To explore the signal mechanism of S100A8 and/or A9-induced endothelial dysfunction, the phosphorylation of three MAPK subtypes, p38, ERK1/2, and JNK was determined by Western blot after HUVECs were treated with S100A8, S100A9 or S100A8/A9 in a dose of 2.0 μg/mL for 10, 30, 60 and 120 min, respectively. Here, S100A9 is linked to endothelial dysfunction.