Wrapping HUVECs reorganize BM of host vessels. (A) BM (blue, collagen IV staining) morphology is normal around unwrapped host vessels (row 1). On wrapping by HUVECs, the collagen IV is more distant from the host ECs, lying outside the HUVEC layer (row 2). In maturing HUVEC segments, the collagen IV pattern appears more normal (row 3). Whole-mount IHC stain; 20×/0.95NA water objective at 3.0× (row 1), 2.0× (row 2), and 4.0× (row 3) digital zoom; scale bar represents 40 μm, 60 μm, and 25 μm for rows 1, 2, and 3, respectively. (B) Typical spatial distributions of collagen IV relative to the host vessels (red line), HUVECs relative to host vessels (green line), and collagen IV relative to HUVEC vessels (blue line) for the areas within the white boxes in the “Merged” panels in panel A. (C) Quantification showing that the collagen IV is closer to normal host vessels than those that are wrapped. **P < .0001.