Glycoprotein IIb/IIIa autoantigenic repertoire in chronic idiopathic thrombocytopenic purpura

The objective of the present study was to further disclose the autoantigenic repertoire carried by the platelet glycoprotein (GP) IIb/IIIa complex. IgG-F(ab')2 fragments were prepared from two prototype ITP patients, and their ability to block the binding of GPIIb/IIIa reactive antibodies derived from other patients with ITP was evaluated using a modified MAIPA asay; a PlA1 alloantiserum and 20 normal sera were included as controls. It was found that the two prototype IgG-F(ab')2 fragments were each able to significantly block the binding of serum IgG to GPIIb/IIa in six (55%) and seven (64%) out of 11 patients with chronic ITP, respectively. No significant blocking effect was observed for IgG-F(ab')2 fragments prepared from normal subjects. Also, the binding of the PlA1 alloantiserum to its epitope on GPIIIa was not affected by any of the blocking IgG-F(ab')2 fragments exploited in the study. These data substantiate that in chronic ITP at least half of the GPIIb/IIIa reactive sera bind to homogenous autoepitopes.