Fig 4.

JEV 2′-O MTase mutant is immunogenic and protective in mice. Mice immunized with 1 × 10⁴ PFU of E218A or in the control group were bled at 14 and 28 days postimmunization. The titers of IgG antibody (A) and neutralization antibody (B) were determined by IFA and PRNT, respectively. JEV-specific cellular immune response induced by E218A virus immunization was assayed by splenocyte proliferation assay (C) and IFN-γ production assay (D). On day 28 postimmunization, the spleens from immunized mice of various experimental groups were separated and the proliferation was tested in the presence of inactivated JEV or the positive control ConA. The culture supernatants were collected after 72 h of stimulation with inactivated JEV and ConA for IFN-γ assay. Challenge experiments were performed with JEV strains SA14 and SX-06 (E). Groups of mice (n = 10) immunized with E218A virus or PBS were challenged with 1 × 10⁸ PFU of SA14 and SX-06. The mortality was recorded daily, and the survival curve from each group was analyzed by Kaplan-Meier survival analysis with log-rank tests.