Effect of S100A9 recombinant protein on invasion and migration of gastric cancer cell lines. In transwell assay, AGS (A) and BGC-823 (C) cells were treated with serum-free medium or medium containing 10, 20, 50 or 100 ng/ml S100A9 recombinant protein. Invasive cells were counted in randomly nine selected microscopic fields (200×). In wound healing assay, AGS (B) and BGC-823 (D) cells were treated with serum-free RPMI-1640 medium or medium containing 100 ng/ml S100A9 recombinant protein. Photos were captured by an inverted phase-contrast microscope at 0 h, 24 h and 48 h after wounding. Three independent experiments were performed. Results were presented as means ± S.D. of these independent experiments. P value vs. control group.