TLR2 Supports γδ T cell IL-17A Response to ocular surface commensals by Metabolic Reprogramming

The ocular surface is a mucosal barrier tissue colonized by commensal microbes, which tune local immunity by eliciting IL-17 from conjunctival γδ T cells to prevent pathogenic infection. The commensal Corynebacterium mastitidis (C. mast) elicits protective IL-17 responses from conjunctival Vγ4 T cells through a combination of γδ TCR ligation and IL-1 signaling. Here, we identify Vγ6 T cells as a major C. mast-responsive subset in the conjunctiva and uncover its unique activation requirements. We demonstrate that Vγ6 cells require not only extrinsic (via dendritic cells) but also intrinsic TLR2 stimulation for optimal IL-17A response. Mechanistically, intrinsic TLR2 signaling was associated with epigenetic changes and enhanced expression of genes responsible for metabolic shift to fatty acid oxidation to support Il17a transcription. We identify one key transcription factor, IκBζ, which is upregulated by TLR2 stimulation and is essential for this program. Our study highlights the importance of intrinsic TLR2 signaling in driving metabolic reprogramming and production of IL-17A in microbiome-specific mucosal γδ T cells.

Too Much of a Good Thing: Extended Duration of Gut Microbiota Depletion Reverses Protection From Experimental Autoimmune Uveitis

Purpose

Using the model of experimental autoimmune uveitis (EAU) induced by immunization with a retinal antigen, two studies have reported contradictory results on disease development following oral antibiotic treatment (ABX). We showed that long-term ABX did not affect EAU, but another study showed that short-term ABX was protective. We therefore studied the effects of ABX on EAU, gut microbiota, and host immune responses as a function of treatment duration.

Methods

EAU-susceptible mice were treated orally with broad-spectrum antibiotics starting at least 10 weeks (long-term) or 1 week (short-term) before immunization until termination of the experiment. Gut microbiota were characterized by 16S amplicon sequencing, and host gut immune elements were studied phenotypically and functionally.

Results

Long-term ABX had no effect, whereas short-term ABX delayed EAU, as previously reported by us and others, respectively. Microbial sequencing revealed progressive reduction of gut microbiota that showed some differences in the two ABX groups. Interestingly, duration of ABX was associated with a gradual disappearance of the CD4+ and CD4+CD8+ subset of gut intraepithelial lymphocytes (IELs). This IEL subset is microbiota dependent and is absent in germ-free mice. Relative abundance of Lactobacillus reuteri correlated with the frequencies of CD4+CD8+ IELs. IELs suppressed antigen-specific activation of autoreactive T cells in culture.

Conclusions

Gut microbiota may play dual roles in uveitis development: They promote EAU development but also help maintain IEL populations that have regulatory function against autoreactive T cells. We propose that the progressive loss of this population during long-term ABX reverses the EAU-ameliorating effects of microbiota depletion.

Microbiota as Drivers and as Therapeutic Targets in Ocular and Tissue Specific Autoimmunity

Autoimmune uveitis is a major cause of blindness in humans. Activation of retina-specific autoreactive T cells by commensal microbiota has been shown to trigger uveitis in mice. Although a culprit microbe and/or its immunogenic antigen remains to be identified, studies from inducible and spontaneous mouse models suggest the potential of microbiota-modulating therapies for treating ocular autoimmune disease. In this review, we summarize recent findings on the contribution of microbiota to T cell-driven, tissue-specific autoimmunity, with an emphasis on autoimmune uveitis, and analyze microbiota-altering interventions, including antibiotics, probiotics, and microbiota-derived metabolites (e.g., short-chain fatty acids), which have been shown to be effective in other autoimmune diseases. We also discuss the need to explore more translational animal models as well as to integrate various datasets (microbiomic, transcriptomic, proteomic, metabolomic, and other cellular measurements) to gain a better understanding of how microbiota can directly or indirectly modulate the immune system and contribute to the onset of disease. It is hoped that deeper understanding of these interactions may lead to more effective treatment interventions.

Regulated Tristetraprolin Overexpression Dampens the Development and Pathogenesis of Experimental Autoimmune Uveitis

Non-infectious uveitis, a common cause of blindness in man, is often mediated by autoimmunity, a process in which cytokines play major roles. The biosynthesis and secretion of pro-inflammatory cytokines are regulated in part by tristetraprolin (TTP), an endogenous anti-inflammatory protein that acts by binding directly to specific sequence motifs in the 3'-untranslated regions of target mRNAs, promoting their turnover, and inhibiting synthesis of their encoded proteins. We recently developed a TTP-overexpressing mouse (TTPΔARE) by deleting an AU-rich element (ARE) instability motif from the TTP mRNA, resulting in increased accumulation of TTP mRNA and protein throughout the animal. Here, we show that homozygous TTPΔARE mice are resistant to the induction of experimental autoimmune uveitis (EAU) induced by interphotoreceptor retinoid-binding protein (IRBP), an established model for human autoimmune (noninfectious) uveitis. Lymphocytes from TTPΔARE mice produced lower levels of the pro-inflammatory cytokines IFN-γ, IL-17, IL-6, and TNFα than wild type (WT) mice. TTPΔARE mice also produced lower titers of antibodies against the uveitogenic protein. In contrast, TTPΔARE mice produced higher levels of the anti-inflammatory cytokine IL-10, and had higher frequencies of regulatory T-cells, which, moreover, displayed a moderately higher per-cell regulatory ability. Heterozygous mice developed EAU and associated immunological responses at levels intermediate between homozygous TTPΔARE mice and WT controls. TTPΔARE mice were able, however, to develop EAU following adoptive transfer of activated WT T-cells specific to IRBP peptide 651-670, and naïve T-cells from TTPΔARE mice could be activated by antibodies to CD3/CD28. Importantly, TTPΔARE antigen presenting cells were significantly less efficient compared to WT in priming naïve T cells, suggesting that this feature plays a major role in the dampened immune responses of the TTPΔARE mice. Our observations demonstrate that elevated systemic levels of TTP can inhibit the pathogenic processes involved in EAU, and suggest the possible use of TTP-based treatments in humans with uveitis and other autoimmune conditions.

Autoimmunity to neuroretina in the concurrent absence of IFN-γ and IL-17A is mediated by a GM-CSF-driven eosinophilic inflammation

IFN-γ and IL-17A can each elicit ocular autoimmunity independently of the other. Since absence of IFN-γ or IL-17A individually failed to abolish pathology of experimental autoimmune uveitis (EAU), we examined EAU development in the absence of both these cytokines. Ifng-/-Il17a-/- mice were fully susceptible to EAU with a characteristic eosinophilic ocular infiltrate, as opposed to a mononuclear infiltrate in WT mice. Retinal pathology in double-deficient mice was ameliorated when eosinophils were genetically absent or their migration was blocked, supporting a pathogenic role for eosinophils in EAU in the concurrent absence of IFN-γ and IL-17A. In EAU-challenged Ifng-/-Il17a-/- mice, ocular infiltrates contained increased GM-CSF-producing CD4+ T cells, and supernatants of retinal antigen-stimulated splenocytes contained enhanced levels of GM-CSF that contributed to activation and migration of eosinophils in vitro. Systemic or local blockade of GM-CSF ameliorated EAU in Ifng-/-Il17a-/- mice, reduced eosinophil peroxidase levels in the eye and in the serum and decreased eosinophil infiltration to the eye. These results support the interpretation that, in the concurrent absence of IFN-γ and IL-17A, GM-CSF takes on a major role as an inflammatory effector cytokine and drives an eosinophil-dominant pathology. Our findings may impact therapeutic strategies aiming to target IFN-γ and IL-17A in autoimmune uveitis.

