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Cell membrane fusion of chimeric HA. 293T cells were cotransfected with HA and EGFP expression plasmids. The cells were treated with acetyl trypsin and subsequently, with buffers of pH 5.0–7.0. The cells were incubated at 37 °C for 2 h. After fixation with paraformaldehyde, cell nuclei were stained with DAPI. Arrowheads indicate cell fusion. +, cell fusion-positive; −, cell fusion-negative.
