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L. Bredow, S. Mahlenbrey, D. Boehringer, T. Reinhard, J. Schwartzkopff; Host Endothelium on Formerly Rejected Corneal Grafts in the Rat. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2837.
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An intact corneal endothelium is essential for the clarity of a corneal graft. Rejection of the corneal endothelium and decrease of mean endothelial cell density below the critical value of 500 cells/ mm2 coincides with graft failure. It is imperative to understand mechanisms of endothelial cell survival on a corneal allograft. Endothelial cells were therefore analyzed following allogenic keratoplasty or following syngenic keratoplasty with prior removal of endothelium in the rat.
Corneal grafts were performed allogenically between Fisher donor and GFP+ Lewis recipient rats (group1), or were transplanted syngenically after mechanical removal of corneal endothelium using GFP+ Lewis recipient rats and negative littermates as donors (group2). Grafts were followed clinically for up to 1 year following keratoplasty. Rejection was defined as complete graft opacity. Endothelial cells were stained on corneal whole mount preparations by Alizarin red and DAPI, and analyzed for GPF-positivity by confocal microscopy. Additionally, corneas were stained for T cell and macrophage infiltration.
Median day of allograft rejection (group 1) was day 17. Contrary to allografts, syngenic grafts denuded of endothelium (group 2) did not reach complete graft opacity. Within 6 weeks all grafts had begun to restore clarity. At this time point, a polymorphic endothelium could be stained on all formerly rejected allografts as well as on all syngenic grafts following endothelial abrasion. These cells proved to be GFP+ in both groups. Allografts showed a dense cellular infiltrate at the time of rejection. After one year, the immunological infiltration had decreased dramatically.
In our rat model, an allogenic keratoplasty leads to rejection with complete graft opacity followed by restoration of graft clarity in the following weeks. As opposed to this, removal of the endothelium on a syngenic graft does not cause complete opacification which is due to the missing allogenic immune reaction. Both allogenic rejected and syngenic de-endothelialized corneal grafts become re-endothelialized by recipients’ endothelial cells.
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