Figure 3.

Mouse immunization, antibody production, and cellular immune response. (A) C57BL/6 mice were intramuscular immunized with inactivated WT SARS-CoV-2 at days 0 and 14, and intranasally infected with 7 × 10⁴ PFU (WT/Gamma/Zeta) at day 28. Blood serum samples collected at 14 and 28 days after immunization, and 3 days after infection, and used for antibody analysis. Spleen organs collected on day 28 and used for lymphoproliferation assay. Three days after infection, mice were euthanized and the lungs collected for analysis. (B) IgM and IgG antibodies production anti-N and anti-S after 14, and 28 days of initial immunization were detected by indirect ELISA. AUC from immunized mice was normalized with AUC from the same mice before infection. (C) Lymphoproliferation assay was performed with splenocytes from immunized and nonimmunized mice stimulated for 5 days with 10 μg of inactivated viral antigens of WT SARS-CoV-2, Gamma or Zeta viral lineage. Statistical analysis was conducted by one-way ANOVA followed by Tukey’s post hoc test. n.s. = not statistically significant; AUC = area under curve; IgM = immunoglobulin M; IgG = immunoglobulin G.