HUVEC morphogenesis on Matrigel. Cells (2 × 10⁵) were plated per 1.25 cm² well precoated with Matrigel and grown for 6 hours (A) in the specific medium alone (positive control) or containing (B) VBL 0.5 pmol/L, (C) 1 pmol/L, or (D) in the medium without FCS (negative control). Sub (A), cells arranged in branching, reciprocally anastomosing tubes forming a closely knit capillary-like plexus; sub (B) and (C), progressive alterations of the plexus parallel with increasing VBL dose. Bar = 30 μm from (A) to (D).