The severity and clinical course of idiopathic thrombocytopenic purpura (ITP) vary from patient to patient. The factors responsible for this variation are not well understood. In this study we attempted to evaluate the role of antiidiotypic antibodies in the immunoregulation of the disease. We investigated 114 cases of chronic ITP in adults. We determined antiidiotypic antibodies against antiplatelet antibodies using (a) idiotype-binding enzyme-linked immunosorbent assay (ELISA), (b) paratope-blocking ELISA, and (c) Western blotting. Results indicated that 80.6%, 11.2%, and 8.3% of the patients, respectively, presented with antiidiotypes against antibodies to GPIIb/IIIa, GPIb/IX, and both GPIIb/IIIa and GPIb/IX. More than 70% of the patients who showed high levels of blocking of antiidiotypic antibodies went into complete remission, compared with less than 5% of patients who showed low levels of such antibodies (P < .01). Disease severity was also found to be inversely related (P < 0.01) to the degree of blocking of antiidiotypic antibodies. The results of this study suggest that antiidiotypic antibodies against antiplatelet antibodies are a potential prognostic marker in chronic ITP.
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