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Stefan Kremers, Simona L Schlereth, Falk Schroedl, Claus Cursiefen, Ludwig M Heindl; Characterization of Antigen-presenting Macrophages in the healthy Human Sclera. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The sclera, a dense and physiologically poorly vascularized collagenous connective tissue, is responsible for the shape of the eye and the maintenance of intraocular pressure. As only little is known about scleral immunological features, we investigated whether the adult human sclera contains different populations of immune cells.
In this study of healthy human anterior episclera and scleral stroma, specimen of ten donor eyes of both sexes (mean age 63.1 +/- 11.3 years, maximum post-mortem time 24 hours) were immunohistochemically stained in accordance with the Declaration of Helsinki and with approval of the local ethics committee. Scleral samples were examined by confocal microscopy and immunopositive cells quantified regarding the expression of CD45 (leucocytes of bone marrow origin), CD68 and CD11b (macrophages) and major histocompatibility complex class II molecules (MHCII; found on antigen presenting cells, APCs). Further differentiation was feasible using a marker panel of chemokine receptor 7 (CCR7, mediates leukocyte trafficking to lymph nodes), lymphatic endothelium hyaluronan receptor 1 (LYVE1; membrane protein of lymphatic endothelium and a subpopulation of macrophages), C-X-C-motif chemokine 12 (CXCL12; regulates leukocyte functions), CCR2 (indicates artherosclerosis), the glial fibrillary acidic protein (GFAP; astrocyte marker) and Ki67 (proliferation marker).
The healthy human episclera contains high amounts of CD68+ macrophages (mean 74.1/mm2). Similarly high numbers of immunopositive cells (mean >45/mm2) were detected for CD45, MHCII, CCR7, LYVE1 and CD11b respectively. Lower amounts of cells (mean <15/mm2) were found for CXCL12, CCR2, Ki67 and GFAP. Except for CCR2 that accounted for similarly low amounts of cells in both episclera and stroma, the episclera showed a significantly higher amount of cells compared to the stroma (p=0.008).
Our study reveals that considerable numbers of different immune cells, amongst them antigen-presenting macrophages, reside in the healthy human sclera and most likely play a role in maintaining the ocular immune privilege. Under pathological circumstances however, these results might have implications e.g. for ocular tumors which infiltrate scleral tissue or inflammatory diseases such as keratitis and scleritis.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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