Redefining the human corneal immune compartment using dynamic intravital imaging

Abstract

The healthy human cornea is a uniquely transparent sensory tissue where immune responses are tightly controlled to preserve vision. The cornea contains immune cells that are widely presumed to be intraepithelial dendritic cells (DCs). Corneal immune cells have diverse cellular morphologies and morphological alterations are used as a marker of inflammation and injury. Based on our imaging of corneal T cells in mice, we hypothesized that many human corneal immune cells commonly defined as DCs are intraepithelial lymphocytes (IELs). To investigate this, we developed functional in vivo confocal microscopy (Fun-IVCM) to investigate cell dynamics in the human corneal epithelium and stroma. We show that many immune cells resident in the healthy human cornea are T cells. These corneal IELs are characterized by rapid, persistent motility and interact with corneal DCs and sensory nerves. Imaging deeper into the corneal stroma, we show that crawling macrophages and rare motile T cells patrol the tissue. Furthermore, we identify altered immune cell behaviors in response to short-term contact lens wear (acute inflammatory stimulus), as well as in individuals with allergy (chronic inflammatory stimulus) that was modulated by therapeutic intervention. These findings redefine current understanding of immune cell subsets in the human cornea and reveal how resident corneal immune cells respond and adapt to chronic and acute stimuli.

Epithelial Immune Cell Response to Initial Soft Contact Lens Wear in the Human Corneal and Conjunctival Epithelium

“…After 2 hours of CL wear, there was no change in EIC density at the central cornea, which is broadly similar to a study reporting EIC density following short-term (3 hours) CL wear at the central cornea and inferior whorl regions in naïve wearers. 30 Conversely, an earlier report showed a twofold increase in EIC density after the same wear duration. 24 Differences may be attributed to variations in inclusion criteria.…”

“…Two recent publications using a combination of flow cytometry and immunohistochemistry in murine models and in human donor corneas, characterized cell type in vitro and used human time-lapse IVCM to explore cell behavior in vivo . 30 , 47 Cells seen in IVCM are likely to be a combination of T cell and dendritic cell populations, 30 , 47 where small, mobile immune cells lacking visible dendrites are believed to be T cells, whereas larger cells with evident dendrites are dendritic cells. 30 We believe these observations do not impact the findings of the current study.…”

“… 30 , 47 Cells seen in IVCM are likely to be a combination of T cell and dendritic cell populations, 30 , 47 where small, mobile immune cells lacking visible dendrites are believed to be T cells, whereas larger cells with evident dendrites are dendritic cells. 30 We believe these observations do not impact the findings of the current study. The morphology grading system used in the current study 18 reports size and morphological characteristics of cells at least 10 µm in cell body diameter and separately considers cells lacking discernible dendrites.…”

Persistence of Contact Lens-Induced Corneal Parainflammation Following Lens Removal

“…It remains evident, however, that both human and murine lens wear involve corneal parainflammatory responses involving resident or infiltrating immune cells and that studying each will provide further insights into the pathogenesis of lens-induced adverse events. Advances in live in vivo imaging of the cornea (e.g., Functional In Vivo Confocal Microscopy 21 ) will likely help bridge the gap between in vivo models by helping to better define immune cell types and their relative roles.…”

The Role of Insulin-like Growth Factor (IGF) System in the Corneal Epithelium Homeostasis—From Limbal Epithelial Stem Cells to Therapeutic Applications

“…Additionally, the interplay between the nervous and immune system may impact limbal stem cells [ 24 , 86 ]. Immune cells residing in the cornea, such as T cells, interact with dendritic corneal cells and sensory nerves, influencing a response to acute and chronic stimuli [ 87 ]. A study with a mouse model of prediabetes demonstrated that dysfunction of corneal nerves, upregulation of inflammatory mediators, and reduction in neutrophil numbers in the limbus may precede a state of hyperglycemia [ 86 ].…”