Figure 4.

Induction of neutralizing antibody and challenge of the immunized mice with cold-adapted attenuated MERS-CoV vaccine strain. K18-hDPP4 mice (n = 13 per group), which were i.n. immunized with 2 × 10⁴ pfu of MERS-CoV vaccine strain (EMC2012-CA 22 °C) were i.n. challenged with 2 × 10⁴ pfu of wild-type MERS-CoV strain (Korean MERS-CoV/2015) at 4 weeks after vaccination. Sera were collected before the challenge and their neutralizing antibody was measured against wild-type MERS-CoV strain (Korean MERS-CoV/2015). The challenged K18-hDPP4 mice were monitored for mortality and body weight change for 14 days. PBS-mock challenged K18-hDPP4 mice (n = 13) were used for the control group. The infected K18-hDPP4 mice (n = 3 per group) were euthanized on day 6 after challenge to measure the viral titration in tissues (nasal turbinate, brain, lung, and kidney). (A) Neutralizing antibody titers in sera; (B) Mouse mortality of challenged K18-hDPP4 mice (%); (C) The change in body weights (%) of challenged K18-hDPP4 mice compared to the body weights before challenge; and (D) Viral titers in terms of log₁₀TCID50/g in tissues (n = 3 per group) in nasal turbinates (0.1 g), brains (0.1 g), lungs (0.1 g), and kidneys (0.1 g) of challenged K18-hDPP4 mice. The viral titers are the mean of 3 tissues ± standard deviation. Dotted line (....): limit of detection. ** p < 0.001.