2.5 Determination of IAV titers
Four mice from each group were sacrificed at the time when the virus titers were highest in the lungs. The MDCK cell-based IPMA was used for lung virus titration as described elsewhere(Ding, Jin, Zhou, et al., 2019).Briefly, the lung tissues were homogenized with DMEM to achieve 10% (w/v) suspension and then centrifuged to remove tissue debris. The MDCK cells (5 × 104 cells/well) were infected with 100 µL of 10-fold serially diluted lung homogenate supernatant. After incubation for 1h, supernatants were removed, then fresh DMEM was added. After incubation for 24 h, these cells were fixed, followed by IPMA to determine virus titration. IAV-specific mAbs were used as primary antibodies. The virus titers were measured by TCID50assay using the Reed and Muench method.