Regulation of T-cell chemotaxis by programmed Death-Ligand 1 (PD-L1) in dry eye-associated corneal inflammation

Purpose. Given that dry eye disease (DED) is associated with T cell-mediated inflammation of the ocular surface and that PD-L1 is an important negative or inhibitory regulator of immune responses constitutively expressed at high levels by corneal epithelial cells, the authors studied the expression and function of PD-L1 in DED. Methods. Dry eye was induced in untreated wild-type mice, PD-L1^-1- mice, and wild-type mice treated with anti-PD-L1 antibody by exposing these mice to a desiccating environment in the controlled environment chamber modified with subcutaneous administration of scopolamine. Real-time PCR was used to quantify the expression of chemokine gene transcript levels of multiple CC and CXC chemokine ligands and receptors. Epifluorescence microscopy was used to evaluate corneal infiltration of CD3⁺ T cells after immunohistochemical staining. Results. The increased expression of specific chemokine ligands and receptors in PD-L1^-1- corneas of normal mice is associated with significant increases in T-cell homing into these corneas. Similar, and more enhanced, increases in T-cell infiltration were observed in PD-L1^-1- DED mice or DED mice treated with anti-PD-L1 antibody compared with controls. In addition, the authors found significantly decreased expression of PD-L1 by corneal epithelial cells in DED and significantly increased corneal fluorescein staining score with PD-L1 functional blockade using anti-PD-L1 antibody. Conclusions. Downregulation of corneal epithelial PD-L1 amplifies dry eye-associated corneal inflammation and epithe-liopathy by increasing the expression of chemokine ligands and receptors that promote T-cell homing to the ocular surface.