IgG opsonization of RBCs induces phagocytosis by neutrophils and monocytes. (A) Percentages of cell types in the spleen (n = 9). (B) RBCs were unopsonized (unops), anti-RhD-opsonized, or anti-GPA-opsonized. Splenocytes and RBCs were incubated for an hour and the phagocytic fraction was obtained using MACS. The absolute numbers of phagocytes are shown. Anti-GPA opsonization causes a drastic increase of phagocytosis. (C) The absolute number of splenocytes that take up RBCs per cell type. Neutrophils are the primary phagocytes in case of anti-GPA opsonization (n = 5-12). ns, nonsignificant difference.