Reactivation of uveitogenic T cells by retinal astrocytes derived from experimental autoimmune uveitis-prone B10RIII mice

Gut microbial signatures and their functions in Behcet's uveitis and Vogt-Koyanagi-Harada disease

BACKGROUND

A number of public metagenomic studies reveal an association between the gut microbiome and various immune-mediated diseases including Behcet's uveitis (BU) and Vogt-Koyanagi-Harada disease (VKH). Integrated-analysis and subsequent validation of these results could be a potentially powerful way to understand the microbial signatures and their functions in these two uveitis entities.

METHODS

We integrated the sequencing data of our previous metagenomic studies on two major uveitis entities, BU and VKH as well as four other publicly available immune-mediated diseases datasets, including Ankylosing Spondylitis (AS), Rheumatoid Arthritis (RA), Crohn's disease (CD) and Ulcerative Colitis (UC). Alpha-diversity and beta-diversity analysis were used to compare the gut microbiome signatures between both uveitis entities and other immune-mediated diseases and healthy controls. Amino acid homology between microbial proteins and a uveitogenic peptide of the interphotoreceptor retinoid-binding protein (IRBP)161-180 was investigated using a similarity search in the NCBI protein BLAST program (BLASTP). Enzyme-linked Immunosorbent Assay (ELISA) was performed to evaluate the cross-reactive responses of experimental autoimmune uveitis (EAU)-derived lymphocytes and BU patients-derived peripheral blood mononuclear cells (PBMCs) against homologous peptides. The area under the curve (AUC) analysis was used to test the sensitivity and specificity of gut microbial biomarkers.

RESULTS

Depleted Dorea, Blautia, Coprococcus, Erysipelotrichaceae and Lachnospiraceae as well as enriched Bilophila and Stenotrophomonas were identified in BU patients. An enriched Alistipes along with a lower level of Dorea were observed in VKH patients. A peptide antigen (SteTDR) encoded by BU specifically enriched Stenotrophomonas was identified to share homology with IRBP161-180. In vitro experiments showed that lymphocytes from EAU or PBMCs from BU patients reacted to this peptide antigen as shown by the production of IFN-γ and IL-17. Addition of the SteTDR peptide to the classical IRBP immunization protocol exacerbated EAU severity. Gut microbial marker profiles consisted of 24 species and 32 species respectively differentiated BU and VKH from each other as well as from the other four immune-mediated diseases and healthy controls. Protein annotation identified 148 and 119 specific microbial proteins associated with BU and VKH, respectively. For metabolic function analysis, 108 and 178 metabolic pathways were shown to be associated with BU and VKH, respectively.

CONCLUSIONS

Our study revealed specific gut microbial signatures and their potentially functional roles in BU and VKH pathogenesis that differ significantly from other immune-mediated diseases as well as healthy controls.

Changes in the Gut Microbiome Contribute to the Development of Behcet's Disease via Adjuvant Effects

Behcet’s disease (BD) is associated with considerable gut microbiome changes. However, it still remains unknown how the composition of the gut microbiome exactly affects the development of this disease. In this study, transplantation of stool samples from patients with active ocular BD to mice via oral gavage was performed. This resulted in decreases of three short chain fatty acids (SCFAs) including butyric acid, propionic acid and valeric acid in the feces of the BD-recipient group. Intestinal barrier integrity of mice receiving BD feces was damaged as shown by a decreased expression of tight junction proteins and was associated with the release of Lipopolysaccharides (LPS) in the circulation. The mice also showed a higher frequency of splenic neutrophils as well as an enrichment of genes associated with innate immune responses in the neutrophils and CD4 + T cells as identified by single cell RNA sequencing. Analysis of neutrophils and T cells functions in these mice showed an enhanced mesenteric lymph node and splenic Th1 and Th17 cell differentiation in association with activation of neutrophils. Transplantation of BD feces to mice and subsequent induction of experimental uveitis (EAU) or encephalomyelitis (EAE) led to an exacerbation of disease in both models, suggesting a microbial adjuvant effect. These findings suggest that the gut microbiome may regulate an autoimmune response via adjuvant effects including increased gut permeability and enhancement of innate immunity.

