Flow cytometric analysis of complement activation in vivo by the 34-3C IgM, IgA, and IgG2a variants. Mouse RBC were obtained 24 h after an intraperitoneal injection of 100 μg of 34-3C anti-RBC Ig variants into BALB/c mice and stained with biotinylated goat anti-mouse C3 antibodies followed by PE-conjugated streptavidin. Shaded areas indicate the background staining obtained with untreated BALB/c mice.