A Th1-skewed immune response in the ocular surface favors corneal nerve damage

Abstract

Purpose : Corneal nerves are damaged by poorly understood mechanisms in dry eye and other immune-based diseases such as herpetic keratitis and graft-versus-host disease but not in ocular allergy. Since the predominant types of immune responses in all these disorders are different, we hypothesized that a particular type of immune response could promote corneal neuropathy.

Methods : OT-II mice [transgenic for an ovalbumin (OVA)-specific CD4-restricted TCR] were immunized with OVA+Freund’s adjuvant or alum to induce a Th1 or Th2-skewed immune response and 2 weeks later challenged with OVA eye drops for 10 days. Also, CD4+ T cells from Th1 or Th2-skewed OT-II mice or that were polarized in vitro were adoptively transferred to RAG1KO mice that were given OVA eye drops for 5 weeks.

Results : Th1-skewing in CFA-immunized mice was confirmed by higher OVA-induced delayed-type hypersensitivity (0.20±0.09 vs 0.05±0.08 mm, p<0.05) and a lower IL-4+/IFN-γ+ CD4+ T cell ratio (2.16±1.05 vs 7.97±8.67, p<0.05) than alum-immunized mice. After OVA challenge, Th1-skewed mice had lower corneal mechanical sensitivity (-25±12% vs +1±10%, p<0.05) and fewer intraepithelial nerve endings (42.4±11.44 vs 85.8±14.65, p<0.05) than Th2-skewed mice. Neither showed corneal epithelial damage (mean fluorescence 4.33±1.49 vs 4.06±0.63, p>0.05). By contrast, Th2-skewed mice showed a drop in corneal sensitivity by 5 days after alum immunization (-12.18±10.84% vs +0.18±6.83%, p<0.05) that did not worsen with ocular OVA challenge. The number of conjunctival CD4+ T cells after OVA challenge was comparable in both groups. In addition, only the adoptive transfer of Th1-skewed CD4+ T cells led to reduced corneal sensitivity (-21.14±6.96% vs -3.06±7.06%, p<0.05) and less corneal nerve density (3.16±0.55 vs 4.83±0.85, % area, p<0.05) in RAG1KO recipients. Finally, while the transfer of in vitro polarized Th2 or Th17 CD4+ T cells did not affect corneal sensitivity or corneal nerve morphology, the transfer of in vitro polarized Th1 CD4+ T cells led to a marked decrease in corneal sensitivity and nerve density in the recipient mice.

Conclusions : These findings show that corneal nerve damage is immune-driven, that is favored only by a Th1 immune response, and more importantly, that is not a direct consequence of corneal epitheliopathy. These models could serve to study the pathophysiology of corneal neuropathy in detail.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.