T cell-intrinsic role for Nod2 in protection against Th17-mediated uveitis

Mutations in nucleotide-binding oligomerization domain-containing protein 2 (NOD2) cause Blau syndrome, an inflammatory disorder characterized by uveitis. The antimicrobial functions of Nod2 are well-established, yet the cellular mechanisms by which dysregulated Nod2 causes uveitis remain unknown. Here, we report a non-conventional, T cell-intrinsic function for Nod2 in suppression of Th17 immunity and experimental uveitis. Reconstitution of lymphopenic hosts with Nod2^-/- CD4⁺ T cells or retina-specific autoreactive CD4⁺ T cells lacking Nod2 reveals a T cell-autonomous, Rip2-independent mechanism for Nod2 in uveitis. In naive animals, Nod2 operates downstream of TCR ligation to suppress activation of memory CD4⁺ T cells that associate with an autoreactive-like profile involving IL-17 and Ccr7. Interestingly, CD4⁺ T cells from two Blau syndrome patients show elevated IL-17 and increased CCR7. Our data define Nod2 as a T cell-intrinsic rheostat of Th17 immunity, and open new avenues for T cell-based therapies for Nod2-associated disorders such as Blau syndrome.

The Cytokine IL-17A Limits Th17 Pathogenicity via a Negative Feedback Loop Driven by Autocrine Induction of IL-24

Dysregulated Th17 cell responses underlie multiple inflammatory and autoimmune diseases, including autoimmune uveitis and its animal model, EAU. However, clinical trials targeting IL-17A in uveitis were not successful. Here, we report that Th17 cells were regulated by their own signature cytokine, IL-17A. Loss of IL-17A in autopathogenic Th17 cells did not reduce their pathogenicity and instead elevated their expression of the Th17 cytokines GM-CSF and IL-17F. Mechanistic in vitro studies revealed a Th17 cell-intrinsic autocrine loop triggered by binding of IL-17A to its receptor, leading to activation of the transcription factor NF-κB and induction of IL-24, which repressed the Th17 cytokine program. In vivo, IL-24 treatment ameliorated Th17-induced EAU, whereas silencing of IL-24 in Th17 cells enhanced disease. This regulatory pathway also operated in human Th17 cells. Thus, IL-17A limits pathogenicity of Th17 cells by inducing IL-24. These findings may explain the disappointing therapeutic effect of targeting IL-17A in uveitis.

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IL-17A deficiency does not reduce the pathogenicity of Th17 cells in uveitis

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IL-17A binds to its own receptor on Th17 cells, activating NF-κB

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NF-κB induces IL-24 production, repressing the Th17 cytokine program through SOCS1/3

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Silencing or depleting IL-24 in Th17 cells exacerbates neuroinflammation

GM-CSF mediates development of eosinophil-dominant autoimmune uveitis in the absence of both IFN-γ and IL-17A

Autoimmune uveitis is a group of blinding diseases triggered by activated retina-specific T cells. Studies in uveitis patients and experiments in animal models of experimental autoimmune uveitis (EAU) support the notion that Th1 and Th17 cells are both pathogenic effectors and each can elicit ocular autoimmunity independently of the other. Since absence of IFN-γ or IL-17A individually failed to abolish pathology of EAU, we examined EAU development in the absence of both cytokines. Ifng−/−Il17a−/− mice were fully susceptible to EAU and displayed eosinophil-dominant ocular infiltrates, as opposed to mononuclear infiltrates in WT mice. EAU was ameliorated in double-deficient mice when eosinophils were genetically absent or their migration was blocked, supporting a pathogenic role of eosinophils in the absence of both IFN-γ and IL-17A. In Ifng−/−Il17a−/− mice immunized for EAU, ocular infiltrates contained increased GM-CSF-producing CD4 T cells, and supernatants of antigen-recalled splenocytes contained enhanced levels of GM-CSF that contributed to activation and migration of eosinophils in vitro. Systemic or local blockade of GM-CSF ameliorated EAU in Ifng−/−Il17a−/− mice. Neutralization of GM-CSF during the induction phase of EAU decreased eosinophil infiltration to the eye and eosinophil peroxidase levels in the eye and in the serum. These results support the interpretation that, in the concurrent absence of IFN-γ and IL-17A, GM-CSF takes on a major role as a pathogenic effector cytokine and induces an eosinophil-dominant pathology. This may impact therapeutic strategies aiming to target IFN-γ and IL-17A in autoimmune uveitis.

Toll-like Receptor 2 is crucial for commensal-specific immune responses on the ocular surface

Conjunctiva of the eye is a mucosal immune tissue and harbors a variety of immune cells. It is exposed to diverse microorganisms that come in contact with the ocular surface. Previously, we demonstrated that colonization of the ocular mucosa with the commensal bacterium, Corynebacterium mastitidis (C. mast), results in increased resistance of the ocular surface to infectious fungal and bacterial pathogens, and that this effect is mediated by IL-17A produced by γδ T cells that respond to C. mast. In this study, we show that Toll-like receptor 2 (TLR2) is important for activation and proliferation of γδ T cells and for their IL-17A production in response to C. mast.

TLR2−/− mice failed to recruit γδ T cells and neutrophils to the conjunctiva upon C. mast inoculation, and IL-17A-producing γδ T cells were reduced in eye-draining lymph nodes of these mice. In vitro experiments revealed that IL-17A production to C. mast by gd T cells was dependent on APC and that TLR2 expression was needed on both γδ T cells and APCs. Exogenous IL-1 could only partly compensate for the deficiency in IL-17A production by TLR2−/− gdT cells, indicating a need for another TLR2-dependent signal. Flow cytometry and RNA-Seq analyses suggested that dependence on TLR2 for IL-17A production and IL-17A related gene expression in response to C. mast is higher in the Vγ6 than in the Vγ4 subset. Notably, the transcriptomic analysis also implicated dysregulation of mitochondrial pathways in TLR2−/− cells, which was functionally confirmed by the Seahorse assay.

We conclude that TLR2 is required for sensing the commensal C. mast in the conjunctiva and eye-draining lymph nodes, to drive the local IL-17 response and maintain immune homeostasis at the ocular surface.

A novel self-regulatory mechanism of Th17 cells controls autoimmune uveitis through interleukin-24

The Th17 response is critical in driving inflammation and is associated with many autoimmune diseases. However, clinical trials targeting the Th17 signature cytokine, IL-17A in some autoimmune diseases, including uveitis, have been disappointing. We investigated the role of IL-17A in determining the pathogenicity of uveitogenic Th17 cells. Unexpectedly, IL-17A deficiency in these cells did not reduce the severity of uveitis in recipient mice. We found that IL-17A deficient Th17 cells produced elevated amounts of other Th17-related cytokines, i.e. IL-17F, GM-CSF and IL-22. RNA-seq analysis and the follow up in-vitro experiments revealed that IL-17A exerts a negative feedback on Th17 cells by inducing them to produce IL-24, which in turn suppresses the production of Th17-related cytokines in an autocrine fashion. In vivo results showed that IL-24 treatment of recipients ameliorated Th17-induced adoptive EAU, and conversely, silencing IL-24 expression in retina-specific Th17 cells increased their pathogenicity, supporting the relevance of this pathway in vivo. Mechanistic studies confirmed that IL-17A activates the NFkB signalling pathway in Th17 cells, whereas site mutagenesis at the NFkB binding sites In IL-24 promoter abrogates the IL-17A-induced IL-24 expression. In vitro experiments implicated SOCS 1 and 3 in the downstream effects of IL-24. Importantly, we also observed a similar inhibitory IL-17A/IL-24 circuit in polarized human Th17 cells. We conclude that IL-17A exerts a negative feedback on Th17 cells by inducing autocrine IL-24, which limits their expression of other Th17-lineage cytokines and dampens their pathogenicity.

The gut as a potential licensing site for central nervous system (CNS)-specific autoimmune lymphocytes

Autoimmune diseases of the CNS, experimental autoimmune encephalomyelitis (EAE) and experimental autoimmune uveoretinitis (EAU) can be induced by adoptive transfer (AT) of activated brain- or retina-specific T cells. The transferred T cells rest for several days in the recipient’s spleen or lungs, where they proliferate and differentiate to a migratory phenotype before invading the CNS, a process termed “licensing” for pathogenicity (PMID: 27986906). Our previous data in a spontaneous uveitis model in R161H mice bearing a retina-specific TCR indicated that the gut may serve as a priming site for uveitogenic T cells through molecular mimicry of gut flora (PMID: 26238373). We now asked if the gut might also serve as a licensing site for autopathogenic T cells.

