A murine model of severe immune thrombocytopenia is induced by antibody- and CD8+ T cell–mediated responses that are differentially sensitive to therapy

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AbstractImmune thrombocytopenia (ITP) is a bleeding disorder characterized by antibody-opsonized platelets being prematurely destroyed in the spleen, although some patients with ITP may have a cell-mediated form of thrombocytopenia. Although several animal models of ITP have been developed, few mimic primary chronic ITP nor have any shown cell-mediated platelet destruction. To create this type of model, splenocytes from CD61 knockout mice immunized against CD61+ platelets were transferred into severe combined immunodeficient (SCID) (CD61+) mouse recipients, and their platelet counts and phenotypes were observed. As few as 5 × 104 splenocytes induced a significant thrombocytopenia and bleeding mortality (80%) in recipients within 3 weeks after transfer. Depletion of lymphocyte subsets before transfer showed that the splenocyte's ability to induce thrombocytopenia and bleeding completely depended on CD4+ T helper cells and that both CD19+ B cell (antibody)– and CD8+ T cell (cell)–mediated effector mechanisms were responsible. Treatment of the SCID mouse recipients with intravenous γ-globulins raised platelet counts and completely prevented bleeding mortality induced by antibody-mediated effector mechanisms but did not affect cell-mediated disease. This novel model not only shows both antibody- and cell-mediated ITP and bleeding but also suggests that these 2 effector mechanisms have a differential response to therapy.