Anti-TPO IgG prevents TPO from binding to its receptor and is directed toward epitopes in the first 163 amino acids of TPO.
(A) 125I-rHuTPO was added to normal platelet-rich plasma and incubated without (−) or with various dilutions of citrated plasma from subject no. 3. The amount (± SD) of platelet-associated (circles) and IgG-associated (triangles) 125I-rHuTPO was then determined as described in “Materials and methods.” (B) IgG subtypes of antibody to TPO. Serum from subject no. 3 (gray bars) or a healthy subject (black bars) was incubated with 125I-rHuTPO followed by addition of IgG subtype-specific antisera and immunoprecipitation. IgG subtype-specific sera was omitted from the control (“C”) lane. (C) PEG-rHuMGDF and rHuTPO compete equally for binding to anti-TPO antibody. Plasma from subject no. 3 was incubated with 125I-rHuTPO in the absence or presence of various concentrations of unlabeled rHuTPO (circles) or PEG-rHuMGDF (triangles) and the amount of 125I-rHuTPO present in the immunoprecipitate measured.
