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A.R. Burns, C.L. Larry, R.A. Bowden, Z. Li, C.W. Smith, M. Petrescu; Neutrophil (PMN) Surface Interactions With Keratocytes During Corneal Wound Healing: A Role for CD18 Integrins . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4362.
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© ARVO (1962-2015); The Authors (2016-present)
Previously, using a mouse model of corneal epithelial injury, we determined that PMN migration and epithelial wound closure were significantly delayed in CD18 –/– mice. Transmission electron microscopy (TEM) revealed that migrating PMNs form close surface associations with keratocytes. While 40% of the surface of wild type PMNs is in close contact with keratocytes, this value decreases to 10% in CD18 –/– mice. While this result seemed to indicate a significant role for CD18 in PMN contact with keratocytes, we sought to determine if anatomic differences within CD18–deficient mice (e.g., diminished keratocyte surface area and enhanced tissue edema) might also be playing a role.
C57BL6 wild type mice and mice deficient in CD18 were anesthetized with Nembutal. Corneal epithelial wounds (2mm diameter) were made with a trephine, leaving the basement membrane intact. Injured corneas were excised at 6 hours (wild type) or 24 hours (CD18 –/–); time points determined previously to have similar levels of emigrated PMNs. Corneas were fixed and prepared for ultrastructural morphometric analysis of keratocyte surface to volume ratios, keratocyte surface and volume densities, and collagen fibril spacing (a measure of tissue edema).
Keratocyte surface to volume ratios were not significantly different between wild type and CD18 –/– mice. However, in CD18–deficient mice, keratocyte surface and volume densities decreased by 30% and 40%, respectively (p<0.05) while collagen fibril spacing increased by 50% (p<0.05).
During PMN migration, CD18 –/– mice have more corneal edema than wild type mice and this contributes to a reduction in keratocyte surface density. However, the observed 30% reduction in keratocyte surface density does not account entirely for the previously observed 75% reduction in PMN surface contact with keratocytes. Collectively, the data suggest that CD18 is an important leukocyte receptor that mediates PMN contact with keratocytes during corneal wound healing.
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