A 53-year-old man with shock and arthritis 1 month after consolidation chemotherapy for acute myeloid leukemia

Summary We recently reported that IgM antibody-related microparticles exist in some patients with idiopathic thrombocytopenic purpura (ITP) [14]. In this study, we investigated the relationship between antiphospholipid (cardiolipin and phosphatidylinositol) antibodies and microparticles in 56 ITP patients. We used an ELISA to detect anti-phospholipid antibodies. IgG antibodies against cardiolipin and phosphatidylinositol were detected in 13 and 12 patients, respectively. The titers of IgG antibodies against these phospholipids did not correlate with the platelet-associated IgG level or the platelet count. Next, we investigated the binding of anti-phospholipid antibodies to platelets and microparticles. Microparticles were obtained by incubating washed platelets with collagen plus thrombin. ITP plasma containing IgG-class anti-phospholipid antibodies showed significantly increase binding to microparticles compared with plasma without such antibodies (p<0.001). Our results suggest that anti-phospholipid antibodies could affect the function of platelet microparticles in ITP.This work was supported in part by a Research Grant for Intractable Diseases from the Ministry of Health and Welfare of Japan.