Characterization of a New Epitope of IRBP That Induces Moderate to Severe Uveoretinitis in Mice With H-2b Haplotype

4-Octyl Itaconate Inhibits Proinflammatory Cytokine Production in Behcet's Uveitis and Experimental Autoimmune Uveitis

4-octyl itaconate (4-OI) is an anti-inflammatory metabolite that activates the nuclear-factor-E2-related factor 2 (NRF2) signaling. In the current work, we investigated whether 4-OI could affect the production of proinflammatory cytokines in Behcet's uveitis (BU) and experimental autoimmune uveitis (EAU). Peripheral blood mononuclear cells (PBMCs) of active BU patients and healthy individuals with in vitro 4-OI treatment were performed to assess the influence of 4-OI on the proinflammatory cytokine production. EAU was induced and used for investigating the influence of 4-OI on the proinflammatory cytokine production in vivo. The flow cytometry, qPCR, and ELISA were performed to detect proinflammatory cytokine expression. NRF2 signaling activation was evaluated by qPCR and western blotting (WB). Splenic lymphocyte transcriptome was performed by RNA sequencing. The NRF2 expression by BU patients-derived PBMCs was lower than that by healthy individuals. After treatment with 4-OI, the proportion of Th17 cells, along with the expression of proinflammatory cytokines (IL-17, TNF-α, MCP-1, and IL-6) by PBMCs, were downregulated, and anti-inflammatory cytokine (IL-10) expression was upregulated, although IFN-γ expression was unaffected. The EAU severity was ameliorated by 4-OI in association with a lower splenic Th1/Th17 cell proportion and increased nuclear NRF2 expression. Additionally, 4-OI downregulated a set of 248 genes, which were enriched in pathways of positive regulation of immune responses. The present study shows an inhibitory effect of 4-OI on the proinflammatory cytokine production in active BU patients and EAU mice, possibly mediated through activating NRF2 signaling. These findings suggest that 4-OI could act as a potential therapeutic drug for the treatment and prevention of BU in the future study.

Comprehensive Grading System for Experimental Autoimmune Uveitis in Mice

Experimental autoimmune uveitis (EAU) is the most commonly used animal model to study the progression of chronic uveitis and to test various therapies to treat the disease. However, to accurately evaluate the effectiveness of such treatments, a grading system that combines the latest imaging techniques with definitive quantitative grading thresholds is required. This study aimed to develop a comprehensive grading system that objectively evaluates EAU progression in C57BL/6J mice. EAU was induced following immunisation with interphotoreceptor retinoid-binding protein (IRBP) and pertussis toxin. Weekly fundus and optical coherence tomography (OCT) images were acquired over 12 weeks using a Micron IV imaging system. Each mouse was graded (between 0 to 4) based on changes seen on both the fundus (optic disc, retinal blood vessels and retinal tissue) and OCT (vitreous and retinal layers) images. A total EAU response (with a maximum score of 48) was calculated for each mouse based on the sum of the individual scores each week. Analysis of the clinical scores depicted a gradual increase in inflammatory signs including optic disc and vascular swelling, leukocyte infiltration in the vitreous, lesions in the retina and formation of granulomas and hyper-reflective foci in the retinal layers in EAU mice, with most signs reaching a plateau towards the end of the study period. Development of these signs into sight-threatening complications such as optic disc atrophy, structural damage to the retina and subretinal oedema were noted in 80-90% of mice suggesting consistent disease induction. Overall, a comprehensive and objective grading system encompassing all pathologies occurring in EAU mice was developed to enhance the preclinical evaluation of novel uveitis treatments.

Growth hormone releasing hormone signaling promotes Th17 cell differentiation and autoimmune inflammation

Dysregulation of Th17 cell differentiation and pathogenicity contributes to multiple autoimmune and inflammatory diseases. Previously growth hormone releasing hormone receptor (GHRH-R) deficient mice have been reported to be less susceptible to the induction of experimental autoimmune encephalomyelitis. Here, we show GHRH-R is an important regulator of Th17 cell differentiation in Th17 cell-mediated ocular and neural inflammation. We find that GHRH-R is not expressed in naïve CD4⁺ T cells, while its expression is induced throughout Th17 cell differentiation in vitro. Mechanistically, GHRH-R activates the JAK-STAT3 pathway, increases the phosphorylation of STAT3, enhances both non-pathogenic and pathogenic Th17 cell differentiation and promotes the gene expression signatures of pathogenic Th17 cells. Enhancing this signaling by GHRH agonist promotes, while inhibiting this signaling by GHRH antagonist or GHRH-R deficiency reduces, Th17 cell differentiation in vitro and Th17 cell-mediated ocular and neural inflammation in vivo. Thus, GHRH-R signaling functions as a critical factor that regulates Th17 cell differentiation and Th17 cell-mediated autoimmune ocular and neural inflammation.

