Corneal, in contrast to conjunctival, dendritic cells (DCs) are resistant to overexpressing MHC class II molecules

Abstract

Abstract: : Purpose: Recent data from our lab demonstrate that the central cornea is endowed with dendritic cells (DCs) with the unique phenotype of being uniformly MHC class II–negative, a characteristic of highly immature or precursor DCs. Experiments were undertaken to examine whether the microenvironment of the anterior segment of the eye prevents maturation of corneal DCs by suppressing MHC class II expression. Methods: Splenic DCs were isolated from transgenic mice expressing green fluorescent protein (GFP) and injected into either the central cornea of syngeneic C57BL/6 mice or control conjunctivae. At different time points after injection, the corneas and conjunctivae were excised and stained with fluorescent–labeled anti–MHC class II antibody. The alteration of surface MHC II antigen level on GFP–DCs was analyzed by confocal microscopy on whole–mount corneas and conjunctivae. To determine the relative contribution of aqueous humor and cornea in affecting DC maturation, bone marrow–derived immature DCs were cultured in the presence or absence of either rabbit aqueous humor or cornea culture supernatant. The changes in DC maturation were evaluated by flow analysis of surface MHC class II expressions. Results: One day after injection, most of the splenic GFP–DCs injected into the conjunctiva (identified as cells with green fluorescence) showed up–regulation of surface MHC class II molecules and acquired a more mature state as revealed by bright surface–encompassing MHC class II staining. In the central cornea, however, no increase in MHC class II expression was observed on injected GFP–DCs. Interestingly, some cornea GFP–DCs increased their surface MHC class II once they migrated to the corneal periphery. Moreover, in vitro culture of immature bone marrow–derived DCs with aqueous humor led to a decrease in surface MHC class II expression, but the same effect was not seen with cells treated with supernatant derived from corneal culture alone. Conclusions: These data demonstrate that exogenously introduced DCs resist over–expression of surface MHC class II molecules in response to the local microenvironment of the central cornea. This effect is most likely via the factor(s) in aqueous humor, suggesting that the immunological unresponsiveness in the cornea may be maintained, in part, by inhibitory effects of aqueous humor on resident DC maturation and hence T cell stimulating capacity.

Keywords: immunomodulation/immunoregulation • anterior segment • cornea: basic science