C3 is rapidly inactivated after binding to transfused incompatible KEL RBCs. (A) Total C3 bound to circulating KEL2 RBCs in animals passively transferred with polyclonal anti-KEL (black bars, solid histograms) or saline (open bars, shaded histograms); representative plots are shown. (B) Active forms of C3 (C3/C3b/iC3b) bound to circulating KEL2 RBCs in animals passively transferred with polyclonal anti-KEL (black bars, solid histograms) or saline (open bars, shaded histograms). These data are representative of 3 independent experiments, with 3-5 animals/group/experiment. *P < .05.