Fig. 5: Type I IFN signaling is essential for the induction of protective immunity by the NVT-adjuvanted intranasal influenza vaccine.

a Experimental design. WT (n = 9 per group) and IFNAR1^−/− mice (n = 9 per group) were immunized i.n. with H3N2 + NVT twice at two-week intervals. Two weeks after the last immunization, immune response analysis (n = 4 per group) (b–e) and H1N1 virus (A/Korea/2785/2009) challenge (n = 5 per group) (f) were performed. Schematic image was created in BioRender. Han, S. (2024) BioRender.com/l89f720. b, c HAI antibody titers against H3N2 or H1N1 in (b) serum and (c) nasal washes were determined by HAI assay. An HAI antibody titer of 1:40 (red dotted line) was considered protective against influenza infection. b, c Data are expressed as dot plots, with horizontal lines representing the medians. d, e (d) The lung CD4⁺ T_RM population and (e) CD4⁺ T-cell responses to H1N1 or H3N2 in the lung and spleen were determined by using flow cytometry. Box and whisker plots showing the median (center), 25th and 75th percentiles (box), and lowest and highest values (whiskers). f The vaccinated mice were infected i.n. with 4 LD₅₀ of H1N1 virus, and body weight and survival were monitored daily. Weight-loss data are shown as mean value ± SD. Survival data are represented as Kaplan‒Meier survival curves, and the significant differences in survival rates were calculated by the log-rank test. b–f Statistical analyses were performed using one-way ANOVA with Tukey’s multiple comparisons test or two-sided Mann–Whitney U test. This study was performed independently at least three times, and one representative set is shown. BW, body weight; N.D., not detected; ns, not significant; NT, non-treated. Source data are provided as a Source Data file.