Figure 5. Nucleocapsid-specific humoral responses improve the control of SARS-CoV-2 infection.

(A) Experimental approach for evaluating viral control after passive immunization with nucleocapsid-specific sera. (B) Weight loss following infection. (C) Viral loads in lungs as determined by RT-pPCR. (D) Viral loads in lungs as assessed by FFAs. C57BL/6 mice were primed intramuscularly with Ad5-N, and after 3 weeks they were boosted with soluble nucleocapsid (N) protein. Two weeks after the boost, sera from these mice were pooled, and 500 μL of these sera were adoptively transferred into naive K18-hACE2 mice. On the following day, the K18-hACE2 mice were challenged intranasally with 10³ PFU SARS-CoV-2. RNA was harvested from the lungs on post-infection day 4, and viral RNA was quantified. Challenges were performed with a total of 4 mice per group in BSL-3 facilities. P values were calculated using the Mann-Whitney U test. Error bars represent the SEM.