Fig 6.

To assess the production of cytokines elicited by the two PHE-CoV vaccine candidates, the frequencies of cells producing IL-2, IL-4, TNF-α, and IFN-γ at the single-cell level were determined using an ELISA kit. The levels of all of the cytokines (IL-2, IL-4, TNF-α, and IFN-γ) produced by the immunized mice show significant differences between the five vaccine groups (IP, IPV, S1, 2S1 + IPV, and IPV + 2S1) and the control groups (PBS and pVAX1) (**, P < 0.01). The IPV group produced mainly IL-4 and did so at a higher level than the S1 group (**, P < 0.01). However, the levels of IL-2 and IFN-γ were not obviously different for the IPV and S1 groups (P > 0.05).