Naive B10.RIII mice received AT of allotype-marked, activated R161H T cells and were monitored for EAU. Donor cells in tissues were detected by flow cytometry. Three days after AT, donor T cells could be detected in spleen, lung and gut, including the mesenteric lymph nodes and lamina propria of the large and small intestine. Similarly to lung and spleen, R161H T cells in the gut showed signs of proliferation by CFSE dilution. This was not altered by antibiotic treatment of recipients before AT to eliminate gut flora, suggesting that microbiota is not needed to retain effector T cells in the gut.

We hypothesize that primed retina-specific T cells can receive licensing signals in the gut. Since in spontaneous uveitis they may also be primed there, this could be of relevance to a disease situation. Further characterization of phenotypic and transcriptomic changes of “licensed” R161H cells retrieved from the gut may help to elucidate the local signals important for licensing at this site.

Association of gut microbiota with spontaneous autoimmune uveitis studied by human flora reconstitution of germ-free mice

Autoimmune uveitis is a T cell driven, intraocular inflammation that affects the neuroretina and can lead to blindness. In a mouse model of spontaneous autoimmune uveitis (R161H), retina-specific T cells are primed in the gut through their TCR and trigger disease (PMID: 26287682). To support the relevance to human disease, we examined development of uveitis and its association with bacterial taxa in gnotobiotic R161H mice harboring human flora. Specifically, fecal samples from three healthy human donors were inoculated into germ-free R161H mice and their wild type (WT) littermates in separate isolators. Fecal pellets from reconstituted mice and their offspring were collected periodically and subjected to 16S amplicon sequencing. Uveitis scores were determined in R161H offspring by histology at termination of the experiment. Our results show that healthy human gut commensals can support uveitis in R161H mice, but to a lesser extent than native mouse flora from the NIH facility. Diversity analyses indicate that human flora-reconstituted mice retained a distinct but simplified gut microbial community compared to the original sample, and R161H mice tended to have a more complex microbiome profile than WT littermates. Among R161H offspring, mice with high disease scores appeared to harbor more diverse gut flora than those with low scores. Differentially abundant bacterial taxa were identified between mice with different disease scores, which may associate with intensity of autoreactive T cell activation and development of autoimmunity. R161H associated with human gut flora could provide a more translatable platform than mouse flora to explore microbial candidates and products that may modulate autoreactive T cells in uveitis.

A novel role for lipoxin A4 in driving a lymph node-eye axis that controls autoimmunity to the neuroretina

The eicosanoid lipoxin A4 (LXA4) has emerging roles in lymphocyte-driven diseases. We identified reduced LXA4 levels in posterior segment uveitis patients and investigated the role of LXA4 in the pathogenesis of experimental autoimmune uveitis (EAU). Immunization for EAU with a retinal self-antigen caused selective downregulation of LXA4 in lymph nodes draining the site of immunization, while at the same time amplifying LXA4 in the inflamed target tissue. T cell effector function, migration and glycolytic responses were amplified in LXA4-deficient mice, which correlated with more severe pathology, whereas LXA4 treatment attenuated disease. In vivo deletion or supplementation of LXA4 identified modulation of CC-chemokine receptor 7 (CCR7) and sphingosine 1- phosphate receptor-1 (S1PR1) expression and glucose metabolism in CD4+ T cells as potential mechanisms for LXA4 regulation of T cell effector function and trafficking. Our results demonstrate the intrinsic lymph node LXA4 pathway as a significant checkpoint in the development and severity of adaptive immunity.

P6257Low systolic blood pressure on admission as a predictor of outcome in octogenarian patients with heart failure and preserved ejection fraction

Background

Heart failure (HF) is an epidemic in healthcare worldwide including Asia. It appears that HF will become more serious with aging of the population. The patients with heart failure and preserved ejection fraction (HFpEF) were older, more often female, and frequently have comorbidities including hypertension. However, lower systolic blood pressure (SBP) on admission is associated with poor outcomes in patients with HF. It remains unclear whether this association is similar in very elderly patients with HFpEF.

Purpose

To investigate clinical features and prognosis in octogenarian HFpEF subjects.

Methods

We analyzed 87 consecutive subjects aged 80 years or older who were hospitalized for acute decompensated HF with left ventricular ejection fraction (LVEF) ≥50% between 2015 and 2017. Clinical characteristics and a composite event of cardiac death and HF hospitalization were compared in two groups according to SBP cut-off of 140 mmHg on admission.

Results

The prevalence of lower SBP subjects (mean BP = 118 mmHg) and higher SBP (mean BP = 166 mmHg) subjects were 41.4% and 58.6%, respectively. Lower SBP subjects were more comorbid with atrial fibrillation (72.2 vs. 45.1%, p=0.01). In the lower SBP group, diuretics, mineralocorticoid receptor antagonists (MRA), beta-blockers and ACE inhibitors/ARBs were more commonly used than higher SBP group (Table). During the observational period (median = 1.0 year), lower SBP on admission was associated with a 2.65-fold [95% confidence interval (CI): 1.29–5.55, p=0.009] greater likelihood of experiencing the composite events of cardiac death and rehospitalization for HF (Figure). This observation was still consistent even after adjusting clinical demographics and comorbidity [hazard ratio = 2.95, 95% CI: 1.30–6.87, p=0.01].

Table 1 Lower SBP group (n=36) Higher SBP group (n=51) P-value Atrial fibrillation (%) 72.2 0.01 0.01 Loop diuretic (%) 97.1 83.7 0.08 MRA (%) 47.1 24.5 0.04 Beta-blocker (%) 52.9 44.9 0.51 ACE inhibitor/ARB (%) 59.2 29.4 0.01

Figure 1

Conclusions

In octogenarian patients with acute decompensated HF and preserved LVEF, SBP on admission less than 140 mmHg is significantly associated with poor outcomes. Future studies need to prospectively evaluate optimal SBP treatment goals in very elderly patients with HFpEF.

Production of IL-17A by different subsets of γδ T cells in response to the commensal Corynebacterium mastitidis has distinct requirements for IL-1R and TCR recognition

The ocular surface is a mucosal site that interacts with the environment and protects the eye. We previously identified an ocular surface commensal, Corynebacterium mastitidis (C. mast.), which induced IL-17A production from γδ T cells in the conjunctiva, affording protection from infection. In the current study we dissect the requirement for IL-17A production in response to C. mast by Vγ4+and Vγ4−γδ T cell subsets. We found that colonization of C. mast-negative mice with C. mast. increased the frequency of IL-17A+ cells in eye-draining lymph nodes by several fold in both subsets. However, whereas Vγ4−γδ T cells upregulated their expression of IL-1R, Vγ4+γδ cells downregulated their CD3 expression, possibly secondary to TCR engagement. To examine this further, we performed in vitro co-cultures of dendritic cells and γδ T cells. With C. mast as the sole stimulant, only Vγ4+ cells, but not Vγ4− cells, produced IL-17A. Addition of exogenous IL1 to the co-cultures elicited production of IL-17A also from the Vγ4− subset, whereas inhibition of downstream TCR signaling events by FK-506 or CsA abrogated IL-17A production in the Vγ4+ subset. Furthermore, C. mast produced a positive Nur77-GFP signal only in the Vγ4+ subset. IL-1R blocking antibody abrogated IL-17A production in both subsets.

We propose that Vγ4+and Vγ4− subsets may sense and respond to C. mast by IL-17A production using distinct pathways. Although an IL-1R signal is needed by both subsets, their level of dependence on this signal differs. IL-1R signaling is dominant in Vγ4−γδ T cells, whose TCR does not appear to respond to C. mast. In contrast, a much lower level of IL-1 appears to be sufficient for triggering IL-17A production from Vγ4+ γδ T cells, which recognize C. mast via their TCR.