IL-27-containing exosomes secreted by innate B-1a cells suppress and ameliorate uveitis

Introduction

IL-27 is a heterodimeric cytokine composed of Ebi3 and IL-27p28 and can exert proinflammatory or immune suppressive effects depending on the physiological context. Ebi3 does not contain membrane-anchoring motifs, suggesting that it is a secreted protein while IL-27p28 is poorly secreted. How IL-27p28 and Ebi3 dimerize in-vivo to form biologically active IL-27 is unknown. Major impediment to clinical use of IL-27 derives from difficulty of determining exact amount of bioavailable heterodimeric IL-27 needed for therapy.

Methods

To understand how IL-27 mediates immune suppression, we characterized an innate IL-27-producing B-1a regulatory B cell population (i27-Breg) and mechanisms i27-Bregs utilize to suppress neuroinflammation in mouse model of uveitis. We also investigated biosynthesis of IL-27 and i27-Breg immunobiology by FACS, immunohistochemical and confocal microscopy.

Results

Contrary to prevailing view that IL-27 is a soluble cytokine, we show that i27-Bregs express membrane-bound IL-27. Immunohistochemical and confocal analyses co-localized expression of IL-27p28 at the plasma membrane in association with CD81 tetraspanin, a BCR-coreceptor protein and revealed that IL-27p28 is a transmembrane protein in B cells. Most surprising, we found that i27-Bregs secrete IL-27-containing exosomes (i27-exosomes) and adoptive transfer of i27-exosomes suppressed uveitis by antagonizing Th1/Th17 cells, up-regulating inhibitory-receptors associated with T-cell exhaustion while inducing Treg expansion.

Discussion

Use of i27-exosomes thus obviates the IL-27 dosing problem, making it possible to determine bioavailable heterodimeric IL-27 needed for therapy. Moreover, as exosomes readily cross the blood-retina-barrier and no adverse effects were observed in mice treated with i27-exosome, results of this study suggest that i27-exosomes might be a promising therapeutic approach for CNS autoimmune diseases.

Optimization of determinant factors associated with the efficiency of experimental autoimmune uveitis induction in C57BL/6 mice

Background

Experimental autoimmune uveitis (EAU) is a widely used animal model for uveitis research. The C57BL/6 mouse strain is the most commonly used mouse strain in the research of genetic modification, but C57BL/6 mice are not sufficiently susceptible to EAU induction, partly due to experimental factors. This work aims to optimize relevant factors to improve the efficiency of EAU induction in C57BL/6 mice.

Methods

To induce EAU, mice were immunized via intraperitoneal injection with pertussis (PTX) and subcutaneous injection with interphotoreceptor retinoid-binding protein peptide 1-20 (IRBP_1-20) emulsified with complete Freund's adjuvant (CFA). The severity of inflammation was assessed using several approaches. The relevant experimental factors were evaluated, including methods of emulsification and doses of peptide and PTX.

Results

Uveitis occurred at 8-12 days after immunization and reached its peak at 18-20 days, while T helper type 17 (Th17) cells peaked earlier at 14-18 days after immunization. Based on clinical and histological scores, 500 µg of IRBP peptide was the optimal dose required to induce EAU. The PTX dose demonstrated no influence on EAU incidence, but potentially affected the severity of uveitis. A single injection of 1,000 ng of PTX induced the most severe EAU and the highest proportion of Th17 cells. Compared to extruded emulsion, sonicated emulsion produced a higher incidence, higher histological score, and a 2-day-earlier onset of EAU. Electron microscopy showed a significantly different microstructure between the 2 emulsions.

Conclusions

This work optimized the protocols of EAU induction and obtained a high and stable induction rate with severe inflammation in the C57BL/6 mouse strain. Our results facilitate future experimental research involving uveitis.

Clinical implications of tristetraprolin (TTP) modulation in the treatment of inflammatory diseases

Abnormal regulation of pro-inflammatory cytokine and chemokine mediators can contribute to the excess inflammation characteristic of many autoimmune diseases, such as rheumatoid arthritis, psoriasis, Crohn's disease, type 1 diabetes, and many others. The tristetraprolin (TTP) family consists of a small group of related RNA-binding proteins that bind to preferred AU-rich binding sites within the 3'-untranslated regions of specific mRNAs to promote mRNA deadenylation and decay. TTP deficient mice develop a severe systemic inflammatory syndrome consisting of arthritis, myeloid hyperplasia, dermatitis, autoimmunity and cachexia, due at least in part to the excess accumulation of proinflammatory chemokine and cytokine mRNAs and their encoded proteins. To investigate the possibility that increased TTP expression or activity might have a beneficial effect on inflammatory diseases, at least two mouse models have been developed that provide proof of principle that increasing TTP activity can promote the decay of pro-inflammatory and other relevant transcripts, and decrease the severity of mouse models of inflammatory disease. Animal studies of this type are summarized here, and we briefly review the prospects for harnessing these insights for the development of TTP-based anti-inflammatory treatments in humans.

