Impact of type I IFN signaling during MHV infection. IFNAR^−/− or wt mice were injected intraperitoneally with 5 pfu MHV A59. (A) Health status of IFNAR^−/− and wt mice was monitored twice daily after infection (n = 6). (B) ALT values were measured at the indicated time points after infection. (C) Liver pathology in IFNAR^−/− and wt mice before or 48 hours after MHV A59 infection. Hematoxylin-eosin staining of 4% formaldehyde-fixed sections. Images were acquired using a Leica DMRA microscope (Leica, Heerbrugg, Switzerland) with a 25×/0.65 NA objective (total magnification, ×162). Images were processed using Adobe Photoshop (Adobe Systems, San Jose, CA). (D) Viral titers in liver, spleen, brain, and lung of MHV A59–infected IFNAR^−/− or wt mice were determined at different time points after infection. Results represent the mean of 6 individual mice per time point. Solid horizontal lines in panel D represent limit of detection in the plaque assay. Data in panels B and D represent means ± SD from 2 experiments with a total of 3 or 6 mice evaluated per time point. Statistical analysis was performed using Student t test (ns, P > .05; *P < .05; **P < .01; ***P < .001).