Increased duration of antibiotic treatment progressively alters gut microbiota and revokes protection from ocular autoimmunity

Autoimmune uveitis, thought to be driven by retina-specific T cells, is a major cause of blindness. Using a model of experimental autoimmune uveitis (EAU), we showed that long-term elimination of commensals by oral antibiotic treatment (ABX) did not affect susceptibility to EAU, but others reported that short-term ABX was protective. To reconcile these contradictory findings, we studied whether duration of ABX differentially affected EAU development, gut microbiota and host-immune responses.

B10.RIII mice were treated orally with a broad-spectrum antibiotic cocktail, starting 12-weeks (long-term) or 1-week (short-term) before IRBP immunization for EAU induction, and continuing until the end of the experiment. Short-term ABX delayed the onset of EAU, whereas long-term ABX showed a pattern of EAU kinetics and severity similar to untreated SPF controls. Metagenomic analyses revealed ABX duration-dependent depletion of gut microbial communities. Interestingly, ABX also resulted in progressive depletion of CD4+ and CD4+CD8+ T cells from the gut intraepithelial lymphocyte (IEL) compartment. Notably, these IELs showed some cytotoxic activity in vitro, and are thought to help preserve gut mucosal barrier integrity.

We propose that microbiota play dual roles in uveitis development: they provide a stimulus for uveitogenic effector cells, but also maintain a “regulatory” IEL population, whose progressive loss reverses the temporary protection seen with short-term ABX. Further understanding of the role of IELs in the microbiota-gut-eye axis may lead to novel treatments for autoimmunity through manipulation of the commensal microbiome and gut epithelium.

AS101 ameliorates experimental autoimmune uveitis by regulating Th1 and Th17 responses and inducing Treg cells

AS101 is an organotellurium compound with multifaceted immunoregulatory properties that is remarkable for its lack of toxicity. We tested the therapeutic effect of AS101 in experimental autoimmune uveitis (EAU), a model for human autoimmune uveitis. Unexpectedly, treatment with AS101 elicited Treg generation in vivo in otherwise unmanipulated mice. Mice immunized for EAU with the retinal antigen IRBP and treated with AS101 developed attenuated disease, as did AS101-treated recipients of retina-specific T cells activated in vitro. In both settings, eye-infiltrating effector T cells were decreased, whereas regulatory T (Treg) cells in the spleen were increased. Mechanistic studies in vitro revealed that AS101 restricted polarization of retina-specific T cells towards Th1 or Th17 lineage by repressing activation of their respective lineage-specific transcription factors and downstream signals. Retina-specific T cells polarized in vitro towards Th1 or Th17 in the presence of AS101 had impaired ability to induce EAU in naïve recipients. Finally, AS101 promoted differentiation of retina-specific T cells to Tregs in vitro independently of TGF-β. We conclude that AS101 modulates autoimmune T cells by inhibiting acquisition and expression of effector function and by promoting Treg generation, and suggest that AS101 could be useful as a therapeutic approach for autoimmune uveitis.

Microbiome and Autoimmune Uveitis

Commensal microbes affect all aspects of immune development and homeostasis in health and disease. Increasing evidence points to the notion that the gut commensals impact not only intestinal diseases but also diseases in tissues distant from the gut. Autoimmune or non-infectious uveitis is a sight-threatening intraocular inflammation that affects the neuroretina. It is strongly T cell driven, but the precise causative mechanisms are not fully understood. We and others observed that depletion of gut microbiota in animal models of uveitis attenuated disease. Using a spontaneous model of the disease, we questioned how retina-specific uveitogenic T cells are primed when their cognate antigens are sequestered within the immune privileged eye. The data suggested that gut commensals provide a signal directly through the retina-specific T cell receptor and cause these autoreactive T cells to trigger uveitis. This activation of retina-specific T cells in the gut appears to be independent of the endogenous retinal antigen. Rather, the findings point to the notion that gut microbiota may mimic retinal antigen(s), however, the actual mimic has not yet been identified. Microbiota may also serve as an “adjuvant” providing innate signals that amplify and direct the host immune response for development of uveitis. In contrast, spontaneous uveitis that develops in AIRE^−/− mice appears to be independent of gut microbiota. To date, available data on human microbiota in association with uveitis are very limited and causative relationships are difficult to establish. This review will summarize the current knowledge on the role of microbiome in uveitis and its underlying mechanisms, and discuss unresolved questions and issues in an attempt to explore the concept of gut-retina axis.

Ocular autoimmunity develops despite concurrent absence of Th1 and Th17 signature cytokines

Th1 and Th17 cells are each a standalone effector phenotype, and each can elicit ocular autoimmunity independently of the other. In this study, we used mice deficient in IL-17A, or IFN-gamma (GKO), or both (DKO) to dissect the role of Th1 and Th17 cytokines in experimental autoimmune uveitis (EAU). EAU was induced by active immunization with the retinal autoantigen IRBP. Previous studies showed that EAU in GKO mice was exacerbated, whereas it was attenuated in IL-17A KO mice. Surprisingly, DKO mice were fully susceptible to EAU with scores similar to wild type (WT) controls, and displayed eosinophil-dominant infiltration along with enhancement of IL-17F, Th2, and proinflammatory cytokines. To test which cytokines contributed to pathology, EAU-challenged DKO mice were treated with blocking antibodies to IL-17F, TNF-a, GM-CSF or IL-4Ra (a shared subunit of receptor for IL-4 and IL-13). Blockade of IL-17F or TNF-a in DKO mice did not affect the severity of EAU. Treatment with an anti-GM-CSF antibody during both induction and expression stages significantly suppressed disease severity in DKO, but not in WT mice. By contrast, treatment of DKO mice with an anti-IL-4Ra antibody worsened EAU. Importantly, a single intravitreal injection of an anti-GM-CSF antibody after the disease onset reduced EAU severity in both WT and DKO mice. These results suggest that, in the absence of both IFN-gamma and IL-17A, (a) GM-CSF plays a major and nonredundant role as a pathogenic cytokine, (b) the Th2 cytokines IL-4 and/or IL-13 are protective, and (c) IL-17F and TNF-a may be dispensable. Our results highlight that ‘classical’ Th1 and Th17 cells are not the only pathogenic effectors, and that other inflammatory cytokine(s) can contribute to uveitis.

STAT-3-independent production of IL-17 by mouse innate-like αβ T cells controls ocular infection

St. Leger et al. identify and examine innate-like αβ T cells that circumvent canonical STAT-3 phosphorylation to produce protective IL-17. These cells can exist in the ocular mucosa and protect the ocular surface from pathogenic Staphylococcus aureus infection.

Appropriate regulation of IL-17 production in the host can mean the difference between effective control of pathogens and uncontrolled inflammation that causes tissue damage. Investigation of conventional CD4⁺ T cells (Th17 cells) has yielded invaluable insights into IL-17 function and its regulation. More recently, we and others reported production of IL-17 from innate αβ+ T cell populations, which was shown to occur primarily via IL-23R signaling through the transcription factor STAT-3. In our current study, we identify promyelocytic leukemia zinc finger (PLZF)–expressing iNKT, CD4⁻/CD8⁺, and CD4⁻/CD8⁻ (DN) αβ+T cells, which produce IL-17 in response to TCR and IL-1 receptor ligation independently of STAT-3 signaling. Notably, this noncanonical pathway of IL-17 production may be important in mucosal defense and is by itself sufficient to control pathogenic Staphylococcus aureus infection at the ocular surface.

