We determined the prevalence of antibodies to β2 glycoprotein-I (β2GPI) in sera of 57 patients with primary or secondary immune thrombocytopenia positive for platelet antibody (PAIgG) and in 16 healthy control subjects. Both isotypes (IgG and IgM) of anti-β2GPI were detected by means of semiquantitative ELISA and platelet antibodies were measured by means of flow cytometry using FITC-labeled anti-human IgG. Six (10.5%) of 57 patients with immune thrombocytopenia had anti-β2GPI, whereas none of the 16 healthy subjects had anti-β2GPI. Four were positive for IgM anti-β2GPI, one for IgG anti-β2GPI, and one was positive both for IgM and IgG anti-β2GPI. There was no significant association between the presence of anti-β2GPI and the severity of thrombocytopenia. Our findings suggest that some patients with immune thrombocytopenia have anti-β2GPI in addition to the increased PAIgG; however, the results do not support a major role for anti-β2GPI in the pathogenesis of immune thrombocytopenia.
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