Loss of Neurokinin-1 Receptor Alters Ocular Surface Homeostasis and Promotes an Early Development of Herpes Stromal Keratitis

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Abstract
Substance P neuropeptide and its receptor, neurokinin-1 receptor (NK1R), are reported to present on the ocular surface. In this study, mice lacking functional NK1R exhibited an excessive desquamation of apical corneal epithelial cells in association with an increased epithelial cell proliferation and increased epithelial cell density, but decreased epithelial cell size. The lack of NK1R also resulted in decreased density of corneal nerves, corneal epithelial dendritic cells (DCs), and a reduced volume of basal tears. Interestingly, massive accumulation of CD11c+CD11b+ conventional DCs was noted in the bulbar conjunctiva and near the limbal area of corneas from NK1R−/− mice. After ocular HSV-1 infection, the number of conventional DCs and neutrophils infiltrating the infected corneas was significantly higher in NK1R−/− than C57BL/6J mice. This was associated with an increased viral load in infected corneas of NK1R−/− mice. As a result, the number of IFN-γ–secreting virus-specific CD4 T cells in the draining lymph nodes of NK1R−/− mice was much higher than in infected C57BL/6J mice. An increased number of CD4 T cells and mature neutrophils (CD11b+Ly6ghigh) in the inflamed corneas of NK1R−/− mice was associated with an early development of severe herpes stromal keratitis. Collectively, our results show that the altered corneal biology of uninfected NK1R−/− mice along with an enhanced immunological response after ocular HSV-1 infection causes an early development of herpes stromal keratitis in NK1R−/− mice.

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