Autophagosome-rich platelets are increased in immune thrombocytopenia

Abstract

Immune thrombocytopenia (ITP) is characterized by increased platelet destruction and reduced platelet production, mediated by antiplatelet autoantibodies. Owing to the absence of definitive tests, diagnosis of ITP mainly involves exclusion of other thrombocytopenic disorders. Accumulating evidence has implicated enhanced autophagy in thrombopoiesis and ITP. However, it remains unknown whether platelet autophagy is enhanced in patients with ITP and has diagnostic potential. To determine this, we measured the proportion of autophagosome-rich platelets (ARPs%) in patients with thrombocytopenia, including ITP. We examined 34 patients with ITP and 52 patients with other types of thrombocytopenic disorders. To detect and quantify autophagosomes within platelets, we used flow cytometry with a cationic fluorescence dye, Cyto-ID, which specifically labels autophagic compartments. Among thrombocytopenic patients, ARPs% was significantly elevated only in ITP patients (p ‹ 0.01) and was found to be significantly correlated with the proportion of reticulated platelets (RPs%) (r = 0.58) and mean platelet volume (r = 0.55). ARPs% showed a greater sensitivity but reduced specificity (88.2% and 71.2%, respectively) compared with those of RPs% (85.3% and 90.4%, respectively). These data suggest that enhanced autophagy of platelets is a characteristic finding in patients with ITP and shows diagnostic potential in thrombocytopenia.