IVIg directly inhibits phagocytosis of IgG-opsonized erythrocytes. (A) Dose-response curve of IVIg inhibiting the phagocytosis of anti-RhD IgG-opsonized erythrocytes by monocyte-derived macrophages cultured with M-CSF (left) and GM-CSF (right). IVIg was added 5 minutes before the start of phagocytosis. Data represent means and standard error of the mean of at least 9 experiments for each concentration. (B) Comparison of the inhibiting effect on phagocytosis when IVIg was added 2 days or 5 minutes before the incubation with erythrocytes. Means and standard error of the mean of at least 3 experiments are shown. P values in this figure were determined using 1-way (A) or 2-way (B) ANOVA.