IL-17 and VEGF are Necessary for Efficient Corneal Nerve Regeneration

Purpose: To explore the molecular mechanisms by which γδ T cells promote corneal nerve regeneration after epithelial wounding.
Methods: A 2 mm diameter central epithelial region was mechanically debrided in male C57BL/6J (WT), TCRdelta-/-, and WT mice with platelet depletion by anti-CD42b, neutrophil depletion by anti-Ly6G, IL-17 blocking by anti-IL-17, or VEGF blocking by anti-VEGF. Corneas from each group were harvested at different times after wounding, and whole mounted corneas were analyzed by deconvolution microscopy for γδ T cell phenotypes in the epithelium, platelet accumulation in the limbus, neutrophil accumulation near the injured subbasal nerve plexus, and subbasal nerve density across corneas.
Results: Abrasion induced accumulation of IL-17+CCR6+IL-22R+IL-23R+RORγT γδ T cells, neutrophils and platelets in the cornea followed by full restoration of the epithelium and ~19% regeneration of sensory nerves within 96 hours. Mice deficient in γδ T cells (TCRδ-/-) or wildtype mice treated with anti-IL-17 had >50% reduction in neutrophil and platelet infiltration and >50% reduction in nerve regeneration. Depletion of either neutrophils or platelets in wild-type mice also resulted in >50% reductions in corneal nerve density. Infiltrating neutrophils and platelets stained positively for VEGF-A, tissue levels of VEGF-A peaked coincident with peak tissue levels of neutrophils and platelets, depletion of neutrophils prior to injury reduced tissue VEGF-A levels by >70%, and wildtype mice treated with anti-VEGF-A antibody exhibited >80% reduction in corneal nerve regeneration.
Conclusion: The data presented here are consistent with the interpretation that CCR6+ IL-17+ γδ T cells and IL-17 are necessary for early neutrophil and platelet-dependent delivery to the injured subbasal nerve plexus of VEGF-A, a trophic factor for neurite regeneration.