The findings from our current study support the conclusions of Monteerarat et al., and we have further extended these to airway epithelial targets of human IAV infection. A combination of these two types of siRNAs might result in broader spectrum synergistic activities, depending upon their targets. Conclusions We demonstrated the in vitro efficacy of siRNAs targeting ST6GAL1 in respiratory epithelial cells for the prevention of IAV infections at the virus entry stage. Further in vivo preclinical testing is required to determine the suitability of these siRNAs for use in humans.

Methods Cells and viruses We used Madin–Darby canine kidney (MDCK) cells for virus propagation and 50% tissue culture-infective dose (TCID50) titration assays. MDCK cells were in minimal essential medium (MEM; Gibco, Carlsbad, CA, USA) supplemented with 10% fetal bovine serum (FBS; learn more Gibco), 100 U/mL penicillin, and 100 μg/mL streptomycin (Gibco) at 37°C/5% CO2. The A549 human lung carcinoma, human bronchial epithelium (HBE), and human laryngeal epidermoid carcinome (HEp-2) cells were used for transfection experiments. These cells were maintained in Dulbecco’s modified

Eagle’s medium (DMEM; Gibco) supplemented with 10% FBS, 100 U/mL penicillin, and 100 μg/mL streptomycin at 37°C 5% CO2. We used a 2009 pandemic influenza A (H1N1) virus (pdmH1N1), strain A/Guangzhou/GIRD07/2009 (GenBank Accession No. HM_014326-HM_014333). A seasonal H3N2 influenza A virus (A/Guangdong/520/2009) was isolated from a patient with influenza-like symptoms. An influenza A H9N2 isolate (A/Chicken/Guangdong/SS/94) was Hedgehog inhibitor Cobimetinib ic50 kindly provided by South China Agricultural University.

The pdmH1N1 and H3N2 viruses were grown in MDCK cells at 35°C, while the H9N2 virus was propagated in allantoic cavities of 10-day-old embryonated hens’ eggs at 37°C. All experiments with pdmH1N1 and H9N2 viruses were conducted under biosecurity level three conditions, and higher. Preparation and transfection of siRNAs The siRNAs against ST6GAL1 were designed using BLOCK-iT™ RNAi Designer [36] and synthesized by Invitrogen ( Invitrogen, Carlsbad, CA, USA). Sequences are available in Additional file 1: Table S1. As a negative control, we used non-targeting Allstars® siRNAs (Qiagen, Valencia, CA, USA). All siRNA duplexes were double-stranded RNA molecules comprising 21 nt with a dTdT overhang at the 3’ ends [37]. Target sequences were subjected to a Basic Local Alignment Search Tool (BLAST) search against GenBank to ensure they were unique to ST6GAL1. Airway epithelial cell lines (A549, HBE, and HEp-2) were transfected with either ST6GAL1 or non-targeting Allstars® siRNAs using Lipofectamine® RNAiMax (Invitrogen) according to the manufacturer’s instructions. At different time points post-transfection, cells were either infected with influenza virus or harvested for downstream experiments.