Blut (1985) 50:1-10 Blur © Springer-Verlag 1985 Original Articles Transient Deficiency of Peripheral Blood Accessory Cells in Supporting T Cell Mitogenesis in Patients Suffering from Chronic Idiopathic Thrombocytopenic Purpura after intravenous Gammagiobulin Treatment* L.M. Larocca 1, N. Maggiano 2, G. Leone 1, M. Piantelli 2, D. Scribano 1, and E Musiani z 1 Division of Haematology, Department of Internal Medicine, and 2 Department of Pathology, Universita' Cattolica, Largo Gemelli 8, 00168 Rome, Italy Summary. Mitogenic response of blood lymphocytes to phytohemagglutinin (PHA) and to OKT 3 monoclonal antibodies was investigated in 7 patients suffer- ing from chronic idiopathic thrombocytopenic purpura (ITP) before, during and after high-dose intravenous (i. v.) immunogammaglobulin (IgG) infusion. The pla- telet count rose above the pre-treatment values during infusion therapy in all pa- tients but one. Five out of seven patients presented elevated platelet-associated IgG (PA-IgG) levels at the time of the first infusion; four of these showed an increase in platelet count and a transient reduction or normalization of PA-IgG after IgG infusion. Five out of seven patients showed an impairement of T lymphocyte mito- genic response to PHA and OKT 3 before therapy. All patients responded to IgG therapy with a transient deficiency of FcR mediated monocytes (Mo) in supporting T cell mitogenesis induced by both mitogens during and after IgG infusion. This reduced cooperative capability of Mo disappeared at various times after the end of therapy (range 3-12 days). The transient alteration of Mo function, possibly due to a modification in the surface number or in the affinity of Fc-receptors, can explain in part, the increase in platelet count during and after IgSRK infusion. Key words: Chronic idiopathic thrombocytopenic purpura - High dose i.v. IgG therapy - OKT 3 monoclonal antibody - OKT 3 lymphocyte mitogenesis The term chronic Idiopathic Thrombocytopenic Purpura (ITP) usually refers to instances of thrombocytopenia, with a duration of at least 6 months, accompanied * This work was supported by grants of the CNR (Progetto Finalizzato: Ematologia; Progetto Finalizzato: Trapianto d'Organo) Offprint request to: G. Leone, Istituto di Semeiotica Medica, Universita' Cattolica S. Cuore, Largo Agostino Gemelli, 8, 00168 Rome, Italy