The role of resident dendritic cells in the maintenance of corneal epithelial sensory nerves

Abstract

Purpose : Dendritic cells (DCs) are resident immune cells in the corneal epithelium. Recent studies suggest DCs are important for sensory nerve regeneration after epithelial injury. We used Cx3cr1^gfp/gfp mice, which spontaneously lack resident corneal epithelial DCs, to determine the contribution of resident DCs to corneal epithelial nerve homeostasis.

Methods : Young Cx3cr1^gfp/gfp mice and wild-type littermates on a C57BL/6J background were used. Spectral domain optical coherence tomography was used to measure corneal epithelial and stromal thickness. Corneal flat mounts were immunostained for sensory nerves using anti-Beta III Tubulin antibody and anti-CD45 antibody (resident DCs). The percentage area of sub-basal nerve plexus (SBNP) and superficial nerve terminals (SNTs), and the density of apically oriented nerve axons were quantified in the central and peripheral cornea using ImageJ. Expression of pro-inflammatory genes in whole corneas were measured by qRT-PCR (IL-1β, TNF-α, IL-6, Cx3cl1/fractalkine, CD103 and ciliary neurotrophic nerve factor/CNTF).

Results : Total corneal and epithelial thickness was similar in both groups. In normal corneas, SBNP density (expressed as percentage area, mean ± SEM) was lower in the central corneal of Cx3cr1^gfp/gfp mice when compared to wild-type littermates (7.9% ± 0.5%; n=7, vs 9.5% ± 0.48%, n=6; P=0.04), but values were similar in the peripheral cornea. The density of vertical axons projecting towards the apical epithelium, and the density of superficial nerve terminals was similar in Cx3cr1^gfp/gfp and WT mice. Baseline gene expression of IL-1β, TNF-α, Cx3cl1/fractalkine and CNTF was significantly lower in corneas from Cx3cr1^gfp/gfp mice compared to WT mice, whereas CD103 and IL-6 were similar in both groups.

Conclusions : In healthy mouse cornea, the absence of resident epithelial DCs influences the density of the sub-basal nerve plexus in the central, but not the peripheral region. The absence of DC does not influence the apically located superficial nerve terminals or affect epithelial thickness, but does influence baseline gene expression of pro-inflammatory cytokines and ciliary neurotrophic nerve factor. These data provide further evidence of the role of resident DCs in maintenance of corneal homeostasis.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.