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Circulating immune complexes (CIC) were frequently observed in patients with idiopathic thrombocytopenic purpura (ITP). To analyse the pathogenic role of CIC, we studied the correlation between the disease activity and the CIC level, and whether platelet antigens were involved in CIC from ITP sera. Elevated CIC levels, measured by C1q. anti-C3 and spermatozoa micro-enzyme-linked immunosorbent assay, were found in 37%, 54% and 52% of the patients, respectively. However, there were no significant correlations (r = -011, -003 and -0.04, respectively) between the platelet count and the CIC level. Platelet antigens in CIC were detected with rabbit anti-human platelet serum. The CIC from 18%, 25% and 25%, respectively, of ITP sera contained platelet antigens, but the CIC from only 3%. 9% and 6% of SLE sera and from 3%, 2% and 5% of the sera of alloimmunized patients, respectively, contained these antigens. There were significant correlations (r = 0.51, 0.80 and 0.65, respectively) between the amount of platelet antigens and the CIC level in ITP sera. However, there were no correlations (r = -0.26, -0.29 and 0-08, respectively) between the platelet count and the amount of platelet antigens in the CIC. We detected platelet antigens in CIC from ITP sera, but surmise that these CIC perhaps do not play an important role in platelet destruction. [ABSTRACT FROM AUTHOR]

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]