Changes in Corneal Immune Cells and Inflammatory Cytokines in the Controlled Environmental Chamber Dry Eye Murine Model

Abstract

Purpose: : The cornea is the most significant target tissue for dry eye syndrome (DES) with respect to visual impairment and disease morbidity. However, very little is known about the acute immune and inflammatory changes in the cornea as opposed to the conjunctiva that accompanies DES. Our purpose was to study the early changes in cellular infiltration and inflammatory cytokines in the controlled environmental chamber murine model of dry eye.

Methods: : Dry eye was induced in female balb/c mice by combined exposure to desiccating environment (relative humidity (RH) =21.7 ± 5.2%, airflow (AF) =15l/min, temperature (T)= 21–23 ^oC) and systemic scopolamine. Age and gender matched control mice were kept in normal environment (RH =50–70%, no AF, T =21–23 ^oC) with no administration of scopolamine. Aqueous tear production (cotton thread test) and corneal fluorescein staining (score 0–15) were measured by a masked observer at day 6. Scanning laser confocal microscopy was used to evaluate corneal expression of following markers after immunohistochemical staining: CD 11b (monocyte/ macrophage), CD3 (T cell) and GR–1 (neutrophils). Corneal expression of inflammatory cytokines IL–1α and TNF–α was determined by total RNA isolation, RT–PCR and real time PCR.

Results: : Significant decrease in aqueous tear secretion and increase in corneal fluorescein staining score was seen in the dry eye group versus controls. A significant increase in the number of CD 11b⁺ cells (monocytes) was seen in both the center and periphery of the dry eye cornea. In addition, there was an increase in MHC Class II expression by the CD 11b⁺ cells. Increased expression of inflammatory cytokines IL–1α and TNF–α was also detected in the cornea by RT–PCR. No T cells or neutrophils were detected at any of the time points studied.

Conclusions: : We report the finding of macrophage infiltration and activation in the cornea of experimentally induced dry eye. The expression of inflammatory cytokines IL–1α and TNF–α is also increased. These findings correspond to the ocular signs of dry eye. This suggests that changes in the number and phenotype of cells that may serve as antigen–presenting cells, may play a role in the corneal pathology early in the course of dry eye.

Keywords: cornea: tears/tear film/dry eye • cornea: basic science • immunohistochemistry