Figure 5 Supernatants of CD40L‐activated HIF promote in vitro tube formation. Tube formation assays were performed with Matrigel™, as detailed in Materials and Methods. Inverted‐phase contrast microscopy was used to assess the formation of endothelia cell (EC)‐like tube structures. Either vascular endothelial growth factor (VEGF) or soluble CD40 ligand (sCD40L) were used as positive controls for EC formation. Results are representative of three independent experiments. Five high‐power fields per culture condition were examined. Magnification ×40. HIFs, human intestinal fibroblasts; HIMECs, human intestinal microvascular endothelial cells.