IL-17A inhibits expression of IL-17-lineage cytokines through a negative feedback loop involving IL-24 and controls autoimmune uveitis

The Th17 response has been associated with autoimmune diseases in patients and in animal models. IL-17A is recognized as the Th17 signature cytokine and IL-17A-producing T cells are pathogenic effectors in models of autoimmunity, including experimental autoimmune uveitis (EAU). Paradoxically, however, injection of IL-17 ameliorates EAU (PMID: 19234216). Using a model of spontaneous uveitis in IRBP T cell receptor transgenic R161H mice, we investigated their susceptibility on the IL-17A−/− background. Surprisingly, IL-17A−/− R161H mice developed essentially undiminished uveitis and IL-17−/− R161H T cells, polarized to Th17 and infused into wild type recipients, induced similar disease to IL-17A sufficient R161H T cells. Interestingly, IL-17A−/− R161H T cells polarized under Th17 conditions produced elevated amounts of other Th17-related cytokines, i.e. IL-17F, GM-CSF and IL-22. Supplementing these cultures with recombinant IL-17A normalized the elevated production of these cytokines. RNAseq analysis revealed that IL-17A−/− T cells expressed lower levels of IL-24 compared to their IL-17A sufficient counterparts. Mechanistic studies indicated a negative feedback loop where IL-17A induces Th17 cells to produce IL-24, which subsequently suppresses production of Th17 lineage cytokines. Finally, injection of recombinant IL-24 ameliorated adoptive Th17-induced EAU, and conversely, silencing IL-24 expression in Th17 cells increased their pathogenicity and enhanced disease severity. Our data suggest that: (a) IL-17A exerts a negative feedback on uveitogenic Th17 cells via IL-24 production, and (b) IL-24 limits the expression of other Th17-related cytokines and controls their pathogenicity.

Nonredundant role for GM-CSF in autoimmune pathology of the neureretina in the absence of IFN-γ and IL-17A

Autoimmune uveitis is a complex group of sight-threatening CNS diseases caused by activated retina-specific Th1 or Th17 cells that acquired the ability to cross the blood-retinal barrier, but their respective contribution to disease is not fully understood. In this study, we used mice deficient in IL-17A, IFN-γ (GKO), or both (DKO) to dissect the role of Th1 and Th17 lineage-specific cytokines in pathogenesis of uveitis. Experimental autoimmune uveitis (EAU) was induced by active immunization with the retinal autoantigen IRBP in CFA. IL-17A−/− mice were protected from EAU, whereas GKO mice had exacerbated disease. Surprisingly, DKO mice were fully susceptible to EAU with scores similar to WT controls. The frequency of macrophages and production of proinflammatory cytokines (GM-CSF, IL-6, and TNF-α) was increased in the spleen and eyes of DKO mice. To test whether other T cell lineage-related cytokines contribute to pathology in the absence of IL-17A and IFN-γ, EAU-challenged DKO mice were treated with blocking Abs to IL-17F, IL-22, TNF-α, or GM-CSF. Blockade of IL-17F, IL-22, or TNF-α in DKO mice did not affect the severity of EAU. By contrast, treatment of DKO mice with an anti-GM-CSF Ab during the expression stage of disease significantly suppressed disease severity in DKO, but not in WT mice. These results suggest that IL-17F, IL-22 or TNF-α individually are dispensable, but GM-CSF appears to play a major and nonredundant role as a pathogenic cytokine in EAU when IFN-γ and IL-17A are both absent. Our results highlight that ‘classical’ Th1 and Th17 cells are not the only pathogenic effectors, and that other inflammatory cytokine(s), such as GM-CSF, can also drive uveitis.

Gut microbiota as a source of signals that trigger spontaneous ocular autoimmunity

Autoimmune uveitis, a major cause of blindness, is thought to be driven by T cells specific for unique retinal antigens that have been activated and acquired the ability to cross the blood-retinal barrier. However, it is unknown where and how they first become activated. The R161H mouse expresses a transgenic TCR specific for the retinal protein IRBP and develops spontaneous uveitis with 100% incidence, permitting to study natural triggers of disease. Retina-specific T cells were activated in the intestine of specific-pathogen-free (SPF) R161H mice. Elimination of gut commensals by oral treatment with antibiotics (ABX) or by rearing under germ-free conditions (GF) significantly attenuated uveitis and reduced Th17 cells in the gut lamina propria. Bacteria-rich extracts of intestinal contents from SPF, but not GF or ABX mice, activated retina-specific T cells in vitro, and R161H T cells signaled through the clonotypic TCR in the gut in vivo, suggesting a role for gut microbiota as a source of stimulating signals for retina-specific T cells. To dissect the contribution of adaptive vs innate microbial signals, gnotobiotic studies were performed: GF R161H mice exposed to SPF conditions developed full-blown uveitis, but mono-colonization with segmented filamentous bacteria (SFB) or a Turicibacter strain (T. H121) only partially restored disease. Unlike intestinal extracts from SPF mice, extracts from monocolonized mice failed to activate R161H T cells in vitro, suggesting lack of “antigen” activity, but SFB (not T. H121) restored gut Th17-producing cells, indicating presence of “adjuvant” activity. Thus, microbial-derived adaptive “antigen” and innate “adjuvant” signals are both required for full development of uveitis.

Visual function in retina-specific TCR-transgenic mice with spontaneous autoimmune uveitis

Autoimmune uveitis is a potentially blinding disease caused by circulating retina-specific T cells. To understand the mechanisms behind autoimmune uveitis, R161 transgenic mice expressing a TCR specific for IRBP, the retinal target protein for autoimmune uveitis in the mouse model, were generated. Three lines of R161 mice expressing the same TCR at different copy numbers have been established: R161H>R161M>R161L. The H and M lines developed spontaneous uveitis with 100% incidence by 2–3 months, whereas the L line developed disease only upon immune perturbation. The expression levels of the R161 TCR transgene correlated with frequency of IRBP-specific CD4 T cells in the peripheral repertoire, and with severity of disease. To study the association of visual function with pathology of uveitis, we examined visual function of R161 lines and compared with their parental strain B10.RIII (WT) by electroretinography (ERG), which measures electrical responses of retinal cells under dark- and light-adapted conditions. Uveitis was monitored and scored weekly by fundoscopy and ERG was performed in the next day following dark adaptation. Overall, as inflammatory scores increased, ERG responses decreased. R161L mice, which develop little or no disease, had visual function equivalent to WT mice. At 16 weeks old when disease in the H and M lines had reached its peak, R161H mice exhibited no and most of R161M mice exhibited poor visual function, whereas only minor reduction of ERG, which is normally observed with age, was detected in R161L and WT mice. The ERG data illustrate an association of visual function with uveitis scores among R161 lines, each of which may serve as a unique model of uveitis with different severity and visual loss.

Vitamin A deficiency impacts acquisition, but not expression, of autoimmunity to the neuroretina

Vitamin A (VitA) and its derivative retinoic acid (RA) are essential for immunological responses. Acquisition of effector responses is impeded in VitA-deficient (VAD) mice, but little is known about maintenance and expression of previously acquired effector function in the VAD environment, or its impact on progression of autoimmune diseases. We examined this using two models of uveitis: experimental autoimmune uveitis (EAU) induced by active immunization and spontaneous uveitis in retina-specific T cell receptor transgenic (R161H) mice, and in the model of experimental autoimmune encephalomyelitis (EAE). VAD was induced by dietary lack of VitA from before birth, or by daily injections of a pan-RA receptor inhibitor BMS493 in adult mice fed with standard diet. VAD mice were essentially resistant to induction of EAU or EAE and displayed impaired effector T cell responses. Defective priming/acquisition of effector function by VAD T cells was also evident in vitro. Interestingly, however, effector T cells primed in a VitA-sufficient environment were able to function in VAD recipients and induced EAU. Furthermore, spontaneously uveitic R161H mice fed with VAD diet, in which priming of pathogenic T cells occurs before onset of full VitA deficiency, appeared to develop unreduced or even exacerbated spontaneous uveitis compared to VitA-sufficient R161H mice. We conclude that although priming of naïve T cells in the VAD environment is defective, effector function acquired under VitA-sufficient conditions is maintained and can be expressed under VAD conditions. Because dietary lack of VitA is rarely profound and may be seasonal, our findings may shed light on immunity and autoimmunity in geographical regions where dietary VitA is limiting.

Gut microbiota as a source of a surrogate antigen that triggers autoimmunity in an immune privileged site

Recent discoveries on the role of commensal microbiota have significantly changed our understanding of human physiology. The host-microbiota interplay is now an important aspect to take into account to understand immune responses and immunological diseases. Autoimmune uveitis is a sight-threatening disease that arises without a known infectious etiology. It is unknown where and how autoreactive T cells become primed to trigger disease in the eye, which is an immune privileged site. We recently reported data supporting the notion that retina-specific T cells receive a signal in the gut from commensal microbiota-derived cross-reactive antigen(s) and trigger autoimmune uveitis in the R161H mouse model. Here we discuss our published findings, as well as our recent attempts to identify the responsible microbe(s) by using different antibiotic treatments, 16S rDNA sequencing and homology searches for candidate antigenic mimic(s) of the retinal antigen.