Association of High-Mobility Group Box-1 with Inflammationrelated Cytokines in the Aqueous Humor with Acute Primary Angle-Closure Eyes

AIM

The aim of this study was to measure the levels of High-mobility group box-1 (HMGB1) and inflammation-related cytokines in the aqueous humor of patients with acute primary angle-closure glaucoma (APAG) and age-related cataract eyes (ARC).

METHODS

Aqueous humor samples were obtained from 59 eyes of 59 Chinese subjects (APAG, 32 eyes; and ARC, 27eyes). The multiplex bead immunoassay technique was used to measure the levels of HMGB1 and IL-8, IL-6, G-CSF, MCP-3, VEGF, sVEGFR- 1, sVEFGR-2, TNF-α, PDGF, and IL-10 in aqueous. The data of Patients' demographics and preoperative intraocular pressure (IOP) were also collected for detailed analysis.

RESULTS

The APAG group showed significantly elevated concentrations of HMGB1, IL- 8, IL-6, G-CSF, VEGF, sVEGFR-1, and TNF-α than those in the ARC group. Aqueous HMGB1 level correlated significantly with IOP, IL-8, IL-6, G-CSF and sVEGFR-1 levels but not with age, TNF-α, or VEGF levels.

CONCLUSION

The aqueous level of HMGB1 is elevated in APAG and associated with aqueous level of inflammation-related cytokines, suggesting an association between elevated levels of HMGB1, APAC and certain inflammatory modulators which, of course, should lead to further investigations in order to demonstrate the cause and effect.

Short chain fatty acids inhibit endotoxin-induced uveitis and inflammatory responses of retinal astrocytes

Short chain fatty acids (SCFAs) are produced by gut microbiota as fermentation products of digestion-resistant oligosaccharides and fibers. Their primary roles are functioning as major energy sources for colon cells and assisting in gut homeostasis by immunomodulation. Recent evidence suggests that they affect various organs both at cellular and molecular levels, and regulate functions in distance sites including gene expression, cell proliferation, cell differentiation, apoptosis and inflammation. In this study, we examined whether SCFAs are present in the mouse eye and whether SCFAs affect inflammatory responses of the eye and retinal astrocytes (RACs). We observed that intra-peritoneal injected SCFAs were detected in the eye and reduced intraocular inflammation induced by lipopolysaccharide (LPS). Moreover, SCFAs displayed two disparate effects on LPS-stimulated RACs - namely, cytokine and chemokine production was reduced, but the ability to activate T cells was enhanced. Our results support the existence of gut-eye cross talk and suggest that SCFAs can cross the blood-eye-barrier via the systemic circulation. If applied at high concentrations, SCFAs may reduce inflammation and impact cellular functions in the intraocular milieu.

Silencing SOCS3 Markedly Deteriorates Spondyloarthritis in Mice Induced by Minicircle DNA Expressing IL23

Objective: Despite extensive studies, the precise mechanism underlying spondyloarthritis, especially ankylosing spondylitis, remains elusive. This study aimed to develop an ideal animal model for an insight into mechanism of spondyloarthritis and functional relevance of SOCS3 in spondyloarthritis.

Methods: Since SOCS3 is a major regulator of IL23-STAT3 signaling, we generated SOCS3 knockdown transgenic (TG) mice for development of an animal model of spondyloarthritis. A hydrodynamic delivery method was employed to deliver minicircle DNA expressing IL23 (mc-IL23) into wild-type (WT) and the TG mice. Knockdown/overexpression systems mediated by lentivirus and retrovirus were used to determine whether SOCS3 regulated osteoblast differentiation.

