Figure 2 Comparison of the effects of route of vaccine administration on IgG and IgA induction.
Mice were immunized twice or thrice by S1-IM, S1-AS03-IM and S1-SF-10-IT every two weeks. At two weeks after the last immunization, serum and BALF samples were collected. ELISA was used to measure the levels of S1-specific IgG in serum (A), IgG in BALF (B), IgA in serum (C) and S-IgA in BALF (D). Data represent S1-specific antibody titer of individual mice (open rhombus) and their geometric mean (solid rhombus) (n = 6 mice per group). Inhibition abilities of Spike/ACE2 binding of serum (E, G) and BALF (F, H) were measured by a colorimetric assay using ACE2 Inhibitor Screening Colorimetric Assay Kit. The serum and BALF samples were diluted serially 2-fold at 1/100 to 1/3200 and 1/2 to 1/64, respectively. The formula used to calculate the binding inhibition (BI) (%) was described in Materials and Methods. Each bar represents the geometric mean ± SEM of BI (%) of each dilution point samples of S1-IM (open bars), S1-AS03-IM (grey bars) and S1-SF-10-IT (closed bars), (n = 6 mice per group). Differences between same-time immunization groups or same serum and BALF dilution groups were analyzed by the non-parametric Mann–Whitney U-test. *P <0.05,**P <0.01 vs S1-IM,P <0.05,††P <0.01 vs. S1-AS03-IM.