The Epithelioma papulosum cyprini (EPC) cell line (ATCC CRL-2872, Pimephales promelas), was grown in Leibovitz’s L-15 medium (Gibco) supplemented with 10% fetal bovine serum (FBS, Eurobio) and penicillin (100 U/mL)-streptomycin (100 μg/mL) (BioValley). The EPC-EC cell line (described below) and its derivatives were grown in L-15 medium supplemented with 10% FBS, penicillin (100 U/mL)-streptomycin (100 μg/mL), 500 μg/mL G418 (Invivogen), 30 μg/mL hygromycin B Gold (Invivogen).