Results: Forced expression of IL23 induced severe joint destruction and extensive bone loss in SOCS3 knockdown TG mice, while this treatment only caused moderate symptoms in WT mice. Furthermore, severe spondyloarthritis was found in IL23-injected TG mice as compared to mild disease observed in WT controls under same condition. Moreover, our studies showed that IL23 promoted osteoblast differentiation via activation of STAT3 pathway and disruption of SOCS3 expression greatly increased phosphorylation of STAT3. In addition, silencing SOCS3 resulted in enhanced osteoblast differentiation through activation of Smad1/5/9 signaling, as evidenced by elevated phosphorylation level of Smad1/5/9. Experiments further demonstrated that SOCS3 interacted with Smad1 and thus suppressed the BMP2-Smad signaling.

Conclusions: The results reveal that SOCS3 is involved in IL23-induced spondyloarthritis and acts as a key regulator of osteoblast differentiation, and suggest that SOCS3 knockdown TG mice may be an ideal animal model for further studies of spondyloarthritis.

HMBG1 as a Driver of Inflammatory and Immune Processes in the Pathogenesis of Ocular Diseases

High-mobility group box 1 (HMGB1) is a nuclear protein that can also act as an extracellular trigger of inflammation, proliferation, and migration in eye diseases. It induces signaling pathways by binding to the receptor for advanced glycation end products (RAGE) and Toll-like receptors (TLRs) 2, 4, and 9. This proinflammatory activity is considered to be important in the pathogenesis of a wide range of ocular diseases resulting from hemodynamic changes, presence of neovascular endothelial cells, secretion of intraocular immune factors or inflammation, and apoptosis of retinal cell layers. Further work is needed to elucidate in detail how HMGB1 contributes to ocular disease and how its damaging activity can be modulated. In this review, we summarize current knowledge on HMGB1 as a ligand that can evoke inflammation and immune responses in ocular diseases.

Local S100A8 Levels Correlate With Recurrence of Experimental Autoimmune Uveitis and Promote Pathogenic T Cell Activity

Purpose

To investigate the role of damage-associated molecular patterns (DAMPs) in recurrent experimental autoimmune uveitis (EAU).

Methods

Recurrent EAU was induced in Lewis rats by interphotoreceptor retinoid-binding protein (IRBP) R16-peptide specific T cells (tEAU). Aqueous humor and serum samples were kinetically collected and DAMPs examined by quantitative proteomics, Western blot analysis, and ELISA. tEAU rats were treated with S100 inhibitor paquinimod followed by disease evaluation. The functions of T effector cells and T regulatory cells (Tregs) were compared between treated and nontreated groups. The expression of costimulatory molecules on antigen-presenting cells was examined by flow cytometry.

Results

S100A8, but not high mobility group box 1 (HMGB1), in the eye was found to be correlated with intraocular inflammatory episodes. Administration of paquinimod significantly protected tEAU rats from recurrence. Treated tEAU rats had fewer R16-specific Th1 and Th17 cells, but increased numbers of Tregs. R16-specific T cells from treated tEAU rats into naïve recipients prevented induction of tEAU by R16-specific T cells from nontreated tEAU rats. Moreover, APCs from treated tEAU rats expressed higher levels of a negative costimulatory molecule, CD200R, and lower levels of CD80, CD86, and MHC class II molecules compared to APCs from nontreated tEAU rats. An opposite pattern of expression of these molecules was observed on APCs incubated in vitro with recombinant S100A8.

Conclusions

Our data demonstrate a link between local expression of DAMPs and autoimmune responses, and suggest that complete S100A8/A9 blockade may be a new therapeutic target in recurrent autoimmune uveitis.

Re-programming immunosurveillance in persistent non-infectious ocular inflammation

Ocular function depends on a high level of anatomical integrity. This is threatened by inflammation, which alters the local tissue over short and long time-scales. Uveitis due to autoimmune disease, especially when it involves the retina, leads to persistent changes in how the eye interacts with the immune system. The normal pattern of immune surveillance, which for immune privileged tissues is limited, is re-programmed. Many cell types, that are not usually present in the eye, become detectable. There are changes in the tissue homeostasis and integrity. In both human disease and mouse models, in the most extreme cases, immunopathological findings consistent with development of ectopic lymphoid-like structures and disrupted angiogenesis accompany severely impaired eye function. Understanding how the ocular environment is shaped by persistent inflammation is crucial to developing novel approaches to treatment.

