An endothelial capillary tube formation assay was used to test the effects of platelet-derived angiostatin. A total of 5 × 10⁴ HUV-EC-C cells were plated out per well, resulting in tube formation. Microscopy of representative experiments: (A) control and (B) vehicle control. Effects of platelet-derived angiostatin and 50 kDa angiostatin standard on capillary tube formation: (C) 3 μg/mL platelet-derived angiostatin, (D) 3 μg/mL 50 kDa angiostatin standard, (E) 0.3 μg/mL platelet-derived angiostatin, and (F) 0.3 μg/mL 50 kDa angiostatin standard. Bar represents 100 μm.