IgG dimers are more potent than IgG monomers in inhibiting phagocytosis of IgG-opsonized erythrocytes. (A) High-performance liquid chromatography (HPLC) fractionation of IVIg (top) and IVIg after dimer enrichment by prior HPLC fractionation (bottom). Graphs are representative graphs of at least 4 independent experiments; percentages indicate the average amount of IgG monomers and IgG dimers. (B) Inhibition of phagocytosis by a preparation of IVIg enriched for dimeric IgG by HPLC fractionations compared with normal IVIg, for M-CSF (top) and GM-CSF (bottom). Means and standard error of the mean of at least 8 experiments for each concentration are shown. (C) Representative HPLC graphs of a recombinant human IgG1 (anti-TNF, adalimumab, top), a human monoclonal IgG1 anti-idiotype against adalimumab (anti-adalimumab, middle), and the combination of these 2 MoAbs (adalimumab × anti-adalimumab, bottom) mixed in equimolar amounts, showing the percentages of IgG monomers, dimers, and multimers. Percentages are means of 3 independent experiments. (D) Inhibition of phagocytosis by monoclonal adalimumab and monoclonal anti-adalimumab compared with the combination of these 2 MoAbs. Data represent means and standard error of the mean of at least 8 experiments. P values in this figure: *statistics by 2-way ANOVA, **statistics by Student t-test.