SR-AI and FX levels in vivo. (A) Citrated plasma was collected from wt or SR-AI–deficient C57BL/6 mice prior or 24 hours after GdCl₃ injection (50 mg/kg). FIX and FX activity were measured (A) and results are expressed in percentage of the normalized mean of wt values. (B-C) C57Bl/6 wt mice were injected in the caudal vein with FX (10 μg per mouse) in the presence of control IgG or polyclonal anti–mSR-AI antibodies (50 μg per mouse; 20 mouse per group). Plasma was collected at various time points (5 minutes, 1 hour, 3 hours, 6 hours, and 24 hours; 4-5 mice per group; 2-3 collections per mouse) and residual FX antigen was measured. Data were fitted to a biexponential decay equation to calculate pharmacokinetic parameters. Shown are the recovery at 5 minutes (B) and MRT (C) for each group. (A-B) Data represent the mean ± SD. (C) Boxes represent mean ± range of the calculated MRT, with the range being obtained from curves plotted with the minimum and maximum SD of residual FX levels. ***P < .001, respectively, in the Mann-Whitney nonparametric unpaired statistical test.