Decreased secretion of GM-CSF in SARS-CoV-3CLpro transfected cells. A549 cells were transfected with EGFP or 3CLpro or C145A plasmids. The supernatants were collected from cell cultures at 6, 12, 24, 48 and 72 hrs and ELISA was performed to evaluate the amount of secreted GM-CSF. The supernatant from the cell culture of A549 cells was used as a control. A significant decrease of GM-CSF was observed in 3CLpro or C145A transfected A549 cells (p = 0.0204 and 0.0236 respectively).