Fig. 6
Post-fusion HA antigen elicits protective serum antibodies against drifted virus. a Native and post-fusion HA antigens were i.p. injected twice at 4-week intervals. Serum were collected at day 14 after boosting, and subjected to ELISA that detects X31 HA- and LAH-binding IgG. Each circle represents the result from an individual mouse. The combined data from two independent experiments are shown. b Immune sera were subjected to a microneutralization assay using H3N2 virus strains (X31 and Guizhou) as challenging viruses. Each circle represents the result from pooled sera (n = 5). c The protective function of the immune sera (blue, native; red, post-fusion HA) and non-immune sera (black, naive) as control were i.p. transferred into the mice, which were then challenged by lethal dose (5 × LD50) of heterogeneous H3N2 (Guizhou) infection. The combined data from two independent experiments (n = 8 per group) are shown. Values represent mean ± s.d. d NOJ mice were reconstituted with human PBMCs and then boosted with native and post-fusion HA antigens (Victoria strain). At day 10 post-vaccination, sera were collected and analyzed for anti-HA and anti-LAH human IgG titers by ELISA. Each circle represents the result from an individual mouse harboring PBMC of single donor. The P-values were determined with a two-tailed Mann–Whitney test (a, b) and log-rank test (c). *P < 0.05; **P < 0.01; ****P < 0.0001. Source data are provided as a Source Data file
