Figure 3.

AP205-RBD induced the Th1-oriented immune response

(A) The indicated Ig isotypes of anti-RBD were examined in sera collected after the second immunization. Colors indicate different immunization groups.

(B) The ratio of RBD-specific IgG2a/c titer to IgG1 titer. One-way ANOVA test was used to determine the significant difference among the three groups. Tukey’s multiple comparisons test was then used to compare between the AP205-RBD-immunized group and one of the RBD protein-immunized groups. The adjusted p value was used to indicate the statistical significance (∗∗p < 0.01, ∗∗∗p < 0.001).

(C) Representative data of IFNγ ELISpot assay. Splenocytes from naive mice or mice immunized with the second dose of AP205-RBD or RBD+Alum 5 d previously were examined for IFNγ⁺ cells. 15-mer peptide pools derived from the RBD sequence were used to stimulate the cells in vitro. Pool1 and pool2 contain peptides derived from 420–459 and 511–549 aa of SARS-CoV-2 S protein, respectively. Intact RBD protein was also used for stimulation.

(D) Quantification of the IFNγ⁺ cells as in (C). Symbols indicate data collected from individual mice. Bars indicate the geometric mean of each group. The numbers (n) of mice examined in each group are shown. See also Figure S3.