BTN3A1 and infection: Further functional experiments validated that overexpression of BTN3A1 and BTN3A3 in A549 cells can effectively suppress H1N1 avian strain infection, while BTN3A3 but not BTN3A1 silencing promotes the infection of the Mallard‐IAV strain, indicating that BTN3A3 plays a more important role in restricting avian IAV replication than BTN3A1.