MHC class II expression and potential antigen-presenting cells in the retina during experimental autoimmune uveitis

Background

Controversy exists regarding which cell types are responsible for autoantigen presentation in the retina during experimental autoimmune uveitis (EAU) development. In this study, we aimed to identify and characterize the retinal resident and infiltrating cells susceptible to express major histocompatibility complex (MHC) class II during EAU.

Methods

EAU was induced in C57BL/6 mice by adoptive transfer of autoreactive lymphocytes from IRBP1-20-immunized animals. MHC class II expression was studied by immunostainings on eye cryosections. For flow cytometry (FC) analysis, retinas were dissected and enzymatically digested into single-cell suspensions. Three MHC class II⁺ retinal cell populations were sorted by FC, and their RNA processed for RNA-Seq.

Results

Immunostainings demonstrate strong induction of MHC class II expression in EAU, especially in the inner retina at the level of inflamed vessels, extending to the outer retinal layers and the subretinal space in severely inflamed eyes. Most MHC class II⁺ cells express the hematopoietic marker IBA1. FC quantitative analyses demonstrate that MHC class II induction significantly correlates with disease severity and is associated with upregulation of co-stimulatory molecule expression. In particular, most MHC class II^hi cells express co-stimulatory molecules during EAU. Further phenotyping identified three MHC class II⁺ retinal cell populations: CD45⁻CD11b⁻ non-hematopoietic cells with low MHC class II expression and CD45⁺CD11b⁺ hematopoietic cells with higher MHC class II expression, which can be further separated into Ly6C⁺ and Ly6C⁻ cells, possibly corresponding to infiltrating macrophages and resident microglia. Transcriptome analysis of the three sorted populations leads to a clear sample clustering with some enrichment in macrophage markers and microglial cell markers in Ly6C⁺ and Ly6C⁻ cells, respectively. Functional annotation analysis reveals that both hematopoietic cell populations are more competent in MHC class II-associated antigen presentation and in T cell activation than non-hematopoietic cells.

Conclusion

Our results highlight the potential of cells of hematopoietic origin in local antigen presentation, whatever their Ly6C expression. Our work further provides a first transcriptomic study of MHC class II-expressing retinal cells during EAU and delivers a series of new candidate genes possibly implicated in the pathogenesis of retinal autoimmunity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0915-5) contains supplementary material, which is available to authorized users.

HMGB1 release triggered by the interaction of live retinal cells and uveitogenic T cells is Fas/FasL activation-dependent

Background

It is not clear how invading autoreactive T cells initiate the pathogenic process inside the diseased organ in T cell-mediated organ-specific autoimmune disease. In experimental autoimmune uveitis (EAU) induced by adoptive transfer of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells in mice, we have previously reported that intraocular inflammation was initiated by infiltrating IRBP-specific T cells that directly interacted with retinal cells and resulted in the active release of high mobility group box 1 (HMGB1), an important member of damage associate molecular patterns (DAMPs). Furthermore, blockade of HMGB1 in our murine model reduced intraocular inflammation via suppression of IRBP-specific T cell functions. These results have demonstrated that HMGB1 is an early and critical mediator of induction of intraocular inflammation. The present study identified the cell surface molecule that triggers HMGB1 secretion.

Methods

Retinal explants from Fas-deficient (Fas^lpr) and wild-type (Wt) C57BL/6 (B6) mice were cultured with activated IRBP 1–20 peptide-specific T cells or with a Fas-activating antibody (Jo2), and then the level of HMGB1 in culture supernatants were detected by ELISA. In addition, released HMGB1 was examined in the eye of Fas^lpr and Wt mice after IRBP-specific T cell transfer. Uveitis was evaluated in the IRBP-specific T cell transferred Fas^lpr mice after recombinant HMGB1 was restored within the eye and in the IRBP-specific T cell transferred Wt mice after they were treated with a Fas antagonist (Met12).