Regulation of Autoimmunity by the Microbiome

Intestinal microbes have profound effects on inflammatory autoimmunity in sites distant from the gut. The mechanisms whereby this happens are only now beginning to be understood and may include such diverse effects as innate stimulation of migrating immune cells and effects of circulating bacterial metabolites. Our studies add to this the demonstration that microbiota may provide a source of cross-reactive antigenic material that activates autoreactive lymphocytes within the gut environment. In a spontaneous model of autoimmune uveitis, T lymphocytes specific to a retinal autoantigen are activated through their specific antigen receptor in the gut and acquire the ability to fuel inflammatory autoimmunity in the eye. In view of the huge diversity of commensals, it is conceivable that they may provide surrogate antigens for activation of autoreactive lymphocytes(s) of other tissue specificities, and might therefore be involved in the etiology of autoimmune diseases more frequently than is currently appreciated.

Spontaneous Ocular Autoimmunity in Mice Expressing a Transgenic T Cell Receptor Specific to Retina: A Tool to Dissect Mechanisms of Uveitis

The "classical" EAU model induced by immunization of mice with the retinal protein IRBP or its peptides has been very useful to study basic mechanisms of ocular inflammation, but is inadequate for some types of studies due to the need for active immunization in the context of strong bacterial adjuvants. We generated transgenic (Tg) mice on the B10.RIII background that express a T cell receptor (TCR) specific for IRBP161-180. Three strains of TCR Tg mice were established. Spontaneous uveitis developed in two of the three strains by 2-3 months of age. Susceptibility correlated with a higher copy number of the transgenic TCR and a higher proportion of TCR Tg T cells in the peripheral repertoire. Even in mice with uveitis, peripheral IRBP-specific CD4(+) T cells displayed mostly a naïve phenotype. In contrast, T cells infiltrating uveitic eyes mostly showed an effector/memory phenotype, and included Th1, Th17 as well as T regulatory cells. These mice thus provide a new and distinct model of uveitis from the "classical" EAU, and may represent some types of uveitis more faithfully. Importantly, this new transgenic model of uveitis can serve as a template for therapeutic manipulations, and as a source of naïve retina-specific T cells for a variety of basic and pre-clinical studies. Several examples of such studies will be discussed.

Dependence of spontaneous autoimmunity to neuroretina on Th1 and Th17 effector cytokines

Autoimmune uveitis is a group of sight-threatening diseases caused by retina-specific autoreactive T cells. Upon activation, these retina-specific T cells differentiate into effector cells that can cross the blood-retinal barrier to cause uveitis. IFN-γ-secreting Th1 cells and IL-17A-secreting Th17 cells are thought to be pathogenic populations in tissue-specific autoimmune diseases, including uveitis. However, the contribution of either subset to disease pathogenesis is still controversial. In this study, we analyzed the role of Th1 and Th17 subsets in the R161H mice, which express a transgenic T cell receptor specific for the retinal protein IRBP and develop spontaneous uveitis with high penetrance. To understand how these effectors and their respective signature cytokines contribute to pathogenesis, we crossed R161H mice with IL-17A−/− and/or IFN-γ−/− (GKO) mice. R161H-GKO mice developed significantly attenuated disease with delayed onset, whereas disease in R161H-IL-17A−/− mice was essentially undiminished, suggesting IFN-γ, but not IL-17A, is critical for pathogenesis. Although the number of ocular infiltrating cells in R161H-GKO mice was decreased, the proportions of Th17 cells and granulocytes were increased, in line with an enhanced Th17 response in the absence of IFN-γ. Surprisingly, R161H mice made deficient in both IL-17A and IFN-γ developed more severe disease than R161H-GKO mice, although its onset was also delayed. These results suggest that ‘classic’ Th1 and Th17 cells are not the only pathogenic effectors in uveitis, and that inflammatory cytokine(s) other than IFN-γor IL-17A can also drive disease. Further mechanistic studies may uncover novel effector pathways in pathogenesis of ocular autoimmunity.

Complete Genome Sequence of Turicibacter sp. Strain H121, Isolated from the Feces of a Contaminated Germ-Free Mouse

Turicibacterbacteria are commonly detected in the gastrointestinal tracts and feces of humans and animals, but their phylogeny, ecological role, and pathogenic potential remain unclear. We present here the first complete genome sequence ofTuricibactersp. strain H121, which was isolated from the feces of a mouse line contaminated following germ-free derivation.

Preparation of Protein-containing Extracts from Microbiota-rich Intestinal Contents

The contribution of microbiota in regulating multiple physiological and pathological host responses has been studied intensively in recent years. Evidence suggests that commensal microbiota can directly modulate different populations of cells of the immune system (e.g., Ivanov et al., 2008; Atarashi et al., 2011). Recently, we showed that protein extracts from gut commensal microbiota can activate retina-specific T cells, allowing these autoreactive T cells to then break through the blood-retinal barrier and trigger autoimmune uveitis in the recipient (Horai et al., 2015). The protocol below describes the method to prepare intestinal protein-rich extracts that can be used in various in vitro andin vivo immunological studies.

Tertiary Lymphoid Tissue Forms in Retinas of Mice with Spontaneous Autoimmune Uveitis and Has Consequences on Visual Function

During chronic inflammation, tertiary lymphoid tissue (TLT) can form within an inflamed organ, including the CNS. However, little is known about TLT formation in the neuroretina. In a novel spontaneous autoimmune mouse model of uveitis (R161H), we identified well-organized lymphoid aggregates in the retina and examined them for TLT characteristics. Presence of immune cells, tissue-specific markers, and gene expression patterns typically associated with germinal centers and T follicular helper cells were examined using immunohistochemistry and gene analysis of laser capture microdissected retina. Our data revealed the retinal lymphoid structures contained CD4(+) T cells and B cells in well-defined zonal areas that expressed classic germinal center markers, peanut lectin (agglutinin) and GL-7. Gene expression analysis showed upregulation of T follicular helper cell markers, most notably CXCR5 and its ligand CXCL13, and immunohistochemical analysis confirmed CXCR5 expression, typically associated with CD4(+) T follicular helper cells. Highly organized stromal cell networks, a hallmark of organized lymphoid tissue, were also present. Positive staining for phospho-Zap70 in retina-specific T cells indicated CD4(+) T cells were being activated within these lymphoid structures. CD138(+)/B220(+) plasma cells were detected, suggesting the retinal lymphoid aggregates give rise to functional germinal centers, which produce Abs. Interestingly, eyes with lymphoid aggregates exhibited lower inflammatory scores by fundus examination and a slower initial rate of loss of visual function by electroretinography, compared with eyes without these structures. Our findings suggest that the lymphoid aggregates in the retina of R161H mice represent organized TLT, which impact the course of chronic uveitis.

Microbiota-Dependent Activation of an Autoreactive T Cell Receptor Provokes Autoimmunity in an Immunologically Privileged Site

Activated retina-specific T cells that have acquired the ability to break through the blood-retinal barrier are thought to be causally involved in autoimmune uveitis, a major cause of human blindness. It is unclear where these autoreactive T cells first become activated, given that their cognate antigens are sequestered within the immune-privileged eye. We demonstrate in a novel mouse model of spontaneous uveitis that activation of retina-specific T cells is dependent on gut commensal microbiota. Retina-specific T cell activation involved signaling through the autoreactive T cell receptor (TCR) in response to non-cognate antigen in the intestine and was independent of the endogenous retinal autoantigen. Our findings not only have implications for the etiology of human uveitis, but also raise the possibility that activation of autoreactive TCRs by commensal microbes might be a more common trigger of autoimmune diseases than is currently appreciated.

