CD4+CD25(Bright)Foxp3+ Are Abundant in Conjunctiva and Exhibit Phenotypic and Functional Characteristics of Natural Regulatory T Cells

Abstract

Purpose:: Homeostasis of the ocular mucosal immune system (OMIS) depends on balance between the immune response to invading pathogens and immune tolerance to self-antigens. The ability to evoke these responses is normally suppressed by naturally occurring CD4+CD25+ T cells (Treg). However, there is no report on OMIS resident Treg and their role in controlling local ocular immune responses. We characterized the phenotype, distribution, and function of resident T cells in normal conjunctiva, the main T cell inductive site of OMIS, and investigated the role conjunctiva-derived Treg play in ocular surface immunity to HSV-1 infection.

Methods:: Conjunctiva, cornea and PBMCs were harvested from HSV-1 infected and uninfected rabbits. CD45+ pan leukocytes were purified and examined by FACS for resident memory effector T and Treg cells. Distribution of Treg was determined by confocal microscopy. Treg isolated from normal conjunctiva were co-cultured in vitro with HSV-specific memory CD4+ and CD8+ T cells, isolated from immune conjunctiva or PBMC, to assess their effect on local and systemic T cell immunity.

Results:: Normal conjunctiva showed a high percentage of CD4+CD25(Bright)Foxp3+ T cells compared to cornea and PBMC. Treg were localized continuously along the conjunctiva, primarily in the lamina propria, intraepithelially at the lid margin. Conjunctiva derived CD4+CD25+ T cells expressed GITR and CTLA-4 markers and produced high levels of IL-10 and TGF-{beta}. CD4+CD25+ Treg cells from the normal conjunctiva suppressed local and systemic HSV-specific CD4+CD25- and CD8+ memory T cell responses. In vivo depletion of CD4+CD25+ T cells improved T cell immunogenicity of HSV-1 epitope peptides and lipopeptides delivered topically to the ocular mucosal surface.

Conclusions:: This is the first report that CD4+CD25(Bright)Foxp3+ T cells, with functional characteristics of Treg cells, are enriched in conjunctiva, and may play a role in ocular mucosal immune system homeostasis.

Keywords: conjunctiva • immunomodulation/immunoregulation • herpes simplex virus