Development of anemia and complement activation in BALB/c mice after the injection of polymeric and monomeric forms of 34-3C IgM or IgA mAb. (A) Ht values of individual mice measured 2 days after intraperitoneal injection of 100 μg of polymeric IgM or IgA (○) or 500 μg of monomeric IgM or IgA (•) mAb are shown. Note significant decreases in Ht values in mice injected with polymeric IgM (P < 0.01) or IgA (P < 0.05) compared with mice receiving monomeric IgM or IgA. Ht values 4 days after injection of monomeric IgM or IgA remained in the normal range. The normal range of Ht values (mean ± 3 SD) of 2- to 3-month-old BALB/c mice is represented as shaded areas. (B) Opsonization of circulating RBC 24 h after intraperitoneal injection of 100 μg of polymeric IgM (pIgM), 500 μg of monomeric IgM (mIgM), 100 μg of polymeric IgA (pIgA), or 500 μg of monomeric IgA (mIgA) mAb is shown. RBC were stained with biotinylated goat anti-mouse C3 or rat anti-mouse k-chain antibody followed by PE-conjugated streptavidin. Shaded areas indicate the background staining obtained with untreated BALB/c mice.