title: Increased circulating Ia-positive T cells in patients with idiopathic thrombocytopenic purpura.
abstract: Peripheral blood T cells from 40 patients with idiopathic thrombocytopenic purpura (ITP) were analysed for the presence of surface Ia antigens using monoclonal antibodies by indirect immunofluorescence. The percentage of Ia-positive (Ia+) T cells was significantly increased in patients with ITP (6.8 +/- 2.9%, P less than 0.005) as compared with normal controls (2.3 +/- 0.9%). There was an inverse correlation between the percentages of Ia+ T cells and platelet counts (r = 0.58, P less than 0.005) and a positive correlation between the percentage of these cells and platelet-associated IgG (PAIgG) values (r = 0.55, P less than 0.01). The percentage of Ia+ T cells was found to decrease within two weeks during therapy with high dose gamma-globulin or corticosteroid. We have previously reported the presence of T cells bearing both helper/inducer (H/I) and suppressor/cytotoxic (S/C) phenotypes (double labelled cells, DLC) in patients with ITP and an inverse correlation between the percentages of DLC and their platelet counts. In the present study, we showed that a major part of Ia+ T cells had both H/I and S/C phenotypes. We also examined the correlation between Ia+ T cells and autologous mixed lymphocyte reaction (AMLR). A defective AMLR was demonstrated in patients with ITP. Furthermore, an inverse correlation was found between the percentages of Ia+ T cells and the proliferative responses to AMLR (r = -0.49, P less than 0.01). These results suggest that increased circulating Ia+ T cells play a role in the abnormalities of the immunoregulatory system of ITP, especially in the regulation of autoantibody production.
mesh_terms: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface / Q000032:analysis; D003601:Cytotoxicity Tests, Immunologic; D000949:Histocompatibility Antigens Class II / Q000032:analysis* / Q000276:immunology*; D007116:Immunization, Passive; D007074:Immunoglobulin G / Q000032:analysis; D007959:Lymphocyte Culture Test, Mixed; D010976:Platelet Count; D011696:Purpura, Thrombocytopenic / Q000276:immunology*; D013601:T-Lymphocytes / Q000032:analysis*
chemical_list: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D000949:Histocompatibility Antigens Class II; D007074:Immunoglobulin G