(A) For all 244 patients, monoclonal (mc) IgGs were purified as previously reported (12, 13, 15). (B) The purity of mc IgGs was verified using isoelectric focusing and immunoblotting; 3 examples (patients P16, P63, and P205) are shown. For certain patients, purified mc IgG (C) and polyclonal IgGs (D) were also studied by mass spectrometry. Only one IgG3 isotype (red circle) was observed in the mc IgG, while the polyclonal IgGs contained 3 isotypes: IgG1 (green circle), IgG2 (blue circle), and IgG3 (red circle), demonstrating the high purity of the mc IgG. The different peaks observed for each isotype correspond to the cumulative mass of the different hexoses carried by the IgG Fc fragment. Experiments were repeated twice.