Immune Cell Characterisation and Distribution in Normal Porcine Cornea

Abstract

Abstract: : Purpose: The normal central cornea has always been considered as an immune–privileged site because of the absence of antigen presenting cells (dendritic cells and macrophages). This phenomenon has been challenged recently as a heterogeneous population of epithelial and stromal dendritic cells has been identified in the normal central murine cornea. It is not known whether this finding is relevant to other species. The purpose of this study was to examine the phenotype and distribution of immune cells within the normal porcine cornea. Methods: Normal and fresh (3 to 4 hours post–mortem) porcine corneas were dissected from the whole pig eyes and frozen immediately. Transverse corneal tissue sections were prepared and immunofluorescence staining was performed using a variety of monoclonal antibodies (CD45 [common leucocyte antigen], MHC class II, 2B10 [macrophages] and 2G6 [monocytes/macrophages]). The phenotype, distribution and density of the immune cells were studied using fluorescence microscopy. Furthermore, tangential sections of normal porcine corneal buttons were used to study the morphology of the immunopositive cells. Results: CD45⁺ cells with pleomorphic morphology were present throughout the entire normal porcine cornea. The density decreased from the limbus (120–400 cells/mm²) and the peripheral cornea (15–50 cells/mm²) towards the centre (6–48 cells/mm²) and majority of these cells did not express MHC class II. Within the central cornea, CD45⁺ cells were identified mainly in the epithelial (42 cells/mm²) and anterior stromal layers (48 cells/mm²). A smaller number of CD45⁺ cells were seen in the central posterior stroma (24 cells/mm²) of the normal pig cornea. In addition, a population of 2G6⁺ cells (macrophages) was observed in the central epithelium (3 cells/mm²), anterior (6 cells/mm²) and posterior stroma (3 cells/mm²) of the normal porcine cornea. Morphologically, these cells were elongated, pleomorphic and bipolar. Conclusions: This study demonstrates for the first time that the normal central porcine cornea contains a significant number of CD45⁺ leucocytes. Majority of these cells are MHC class II–negative. Furthermore, a subpopulation of macrophages (2G6⁺ cells) with pleomorphic and elongated morphology is present within the central epithelial and stromal layers of the normal porcine cornea.

Keywords: cornea: basic science • immune tolerance/privilege • immunohistochemistry