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Jin Zhao, Takayuki Nagasaki; Myeloid cells in Corneal Angiogenesis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3227. doi: https://doi.org/.
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It has been suggested that anastomosis of new vascular network is assisted by residential myeloid cells, but documented evidence seems limited. The aim of this study is to further examine the participation of these cells, in particular macrophages, during pathological corneal angiogenesis by histology.
Four corneal angiogenesis models in the mouse eye were used. 1) suture placement, 2) topical application of ML9 (MLCK inhibitor), 3) Dstncorn1 mouse (spontaneous corneal vascularization model), 4) corneal conjunctivalization following total epithelial removal. Macrophage distribution was determined by whole-mount immunofluorescence with F4/80 or CD11b. Vascular endothelial cells were identified by CD31. 3-D images of vascular junctions as well as spouting tips were reconstructed with 1-µm steps and examined to determine the relationship between vascular endothelial cells and macrophages. Ultra-structural features of vascular network formation were assessed by transmission electron microscopy of 70 nm epoxy resin serial sections.
Some cells in newly formed vascular junctions were found to express both macrophage and endothelial markers, indicating involvement of macrophages in the anastomosis. Some tip cells of vascular sprouts were also positive with both macrophage and endothelial markers, suggesting that macrophages may play a role in capillary sprout growth. Electron microscopy showed an abundance of macrophages and Langerhans cells in the vicinity of blood vessels; some were in direct contact with vascular endothelial cells. Activated and quiescent keratocytes, on the other hand, were generally not in contact with endothelial cells. Polymorphonuclear leukocytes were mostly inside the lumen of vessels; those outside were pyknotic.
Histological observations are consistent with an idea that myeloid cells, those of monocyte/macrophage lineages in particular, play a role in network formation of pathological corneal vasculature by direct interactions with endothelial tip cells of vascular sprouts, possibly becoming part of a blood vessel structure.
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