Anti-CR1/tPA loading does not damage carrier RBCs.⁵¹Cr-labeled RBCs obtained from TgN-hCR1 mice, either naive (▵ and ▨) or loaded with anti-CR1/tPA in vitro (closed symbols), were injected into naive TgN-hCR1 mice. The blood level (inset) was determined at indicated times. The animals were humanely killed 1 hour after injection and the amount of ⁵¹Cr in the organs was measured (n = 5).