Fig 2. Schematics of an invasion assay system.

(A) Boyden transwell invasion assay. Tumor cells were suspended in the upper chamber, while neutrophils or medium alone (control) were placed in the lower chamber. Semipermeable inserts coated with matrigel (extracellular matrix) were inserted in the filter. In response to NE secreted by N2 neutrophils in the lower chamber, tumor cells degrade the heavy extracellular matrix proteolytically and invade the lower chamber. The number of neutrophils on the lower surface of the permeable insert was counted after 22h in the absence and presence of neutrophils in the lower chamber. (B) TGF-β (G), NE (E), NE inhibitor (D), CXCL8 (C), MMP (P), TIMP (M) and tumor cells (n) can cross the semi-permeable membrane, but neither type of neutrophils (N₁, N₂) can cross it. Initially, the tumor cells reside in the upper chamber (domain Ω₊) while neutrophils are placed in the lower chamber (domain Ω₋). An extracellular matrix (ECM) layer (S) surrounds the filter, semi-permeable membrane ($\mathbb{M}$).