Treatment With FoxP3+ Antigen-Experienced T Regulatory Cells Arrests Progressive Retinal Damage in a Spontaneous Model of Uveitis

Abstract

We specify the clinical features of a spontaneous experimental autoimmune uveitis (EAU) model, in which foreign hen-egg lysozyme (HEL) is expressed in the retina, controlled by the promoter for interphotoreceptor retinol binding protein (IRBP). We previously reported 100% P21 (post-partum day) IRBP:HEL single transgenic (sTg) mice, when crossed to transgenic T cell receptor mice (3A9) generating the double transgenic (dTg) genotype, develop EAU despite profound lymphopenia (thymic HEL-specific T cell deletion). In this work, we characterized the immune component of this model and found conventional dTg CD4+ T cells were less anergic than those from 3A9 controls. Furthermore, prior in vitro HEL-activation of 3A9 anergic T cells (T an) rendered them uveitogenic upon adoptive transfer (Tx) to sTg mice, while antigen-experienced (AgX, dTg), but not naïve (3A9) T cells halted disease in P21 dTg mice. Flow cytometric analysis of the AgX cells elucidated the underlying pathology: FoxP3+CD25 hi CD4+ T regulatory cells (T reg) comprised ∼18%, while FR4+CD73+FoxP3-CD25 lo/− CD4+ T an comprised ∼1.2% of total cells. Further T reg-enrichment (∼80%) of the AgX population indicated FoxP3+CD25 hi CD4+ T reg played a key role in EAU-suppression while FoxP3-CD25 lo/− CD4+ T cells did not. Here we present the novel concept of dual immunological tolerance where spontaneous EAU is due to escape from anergy with consequent failure of T reg induction and subsequent imbalance in the [T reg :T effector ] cell ratio. The reduced numbers of T an , normally sustaining T reg to prevent autoimmunity, are the trigger for disease, while immune homeostasis can be restored by supplementation with AgX, but not naïve, antigen-specific T reg .

Immune Privilege: The Microbiome and Uveitis

“…These anergy-derived Treg suppress immunopathology and reinforce anergy induction ( 215 ). In this context, we have recently shown, in a transgenic model of spontaneous uveitis due to failure of Treg induction, that Tan convert to Treg cells as the inflammation resolves ( 119 ). Furthermore, adoptive transfer of antigen-experienced Treg completely prevented development of this spontaneous disease, showing the importance of Treg in the control of uveoretinitis.…”

“…Prevailing dogmata support a pathogenesis which depends on precursor frequency and antigen dosage/ availability, both of which determine whether, stochastically, such cells will become pathogenic (115)(116)(117)(118). Most recently, in a neoantigen transgenic model of spontaneous uveo-retinitis, an absolute requirement for antigen-specific T cell activation has been demonstrated while non-specifically TCR-activated T cells fail to induce disease (119). These questions have exercised researchers over many years and the concept that cross-reactive T cells, activated by a dysbiotic microbiome, might be the guilty party adds significantly to pathogenetic possibilities.…”

A Role for Folate in Microbiome-Linked Control of Autoimmunity

“…This qualitative and quantitative shift in bacterial colonization is associated with decreased microbial folate and SCFA production and a consequential relative increase in autoreactive immunogenic T effector cells (T eff ) [87]. T eff have been shown to traffic from the colon to target sites of autoimmunity [85,86] (e.g., intraocular tissue in the case of autoimmune uveitis), skewing the ratio of immunogenic (T eff ) to regulatory cells (T reg ) at target sites [88][89][90], ultimately breaching ocular immune privilege (IP) through unknown mechanisms, and thereby triggering autoimmune disease. Due to impaired intestinal barrier integrity in dysbiosis, pathogenic bacterial/viral/fungal/environmental antigens have facilitated access to the circulation, possibly triggering inflammation through adjuvant effects at affected sites (following antigen presentation; APC) (b).…”

“…In another model, in which EAU develops spontaneously due to lymphopenia and imbalance in [ T eff : T reg ] ratio, we have shown that disease can be prevented by adoptive transfer of antigen-experienced T reg , but not by naïve T reg . Furthermore, there was evidence of T an to T reg conversion [ 90 ].…”

“…Hence, folate exerts its modulatory effects at two levels in vivo, namely, (1) as a mediator of epigenetic control in thymic n T reg ; and (2) as an antiapoptotic signal in induced p T reg supporting their survival in the circulation. As adoptive transfer of antigen-experienced T reg prevents development of EAU [ 88 , 90 ], it would be interesting to see whether folate-treated antigen-experienced (or even naïve) T reg were more effective in control of AD. This could be combined with SCFA to maximize the differentiation of naϊve T cells to T reg .…”