Activated platelet‐derived microparticles in thalassaemia

Abstract

Summary Thromboembolic complications have been documented in thalassaemia patients. The aggregability of abnormal red blood cells and the high level of membrane‐derived microparticles (MPs) stemming from blood cells are thought to be responsible for the associated thrombotic risk. We investigated the number of MPs, their cellular origin and their procoagulant properties in β‐thalassaemia. Fresh whole blood was simultaneously stained for annexin V, cellular antigens and the known density beads. The procoagulant properties of these phosphatidylserine (PS)‐bearing MPs were also measured by assessing the platelet factor‐3‐like activity in the blood. Flow cytometric results showed that splenectomised β‐thalassaemia/HbE patients had significantly higher levels of PS‐bearing MPs than non‐splenectomised β‐thalassaemia/HbE patients and normal individuals (P < 0·0001). There was a good correlation between PS‐bearing MPs and PS‐bearing platelets, reflecting the existence of chronic platelet activation in β‐thalassaemia/HbE patients (rs = 0·511, P < 0·001). The cellular origin of PS‐bearing MPs showed mostly activated‐platelet origin with adhesion (CD41a/CD62P/CD36). Moreover, the platelet procoagulant activity was higher in splenectomised β‐thalassaemia/HbE patients when compared with non‐splenectomised (P < 0·05) and normal individuals (P < 0·01), and the amount correlated with PS‐bearing MPs (rs = 0·560, P < 0·001). These findings suggest that MPs originate from activated platelets with a potential to aggravate thrombotic events when the numbers are excessive, as is commonly seen in splenectomised β‐thalassaemia/HbE patients.

Circulating erythrocyte-derived microparticles are associated with coagulation activation in sickle cell disease

“…The majority of circulating microparticles in SCD originate from erythrocytes and platelets and may support coagulation activation by exposure of phosphatidylserine to facilitate complex formation between coagulation factors in the coagulation activation cascade; an increased exposure of tissue factor has been demonstrated on monocyte-derived microparticles. 8,15 A more thorough understanding of the mechanism by which circulating microparticles affect coagulation and endothelial activation might be helpful in the development of new therapies in SCD.…”

Hypercoagulability and thrombotic complications in hemolytic anemias

“…[17][18][19][20][21] The total number of microparticles, total tissue factor-positive microparticles, monocyte-derived tissue factor-positive microparticles and RBC-derived microparticles are correlated with Ddimer, thrombin-antithrombin complexes and F1+2 levels in SCD patients, 17 suggesting that microparticles may contribute to the hypercoagulable state observed in patients with SCD and other hemolytic anemias.…”

Enumeration of the absolute CD4 T‐lymphocyte count by cell‐bead assay

“…The conventional method for quantitation of CD4þ Tlymphocytes is with the use of CLB, where the flow cytometric counts are compared to the known quantity of the CLB suspension (6,11). Although this method is accurate, it is labor-intensive and expensive (US$ 19-20, a range of cost per one sample), because the samples have to be added to every CLB tube.…”

“…Immunofluorescene analysis by flow cytometry is the standard method for enumeration of CD4þ T-lymphocyte (3,4). A quantitation by commercial latex bead (CLB) method is the conventional method for measuring the absolute cell number in various cell types as well as circulating CD4þ T-lymphocyte (5,6). However, the drawback of this method is relatively expensive, because the samples have to be added to every CLB tube.…”