Binding Form of Platelet-Binding IgG Using Unfixed Platelets in Idiopathic Thrombocytopenic Purpura

We investigated the binding form of platelet-binding IgG (PBIgG) in idiopathic thrombocytopenic purpura (ITP). When fixed platelets were incubated with ITP plasama, the PBIgG value did not change with incubation time, whereas that of unfixed platelets increased with incubation time. On the other hand, with systemic lupus erythematosus (SLE) and leukemia plasma there was no significant difference for fixed or unfixed platelets. Furthermore, when 5 ,uM ADP was added to unfixed platelets prepared in ITP, SLE & Leukemia, or normal plasma, the detected PBIgG value increased slightly compared with that of unstimulated platelets. In ITP plasma, the time-dependent increase of PBIgG in ADP-stimulated platelets tended to higher than that in unstimulated platelets. These results suggest that the timedependent increase of PBIgG is caused by the quantitative increase of antigens for anti-platelet antibodies or the internalization of PBIgG.