Abstract
Purpose :
While much effort has been put into defining molecular components of the immune response involved in intraocular inflammation, the anatomic location where uveitogenic T cells are activated during autoimmune uveitis remains a mystery. Understanding how ocular antigens interface with the adaptive immune system could yield mechanistic insights into uveitis pathogenesis leading to novel targets for uveitis.
Methods :
We utilized intraocular injection of a variety of tracers to define where intraocular antigen drains, and multiparametric flow cytometry to evaluate the immune composition in anatomic compartments that receive antigen drainage from the eye. We further evaluated how this ocular immunity changes during autoimmune disease by immunizing C57Bl/6 mice with IRBP 651-670 and exploring alterations in the immune compartments in the eye. Finally, we utilized confocal microscopy, in vivo two-photon microscopy, and transgenic mice expressing photoconvertible fluorescent protein to explore trafficking of activated lymphocytes within the inflamed eye.
Results :
Ocular antigen drains outside of the blood-retinal barrier to the choroid, cervical lymph nodes, and spleen. Locally, MHCII positive cells in the choroid take up ocular antigens and present them to choroid-resident T cells. In the context of experimental autoimmune uveitis, this leads to proliferation of T cells in the choroid in an antigen-specific manner, where they obtain a pro-inflammatory TH17 phenotype. Intriguingly, this choroidal T cell activation happens prior to infiltration of peripheral immune cells into the retina suggesting that the choroid could be a site of immune activation prior to retinal infiltration. Indeed, choroidal whole mounts during EAU demonstrate T cells within the RPE monolayer, and photo-labelling of choroidal cells in KikGR mice during EAU show that these T cells cross the RPE to gain access to the retina.
Conclusions :
While local adaptive immunity in the eye has largerly been ignored, the choroid contains abundant adaptive and innate immune cells and receives antigen drainage from the intraocular space. During inflammation, T cells activated in the choroid directly invade the subretinal space by migrating through the RPE. Together, these results implicate several new pathways that can be targeted in the treatment of autoimmune uveitis.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.