume, as well as other hemostatic parameters, did not differ between patients and controls, while patients demonstrated prolonged closure times on platelet function analyzer-100 (Dade Behring Inc). Principal component analysis highlighted distinct glycoprotein expression patterns between immature and mature platelets in both their resting state and after activation in patients and healthy controls. In patients, immature platelets expressed lower levels of CD62P, CD36, CD31, TLR2, and TLR4 but increased TLR9 expression, while mature platelets showed no differences. These distinct surface receptor patterns of immature platelets were partly associated with reduced thrombin receptor activator peptide 6-induced platelet aggregation. CONCLUSION: This study demonstrates significant alterations in surface receptor expression on immature platelets in patients with suspected PFD, underscoring immature platelets as crucial link to platelet biology and clinical symptoms in this patient population.