Dry eye-induced conjunctival epithelial squamous metaplasia is modulated by interferon-γ

PURPOSE. To investigate the role of interferon (IFN)-γ in the pathogenesis of conjunctival squamous metaplasia in dry eye. METHODS. Experimental dry eye was created by subjecting C57BL/6 and IFN-γ-knockout mice to desiccating environmental stress for 5 or 10 days. T-cell antigens and IFN-γ were detected by immunohistochemistry. Goblet cells were counted in periodic acid Schiff (PAS)-stained sections. Expression of small, proline-rich protein (SPRR)-2 was evaluated by confocal microscopy. Tear IFN-γ was measured by immunobead assay. RESULTS. Dry eye promoted migration of CD4 ⁺ T cells and IFN-γ⁺ cells into goblet cell zones of the conjunctiva and increased the concentration of IFN-γ in tears. This migration was accompanied by progressive goblet cell loss and an increase in SPRR-2 expression in the conjunctival epithelium. A significant inverse correlation was observed between the density of infiltrating CD4⁺ T cells and goblet cells. Dry eye had no effect on conjunctival goblet cell density in IFN-γ-knockout mice; however, exogenous administration of IFN-γ significantly decreased goblet cell density after 5 days. CONCLUSIONS. Conjunctival epithelial response to experimental dryness is related to the degree of CD4⁺ T-cell infiltration and the level of IFN-γ production. These findings suggest that IFN-γ plays a pivotal role in promoting conjunctival squamous metaplasia in dry eye, and they provide insight into the immune pathogenesis of keratoconjunctivitis sicca.