Results

In contrast to retinal explants from Wt mice, those from Fas^lpr mice did not release HMGB1 after exposure to IRBP-specific T cells or to Jo2. The release of HMGB1 by Wt retinal explants was suppressed by Met 12. Moreover, after IRBP-specific T cell injection, Fas^lpr mice did not release HMGB1 in the eye or develop EAU, but intravitreous injection of HMGB1 resulted in intraocular inflammation. Finally, tEAU in Wt mice was attenuated by local treatment with Met 12. Unlike HMGB1, Fas-induced IL-1 and IL-18 were not essential for tEAU induction.

Conclusion

Our results show that interaction of retinal cells with infiltrating uveitogenic T cells leads to rapid release of HMGB1 via the Fas/FasL inflammatory signaling pathway.

HMGB1 is an early and critical mediator in an animal model of uveitis induced by IRBP-specific T cells

It is largely unknown how invading autoreactive T cells initiate the pathogenic process inside the diseased organ in organ-specific autoimmune disease. In this study, we used a chronic uveitis disease model in mice--EAU--induced by adoptive transfer of uveitogenic IRBP-specific T cells and showed that HMGB1, an important endogenous molecule that serves as a danger signal, was released rapidly from retinal cells into the ECM and intraocular fluid in response to IRBP-specific T cell transfer. HMGB1 release required direct cell-cell contact between retinal cells and IRBP-specific T cells and was an active secretion from intact retinal cells. Administration of HMGB1 antagonists inhibited severity of EAU significantly via mechanisms that include inhibition of IRBP-specific T cell proliferation and their IFN-γ and IL-17 production. The inflammatory effects of HMGB1 may signal the TLR/MyD88 pathway, as MyD88(-/-) mice had a high level of HMGB1 in the eye but did not develop EAU after IRBP-specific T cell transfer. Our study demonstrates that HMGB1 is an early and critical mediator of ocular inflammation initiated by autoreactive T cell invasion.

Exosomes from retinal astrocytes contain antiangiogenic components that inhibit laser-induced choroidal neovascularization

Exosomes released from different types of host cells have different biological effects. We report that exosomes released from retinal astroglial cells (RACs) suppress retinal vessel leakage and inhibit choroidal neovascularization (CNV) in a laser-induced CNV model, whereas exosomes released from retinal pigmental epithelium do not. RAC exosomes inhibit the migration of macrophages and the tubule forming of mouse retinal microvascular endothelial cells. Further, we analyzed antiangiogenic components in RAC exosomes using an angiogenesis array kit and detected several endogenous inhibitors of angiogenesis exclusively present in RAC exosomes, such as endostatin. Moreover, blockade of matrix metalloproteinases in the cleavage of collagen XVIII to form endostatin using FN-439 reverses RAC exosome-mediated retinal vessel leakage. This study demonstrates that exosomes released from retinal tissue cells have different angiogenic effects, with exosomes from RACs containing antiangiogenic components that might protect the eye from angiogenesis and maintain its functional integrity. In addition, by identifying additional components and their functions of RAC exosomes, we might improve the antiangiogenic therapy for CNV in age-related macular degeneration and diabetic retinopathy.

