Platelet-derived soluble factors promote EVT migration. (A) Isolated human EVTs were allowed to invade through Matrigel toward human PBMCs or platelets that were cultured on collagen type I. After 12 hours, the EVTs that reached the lower surface were immunostained with cytokeratin 7 antibody (bottom) and counted for quantification using NIH Image 1.61 (top). Scale bars indicate 100 μm. Original magnification × 70. (B) At the end of the invasion assay, the culture medium was harvested from the upper well to evaluate the activity of MMP-2 and MMP-9 by gelatin zymography. (C) Matrigel invasion of isolated human EVTs toward PBMC-conditioned medium (CM) or platelet-CM was assessed by invasion assays.*P < .05; **P < .01.