Increased circulating Ia-positive T cells in patients with idiopathic thrombocytopenic purpura.

Peripheral blood T cells from 40 patients with idiopathic thrombocytopenic purpura (ITP) were analysed for the presence of surface la antigens using monoclonal antibodies by indirect immunofluorescence. The percentage of la-positive (Ia &plus;) T cells was significantly increased in patients with ITP (6.8±2.9%. P<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<0.005)and a positive correlation between the percentage of these cells and platelet-associated IgG (PAIgG) values (r = 0.55, P<0.01), The percentage of la+ T cells was found to decrease within two weeks during therapy with high dose γ - 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. DI.C) 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 lyniphocyle reaction (AMLR). A defective AMLR was demonstrated in patients with ITP. Furthermore, an inverse correlation was found between the percentages of la+ T cells and the proliferative responses to AMLR (r= --0.49, P< 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. [ABSTRACT FROM AUTHOR]