Fig. 9
Extracellular galectin-3 enhances influenza virus infection. a–c A549 cells (4.2 × 105) cultured in 6-well plates overnight were infected with IAV at an MOI of 1 at 37 °C for 1 h (at − 1 to 0 h). The cells were then washed with PBS for three times to remove the residual viruses and replenished with fresh serum-free DMEM containing 1 µg/ml of TPCK-trypsin at 37 °C. Human recombinant galectin-3 proteins (0.12, 0.25, 0.5, 1, and 2 µg/ml) were present throughout the whole 10-h duration of the experiment (1 h before infection, during 1 h-infection, and after infection for 8 h). Treatment schedule (a) as well as detection (b) and quantification (c) of the viral NS1 protein by immunoblotting at the end of the experiment. d–f A549 cells were infected with IAV as described in a–c and treated with 2 µg/ml of human recombinant galectin-3 proteins at − 2 to − 1, − 1 to 0, 0 to 2, 2 to 4, 4 to 6, 6 to 8 h, or during the whole duration (− 2 to 8 h). Treatment schedule of galectin-3 in the time-of-addition experiment (d) as well as detection (e) and quantification (f) of the viral NS1 protein by immunoblotting at the end of the experiment. Expression of β-actin served as the loading control. Values shown are mean ± SD (n = 3). Ratios of cells without galectin-3 treatment were arbitrarily set to 1