Lipoxin A₄ Regulates T cell Responses in Experimental Autoimmune Uveitis

Abstract

Purpose : CD4 T cells differentiate into T helper subsets and T regulatory cells to initiate or control adaptive immune responses. Aberrant T cell response during ocular inflammation can result in irreversible tissue damage that leads to blindness. We recently published that T effector functions is controlled by lipoxin A₄ (LXA₄) in an autoimmune dry eye model, demonstrated by LXA₄ formation in the cervical draining lymph nodes. LXA₄ is generated in tissues and lymph nodes and mediates its effects by signaling through the GPCR ALX, which is expressed in T cells. We sought to understand whether LXA₄ regulates T cell response in experimental autoimmune uveitis (EAU) and AIRE knockout mouse models, which recapitulate key features of spontaneous and chronic uveitis that is driven by autoreactive T cells.

Methods : LXA₄ regulation of T effector and T regulatory cells was assessed in vitro and in vivo using flow cytometry and cytokine/chemokine arrays. Lipidomic analyses and QPCR were used to compare levels of lipid mediator (LM) formation and expression of biosynthetic enzymes and LM receptors in EAU and AIRE knockout mouse models. LXA₄’s ability to inhibit uveitis pathogenesis was assessed by OCT and immunohistology.

Results : LXA₄ levels in the healthy choroid and retina and during uveitis pathogenesis ranged from from 47-85 pg/eye. In vitro, LXA₄ inhibits T effector cells and amplifies TGF-β and IL-2 induced Treg polarization by 90% (p=0.0038, n=5). In vivo, treatment with LXA₄ was protective and limited inflammation and disease progression of EAU.

Conclusions : The findings demonstrate for the first time that the immune regulatory LXA₄ is formed in the retina and choroid and is a significant LM mediating the pathogenesis of posterior autoimmune uveitis. In vitro and in vivo data demonstrate that the LXA₄ circuit is protective and a key regulator of T cell driven uveitis. Emerging evidence demonstrates LXA₄ regulation of adaptive immune responses and delineating the mechanism of action warrants further investigation.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.