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      Pathogenesis and Therapeutic Mechanisms in Immune Thrombocytopenia (ITP)

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          Abstract

          Immune thrombocytopenia (ITP) is a complex autoimmune disease characterized by low platelet counts. The pathogenesis of ITP remains unclear although both antibody-mediated and/or T cell-mediated platelet destruction are key processes. In addition, impairment of T cells, cytokine imbalances, and the contribution of the bone marrow niche have now been recognized to be important. Treatment strategies are aimed at the restoration of platelet counts compatible with adequate hemostasis rather than achieving physiological platelet counts. The first line treatments focus on the inhibition of autoantibody production and platelet degradation, whereas second-line treatments include immunosuppressive drugs, such as Rituximab, and splenectomy. Finally, third-line treatments aim to stimulate platelet production by megakaryocytes. This review discusses the pathophysiology of ITP and how the different treatment modalities affect the pathogenic mechanisms.

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          Most cited references199

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          International consensus report on the investigation and management of primary immune thrombocytopenia.

          Previously published guidelines for the diagnosis and management of primary immune thrombocytopenia (ITP) require updating largely due to the introduction of new classes of therapeutic agents, and a greater understanding of the disease pathophysiology. However, treatment-related decisions still remain principally dependent on clinical expertise or patient preference rather than high-quality clinical trial evidence. This consensus document aims to report on new data and provide consensus-based recommendations relating to diagnosis and treatment of ITP in adults, in children, and during pregnancy. The inclusion of summary tables within this document, supported by information tables in the online appendices, is intended to aid in clinical decision making.
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            Th22 cells represent a distinct human T cell subset involved in epidermal immunity and remodeling.

            Th subsets are defined according to their production of lineage-indicating cytokines and functions. In this study, we have identified a subset of human Th cells that infiltrates the epidermis in individuals with inflammatory skin disorders and is characterized by the secretion of IL-22 and TNF-alpha, but not IFN-gamma, IL-4, or IL-17. In analogy to the Th17 subset, cells with this cytokine profile have been named the Th22 subset. Th22 clones derived from patients with psoriasis were stable in culture and exhibited a transcriptome profile clearly separate from those of Th1, Th2, and Th17 cells; it included genes encoding proteins involved in tissue remodeling, such as FGFs, and chemokines involved in angiogenesis and fibrosis. Primary human keratinocytes exposed to Th22 supernatants expressed a transcriptome response profile that included genes involved in innate immune pathways and the induction and modulation of adaptive immunity. These proinflammatory Th22 responses were synergistically dependent on IL-22 and TNF-alpha. Furthermore, Th22 supernatants enhanced wound healing in an in vitro injury model, which was exclusively dependent on IL-22. In conclusion, the human Th22 subset may represent a separate T cell subset with a distinct identity with respect to gene expression and function, present within the epidermal layer in inflammatory skin diseases. Future strategies directed against the Th22 subset may be of value in chronic inflammatory skin disorders.
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              Megakaryocytes regulate hematopoietic stem cell quiescence via Cxcl4 secretion

              In the bone marrow (BM), hematopoietic stem cells (HSCs) lodge in specialized microenvironments that tightly control their proliferative state to adapt to the varying needs for replenishment of blood cells while also preventing exhaustion 1 . All putative niche cells suggested thus far have a non-hematopoietic origin 2-8 . Thus, it remains unclear how feedback from mature cells is conveyed to HSCs to adjust proliferation. Here we show that megakaryocytes (Mk) can directly regulate HSC pool size. Three-dimensional whole-mount imaging revealed that endogenous HSCs are frequently located adjacent to Mk in a non-random fashion. Selective in vivo depletion of Mk resulted in specific loss of HSC quiescence and led to a marked expansion of functional HSCs. Gene expression analyses revealed that Mk were the source of chemokine C-X-C motif ligand 4 (Cxcl4, also named platelet factor 4, Pf4) in the BM and Cxcl4 injection reduced HSC numbers via increased quiescence. By contrast, Cxcl4 −/− mice exhibited increased HSC numbers and proliferation. Combined use of whole-mount imaging and computational modelling was highly suggestive of a megakaryocytic niche capable of influencing independently HSC maintenance by regulating quiescence. Thus, these results indicate that a terminally differentiated HSC progeny contributes to niche activity by directly regulating HSC behavior.
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                Author and article information

                Contributors
                Role: Academic Editor
                Journal
                J Clin Med
                J Clin Med
                jcm
                Journal of Clinical Medicine
                MDPI
                2077-0383
                09 February 2017
                February 2017
                : 6
                : 2
                : 16
                Affiliations
                [1 ]Keenan Research Centre for Biomedical Science, St. Michael’s Hospital, Toronto, ON M5B 1W8, Canada; Anne.Zufferey-Bakos@ 123456crchudequebec.ulaval.ca (A.Z.); kapurri@ 123456smh.ca (R.K.)
                [2 ]The Toronto Platelet Immunobiology Group, St. Michael’s Hospital, Toronto, ON M5B 1W8, Canada
                [3 ]Canadian Blood Services, Toronto, ON M5B 1W8, Canada
                [4 ]Department of Pharmacology, Medicine, and Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5B 1W8, Canada
                [5 ]Division of Hematology and Transfusion Medicine, Lund University, 221 84 Lund, Sweden
                Author notes
                [* ]Correspondence: john_w.semple@ 123456med.lu.se ; Tel.: +46-70-3012-2725
                Article
                jcm-06-00016
                10.3390/jcm6020016
                5332920
                28208757
                b3d4ee5a-6245-4ed5-b770-6202f946fece
                © 2017 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 28 December 2016
                : 04 February 2017
                Categories
                Review

                immune thrombocytopenia (itp),autoimmunity,t cells,b cells,platelets

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