MX1 and infection: Similarly, when we applied 104 PFU of the H7N7 influenza A virus strain SC35M intranasally in a standard 40 μl volume, we noted that Mx1-competent animals carrying a defective IFN-λ receptor (Ifnlr1−/−) supported similar virus replication in the lungs on day three post infection, compared with Mx1-competent wild-type (WT) animals.