Photoreceptor Cells Constitutively Express IL-35 and Promote Ocular Immune Privilege

Interleukin-27 is constitutively secreted by microglia in the retina or brain, and upregulation of IL-27 during neuroinflammation suppresses encephalomyelitis and autoimmune uveitis. However, while IL-35 is structurally and functionally similar to IL-27, the intrinsic roles of IL-35 in CNS tissues are unknown. Thus, we generated IL-35/YFP-knock-in reporter mice (p35-KI) and demonstrated that photoreceptor neurons constitutively secrete IL-35, which might protect the retina from persistent low-grade inflammation that can impair photoreceptor functions. Furthermore, the p35-KI mouse, which is hemizygous at the il12a locus, develops more severe uveitis because of reduced IL-35 expression. Interestingly, onset and exacerbation of uveitis in p35-KI mice caused by extravasation of proinflammatory Th1/Th17 lymphocytes into the retina were preceded by a dramatic decrease of IL-35, attributable to massive death of photoreceptor cells. Thus, while inflammation-induced death of photoreceptors and loss of protective effects of IL-35 exacerbated uveitis, our data also suggest that constitutive production of IL-35 in the retina might have housekeeping functions that promote sterilization immunity in the neuroretina and maintain ocular immune privilege.

The pro-inflammatory effect of triglyceride on human CD4+ T cells and experimental autoimmune uveitis

Aberrant lipid metabolism plays a role in inflammation and progression of autoimmune diseases but the definite mechanism remains unclear. In this study we investigate lipidomic profiles in Behçet's disease (BD) and the role of triglyceride (TAG) in the pathogenesis of autoimmune uveitis. Lipidomics revealed a distinct lipid metabolite profile including increased TAG metabolites in plasma of active BD patients. TAG could stimulate the proliferation, IL-17 and IFN-γ expression by CD4⁺ T cells and Th1, Th17 cell differentiation in vitro, but did not influence neutrophils. A922500 inhibited the TAG generation, ameliorated the EAU severity, decreased Th17 frequency and IL-17 expression by CD4⁺ T cells in vivo. The proteomocis analysis showed an up-regulation of apoptosis-related protein, Pik3r2, in CD4⁺ T cells from A922500-treated mice. In conclusion, TAG can stimulate human CD4⁺ T cells and the inhibition of its generation could significantly ameliorate EAU activity in association with down-regulated Th17 cell response.

Uveitis-mediated immune cell invasion through the extracellular matrix of the lens capsule

While the eye is considered an immune privileged site, its privilege is abrogated when immune cells are recruited from the surrounding vasculature in response to trauma, infection, aging, and autoimmune diseases like uveitis. Here, we investigate whether in uveitis immune cells become associated with the lens capsule and compromise its privilege in studies of C57BL/6J mice with experimental autoimmune uveitis. These studies show that at D14, the peak of uveitis in these mice, T cells, macrophages, and Ly6G/Ly6C+ immune cells associate with the lens basement membrane capsule, burrow into the capsule matrix, and remain integrated with the capsule as immune resolution is occurring at D26. 3D surface rendering image analytics of confocal z‐stacks and scanning electron microscopy imaging of the lens surface show the degradation of the lens capsule as these lens‐associated immune cells integrate with and invade the lens capsule, with a subset infiltrating both epithelial and fiber cell regions of lens tissue, abrogating its immune privilege. Those immune cells that remain on the surface often become entwined with a fibrillar net‐like structure. Immune cell invasion of the lens capsule in uveitis has not been described previously and may play a role in induction of lens and other eye pathologies associated with autoimmunity.

Overexpressing Kallistatin Aggravates Experimental Autoimmune Uveitis Through Promoting Th17 Differentiation

Kallistatin or kallikrein-binding protein (KBP) has been reported to regulate angiogenesis, inflammation and tumor progression. Autoimmune uveitis is a common, sight-threatening inflammatory intraocular disease. However, the roles of kallistatin in autoimmunity and autoreactive T cells are poorly investigated. Compared to non-uveitis controls, we found that plasma levels of kallistatin were significantly upregulated in patients with Vogt-Koyanagi-Harada (VKH) disease, one of the non-infectious uveitis. Using an experimental autoimmune uveitis (EAU) model induced by human interphotoreceptor retinoid-binding protein peptide 651-670 (hIRBP_651-670), we examined the effects of kallistatin on the pathogenesis of autoimmune diseases. Compared to wild type (WT) mice, kallistatin transgenic (KS) mice developed severe uveitis with dominant Th17 infiltrates in the eye. In addition, the proliferative antigen-specific T cells isolated from KS EAU mice produced increased levels of IL-17A, but not IFN-γ or IL-10 cytokines. Moreover, splenic CD4⁺ T cells from naïve KS mice expressed higher levels of Il17a mRNA compared to WT naïve mice. Under Th17 polarization conditions, KS mice exhibited enhanced differentiation of naïve CD4⁺ T cells into Th17 cells compared to WT controls. Together, our results indicate that kallistatin promotes Th17 differentiation and is a key regulator of aggravating autoinflammation in EAU. Targeting kallistatin might be a potential to treat autoimmune disease.

