Figure 4
Immunohistochemistry of capillary-like structures arising from different aortic rings paraffin-embedded after 72 to 96 hours of culture in collagen matrix. a, Cross-section of an aortic ring showing many CD31-positive cells organized into capillary-like channels. These outgrowths appear to arise from a mass of undifferentiated mesenchymal cells at the periphery of the explant. b, Higher magnification of a selected area of the same explant represented in Panel a showing the formation of long and branched channels. c, Capillary-like structures photographed at high magnification showing intense CD34 positivity; surrounding mesenchymal cells are negative. d, Cells of incipient capillary-like channels within a mass of undifferentiated mesenchymal cells are immunoreactive for von Willebrand factor (vWF). e and f, Cross-section of an aortic ring photographed at different magnification showing Flk-1 expression by endothelial cells lining the lumen and by cells organized to form vascular-like channels. In this rare case, the vascular structures seem to originate from the internal layer of endothelial cells. Scale bars: 100 μm (a, e), 50 μm (b, d, f), 25 μm (c).
