Fig. 5

Intranasal boost immunization with DCs targeting nanoparticles stimulated the maturation of CD11b⁺ DCs in the lungs of mice. Plasmids pYL172 and pYL273, which synthesize 3M2e-ferritin or DCpep3-fused 3M2e-ferritin, were constructed, and the expression of M2e was confirmed by non-reducing western blotting, transmission electron microscopy (TEM) and immune electron microscopy (A). The purified DCs targeting/non-targeting nanoparticles from pYL273/pYL272, named N273/N272, were labeled with Flamma 496 NHS (green) and incubated with BMDCs for 16 h. After that, cellular lysosomes and nuclei were stained with LAMP1 antibody (red) and DAPI (blue), respectively (B). An illustration of the animal experiment (Study 2) is shown (C) in which mice were orally immunized with S230 twice, followed by an additional 3rd intranasal boost immunization with N272 or N273. One day after the 3rd intranasal boost immunization, lung DCs were analyzed by flow cytometry to determine the percentages and activation of CD103⁺ (D–F) and CD11b⁺ DCs (G–I). (n = 4, *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001). Notably, two oral immunizations with S230 followed by the 3rd intranasal boost immunization with either N272 or N273 were named S230in and S230inDC, respectively