STAT3-Specific Single Domain Nanobody Inhibits Expansion of Pathogenic Th17 Responses and Suppresses Uveitis in Mice

STAT3 activates transcription of genes that regulate cell growth, differentiation, and survival of mammalian cells. Genetic deletion of Stat3 in T cells has been shown to abrogate Th17 differentiation, suggesting that STAT3 is a potential therapeutic target for Th17-mediated diseases. However, a major impediment to therapeutic targeting of intracellular proteins such as STAT3 is the lack of efficient methods for delivering STAT3 inhibitors into cells. In this study, we developed a novel antibody (SBT-100) comprised of the variable (V) region of a STAT3-specific heavy chain molecule and demonstrate that this 15 kDa STAT3-specific nanobody enters human and mouse cells, and induced suppression of STAT3 activation and lymphocyte proliferation in a concentration-dependent manner. To investigate whether SBT-100 would be effective in suppressing inflammation in vivo, we induced experimental autoimmune uveitis (EAU) in C57BL/6J mice by active immunization with peptide from the ocular autoantigen, interphotoreceptor retinoid binding protein (IRBP_651-670). Analysis of the retina by fundoscopy, histological examination, or optical coherence tomography showed that treatment of the mice with SBT-100 suppressed uveitis by inhibiting expansion of pathogenic Th17 cells that mediate EAU. Electroretinographic (ERG) recordings of dark and light adapted a- and b-waves showed that SBT-100 treatment rescued mice from developing significant visual impairment observed in untreated EAU mice. Adoptive transfer of activated IRBP-specific T cells from untreated EAU mice induced EAU, while EAU was significantly attenuated in mice that received IRBP-specific T cells from SBT-100 treated mice. Taken together, these results demonstrate efficacy of SBT-100 in mice and suggests its therapeutic potential for human autoimmune diseases.

High Ambient Temperature Aggravates Experimental Autoimmune Uveitis Symptoms

Whether ambient temperature influences immune responses leading to uveitis is unknown. We thus tested whether ambient temperature affects the symptoms of experimental autoimmune uveitis (EAU) in mice and investigated possible mechanisms. C57BL/6 mice were kept at a normal (22°C) or high temperature (30°C) housing conditions for 2 weeks and were then immunized with human interphotoreceptor retinoid-binding protein (IRBP651–670) peptide to induce EAU. Histological changes were monitored to evaluate the severity of uveitis. Frequency of Th1 cells and Th17 cells was measured by flow cytometry (FCM). The expression of IFN-γ and IL-17A mRNA was measured by real-time qPCR. The generation of neutrophil extracellular traps (NETs) was quantified by enzyme-linked immunosorbent assay (ELISA). Differential metabolites in the plasma of the mice kept in the aforementioned two ambient temperatures were measured via ultra-high-performance liquid chromatography triple quadrupole mass spectrometry quadrupole time of flight mass spectrometry (UHPLC-QQQ/MS). The differential metabolites identified were used to evaluate their effects on differentiation of Th1 and Th17 cells and generation of NETs in vitro. The results showed that EAU mice kept at high temperature experienced a more severe histopathological manifestation of uveitis than mice kept at a normal temperature. A significantly increased frequency of Th1 and Th17 cells in association with an upregulated expression of IFN-γ and IL-17A mRNA was observed in the splenic lymphocytes and retinas of EAU mice in high temperature. The expression of NETs as evidenced by myeloperoxidase (MPO) and neutrophil elastase (NE), was significantly elevated in serum and supernatants of neutrophils from EAU mice kept at high temperature compared to the normal temperature group. The metabolites in the plasma from EAU mice, fumaric acid and succinic acid, were markedly increased in the high temperature group and could induce the generation of NETs via the NADPH oxidase-dependent pathway, but did not influence the frequency of Th1 and Th17 cells. Our findings suggest that an increased ambient temperature is a risk factor for the development of uveitis. This is associated with the induction of Th1 and Th17 cells as well as the generation of NETs which could be mediated by the NADPH oxidase-dependent pathway.

Deletion of Irf4 in T Cells Suppressed Autoimmune Uveitis and Dysregulated Transcriptional Programs Linked to CD4+ T Cell Differentiation and Metabolism

Interferon regulatory factor-4 (IRF4) and IRF8 regulate differentiation, growth and functions of lymphoid and myeloid cells. Targeted deletion of irf8 in T cells (CD4-IRF8KO) has been shown to exacerbate colitis and experimental autoimmune uveitis (EAU), a mouse model of human uveitis. We therefore generated mice lacking irf4 in T cells (CD4-IRF4KO) and investigated whether expression of IRF4 by T cells is also required for regulating T cells that suppress autoimmune diseases. Surprisingly, we found that CD4-IRF4KO mice are resistant to EAU. Suppression of EAU derived in part from inhibiting pathogenic responses of Th17 cells while inducing expansion of regulatory lymphocytes that secrete IL-10 and/or IL-35 in the eye and peripheral lymphoid tissues. Furthermore, CD4-IRF4KO T cells exhibit alterations in cell metabolism and are defective in the expression of two Ikaros zinc-finger (IKZF) transcription factors (Ikaros, Aiolos) that are required for lymphocyte differentiation, metabolism and cell-fate decisions. Thus, synergistic effects of IRF4 and IkZFs might induce metabolic reprogramming of differentiating lymphocytes and thereby dynamically regulate relative abundance of T and B lymphocyte subsets that mediate immunopathogenic mechanisms during uveitis. Moreover, the diametrically opposite effects of IRF4 and IRF8 during EAU suggests that intrinsic function of IRF4 in T cells might be activating proinflammatory responses while IRF8 promotes expansion of immune-suppressive mechanisms.

