Modeling the Early Stages of Autoimmunity Through the Study of Immunological Thrombocytopenic Purpura and Juvenile Lupus

* Inclusion criteria: * For patients : * Child or adolescent with newly diagnosed ITP or SLE according to the specific definitions of ITP or SLE, prior to any treatment, * Over 1 and under 18 years of age at diagnosis, weighing more than 7 kg. * Written consent from parents or guardians, * Patient affiliated to a social security scheme. * For controls : * Over 1 and under 18 years of age at diagnosis, weighing more than 7 kg. * Follow-up in the day hospital at the Bordeaux University Hospital, for a condition that does not affect the immune system * Matched on age, * Written consent from parents or guardians, * Patient affiliated to a social security scheme * Exclusion criteria: * For patients : * ITP secondary to a known cause: previous or concomitant immune deficiency, bone marrow or organ transplantation, other autoimmune disease, Evans syndrome (autoimmune hemolytic anemia or autoimmune neutropenia present at ITP diagnosis) or cancer with immunosuppressive therapy. * Treatment with immunomodulation or immunosuppressants (including immunoglobulins, corticoids, hydroxychloroquine), started prior to inclusion (day of sampling). * Pregnant women, women in labour and breastfeeding women * For controls : * Suffering from an immunological disease, * Infection within fifteen days prior to inclusion, * Immunomodulatory therapy. * Pregnant women, women in labour and breastfeeding women