Immune thrombocytopenia in children: the immune character of destructive thrombocytopenia and the treatment of bleeding

Comparison of thrombopoiesis during ITP and HIV-ITP and response to intravenous gammaglobulin treatment

Immune thrombocytopenic purpura's diagnosis (ITP) is based on low platelet count and exclusion of clinical conditions rather than a specific diagnostic test. We used the reticulated platelet (RP) assay to study ITP and thrombocytopenia associated with HIV infection (HIV-ITP). Data from 96 ITP and 23 HIV-ITP patients showed low platelet counts (PC) with both high or low %RP suggesting that individuals have different degrees of thrombopoiesis. About 20% of ITP and 46% of HIV-ITP patients had %RP in the 'low' or 'normal' ranges. Grouped by platelet count <30x10(9)/L, 24% ITP and 36% HIV-ITP patients had 'low' to 'normal' %RP. The patient population did not show correlation between PC and %RP, but individuals showed an inverse relationship. Within a week of receiving IVIG, 18 ITP and 9 HIV-ITP patients' PC increased, %RP decreased. Patients with %RP measured within 24 h of IVIG treatment had lower %RP than expected, suggesting dilution by an older platelet population. ITP and HIV-ITP patients' responses to i.v. gammaglobulins were similar. Thrombopoietin levels of ITP patients did not correlate with PC, %RP, or RP count. Estimation of thrombopoiesis by RP assay provides useful information for differentiation among thrombocytopenias.

The cellular immunology associated with autoimmune thrombocytopenic purpura: an update

Chronic autoimmune thrombocytopenic purpura (AITP) is an organ specific autoimmune bleeding disease in which autoantibodies are directed against the individual's own platelets, resulting in increased Fc-mediated platelet destruction by macrophages in the reticuloendothelial system. Although AITP is primarily mediated by IgG auto-antibodies, their production is regulated by the influence of T lymphocytes and antigen presenting cells (APC). This review argues that enhanced T helper cell/antigen presenting cell interactions in patients with AITP may be responsible for IgG anti-platelet auto-antibody production. Understanding these cellular immune responses in AITP may lead to the development of more immune specific therapies for the management of this disease.

Immunobiology of T helper cells and antigen-presenting cells in autoimmune thrombocytopenic purpura (ITP)

Autoimmune thrombocytopenic purpura (AITP) is a bleeding disease in which autoantibodies are directed against the individual's own platelets, resulting in enhanced Fc-mediated platelet destruction by macrophages in the reticuloendothelial system. Most research in AITP has focused on characterization of the autoantibodies, while little has been devoted to the cellular immune mechanisms leading to autoantibody production. This report summarizes the current state of the literature and argues that enhanced T helper cell/antigen-presenting cell interactions in patients with AITP are the primary stimulus for the development of antiplatelet autoantibody production. Understanding these events is important for eventually identifying disease-initiating platelet autoantigens and ultimately developing specific immunotherapies for AITP.

Protein A immunoadsorption in chronic refractory ITP reverses increased platelet activation but fails to achieve sustained clinical benefit

Adults with chronic relapsing ITP present a difficult therapeutic challenge. The ongoing antibody-mediated platelet destruction in this group might be expected to be associated with increased expression of platelet surface membrane activation antigens. We have studied a group of 10 patients with refractory ITP and 35 healthy controls. Using an immediate, sensitive, unfixed, whole blood, flow cytometric method to detect platelet surface P-selectin and GP53, we have detected markedly increased platelet activation in the ITP group compared with the controls (P-selectin; patient median 24.5% v control median 2.0%. GP53 median 6.5% v 2.1%, P < 0.01 for both). Five patients underwent protein A immunoadsorption therapy. The effect of protein A immunoadsorption on platelet activation before, during and after 18 treatments in these patients was studied and patients were followed-up to assess clinical outcome. Platelet-associated immunoglobulin measurements were made before and at the end of six treatments. Platelet activation decreased after immunoadsorption. P-selectin expression fell significantly; pre- and post-treatment median values differed by 15.5%, P < 0.01, for GP53 the difference was 2.5%, P = NS. A reduction in both platelet-associated IgG (median reduction of 11.8 ng/10(6) platelets, P = 0.08) and IgM (7.6 ng/10(6) platelets, P = 0.06) was recorded.