Immune thrombocytopenia: antiplatelet autoantibodies inhibit proplatelet formation by megakaryocytes and impair platelet production in vitro.

Primary immune thrombocytopenia is an autoimmune disease mediated by antiplatelet autoantibodies that cause platelet destruction and suppression of platelet production. In vitro effects of autoantibodies on megakaryocyte production and maturation have been reported recently. However, the impact of these autoantibodies on crucial megakaryocyte functions, proplatelet formation and subsequent platelet release, has not been evaluated. We examined the effects of serum and IgG from 19 patients with immune thrombocytopenia using day 8 or 9 megakaryocytes (66.3 ± 10.6% CD41(+)), derived from cord blood hematopoietic stem cells (CD34(+)). The number of proplatelet-bearing megakaryocytes, the number of platelets released in the culture, total megakaryocyte numbers, ploidy pattern and caspase activation were measured at various times after treatment. After 5 days of treatment the number of proplatelet-bearing megakaryocytes was significantly decreased by 13 immune thrombocytopenia autoantibodies relative to the control group (P<0.0001) and this decrease was accompanied by a corresponding reduction of platelet release. Other features, including total megakaryocyte numbers, maturation and apoptosis, were not affected by immune thrombocytopenia antibodies. Treating the megakaryocytes with the thrombopoietin receptor agonists romiplostim and eltrombopag reversed the effect of the autoantibodies on megakaryocytes by restoring their capacity to form proplatelets. We conclude that antiplatelet antibodies in immune thrombocytopenia inhibit proplatelet formation by megakaryocytes and hence the ability of the megakaryocytes to release platelets. Treatment with either romiplostim or eltrombopag regenerates proplatelet formation from the megakaryocytes.

The prevalence of factor V Leiden (G1691A), prothrombin G20210A and methylenetetrahydrofolate reductase C677T mutations in Jordanian patients with beta-thalassemia major.

One hundred beta-thalassemia major (beta-TM) patients and 100 individuals as control were included. Factor V Leiden and prothrombin G20210A and methylenetetrahydrofolate reductase (MTHFR) gene mutations were genotyped by PCR and allele-specific restriction enzyme techniques. The prevalence of factor V Leiden G1691A, MTHFR C677T and prothrombin G20210A in patients was insignificantly higher than controls. Patients with beta-TM have insignificantly higher frequencies of mutant A allele in factor V Leiden G1691A (11.5 vs. 10.5%), mutant T allele in MTHFR C677T (21.5 vs. 21%) and mutant A allele in prothrombin G20210A (3 vs. 2.5%) than controls. Double heterozygosity for two of the three mutations discussed in this study was found in (10 vs. 8%, P = 0.62) in beta-TM patients and controls. The prevalence of factor V Leiden G1691A, prothrombin G20210A and MTHFR C677T mutations was slightly but insignificantly higher in beta-TM patients than controls. beta-TM is a chronic hypercoagulable condition independent of predisposing genetic factors.