Protective role for CD1d-reactive invariant natural killer T cells in cauterization-induced corneal inflammation

PURPOSE. Corneal inflammation can be induced by various stimuli, such as chemical burns, trauma, and acute bacterial infection, and directly impairs visual acuity. Natural killer T (NKT) cells belong to a specialized population of leukocytes that coexpress the T-cell receptor and NK markers. This study examined the role of CD1d-reactive invariant NKT cells in cauterization-induced acute corneal inflammation. METHODS. The corneas of CD1d-knockout (KO) mice and Jα18-KO mice (both of which are NKT cell deficient) and control mice were cauterized with silver nitrate. Corneal edema and opacity were examined, and the phenotypes of the corneal-infiltrating cells were analyzed histologically at 24 hours and by flow cytometry at 96 hours. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the expression of vascular endothelial growth factor (VEGF), interferon (IFN)γ, and tumor necrosis factor (TNF)α in the cauterized corneas. RESULTS. The CD1d-KO and Jα18-KO mice had significantly greater levels of corneal edema and opacity than did the control mice. Although the number of infiltrating cells was not significantly different at 96 hours, both groups of NKT celldeficient mice demonstrated increased early neutrophil accumulation at 24 hours and early expression of VEGF, IFNγ, and TNFα. There was no difference in the level of VEGF-induced corneal neovascularization. CONCLUSIONS. NKT cells appear to regulate the early accumulation of neutrophils, protect the cornea from excessive inflammation, and maintain corneal clarity. However, in this study, they did not affect the corneal revascularization process induced by VEGF.