Retina-specific T cells provide neuroprotection in a mouse model of glaucoma (BA6P.140)

Glaucoma is a disease that leads to degeneration of retinal ganglion cells (RGC) and is potentially blinding if left untreated. Based on the concept of “beneficial autoimmunity”, we examined whether naïve, retina-specific T lymphocytes can provide neuroprotection to retinal ganglion cells in an optic nerve crush injury glaucoma model. Purified T cells from mice that express the transgenic R161H TCR for the retinal antigen IRBP, as well as eGFP (R161H-eGFP), were adoptively transferred into wild type (WT) mice. Also, irradiated bone marrow (BM) chimeras were stably engrafted with <10% circulating R161H-eGFP cells. Recipient mice were subjected to retrograde fluorogold labeling for quantification of RGC prior to an optic nerve crush injury. Retinas were imaged 4 or 7 days later for quantification of RGCs and donor R161H-eGFP T cells were detected by confocal microscopy. In both types of recipients, T cell influx into the eye and neuroprotection were apparent, but differed in kinetics. In adoptively transferred mice, R161H T cells were detected in the eye 4 days post injury and were associated with 27% less RGC loss compared to controls infused with normal polyclonal eGFP+ T cells (p<0.05). In the BM chimeric mice, major influx of R161H-eGFP cells occurred at 7 days post injury and was associated with a 16% statistically significant reduction in RGC loss. We conclude that naïve retina-specific T cells can mediate neuroprotection of retinal ganglion cells.

Retina-specific T regulatory cells bring about resolution and maintain remission of autoimmune uveitis

Experimental autoimmune uveitis (EAU) induced in mice by immunization with the retinal Ag interphotoreceptor retinoid-binding protein (IRBP) is a model of human autoimmune uveitis. We examined whether T regulatory cells (Tregs) found in uveitic eyes are IRBP specific, functionally suppressive, and play a role in natural resolution of disease and in maintenance of remission. Progressive increase of Foxp3(+) Treg to T effector cell (Teff) ratio in uveitic eyes correlated with resolution of disease. At peak disease, up to 20% of Tregs (CD4(+)Foxp3(+)) and up to 60% of Teffs (CD4(+)Foxp3(-)) were IRBP specific, whereas in lymphoid organs retina-specific T cells were undetectable. Tregs isolated from eyes of mice with EAU efficiently suppressed IRBP-specific responses of Teffs from the same eyes. Importantly, systemic depletion of Tregs at peak disease delayed resolution of EAU, and their depletion after resolution triggered a relapse. This could be partially duplicated by depletion of Tregs locally within the eye. Thus, the T cell infiltrate in uveitic eyes of normal mice with a polyclonal T cell repertoire is highly enriched in IRBP-specific Tregs and Teffs. Unlike what has been reported for Tregs in other inflammatory sites, Tregs from uveitic eyes appear unimpaired functionally. Finally, Foxp3(+) Tregs play a role in the natural resolution of uveitis and in the maintenance of remission, which occurs at least in part through an effect that is local to the eye.

Activation of autoreactive T cells by endogenous microflora induces spontaneous autoimmunity in the immunologically privileged retina (BA8P.130)

Autoimmune uveitis (AU) has an incidence similar to multiple sclerosis, it develops spontaneously and is a major cause of blindness. We hypothesized that AU could be triggered by endogenous microbiota in view of anecdotal evidence linking AU to systemic infections. We tested this in R161H mice, a new model of AU developed in our lab. R161H mice express a transgenic T cell receptor (TCR) specific to retinal protein IRBP and develop spontaneous uveitis starting at 4 weeks of age. R161H mice treated with an antibiotic cocktail, or reared under germ free conditions, had a significant delay in disease onset and intensity compared to controls, as well as fewer IL-17-secreting T cells in the gut LP. Notably, conventionally housed R161H mice consistently displayed 2-5x more Th17 cells in their LP compared to WT littermates, even when crossed onto an IRBP-deficient background. Compared to polyclonal T cells, R161H TCR transgenic T cells were more readily activated by extracts of gut contents in vitro and adopted the Th17 phenotype in the gut with higher frequency in vivo. Experiments utilizing Nur77 reporter mice and pZap70, revealed clear evidence that IRBP-specific T cells receive an activation signal through their TCR in the gut. These data not only have implications for etiology of human uveitis, but also raise the possibility that activation of autoreactive TCRs by commensal microflora may be a more common trigger of autoimmune diseases than is currently appreciated

IL-27p28 inhibits central nervous system autoimmunity by concurrently antagonizing Th1 and Th17 responses

Central nervous system (CNS) autoimmunity such as uveitis and multiple sclerosis is accompanied by Th1 and Th17 responses. In their corresponding animal models, experimental autoimmune uveitis (EAU) and experimental autoimmune encephalomyelitis (EAE), both responses are induced and can drive disease independently. Because immune responses have inherent plasticity, therapeutic targeting of only one pathway could promote the other, without reducing pathology. IL-27p28 antagonizes gp130, required for signaling by IL-27 and IL-6, which respectively promote Th1 and Th17 responses. We therefore examined its ability to protect the CNS by concurrently targeting both effector responses. Overexpression of IL-27p28 in vivo ameliorated EAU as well as EAE pathology and reduced tissue infiltration by Th1 and Th17 cells in a disease prevention, as well as in a disease reversal protocol. Mechanistic studies revealed inhibition of Th1 and Th17 commitment in vitro and decreased lineage stability of pre-formed effectors in vivo, with reduction in expression of gp130-dependent transcription factors and cytokines. Importantly, IL-27p28 inhibited polarization of human T cells to the Th1 and Th17 effector pathways. The ability of IL-27p28 to inhibit generation as well as function of pathogenic Th1 and Th17 effector cells has therapeutic implications for controlling immunologically complex autoimmune diseases.

Comparative analysis of induced vs. spontaneous models of autoimmune uveitis targeting the interphotoreceptor retinoid binding protein

Animal models of autoimmunity to the retina mimic specific features of human uveitis, but no model by itself reproduces the full spectrum of human disease. We compared three mouse models of uveitis that target the interphotoreceptor retinoid binding protein (IRBP): (i) the "classical" model of experimental autoimmune uveitis (EAU) induced by immunization with IRBP; (ii) spontaneous uveitis in IRBP T cell receptor transgenic mice (R161H) and (iii) spontaneous uveitis in Autoimmune Regulator (AIRE)(-/-) mice. Disease course and severity, pathology and changes in visual function were studied using fundus imaging and histological examinations, optical coherence tomography and electroretinography. All models were on the B10.RIII background. Unlike previously reported, IRBP-induced EAU in B10.RIII mice exhibited two distinct patterns of disease depending on clinical scores developed after onset: severe monophasic with extensive destruction of the retina and rapid loss of visual signal, or lower grade with a prolonged chronic phase culminating after several months in retinal degeneration and loss of vision. R161H and AIRE(-/-) mice spontaneously developed chronic progressive inflammation; visual function declined gradually as retinal degeneration developed. Spontaneous uveitis in R161H mice was characterized by persistent cellular infiltrates and lymphoid aggregation, whereas AIRE(-/-) mice characteristically developed multi-focal infiltrates and severe choroidal inflammation. These data demonstrate variability and unique distinguishing features in the different models of uveitis, suggesting that each one can represent distinct aspects of uveitis in humans.

The Arf GAP SMAP2 is necessary for organized vesicle budding from the trans-Golgi network and subsequent acrosome formation in spermiogenesis

SMAP2 is an Arf GAP and modulates clathrin-coated vesicle formation. SMAP2-deficient male mice exhibited globozoospermia due to acrosome deformation. In SMAP2(−/−) spermatids, budding of proacrosomal vesicles from the TGN was distorted and clathrin traffic–related molecules such as CALM and syntaxin2 were mislocated.