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.

STAT3 deficiency in B cells exacerbates uveitis by promoting expansion of pathogenic lymphocytes and suppressing regulatory B cells (Bregs) and Tregs

STAT3 transcription factor induces differentiation of naïve T cells into Th17 cells and loss of STAT3 in T cell prevents development of CNS autoimmune diseases. However, function of STAT3 in the B lymphocyte subset is not well understood. In this study, we have generated mice lacking STAT3 in CD19⁺ B cells (CD19-STAT3KO) and investigated intrinsic and extrinsic functions of STAT3 in B cells and its potential role in resistance or pathogenesis of organ-specific autoimmune diseases. We show that STAT3 regulates metabolic mechanisms in B cells with implications for bioenergetic and metabolic pathways that control cellular homeostasis in B cells. Thus, loss of STAT3 in CD19-STAT3KO cells perturbed growth and apoptosis by inducing rapid entry of B cells into the S-phase of the cell cycle, decreasing expression of cyclin-dependent kinase inhibitors and upregulating pro-apoptotic proteins. We further show that the CD19-STAT3KO mice develop severe experimental autoimmune uveitis (EAU), an animal model of human uveitis. Exacerbated uveitis in CD19-STAT3KO mice derived in part from enhanced expression of costimulatory molecules on B cells, marked increase of Th17 responses and increased recruitment of granulocytes into the neuroretina. The enhanced autoimmunity upon deletion of STAT3 in B cells is also recapitulated in experimental autoimmune encephalitis, a mouse model of multiple sclerosis and thus support our conclusion that STAT3 deletion in B cells enhanced inflammation and the effects observed are not model specific. Our data further indicate that STAT3 pathway modulates interactions between B and T cells during EAU resulting in alteration of lymphocyte repertoire by increasing levels of autoreactive pathogenic T cells while suppressing development and/or expansion of immune-suppressive lymphocytes (Bregs and Tregs). Taken together, STAT3 exerts diametrically opposite effects in lymphocytes, with loss of STAT3 in B cells exacerbating uveitis whereas Stat3 deletion in T cells confers protection.

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.

•

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

•

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

•

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

•

Silencing or depleting IL-24 in Th17 cells exacerbates neuroinflammation

Interleukin 35-Producing Exosomes Suppress Neuroinflammation and Autoimmune Uveitis

Corticosteroids are effective therapy for autoimmune diseases but serious adverse effects preclude their prolonged use. However, immune-suppressive biologics that inhibit lymphoid proliferation are now in use as corticosteroid sparing-agents but with variable success; thus, the need to develop alternative immune-suppressive approaches including cell-based therapies. Efficacy of ex-vivo-generated IL-35-producing regulatory B-cells (i35-Bregs) in suppressing/ameliorating encephalomyelitis or uveitis in mouse models of multiple sclerosis or uveitis, respectively, is therefore a promising therapeutic approach for CNS autoimmune diseases. However, i35-Breg therapy in human uveitis would require producing autologous Bregs from each patient to avoid immune-rejection. Because exosomes exhibit minimal toxicity and immunogenicity, we investigated whether i35-Bregs release exosomes that can be exploited therapeutically. Here, we demonstrate that i35-Bregs release exosomes that contain IL-35 (i35-Exosomes). In this proof-of-concept study, we induced experimental autoimmune uveitis (EAU), monitored EAU progression by fundoscopy, histology, optical coherence tomography and electroretinography, and investigated whether i35-Exosomes treatment would suppress uveitis. Mice treated with i35-Exosomes developed mild EAU with low EAU scores and disease protection correlated with expansion of IL-10 and IL-35 secreting Treg cells with concomitant suppression of Th17 responses. In contrast, significant increase of Th17 cells in vitreous and retina of control mouse eyes was accompanied by severe choroiditis, massive retinal-folds, and photoreceptor cell damage. These hallmark features of severe uveitis were absent in exosome-treated mice and visual impairment detected by ERG was modest compared to control mice. Absence of toxicity or alloreactivity associated with exosomes thus makes i35-Exosomes attractive therapeutic option for delivering IL-35 into CNS tissues.

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.

T Regulatory Cells From Non-obese Diabetic Mice Show Low Responsiveness to IL-2 Stimulation and Exhibit Differential Expression of Anergy-Related and Ubiquitination Factors

