This study aims to determine the hemato-immunological parameters predictive of the evolution of a Immune thrombocytopenic purpura (ITP) towards chronicity, and to identify possible differences between the child and the adult.

Immune thrombocytopenic purpura (ITP) is a rare autoimmune thrombocytopenia whose incidence is 2 to 5 cases / 100,000 inhabitants / year. The potentially serious haemorrhagic risk is the major issue of management. A recent international consensus conference classifies PTI according to the duration of thrombocytopenia: acute ITP (<3 months), persistent ITP (3-12 months) and chronic ITP (> 12 months) (Rodeghiero 2009). In the acute or persistent phase, polyvalent immunoglobulins (IVIG) and / or corticosteroids are proposed. In the chronic phase, splenectomy is a possible cure for 70% of patients. No predictor of treatment response is known.

The pathophysiology of ITP is multifactorial: platelet phagocytosis, mediated by autoantibody, macrophages of the reticuloendothelial system, and destruction in the spleen, genetic background and / or environmental factor favoring the role of certain lymphocyte subpopulations, cytotoxic or regulatory T, via their cytokine environment, abnormalities of thrombopoiesis.

ITP affects children as well as adults, but the evolutionary profile is very different. In children, ITP, which is often post-infectious, is acute in 80% of cases, whereas ITP in adults has a chronic evolution in 80% of cases. The primary diagnostic and therapeutic practices are similar. The reasons for these evolutionary differences are not known and little studied.

Is the orientation of the hemato-immunological response observed during the first episode of ITP different in children and adults? Do these differences explain the evolutionary specificities of the two age groups? Are there hematologic parameters predictive of a response to initial treatments?

Inclusion Criteria:

• Minor patients aged 2 to 18 recruited at the Children's Hospital, in the service of Prof. Y. PEREL, Dr. N. ALADJIDI, CEREVANCE,
• Adult patients (> 18 years old) recruited at the Haut-Lévêque hospital, Pr JL PELLEGRIN, Pr JF VIALLARD, GECAI,
• Patient with acute Immune thrombocytopenic purpura, seen at initial diagnosis or within 8 days (defined as thrombocytopenia <100 G / L, after an infectious cause, drug or related to autoimmune disease, hematological malignancy or deficit Immune have been eliminated, Rodeghiero criteria, 2009).
• Patient who received immunoglobulins more than 4 weeks before inclusion
• Written consent given by the patient, if he is of age, or by the person (s) having parental authority
• Patient affiliated or beneficiary of a social security scheme

Exclusion Criteria:

• Patient who has received specific treatment from an Immune thrombocytopenic purpura
• Patient with secondary Immune thrombocytopenic purpura (hematological malignancy, autoimmune disease, immunodeficiency, pregnancy)
• Patient placed under the protection of justice