IL–1R1–Deficient Mice Show Altered Ocular Surface Cytokine and Defensin Expression in Experimental Dry Eye

Abstract

Abstract: : Purpose: To compare cytokine and defensin expression in response to experimental dry eye in an IL–1 Receptor–1 (IL–1R1) deficient (KO) mouse strain with matched littermates (WT). Methods: Experimental dry eye was induced by subcutaneous scopolamine injection (2.5 mg/ml), exposure to low humidity and an air draft for 5 days in 4–6 week old KO and WT mice (2 independent experiments). mRNA expression of GADPH, cytokines IL–1α, IL–1ß, TNF–α, IL–6 and ß–defensins mBD–1, mBD–2 and mBD–3 was studied by real–time PCR in scraped corneal epithelial cells (Cornea) and whole conjunctival tissue (Conjunctiva). mRNA expression was normalized with GAPDH expression, which was set at 1.0. The expression of treated to untreated mice in each group is described as a fold–change. A multiplex bead assay was performed to study IL–1α, IL–1ß, IL–2, IL–4, IL–10, IL–13, IFN–γ and TNF–α levels in tear fluid. Results: Experimental dry eye increased IL–1α and IL–6 mRNA expression in both groups of mice. In the WT mice, TNF–α increased with dry eye to 1.85 (Cornea) and 6.68 (Conjunctiva) fold, while it decreased to 0.82 (Cornea) and 0.13 fold (Conjunctiva) in the KO mice. IL–1ß decreased with dry eye in the Cornea of both groups (0.67 fold WT, 0.82 fold KO), while in Conjunctiva, IL–1ß increased to 5.56 fold in WT and decreased to 0.13 fold in the KO mice. These findings were supported by the tear fluid multiplex cytokine assay. Notably, TNF–α increased in tears to 13–fold from day 1 through day 4 in the WT mice, but only increased 2.7–fold by day 2 in the KO mice and then decreased. IFN–γ, IL–2 and IL–4 were not detected in mouse tears, while IL–13 increased in both groups over the treatment period. mRNA expression of mBD–1 showed no change with dry eye in both groups of mice in either tissue, while mBD–2 was detected only in Cornea of untreated WT mice. mBD–3 was not detected in Cornea of WT mice and Conjunctiva of both groups, while it increased to 3.67 fold in Cornea in KO mice with dry eye. Conclusions: Differences in cytokine and defensin expression in the IL–1R1 KO mice demonstrates that IL–1 plays a role in the pathophysiology of dry eye by regulating the expression of itself and other cytokines at the ocular surface.

Keywords: cornea: tears/tear film/dry eye • cornea: epithelium • conjunctiva