supplemented with 5% fetal bovine serum (FBS)(Atlanta Biologicals, Lawrenceville, GA), penicillin–streptomycin,and amphotericin B (GIBCO/BRL, Grand Island, NY), at 37◦C with5% CO2. All the viruses were propagated in MDCK cells cultured inOpti-MEM medium (GIBCO/BRL, Grand Island, NY) supplementedwith 1 g/ml TPCK-Trypsin (Sigma–Aldrich, St. Louis, MO) at 37◦Cwith 5% CO2