Foxp3+ Regulatory T cells (Tregs) are pivotal for the maintenance of tolerance. Alterations in their number and/or function have been proposed to occur in the autoimmune-prone non-obese diabetic (NOD) mouse. Comparing the frequencies and absolute numbers of CD4+Foxp3+CD25+ Tregs among 4 to 6-week old NOD, B6, and BALB/c mice, we observed differences in counts and Foxp3 expression in Tregs from secondary lymphoid organs, but not in the thymus. Upon TCR and IL-2 stimulation, NOD Tregs showed lower responses than Tregs from B6 and BALB/c mice. Indeed, NOD Tregs responded with less proliferation and with smaller increments in the expression of CD25, LAP-1, CD39, PD-1, PD-L1, and LAG-3, when in vitro cultured for 3 days with anti-CD3/CD28 in the absence or presence of IL-2, Tregs from NOD mice showed to be highly dependent on IL-2 to maintain Foxp3 expression. Moreover, NOD Tregs become producers of IL-17 and INF-gamma more easily than Tregs from the other strains. In addition, NOD Tregs showed lower responsiveness to IL-2, with significantly reduced levels of pSTAT5, even at high IL-2 doses, with respect to B6 and BALB/c Tregs. Interestingly, NOD Tregs exhibit differences in the expression of SOCS3, GRAIL, and OTUB1 when compared with Tregs from B6 and BALB/c mice. Both, at steady state conditions and also after activation, Tregs from NOD mice showed increased levels of OTUB1 and low levels of GRAIL. In addition, NOD Tregs had differences in the expression of ubiquitin related molecules that play a role in the maintenance of Foxp3 cellular pools. Indeed, significantly higher STUB1/USP7 ratios were detected in NOD Tregs, both at basal conditions and after stimulation, compared to in B6 and BALB/c Tregs. Moreover, the addition of a proteasome inhibitor to cell cultures, conferred NOD Tregs the ability to retain Foxp3 expression. Herein, we provide evidence indicating a differential expression of SOCS3, GRAIL, and STUB1/USP7 in Tregs from NOD mice, factors known to be involved in IL-2R signaling and to affect Foxp3 stability. These findings add to the current knowledge of the immunobiology of Tregs and may be related to the known insufficiency of Tregs from NOD mice to maintain self-tolerance.

AAV Mediated Delivery of Myxoma Virus M013 Gene Protects the Retina against Autoimmune Uveitis

Uveoretinitis is an ocular autoimmune disease caused by the activation of autoreactive T- cells targeting retinal antigens. The myxoma M013 gene is known to block NF-κB (Nuclear Factor kappa-light-chain-enhancer of activated B cells) and inflammasome activation, and its gene delivery has been demonstrated to protect the retina against lipopolysaccharide (LPS)-induced uveitis. In this report we tested the efficacy of M013 in an experimental autoimmune uveoretinitis (EAU) mouse model. B10RIII mice were injected intravitreally with AAV (adeno associated virus) vectors delivering either secreted GFP (sGFP) or sGFP-TatM013. Mice were immunized with interphotorecptor retinoid binding protein residues 161–180 (IRBP_161–180) peptide in complete Freund’s adjuvant a month later. Mice were evaluated by fundoscopy and spectral domain optical coherence tomography (SD-OCT) at 14 days post immunization. Eyes were evaluated by histology and retina gene expression changes were measured by reverse transcribed quantitative PCR (RT-qPCR). No significant difference in ERG or retina layer thickness was observed between sGFP and sGFP-TatM013 treated non-uveitic mice, indicating safety of the vector. In EAU mice, expression of sGFP-TatM013 strongly lowered the clinical score and number of infiltrative cells within the vitreous humor when compared to sGFP treated eyes. Retina structure was protected, and pro-inflammatory genes expression was significantly decreased. These results indicate that gene delivery of myxoma M013 could be of clinical benefit against autoimmune diseases.

Complement-Mediated Activation of the NLRP3 Inflammasome and Its Inhibition by AAV-Mediated Delivery of CD59 in a Model of Uveitis

Uveitis is an inflammatory disorder of the eye responsible for approximately 10%-15% of blindness in the US. In this study, we examined the role of the complement membrane attack complex (MAC) and the NLRP3 inflammasome in the pathogenesis of experimental autoimmune uveitis (EAU) in normal and C9^-/- mice that are incapable of assembling the MAC. We discovered that the MAC and the NLRP3 inflammasome and associated production of IL-1β are elevated in EAU mice and that MAC may be involved in regulation of Th1 and Th17 cell differentiation. In contrast, MAC and the NLRP3 inflammasome were not elevated in C9^-/- mice. However, EAU-associated pathophysiology including retinal structure and function were not rescued in C9^-/- mice. Unexpectedly, AAV-mediated delivery of sCD59, an inhibitor of C9 incorporation into the MAC, successfully attenuated activation of the NLRP3 inflammasome and EAU pathology as well as MAC. Our studies provide an improved understanding of the role of the MAC and the NLRP3 inflammasome in EAU as well as suggest a novel approach for the treatment of uveitis.

Targeting CD6 for the treatment of experimental autoimmune uveitis

OBJECTIVE

CD6 is emerging as a new target for treating many pathological conditions in which T cells are integrally involved, but even the latest data from studies of CD6 gene engineered mice were still contradictory. To address this issue, we studied experimental autoimmune uveitis (EAU), a model of autoimmune uveitis, in wild-type (WT) and CD6 knockout (KO) mice.

