HSS1 inhibits HUVEC tube formation in a concentration-related manner. HUVEC growing on top of matrigel were treated with different concentrations of purified hHSS1 or vehicle control (PBS). Cells were pre-treated with hHSS1-His protein or vehicle control for 3 h before plating on top of matrigel. After 8 h, cells were stained with crystal violet and tube formation was evaluated. Images (100x, magnification) are representative of two independent experiments done in duplicate. A and C) Inhibitory effect of purified hHSS1-His on tube formation using 500 nM and 200 nM of hHSS1 protein, respectively. B and D) Vehicle control was diluted following the protein dilution scheme.