The miRNA expression patterns in WSN-infected A549 cells at various time points post-infection.

To identify miRNAs that are affected by IAV infection, we adopted a systematic approach, and performed a miRNA microarray analysis using a human alveolar adenocarcinoma cell line, A549, which was infected with a common laboratory strain of influenza A/WSN/33(H1N1) virus (WSN). We compared miRNA expression profiles in A549 cells infected with WSN for 2, 6, and 10 hours at a multiplicity of infection (MOI) of 2. Among 955 miRNAs on the microarray, 209 miRNAs were detected in all three infected A549 samples, but when compared with analysis results from mock-infected A549 cells, most expression changes were less than 1.5-fold , which was consistent with a previous report (Buggele et al., 2013). Therefore, we established 1.5-fold expression change as a threshold to select for miRNAs potentially affected by WSN infection. Further screening revealed 116 miRNAs that underwent 1.5-fold or greater expression changes at any timepoint following WSN infection. The A549 cells were infected with WSN at an MOI of 2 in serum-free MEM medium for 2, 6 and 10 hours.