KRT18 and infection: To ascertain the specific contribution of nucleocapsid-specific antibody, we treated K18-hACE2 mice with a nucleocapsid-specific mAb or an isotype control antibody, and on the next day, mice received a low-dose intranasal SARS-CoV-2 challenge (103 PFU) followed by evaluation of viral loads in lungs on day 7 after infection (Figure 6A).