IFN-I increases erythrophagocytosis of low-level alloantibody sensitized RBCs in SCD. (A) Mean fluorescence intensity (MFI) of CD64 on purified CD14⁺ monocytes from HD (n = 14) and SCD (n = 7) after overnight culture with media or IFN-α (1000 IU/mL). (B) Percentage of CFSE⁺ monocytes in cultures of purified monocytes from HD (n = 10) and SCD (n = 9) following overnight co-incubation with CFSE-stained RhD⁺ RBCs coated using serially diluted anti-D antibody (from 4 to 0.06 and 0 µL in 100 µL staining buffer). (C) Percentage of CFSE⁺ monocytes in cultures of purified monocytes from HD (n = 10) and SCD (n = 9) as in panel B using low-dose anti-D antibody (0.25 µL in 100 µL staining buffer) in the absence (media alone) or presence of IFN-α (1000 IU/mL). (D) MFI of CD64 in liver CMo, Ly-6C⁺MHC-II⁺ monocyte, Tim-4⁻ MoMⲫ, and Tim-4⁺ Mⲫ of WT mice and ifnar1^−/− mice at 20 hours after IV injection with PBS as control (200 µL/20 g body weight) or hemin (35 µmol/kg body weight) (n = 4-5). (E) Survival of transfused CFSE-labeled RBCs from hGPA-Tg mice at 1 day in recipient WT and ifnar1^−/− mice treated with anti-hGPA antibody (0.75 µg/20 g body weight, 1 hour after RBC transfusion) or isotype IgG as control, after pretreatment with hemin (35 µmol/kg body weight, 1 day before RBC transfusion) or PBS as control. (F) MFI of CD64 in liver CMo, Ly-6C⁺MHC-II⁺ monocyte, Tim-4⁻ MoMⲫ, and Tim-4⁺ Mⲫ of control and sickle treated with anti-IFNAR1 antibody (2 mg/20 g body weight for 3 consecutive days) or isotype IgG as control (n = 3). (G) Survival of transfused CFSE-labeled hGPA RBCs in mice as shown in panel F at 1 day after receiving transfused RBC and anti-hGPA antibody (0.75 µg/20 g body weight), or isotype IgG as control (n = 5-6). Data represent mean ± SEM; means were compared using 2-tailed Student t test. *P < .05.