IgG from thrombocytopenic subjects binds to TPO and neutralizes its biological activity.

(A) rHuTPO (lanes 2,4,6) and PEG-rHuMGDF (lanes 1,3,5) were subjected to native PAGE (10% Tris-glycine, pH 8.3, without SDS, heat denaturation, or reduction) and blotted with IgG from subject no. 3 (lanes 1,2), IgG from a control subject (lanes 3,4), or a polyclonal goat antibody to TPO (lanes 5,6). (B) BaF3-mpl cells were grown in the presence of varying concentrations of IL-3 (gray bars), rHuTPO (black bars), or PEG-rHuMGDF (white bars) in the absence (−) or presence (+) of IgG from subjects no. 1 or 3 and the effect on cell growth measured.