The detection of blocking antibody against plasma thrombopoietin in subjects with childhood idiopathic thrombocytopenic purpura

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Idiopathic thrombocytopenic purpura (ITP) is a relatively common hermorrhagic disorder characterized by isolated thrombocytopenia without any identifiable systemic disease. Although it is widely believed that the autoantibody-mediated platelet clearance through phagocytic system contributes to thrombocytopenia, the alteration of megakaryocyte maturation and subsequent platelet production is also evidenced indicating "mixed" pathophysiology of ITP. We prebiously reported that marked decrease of TPO-dependent megikaryocytopoiesis of CBMC was noted concomitant with a drop in number of cells morphologically identified as megakaryocytes when cultured in the existence of sera from ITP patients. To further identify pathophysiology of ITP, we developed new ELISA system to detect anti-TPO autoantibodies in patients' sera. Briefly, 96-well plate was coated with polyclonal antibody against TPO followed by adding satulating amount of rhTPO. Sera from ITP patients were then added replicately to wells, and bound IgG antibody was detected by biotin-labeled monoclonal antibody against human IgG and avidin-biotin-peroxidase sy stem. Study protocol was explained and informed consent was obtained for all enrolled. Of 80 sera from patients with ITP (37 acute, 43 chronic) 3 had positive results for anti TPO antibody. Specificity of these ELISA activities was analized by adsorption test, none of which revealed specific antibody activity. From these data we concluded that intrinsic anti TPO antibody is not likely to account for impaired megakaryocytopoiesis in ITP patients.