Corneal Stroma Macrophages Take Up Soluble Antigen Following Intracameral and Subconjunctival Injections: An in vivo and in vitro Study in the Rat

Abstract

Abstract: : Purpose: To determine the capacity of resident corneal and limbal dendritic cells (DC) and macrophages to capture antigen (Ag) Methods: To investigate Ag uptake in vivo 2–3µl (20–30µg) of fluorescently labeled Dextran, BSA or OVA were injected into the anterior chamber (AC) or the subconjunctival space. The presence of Ag⁺ cells in the cornea 24h post–injection was examined using in vivo video fluorescence microscopy. The distribution and phenotype of Ag⁺ cells were analysed by fluorescence and confocal microscopy in corneal tissue wholemounts or sections from animals sacrificed 24 hours post–injections. To investigate Ag uptake in vitro; corneoscleral tissues from Lewis rats were placed in culture with or without FITC–Dextran for 48h and examined by epi–fluorescence microscopy and the phenotype of Ag⁺ cells in the supernatant was analyzed by flow cytometry. Results: In vivo observations and microscopic examination of corneas 24h following Ag exposure revealed Ag⁺ cells within the corneal stroma and epithelium. Corneal Ag⁺ cells express mainly CD68, CD172 and rarely MHC class II molecules in situ. Following exposure to soluble Ag alone or in the presence of LPS in organ culture conditions cells derived from the corneal buttons captured fluorescent labeled Ag in vitro and expressed CD163 and CD11b but not the DC markers CD11c or OX62. Conclusions: These observations show that Ag injected into the AC or subconjunctival space is internalised by corneal stroma and limbal macrophages but not by DC. The lack of obvious Ag trapping by corneal/limbal DC might partly explain its immune privileged properties.

Keywords: cornea: basic science • immune tolerance/privilege • anterior segment