Cells and Virus
Madin-Darby canine kidney (MDCK) cells were maintained in Dulbecco's modified Eagle medium (DMEM) supplemented with 5% fetal calf serum (FCS). The stock of the IAV A/PR/8/34 (H1N1) was prepared with a plaque purified strain [22] in 10-day-old specific pathogen-free embryonated hens’ eggs. Virus stocks were stored as aliquots of allantoic fluid from infected embryos at −80°C until use. The titer of the virus stock was determined to be 1.78×108 median tissue culture infective dose (TCID50) mL−1. All virus titration experiments were performed in MDCK cells.