Inhibition of complement activation by CR1 derivatives. (A) The amount of hemoglobin released in the plasma of human group A–transfused mice treated without (mock, n = 15) or with different CR1 derivatives (sCR1, n = 9; LHR-A, n = 9; LHR-B, n = 5) was measured at OD 405 at the indicated times after transfusion and was subtracted from the pretransfusion levels. Data are presented as the percentage of hemolysis in the plasma of mock-treated mice at indicated time points after transfusion with the error bars depicting SEM. (B-D) The level of reactivity of anti-C4 (B), anti-C3, using FITC-conjugated anti–mouse C3 (C), and anti-IgG (D), with transfused human group A RBCs at indicated times after transfusion was measured by flow cytometry and is presented in fluorescence intensity units on the y-axis. Mock, n = 15; sCR1, n = 9; LHR-A, n = 9; and LHR-B, n = 5. (E) The level of reactivity of anti-C3, with transfused group O RBCs in fluorescence units. Mock, n = 8; sCR1, n = 8; LHR-A, n = 4; and LHR-B, n = 6.