Sialic acid receptors on progenitor epithelial cells were detected by flowcytometry [57] . Madin-Darby canine kidney (MDCK) cells have been shown to express both a-2,3-linked sialic acid receptors and a-2,6-linked sialic acid receptors; avian and mammalian influenza virus receptors, respectively. Therefore, MDCK cells were included as positive controls. The cells were incubated with FITC-labeled Maackia amurensis lectin II (MAA) or Sambucus niagra agglutinin (SNA) (EY Laboratories) at 4uC for 30 min in dark and acquired by Accuri C6 flow cytometer (BD Accuri) and analyzed using CFlow plus software (Accuri).