Fig. 2
HD-Ad_RBD induces high levels of IgG, IgA and neutralizing antibody. A Experimental scheme. BALB/c mice were immunized with HD-Ad_RBD or HD-Ad via an intranasal route. B Antibody responses after single vaccination with different doses. RBD-specific IgG in sera were measured by ELISA. C, D Antibody responses after prime-boost vaccination with different doses. RBD-specific IgG (C) and IgA (D) in sera were measured by ELISA. E, F Antibody responses detected in BALs. BALs from single (5 × 109) or prime-boost vaccinated (5 × 109 + 5 × 109) mice were collected and RBD-specific IgG (E) and IgA (F) were measured by ELISA. G SARS-CoV-2 neutralizing activity of sera. H Intracellular cytokine (IFN-γ) staining and flow cytometry analysis of CD4+ T cells. Harvested lung cells were stimulated with or without purified RBD (10 μg/ml) for 12 h at 37 °C and subjected to ICS analysis. In all figures, each dot represents an animal. Bars and errors represent the geometric mean with geometric SD. The red dotted lines indicate the limit of detection (LOD) of the assays. Statistical analyses were performed by Mann–Whitney test: *p < 0.05; **p < 0.01; ***p < 0.001