Exhausted effector memory CD8 T cells expand in chronic EAU

Abstract

Purpose: Using CD4 T cell mediated Experimental Autoimmune Uveitis (EAU) as a model for human non-infectious intraocular inflammation (uveitis) we have demonstrated short and long scale temporal variation in leukocyte populations that infiltrate the retina during RBP-3 (IRBP) peptide induced disease. CD8 T cells are particularly prominent in the late phase of disease, where their role in retinal inflammation is unclear. As CD8 T cells may be both pathogenic and regulatory in autoimmunity our purpose was to interrogate the function and phenotype of our recently identified CD8 T cell population during secondary progressive EAU.

Methods: C57BL/6J mice were immunised with RBP-3 1-20 peptide. Disease progression was assessed by Topical Endoscopic Fundal Imaging (TEFI) and retinal infiltrate quantified by flow cytometry. Cytokine production was measured by intracellular cytokine staining. Cytotoxic potential and function was assessed by flow cytometric CD107a and granzyme B expression. Monoclonal antibodies YTS 169.4 and 156.7 directed against CD8 were used for in vivo depletion of CD8 T cells.

Results: In the secondary progressive phase of EAU the infiltrating effector memory CD8 T cells expressed cell surface markers associated with recent antigen stimulation. From day 35 post immunisation there was a significant expansion of CD8 T cells that lacked cytokine production and evidence of recent degranulation, as determined by CD107a expression. Surface expression of PD-1 increased and was associated with a lack of effector function, with approximately 90% of PD-1⁺ CD8 T cells phenotypically CD69^highLy6C^low. In vivo depletion of CD8 T cells resulted in the removal from systemic and local tissues without altering the clinical phenotype.

Conclusions: In contrast to peak disease, the retinal infiltrate during persistent disease was characterised by CD8 T cells that lacked effector function and showed some signature changes of exhaustion (increased PD-1) associated with chronic antigen stimulation.

Keywords: 432 autoimmune disease • 746 uveitis-clinical/animal model • 688 retina