The trans-Golgi network (TGN) functions as a hub organelle in the exocytosis of clathrin-coated membrane vesicles, and SMAP2 is an Arf GTPase-activating protein that binds to both clathrin and the clathrin assembly protein (CALM). In the present study, SMAP2 is detected on the TGN in the pachytene spermatocyte to the round spermatid stages of spermatogenesis. Gene targeting reveals that SMAP2-deficient male mice are healthy and survive to adulthood but are infertile and exhibit globozoospermia. In SMAP2-deficient spermatids, the diameter of proacrosomal vesicles budding from TGN increases, TGN structures are distorted, acrosome formation is severely impaired, and reorganization of the nucleus does not proceed properly. CALM functions to regulate vesicle sizes, and this study shows that CALM is not recruited to the TGN in the absence of SMAP2. Furthermore, syntaxin2, a component of the soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) complex, is not properly concentrated at the site of acrosome formation. Thus this study reveals a link between SMAP2 and CALM/syntaxin2 in clathrin-coated vesicle formation from the TGN and subsequent acrosome formation. SMAP2-deficient mice provide a model for globozoospermia in humans.

Use of optical coherence tomography and electroretinography to evaluate retinal pathology in a mouse model of autoimmune uveitis

Experimental autoimmune uveoretinitis (EAU) in mice is a model for human autoimmune uveitis. Longitudinal follow-up is only possible by non-invasive techniques, but the information obtained by visual fundus examination can be limited. We therefore evaluated the efficacy of optical coherence tomography (OCT) and electroretinography (ERG) to monitor pathological and functional changes of the retina in vivo. OCT imaging and ERG recording as a measure of visual function were compared with visual fundoscopic imaging and histology findings in the same mouse. Our results showed that OCT imaging of the retina was well correlated with clinical and histological observations in mice during EAU. However, OCT imaging was more sensitive than fundoscopic imaging in detecting the cell infiltrates at the early phase of disease onset. Furthermore, by allowing multi-layer cross- and horizontal-sectional visualizations of retinal lesions longitudinally in a noninvasive fashion, OCT added information that could not be obtained by fundoscopic and histological examinations. Lastly, retinal thickness obtained by OCT imaging provided a key indicator reflecting disease activity, which showed a close association with visual dysfunction as measured by ERG recordings in EAU mice. Thus, our findings demonstrate that OCT is a highly sensitive and reliable technique, and a valuable method for the semi-quantitative evaluation of retinal inflammation in vivo in the mouse.

Reciprocal interaction between NK cells and DCs regulates the Th17 response by controlling the innate IFN-γ/IL-27 axis (P4067)

Experimental autoimmune uveitis (EAU) is a model for human uveitis. IFN-γ deficient mice develop enhanced EAU with elevated Th17 responses. This protective effect of IFN-γ appears at odds with the ability of IFN-γ-producing Th1 cells to induce EAU. We previously showed that it is innate IFN-γ that is protective, whereas adaptive IFN-γ is pathogenic. We now demonstrate that NK cells, a major cellular source of innate IFN-γ, interact with DCs in draining lymph nodes of EAU-challenged mice to ameliorate disease by controlling the innate IFN-γ/IL-27 axis. After immunization, both NK cells and DCs were recruited to the draining lymph nodes, with recruitment of NK cells being at least partially dependent on DCs and CXCR3. Infusion of IFN-γ-sufficient WT NK cells into IFN-γ-/- recipients reduced their EAU scores and enhanced production of IL 27, a suppressor of the Th17 response, from DCs of these mice. In vivo neutralization of IL-27 abolished the protective effect of WT NK cells on EAU. In vitro experiments revealed that mature DCs induced NK cells to produce IFN-γ, which in turn caused DCs to produce IL-27. IL-27 then stimulated NK cells to produce more IFN-γ, suggesting the presence of a positive feedback loop. IL-27 also promoted generation of IL-10-producing Tr1-like cells. Our results suggest that the magnitude of the Th17 response, and consequently the severity of disease, is controlled by the interaction between NK cells and DCs through the IFN-γ/IL-27 axis.

Tertiary lymphoid tissue with germinal centers and T follicular helper cells in immunologically privileged retinas of mice with chronic autoimmune uveitis (P4172)

Mice transgenic for a retina-specific T cell receptor develop spontaneous autoimmune uveitis. In contrast to induced models of uveitis the disease is prolonged and the mice display distinct retinal lesions that resemble tertiary lymphoid tissue. Here we investigate these lesions for presence of germinal center (GC) and T follicular helper cell (TfH) markers. Retinas were immunohistochemically stained for CD4+ T cells, CD8+ T cells, and B cells, as well as the GC markers PNA and GL-7. The retinal lesions stained positively for CD4+ T cells and B cells and also for PNA and GL-7. Laser capture microdissection was then used to isolate the retinal lesions and microarray analysis was performed to assess expression of GC- and TfH-associated genes. The microdissected lesions consistently showed upregulation of germinal center markers and T follicular helper cell markers with a 4 fold increase in Btla, Fas, and CXCL13, a 3.5 fold increase in CXCR5, and a doubling in CXCR4 compared to control retina. Heat map analysis revealed a similar gene expression profile of the retinal lesions to that of germinal centers present in 5 day-immunized spleen and lymph nodes. We conclude that despite the immunologically privileged status enjoyed by the eye, chronic autoimmune uveitis precipitates development of tertiary lymphoid tissue in the retina, expressing genes and immunological markers characteristic of GC and TfH.

IL27p28 inhibits induction and expression of experimental autoimmune uveitis by concurrently antagonizing autoaggressive Th1 and Th17 responses. (123.43)

Human autoimmune uveitis is accompanied by elevated Th1 and Th17 responses. In experimental autoimmune uveitis (EAU) induced in mice with the retinal antigen IRBP, both responses are present and each effector lineage can mediate disease independently. A therapeutic approach that targets both Th1 and Th17 would therefore be attractive. IL27p28 is an antagonist of gp130, which is required for IL-6 and for IL-27 signaling. Since IL-6 and IL 27 promote Th17 and Th1 responses respectively, we hypothesized that IL27p28 would regulate EAU by affecting both responses concurrently. Overexpression of IL27p28 reduced IFN-γ and IL-17A production from eye-infiltrating CD4+ T cells and ameliorated EAU induced by active immunization. Mechanistic studies revealed that IL27p28 suppressed IL6-mediated STAT3 and IL27-mediated STAT1 phosphorylation during Th17 and Th1 polarization, respectively. Furthermore, overexpression of IL27p28 ameliorated EAU induced by passive transfer of uveitogenic effector Th1 or Th17 cells obtained from donors expressing an IRBP-specific TCR. Donor TCR-transgenic T cells recovered from these mice expressed reduced levels of Th17 and Th1 signature cytokines, IL-17A and IFN-γ, and of their corresponding transcription factors, RORγt and Tbet. The ability of IL27p28 to inhibit both Th1 and Th17 responses and to ameliorate not only the induction, but also the effector phase of EAU, bodes well for clinical usefulness of IL27p28 augmentation to control autoimmunity.

The living eye "disarms" uncommitted autoreactive T cells by converting them to Foxp3(+) regulatory cells following local antigen recognition

Immune privilege is used by the eye, brain, reproductive organs, and gut to preserve structural and functional integrity in the face of inflammation. The eye is arguably the most vulnerable and, therefore, also the most "privileged" of tissues; paradoxically, it remains subject to destructive autoimmunity. It has been proposed, although never proven in vivo, that the eye can induce T regulatory cells (Tregs) locally. Using Foxp3-GFP reporter mice expressing a retina-specific TCR, we now show that uncommitted T cells rapidly convert in the living eye to Foxp3(+) Tregs in a process involving retinal Ag recognition, de novo Foxp3 induction, and proliferation. This takes place within the ocular tissue and is supported by retinoic acid, which is normally present in the eye because of its function in the chemistry of vision. Nonconverted T cells showed evidence of priming but appeared restricted from expressing effector function in the eye. Pre-existing ocular inflammation impeded conversion of uncommitted T cells into Tregs. Importantly, retina-specific T cells primed in vivo before introduction into the eye were resistant to Treg conversion in the ocular environment and, instead, caused severe uveitis. Thus, uncommitted T cells can be disarmed, but immune privilege is unable to protect from uveitogenic T cells that have acquired effector function prior to entering the eye. These findings shed new light on the phenomenon of immune privilege and on its role, as well as its limitations, in actively controlling immune responses in the tissue.