Fig. 1.
Analysis by ELISA of the ferritin reactivity and IgG content of various fractions.
(A) Antiferritin reactivity of IVIG in presence of human serum. Reactivity was measured in ELISA in presence (▧) or absence (●) of a fixed volume of human serum corresponding to a final IgG concentration of 25 μg/mL. (B) Amount of total IgG in PEG precipitates. Quantification of IgG was done by ELISA. (C) Proportion of total biotin-labeled IVIG in PEG precipitates. Biotin-IgG was quantified by ELISA using streptavidin-HRP conjugate and the starting biotin-IVIG solution as standard. (D) Proportion of ferritin-reactive biotin-IVIG in the PEG precipitates. Ferritin reactivity of serial dilutions of the PEG-precipitated fractions was measured by ELISA and detected using a streptavidin-HRP conjugate. One unit of ferritin reactivity was defined as the volume of each fraction, which produced an OD of 0.4.