Human Corneal Endothelial Cells Expressing Programmed Death-Ligand 1 (PD-L1) Suppress PD-1+ T Helper 1 Cells by a Contact-Dependent Mechanism

¹ Department of Ophthalmology, Tokyo Medical & Dental Univ., Yushima1-5-45, Bunko-ku, Tokyo, 113-8519, Japan
² Ophthalmology, Tokyo Medical University, Tokyo, Japan
³ Ophthalmology, Tokyo Medical and Dental University, Tokyo, Japan
⁴ Molecular Medicine, Sapporo Medical University, Sapporo, Japan
⁵ Ophthalmology, University of Tokyo, Tokyo, Japan
⁶ Ophthalmology, Tokyo Women's Medical University, Tokyo, Japan

^* To whom correspondence should be addressed. E-mail: sunaoph{at}tmd.ac.jp.

	Abstract

Purpose. To determine whether a human corneal endothelial (CE) cells could regulate the activation of bystander T cells in vitro. Methods. Human CE (HCE) cell lines were established from primary HCE cells. Targetactivated T cells were used allogeneic T cells and Jurkat T cell lines. As an additional target, T cell clones from uveitis patients were established from aqueous humor via a limiting dilution. Tcell activation was assessed for proliferation by [³H]-thymidine incorporation, CFSEincorporation, or IFN production. Expression of co-stimulatory molecules on IFN-treated CE & non-treated cells were evaluated by flow cytometry, RT-PCR, or immunohistochemistry. Expression of co-stimulatory receptors on target T cells was evaluated by flow cytometry. Blocking antibodies was used to abolish the HCE-inhibitory function. Results. HCE cells suppressed both in vitro proliferation and IFN production by CD4⁺ T cells via a cell contact-dependent mechanism. HCE constitutively expressed co stimulatory molecules programmed death-ligand 1 (PD-L1) and PD-L2, and their expression was enhanced by IFN. HCE efficiently inhibited the proliferation of Th1 cells that overexpressed PD-1 among various activated T cell lines and clones established from patients with uveitis or corneal endotheliitis. A neutralizing mAb for PD-L1, but not PD-L2, blocked the suppressive effect of HCE on Th1 cells. Conclusions. HCE can impair the effector functions and activation of Th1 infiltrating CD4⁺ T cells via the PD-1/PD-L1 interaction. Our data support the hypothesis that corneal endothelium may contribute to maintenance of the privileged immune status of the anterior chamber of the eye by inducing peripheral immune tolerance.

Key Words: suppression, corneal endothelial cells, immune privilege, immunoregulation, uveitis

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