Percent starting weight of 10–12-week-old female Ces1c−/− hDPP4 mice infected with 5E + 04 pfu MERS M35C4 and treated with a subcutaneous vehicle for RDV (N = 13) or remdesivir (RDV, 25 mg/kg, N = 14) BID beginning 1 dpi or b vehicle for LPV/RTV-IFNb (N = 15), LPV/RTV-IFNb low (N = 16) or LPV/RTV-IFNb high (N = 16) beginning 1 dpi. Oral vehicle or lopinavir/ritonavir (160/40 mg/kg) was administered orally once daily. IFNb low (1x human equivalent dose of 1.6 MIU/kg) and high (25x human equivalent dose of 40 MIU/kg) or PBS vehicle were administered via subcutaneous injection every other day. Asterisks indicate statistical differences by two-way ANOVA with Tukey’s multiple comparison test. c Lung hemorrhage 6 dpi for all animals in a, b scored on a scale of 0–4, where 0 is a normal pink healthy lung and 4 is a diffusely discolored dark red lung. d MERS-CoV lung titer 6 dpi in mice as described in a, b. Asterisks indicate statistical significance (N group described in a and b, P < 0.05) by one-way ANOVA with Kruskal–Wallis test for (c, d). Data for a–d are compiled from two independent experiments. For the box and whisker plots, the boxes encompass the 25th to 75th percentile, the line is at the median, while the whiskers represent the range. e Representative photomicrographs of MERS-CoV antigen (brown) and hematoxylin stained nuclei (blue) in mouse lung tissue sections from 6 dpi. The black bar is 100 µM.