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. 2021 Jan 21;9(2):76. doi: 10.3390/vaccines9020076

Figure 3.

Figure 3

Humoral responses to SARS-CoV-2 antigens in immunized BALB/C mice. Mice were immunized intramuscularly with naked mRNA-RBD, complexes of mRNA with conjugate polyglucin:spermidine (mRNA-RBD-PGS or mRNA-GFP-PGS), or saline, three times at 0, 21, and 35 days (10 µg mRNA per mouse). Sera samples were collected on mice 48 days after the first immunization. (A) The SARS-CoV-2 RBD specific IgG antibody titers and (B) the SARS-CoV-2 S specific IgG antibody titers were determined by ELISA. Statistical analysis was performed using GraphPad Prism 6.0 software. Data are presented as mean ± standard error of the mean. Significance was calculated using two-way analysis of variance with multiple comparison tests (n.s., not statistically significant; * p < 0.05, ** p < 0.01, *** p < 0.001). (C) Data of ELISA and virus neutralizing activity of sera from mRNA-RBD-PGS immunized mice. Abscissa axis: 1–6—mouse number. The left ordinate axis is the reciprocal antibody titer obtained by ELISA, the right ordinate axis is the reciprocal value of the neutralizing serum titer: grey bar—anti-RBD specific antibodies, white bar—anti-RBD specific antibodies, black bar—virus-neutralizing antibodies.