Cell, Virus, and Viral Infection

293T (American Type Culture Collection (ATCC) CRL-11268), A549 (ATCC CCL-185), MDCK (ATCC CRL-2935), and RAW264.7 (ATCC TIB-71) cells were maintained in Dulbecco's modified Eagle's medium (DMEM) (Gibco-BRL, Gaithersburg, MD, USA), or THP1 (ATCC TIB-202) cells in RPMI1640 (Gibco-BRL, Gaithersburg, MD, USA), containing 10% fetal bovine serum (FBS) (Gibco-BRL, Gaithersburg, MD, USA) supplemented with penicillin (100 U/mL) and streptomycin (100 μg/mL). IAV H1N1 strains including A/WSN/33 (WSN), A/PR/8/34 wild type (PR8) and A/CA/04/09 (CA04) were propagated in specific-pathogen-free (SPF) chicken embryo as previously described (35). For viral infection, cells were infected with virus at the indicated multiplicity of infection (MOI). After adsorption for 45 min at 37°C, the cells were washed with phosphate-buffered saline (PBS) and cultured in DMEM with 2 μg/mL trypsin for indicated time.