dr. A. Carrer Clinica Ematologica ASST- Monza IT P

- generated from hematopoietic stem cells - several days for maturation (endomitosis – multinucleated cells, maturation of granules and internal membrane system) - pseudopodes > pro-platelets platelets for each MK platelets each day in normal subjects - MK can increase 10-fold upon demand MK

A hypothetical model showing bone marrow megakaryocytes transitioning (left to right) from the endosteal to vascular niche generating podosome structures in response to ECM and vascular sinusoidal basement membrane. Deborah L. French Blood 2013;121: ©2013 by American Society of Hematology

Mechanism of activation of the TPO receptor by TPO. TPO binds the distal CRM (CRM 1) of the inactive TPO (c-Mpl) receptor and creates an activated receptor that initiates many downstream signal transduction events (see “First-generation thrombopoietic growt... David J. Kuter Blood 2007;109: ©2007 by American Society of Hematology

- produced in the liver - regulated primarily by PLT clearance - c-MPL (TPO receptor) TPO

Hypothetical model of mRNA sorting in megakaryocytes. Robert Flaumenhaft Blood 2011;118: ©2011 by American Society of Hematology

Algorithm for workup of thrombocytopenia based on the observation of the peripheral blood film. Terry Gernsheimer et al. Blood 2013;121:38-47 ©2013 by American Society of Hematology

-Immune thrombocytopenia -4/6 cases/100000/y -F:M ratio 3-4/1 ITP (Immune Thrombocytopenic Purpura)

Incidence of ITP by age group and gender Schoonen WM, et al. Br J Haematol 2009;145(2): Image reproduced from Br J Haematol

Classification of ITP DurationClassification < 3 monthsNewly diagnosed 3 – 12 monthsPersistent > 12 monthsChronic Provan D, et al. Blood 2009;115:

Estimated fraction of the various forms of secondary ITP based on clinical experience of the authors. Douglas B. Cines et al. Blood 2009;113: ©2009 by American Society of Hematology

B-cell tolerance checkpoints and loss of self-tolerance in different forms of secondary ITP. Tolerance pathways are denoted by green dashed lines. Douglas B. Cines et al. Blood 2009;113: ©2009 by American Society of Hematology

- rapid passive induction of acute thrombocytopenia in normal hosts by ITP plasma (not in splenectomized host!) - shortened suvival of In-111 labeled platelets in ITP - response to splenectomy and IgV or IgD (acts by impeding IgG-Fcgamma receptor-mediated clearance) Clues of antibodies role

- class IgG1 - against glicoproteins (GP): llbIIIa and Ib-IX-V - also to cytoplasmic proteins (from PLT destruction) - directed to MK in BM Antibodies

-lack granularity -reduced ploidy -few PLT budding from plasma membrane *alterations due to ab-mediated injury (MK express Gpllbllla) > 2/3 of ITP plasmas suppress MK developement from TPO induced CD34+ progenitors, increase apoptosis and reduce ploidy - evidence for anti c-MPL antibodies in some pts MK in ITP

-CD4+ cells are divided into Thelper and Treg -Treg are usually identified by markers such as CD25, CTLA-4, CD127, and Foxp3 -role: maintaining self-tolerance - in ITP, APCs, Th cells, and B cells play a crucial role in its pathogenesis. Autoreactive Th cells and B cells escape Treg surveillance and thus are allowed to become activated and proliferate Treg cells

Treg suppression of pathogenic immune cells in ITP. (Professional illustration by Marie Dauenheimer.). Beng H. Chong Blood 2010;116: ©2010 by American Society of Hematology

Evolution of antiplatelet antibodies after HP infection. Douglas B. Cines et al. Blood 2009;113: ©2009 by American Society of Hematology

Relationship between tolerance defect(s) and clinical outcome in secondary ITP. The abscissa indicates whether platelets are the sole hematopoietic lineage affected (right) or whether there is often concurrent hemolytic anemia and immune neutropenia (left). Douglas B. Cines et al. Blood 2009;113: ©2009 by American Society of Hematology

How is ITP diagnosed?  There is no standard test for ITP: diagnosis of ITP is usually made by exclusion  Diagnosis involves medical history, complete blood count, peripheral blood smear, and a physical examination  Drug history (including non-prescription drugs) should also be taken  Further tests are often needed to eliminate causes of secondary ITP (e.g. HIV) 1. Cines DB, Bussel JB. Blood 2005;106(7): Cines DB, et al. Blood 2009;113(26): Provan D, et al. Blood 2009;115(2): Stevens W, et al. Neth J Med 2006;64(10):

Recommended diagnostic approaches for ITP Provan D, et al. Blood 2009;115(2):

Bromberg ME. N Engl J Med 2006;355: Approaches to the Treatment of ITP.

Treating ITP  Several ITP treatment guidelines exist, primarily based on expert opinion due to the lack of randomised controlled trials  Treatment choices are highly individualised and are affected by factors such as:  Therapy tolerance  Lifestyle  Comorbidities  Patients with platelet counts > 50 x 10 9/L generally do not require treatment  Patients with platelet counts < 50 x 109/L may require treatment depending on the symptoms they present and bleeding risk Pts with PLT counts < 20K, always requires treatment 1. Provan D, et al. Blood 2009;115(2): British Committee for Standards in Haematology General Haematology Task Force. Br J Haematol 2003;120(4): Neunert C, et al. Blood. 2011;117(16):

Deciding who and when to treat Platelet count (x 10 9/L) Treatment > 50No treatment 30 – 50 No treatment, or prednisolone (1 – 1.5 mg/kg/day) for patients at higher risk of haemorrhage (e.g. hypertensive, concomitant medication use, head trauma, etc.) < 30Prednisolone (0.5 – 2 mg/kg/day) Haemorrhage or life-threatening bleed Emergency treatment: Platelet transfusion Intravenous immunoglobulin (IVIg); 1 g/kg/day, 2 – 3 days Methylprednisolone (1 g/day, 3 days) Stasi R. Eur J Haematol 2009;82(Suppl 71):13-19.

Therapies for the treatment of ITP. Drew Provan et al. Blood 2010;115: ©2010 by American Society of Hematology