METHODS

After EAU induction in WT and CD6 KO mice, we evaluated ocular inflammation and compared retinal antigen-specific T-cell responses using scanning laser ophthalmoscopy, spectral-domain optical coherence tomography, histopathology, and T cell recall assays. Uveitogenic T cells from WT and CD6 KO mice were adoptively transferred into WT naïve mice to confirm the impact of CD6 on T cells. In addition, we immunized CD6 KO mice with recombinant CD6 protein to develop mouse anti-mouse CD6 monoclonal antibodies (mAbs) in which functional antibodies exhibiting cross-reactivity with human CD6 were screened and identified for treatment studies.

RESULTS

In CD6 KO mice with EAU, we found significantly decreased retinal inflammation and reduced autoreactive T-cell responses, and confirmed the impaired uveitogenic capacity of T cells from these mice in an adoptive transfer experiment. Notably, one of these cross-reactive mAbs significantly ameliorated retinal inflammation in EAU induced by the adoptive transfer of uveitogenic T cells.

CONCLUSIONS

Together, these data strongly suggest that CD6 plays a previously unknown, but pivotal role in autoimmune uveitis, and may be a promising new treatment target for this blinding disease. In addition, the newly developed mouse anti-mouse/human CD6 mAbs could be valuable tools for testing CD6-targeted therapies in other mouse models of human diseases.

Neuroprotective effect of tetramethylpyrazine against all-trans-retinal toxicity in the differentiated Y-79 cells via upregulation of IRBP expression

It is estimated that abnormal accumulation of all-trans-retinal (atRAL) is a leading cause of photoreceptor degeneration in retinal degenerative diseases. Deficiency of interphotoreceptor retinoid-binding protein (IRBP), a retinoid transporter in the visual cycle, is responsible for the impaired clearance of atRAL and results in atRAL toxicity in retina. Therefore, IRBP has been proposed to be a potent target in preventing atRAL-induced photoreceptor degeneration. In this study, the neuroprotective effect of tetramethylpyrazine (TMP) against atRAL toxicity in the differentiated Y-79 cells, a in vitro model of photoreceptor, was first investigated. Our findings showed that atRAL could induce cytotoxicity, oxidative/nitrosative stresses, apoptosis and leukostasis in the differentiated Y-79 cells; however, the pre-treatment of TMP significantly attenuated such effects in a dose-dependent manner. Furthermore, our results indicated that TMP exerted its neuroprotective effect mainly through upregulating IRBP expression. The present study significantly contributes to better understanding the important role of IRBP in retinal degenerative diseases and forms the basis of the therapeutic development of TMP in such diseases in the future.

In Vivo Bioluminescence Imaging for Longitudinal Monitoring of Inflammation in Animal Models of Uveitis

Purpose

We develop a quantitative bioluminescence assay for in vivo longitudinal monitoring of inflammation in animal models of uveitis.

Methods

Three models of experimental uveitis were induced in C57BL/6 albino mice: primed mycobacterial uveitis (PMU), endotoxin-induced uveitis (EIU), and experimental autoimmune uveitis (EAU). Intraperitoneal injection of luminol sodium salt, which emits light when oxidized, provided the bioluminescence substrate. Bioluminescence images were captured by a PerkinElmer In Vivo Imaging System (IVIS) Spectrum and total bioluminescence was analyzed using Living Image software. Bioluminescence on day zero was compared to bioluminescence on the day of peak inflammation for each model. Longitudinal bioluminescence imaging was performed in EIU and EAU.

Results

In the presence of luminol, intraocular inflammation generates detectable bioluminescence in three mouse models of uveitis. Peak bioluminescence in inflamed PMU eyes (1.46 × 10⁵ photons/second [p/s]) was significantly increased over baseline (1.47 × 10⁴ p/s, P = 0.01). Peak bioluminescence in inflamed EIU eyes (3.18 × 10⁴ p/s) also was significantly increased over baseline (1.09 × 10⁴ p/s, P = 0.04), and returned to near baseline levels by 48 hours. In EAU, there was a nonsignificant increase in bioluminescence at peak inflammation.

Conclusions

In vivo bioluminescence may be used as a noninvasive, quantitative measure of intraocular inflammation in animal models of uveitis. Primed mycobacterial uveitis and EIU are both acute models with robust anterior inflammation and demonstrated significant changes in bioluminescence corresponding with peak inflammation. Experimental autoimmune uveitis is a more indolent posterior uveitis and generated a more modest bioluminescent signal. In vivo imaging system bioluminescence is a nonlethal, quantifiable assay that can be used for monitoring inflammation in animal models of uveitis.

Quantitative Assessment of Anterior Segment Inflammation in a Rat Model of Uveitis Using Spectral-Domain Optical Coherence Tomography

Purpose

To develop anterior segment spectral-domain optical coherence tomography (SD-OCT) and quantitative image analysis for use in experimental uveitis in rats.

Methods

Acute anterior uveitis was generated in Lewis rats. A spectral domain anterior segment OCT system was used to image the anterior chamber (AC) and ciliary body at baseline and during peak inflammation 2 days later. Customized MatLab image analysis algorithms were developed to segment the AC, count AC cells, calculate central corneal thickness (CCT), segment the ciliary body and zonules, and quantify the level of ciliary body inflammation with the ciliary body index (CBI). Images obtained at baseline and during peak inflammation were compared. Finally, longitudinal imaging and image analysis was performed over the 2-week course of inflammation.

