Discrepancy between neurokinin 1 receptor antagonist treatment and neurokinin 1 receptor knockout mice in the CD8 T cell response to corneal HSV-1 infection

Abstract

Abstract The purpose of this study is to evaluate the effect blocking neurokinin 1 receptor (NK1R) signaling has on the CD8 T cell response to corneal herpes simplex 1 (HSV-1) infection, using NK1R antagonist (L 760735) or NK1R−/− mice. Corneal HSV-1 infection was carried out on C57BL/6 and NK1R−/− mice. Our results showed an enhanced CD8 T cell response to corneal HSV-1 infection by NK1R−/− mice compared to C57BL/6 mice. The data illustrates that at day 5 post infection, draining lymph nodes (DLNs) in NK1R−/− mice exhibit an increased CD8 T cell IFN-γ response as measured by intracellular cytokine staining. In addition, an increased CD8 T cell proliferation is noted in NK1R−/− mouse DLNs. Interestingly, L 760735 treatment given to HSV-1 infected C57BL/6 mice did not show an increase in CD8 T cell proliferation or IFN-γ production; in comparison to infected, vehicle treated control mice. To determine the underlying cause of this discrepancy, we detected pre-existing LYVE+ vessels in unmanipulated corneas of NK1R−/− mice. This was associated with higher levels of VEGF-C protein in ocular tissue (cornea + limbal conjunctiva) of unmanipulated NK1R−/− compared to C57BL/6 mice, as measured via western blot. We recently reported a massive accumulation of CD11b and CD11c expressing cells near the limbal area in unmanipulated eyes of NK1R−/− mice [J Immunol., 2016, 197 (10) 4021–4033]. Confocal microscopy results showed VEGF-C colocalization with these cells near the limbal area in NK1R−/− mice. Since corneal lymphatics play an important role in generating the CD8 T cell response to corneal HSV-1 infection, our results suggest an enhanced CD8 T cell response in NK1R−/− mice, likely due to a notable increase in corneal lymphatics in NK1R−/− compared to C57BL/6 mice.