Fig. 1.

The heterogeneity of mouse response to influenza infection is closely associated with the gut microbiota. a, b SPF C57BL/6 mice were intranasally infected with a LD₅₀ dose of the virulent H7N9 virus strain GX (n = 30, 50 μL/mouse), the same dose of the attenuated H7N9 virus strain HB (n = 10, 50 μL/mouse), or were administered an equal volume of PBS (NC group) (n = 10, 50 μL/mouse). a Mouse survival rate. b Mouse weight loss. Based on survivability, the GX-infected mice were divided into a group that survived the infection (GX.SG) and a group that succumbed to the infection (GX.DG). The data are presented as the mean ± SD. c H&E staining of the mouse lung. The mice were sacrificed on day 10 post-infection of another repeat experiment, and the lungs were collected. The mice in the GX group that succumbed to the infection comprised the GX.DG group (n = 3), and the mice in the GX group that started to show improvement were defined as the GX.SG group (n = 3), as well as the HB group (n = 3) and NC group (n = 3). Representative images are shown. d Experimental setup for FMT experiments. Fecal microbes were collected on days 3 and 9 after GX infection (n = 20) and were divided into the GX.SG (n = 10) and GX.DG (n = 10) groups based on whether the mice from which the samples were collected succumbed to or survived the infection. SPF mice that had been treated with an antibiotic solution (ATB) for 3 days underwent FMT of the fecal microbes, as indicated. One day after FMT, the mice were infected with a LD₅₀ dose of GX. e, f The survival of GX infection by mice after FMT of feces from GX-infected mice obtained on days 3 (e) or 9 (f) after the infection or feces from NC mice; survival of mice administered PBS before GX infection is shown as a control (n = 20 mice per group). Statistics in survival assay were done with the log-rank (Mantel-Cox). All experiments were performed at least twice under similar conditions and yielded similar results