Results

Spectral-domain optical coherence tomography identifies structural features of inflammation. Anterior chamber cell counts at peak inflammation obtained by automated image analysis and human grading were highly correlated (r = 0.961), and correlated well with the histologic score of inflammation (r = 0.895). Inflamed eyes showed a significant increase in average CCT (27 μm, P = 0.02) and an increase in average CBI (P < 0.0001). Longitudinal imaging and quantitative image analysis identified a significant change in AC cell and CBI on day 2 with spontaneous resolution of inflammation by day 14.

Conclusions

Spectral-domain optical coherence tomography provides high-resolution images of the structural changes associated with anterior uveitis in rats. Anterior chamber cell count and CBI determined by semi-automated image analysis strongly correlates with inflammation, and can be used to quantify inflammation longitudinally in single animals.

LYN- and AIRE-mediated tolerance checkpoint defects synergize to trigger organ-specific autoimmunity

Studies of the genetic factors associated with human autoimmune disease suggest a multigenic origin of susceptibility; however, how these factors interact and through which tolerance pathways they operate generally remain to be defined. One key checkpoint occurs through the activity of the autoimmune regulator AIRE, which promotes central T cell tolerance. Recent reports have described a variety of dominant-negative AIRE mutations that likely contribute to human autoimmunity to a greater extent than previously thought. In families with these mutations, the penetrance of autoimmunity is incomplete, suggesting that other checkpoints play a role in preventing autoimmunity. Here, we tested whether a defect in LYN, an inhibitory protein tyrosine kinase that is implicated in systemic autoimmunity, could combine with an Aire mutation to provoke organ-specific autoimmunity. Indeed, mice with a dominant-negative allele of Aire and deficiency in LYN spontaneously developed organ-specific autoimmunity in the eye. We further determined that a small pool of retinal protein-specific T cells escaped thymic deletion as a result of the hypomorphic Aire function and that these cells also escaped peripheral tolerance in the presence of LYN-deficient dendritic cells, leading to highly destructive autoimmune attack. These findings demonstrate how 2 distinct tolerance pathways can synergize to unleash autoimmunity and have implications for the genetic susceptibility of autoimmune disease.

Digoxin Inhibits Induction of Experimental Autoimmune Uveitis in Mice, but Causes Severe Retinal Degeneration

PURPOSE

Digoxin, a major medication for heart disease, was recently reported to have immunosuppressive capacity. Here, we determined the immunosuppressive capacity of digoxin on the development of experimental autoimmune uveitis (EAU) and on related immune responses.

METHODS

The B10.A mice were immunized with interphotoreceptor retinoid-binding protein (IRBP) and were treated daily with digoxin or vehicle control. On postimmunization day 14, the mouse eyes were examined histologically, while spleen cells were tested for cytokine production in response to IRBP and purified protein derivative. The immunosuppressive activity of digoxin was also tested in vitro, by its capacity to inhibit development of Th1 or Th17 cells. To investigate the degenerative effect of digoxin on the retina, naïve (FVB/N × B10.BR)F1 mice were similarly treated with digoxin and tested histologically and by ERG.

RESULTS

Treatment with digoxin inhibited the development of EAU, as well as the cellular response to IRBP. Unexpectedly, treatment with digoxin suppressed the production of interferon-γ to a larger extent than the production of interleukin 17. Importantly, digoxin treatment induced severe retinal degeneration, determined by histologic analysis with thinning across all layers of the retina. Digoxin treatment also induced dose-dependent vision loss monitored by ERG on naïve mice without induction of EAU.

CONCLUSIONS

Treatment of mice with digoxin inhibited the development of EAU and cellular immune response to IRBP. However, the treatment induced severe damage to the retina. Thus, the use of digoxin in humans should be avoided due to its toxicity to the retina.

Complement anaphylatoxin receptors C3aR and C5aR are required in the pathogenesis of experimental autoimmune uveitis

Recent studies have suggested that reagents inhibiting complement activation could be effective in treating T cell mediated autoimmune diseases such as autoimmune uveitis. However, the precise role of the complement anaphylatoxin receptors (C3a and C5a receptors) in the pathogenesis of autoimmune uveitis remains elusive and controversial. We induced experimental autoimmune uveitis in mice deficient or sufficient in both C3a and C5a receptors and rigorously compared their retinal phenotype using various imaging techniques, including indirect ophthalmoscopy, confocal scanning laser ophthalmoscopy, spectral domain optical coherence tomography, topical endoscopic fundus imaging, and histopathological analysis. We also assessed retinal function using electroretinography. Moreover, we performed Ag-specific T cell recall assays and T cell adoptive transfer experiments to compare pathogenic T cell activity between wild-type and knockout mice with experimental autoimmune uveitis. These experiments showed that C3a receptor/C5a receptor-deficient mice developed much less severe uveitis than did control mice using all retinal examination methods and that these mice had reduced pathogenic T cell responses. Our data demonstrate that both complement anaphylatoxin receptors are important for the development of experimental autoimmune uveitis, suggesting that targeting these receptors could be a valid approach for treating patients with autoimmune uveitis.