Fig 1: Smad2/3 level in A549 cells of all groups. C: control group without treatment; G: TGF-β inhibitor added group; P: PM2.5 added group; PG: PM2.5 and TGF-β inhibitor simultaneously added group. (a,b) Smad2 gene and protein expression did not change significantly after PM2.5 exposure. (c,d) PM2.5 induced up-regulation of Smad3 gene and reversed protein expression after TGF-β inhibitor treatment. *: p < 0.05; **: p < 0.01; ***: p < 0.001.