IFNL1 and viral infectious disease: Type III interferons (IFN) are the major player of mucosal immunity in the intestines of human and mouse.29 IFN lambda-1 (IFNL1) and IFNL3 were highly induced in human intestinal organoids upon viral infections.21,26 We first determined the sequences of horseshoe bat type III IFNs using RACE PCR.