Changes in Corneal Endowment of Immune Cells in Novel Dry Eye Model

Abstract

Abstract: : Purpose: The cornea is the most significant target tissue of dry eye syndrome (DES) with respect to the 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 the cells of the adaptive immune system in the novel mouse dry eye model reported from our laboratory. Methods: Dehumidified air was pumped by a silent compressor into a controlled environmental chamber (CEC) containing 8–12 weeks old male Balb/c mice, exposed for 7 days to relative humidity (RH) 20.4 ± 4.3%, airflow (AF) 15l/min, and temperature (T) 21–23 ^oC. Control mice were kept in normal environment (RH 50–70%, no AF, T 21–23 ^oC) for same duration. Aqueous tear production (cotton thread test) and corneal fluorescein staining (score 0–15) were measured by a masked observer at day 7. Immunohistochemical staining of whole mount corneal stromas was done for the following immune markers: CD 11b (monocyte/ macrophage), CD 3 (T cell) and GR–1 (neutrophils). The expression of these markers was evaluated by scanning laser confocal microscope. Results: Significant decrease in aqueous tear secretion (0.6 ± 0.2 mm vs 1.26 ± 0.4 mm; p=0.01; t–test) and significant increase in corneal fluorescein staining score (6 ± 3 vs 2 ± 1; p= 0.001; Wilcoxon test) was seen in CEC–kept mice as opposed to the controls. Significant increase in mean number of CD 11b+ monocytes/ macrophages per tissue block was noted in both the center (35.83 ± 4.57 vs 22.00 ± 2.00; p= 0.002; t–test) and the periphery (38.00 ± 4.77 vs 25.33 ± 1.53; p= 0.003; t–test) of the stroma. A small number of CD 3+ T cells were seen in the anterior stroma which were absent in the controls. Both groups were negative for neutrophils. Conclusions: We report the novel finding of early infiltration of monocytes/ macrophages and T cells in the corneal stroma of non–pharmacologically modified normal mice upon exposure to a low humidity environment. These findings correspond to the ocular signs of dry eye. This suggests that changes in the cells of adaptive immunity may play a role in corneal pathology early in the course of dry eye induced solely by environmental conditions in otherwise healthy mice.

Keywords: cornea: tears/tear film/dry eye • cornea: basic science • microscopy: confocal/tunneling