Abstract
Purpose :
Experimental autoimmune uveitis (EAU) is used to gain a better understanding of human autoimmune uveitis. EAU-resolution is in part due to emergence of ocular antigen specific regulatory T cells (Tregs) found in the spleen of EAU-resolved mice. Multiple FoxP3+CD25+CD4+ Treg subsets in EAU-resolved mice (post-EAU Tregs) are PD-1+ (PD-1 Treg) or TIGIT+ (TIGIT Treg). The adenosine 2A receptor (A2Ar) is required for ocular Tregs at EAU-onset, but A2Ar-/- mice still recover from EAU. This suggests each Treg subset may function through different mechanisms. One such mechanism is where the Tregs home to suppress disease, CCR6 homes to tissue, CCR7 to lymph. We asked where post-EAU Tregs home, and the chemokine receptors (CCR) required for each Treg subset to suppress disease.
Methods :
CCR expression was determined on post-EAU Tregs by NanoString. Then the influence of the identified CCRs on EAU and Treg suppression was determined by transferring specific CCR+ post-EAU T cells, and TIGIT or PD-1 Tregs from CCR6-/- or CCR7-/- mice to recipient EAU mice. Homing to the eye and secondary lymphoid tissue by post-EAU Tregs was also monitored in recipient mice. Peripheral blood mononuclear cells from uveitis patients and healthy volunteers were A2Ar-stimulated, and assayed for CCR6 and CCR7 expression in each Treg subset.
Results :
Post-EAU Tregs had transcript and protein for CCR6 and CCR7, homed to the eye, and lymphoid tissue, and CCR6+ and CCR7+ post-EAU Tregs suppressed EAU. Elimination of CCR6-CCL20 signaling in CCR6-/- and CCL20-/- mice delayed resolution, but CCR7-/- mice had similar disease as WT mice, and more Tregs were in post-EAU CCR7-/- mice compared to CCR6-/- mice. CCR7 was not necessary for EAU suppression by PD-1 or TIGIT Tregs. Whereas, CCR6 was necessary for PD-1, but not TIGIT Treg EAU suppression. A2Ar-/- mice had fewer CCR6 and CCR7 post-EAU Tregs compared to WT mice. A2Ar-induction of PD-1+ CCR6+ Tregs was reduced in uveitis patients (n=20) compared to healthy volunteers (n=19), but was not significantly different for TIGIT+CCR6+, PD-1+CCR7+, or TIGIT+CCR7+ Treg subsets.
Conclusions :
This work indicates that different Treg subsets that may function during different phases of disease, have different homing requirements to suppress disease. Importantly, induction of the tissue homing Tregs in uveitis patients may be impaired. Therefore, a defect in Treg homing capacity may contribute to autoimmune uveitis.
This is a 2021 ARVO Annual Meeting abstract.