Immunological homeostasis of the eye

Uveitis is a sight-threatening disease caused by autoimmune or infection-related immune responses. Studies in experimental autoimmune uveitis and in human diseases imply that activated CD4(+) T cells, Th1 and Th17 cells, play an effector role in ocular inflammation. The eye has a unique regional immune system to protect vision-related cells and tissues from these effector T cells. The immunological balance between the pathogenic CD4(+) T cells and regional immune system in the eye contributes to the maintenance of ocular homeostasis and good vision. Current studies have demonstrated that ocular parenchymal cells at the inner surface of the blood-ocular barrier, i.e. corneal endothelial (CE) cells, iris pigment epithelial (PE) cells, ciliary body PE cells, and retinal PE cells, contribute to the regional immune system of the eye. Murine ocular resident cells directly suppress activation of bystander T cells and production of inflammatory cytokines. The ocular resident cells possess distinct properties of immunoregulation that are related to disparate anatomical location. CE cells and iris PE cells, which are located at the anterior segment of the eye and face the aqueous humor, suppress activation of T cells via cell-to-cell contact mechanisms, whereas retinal PE cells suppress the activation of T cells via soluble factors. In addition to direct immune suppression, the ocular resident cells have another unique immunosuppressive property, the induction of CD25(+)Foxp3(+) Treg cells that also suppress the activation of bystander T cells. Iris PE cells convert CD8(+) T cells into Treg cells, while retinal PE cells convert CD4(+) T cells greatly and CD8(+) T cells moderately into Treg cells. CE cells also convert both CD4(+) T cells and CD8(+) T cells into Treg cells. The immunomodulation by ocular resident cells is mediated by various soluble or membrane-bound molecules that include TGF-β TSP-1, B7-2 (CD86), CTLA-2α, PD-L1 (B7-H1), galectin 1, pigment epithelial-derived factor PEDF), GIRTL, and retinoic acid. Human retinal PE cells also possess similar immune properties to induce Treg cells. Although there are many issues to be answered, human Treg cells induced by ocular resident cells such as retinal PE cells and related immunosuppressive molecules can be applied as immune therapy for refractive autoimmune uveitis in humans in the future.

Retinal astrocytes pretreated with NOD2 and TLR2 ligands activate uveitogenic T cells

On entering the tissues, infiltrating autoreactive T cells must be reactivated locally to gain pathogenic activity. We have previously reported that, when activated by Toll-like receptor 3 (TLR3) and TLR4 ligands, retinal astrocytes (RACs) are able to function as antigen-presenting cells to re-activate uveitogenic T cells and allow responder T cells to induce uveitis in mice. In the present study, we found that, although the triggering of TLR2 or nucleotide-binding oligomerization domain receptor 2 (NOD2) alone did not activate RACs, their combined triggering induced RACs with the phenotypes required to efficiently re-activate interphotoreceptor retinoid-binding protein (IRBP)-specific T cells. The synergistic effect of TLR2 and NOD2 ligands on RAC activation might be explained by the observations that bacterial lipoprotein (BLP, a TLR2 ligand) was able to upregulate NOD2 expression and the combination of BLP and muramyldipeptide (MDP, a NOD2 ligand) enhanced the expression of RICK (Rip2), the signaling molecule of NOD2. Moreover, the synergistic effect of MDP and BLP on RACs was lost when the RACs were derived from NOD2 knockout mice or were pre-treated with Rip2 antagonist. Thus, our data suggest that exogenous or endogenous molecules acting on both TLR2 and NOD2 on RACs might have an enhancing effect on susceptibility to autoimmune uveitis.

Interferon-γ regulates discordant mechanisms of uveitis versus joint and axial disease in a murine model resembling spondylarthritis

OBJECTIVE

The spondylarthritides (such as ankylosing spondylitis) are multisystem inflammatory diseases that frequently result in uveitis. Despite the common co-occurrence of uveitis with arthritis, there has been no explanation for the susceptibility of the eye to inflammation. Using an innovative intravital videomicroscopic approach, we discovered the coexistence of uveitis with axial and peripheral joint inflammation in mice immunized with cartilage proteoglycan (PG). The aim of this study was to elucidate the characteristics of uveitis and test the impact of interferon-γ (IFNγ) deficiency on the eye versus the joint and spine.

METHODS

Female T cell receptor (TCR)-transgenic mice or IFNγ-knockout mice crossed to TCR-transgenic mice were immunized with PG. Uveitis was assessed by intravital videomicroscopy and histology. The clinical and histopathologic severity of arthritis and spondylitis were evaluated. The bone remodeling process within the spine was assessed by whole-body near-infrared imaging. Immunoblotting and immunofluorescence staining were used to examine the expression of PG and ADAMTS-5 and to examine the cellular composition of eyes with uveitis.

RESULTS

PG neoepitopes along with the aggrecanase ADAMTS-5 were present in the eye, as they were the joint. Anterior uveitis developed in response to PG immunization. The cellular infiltrate consisted mainly of neutrophils and eosinophils. Unexpectedly, IFNγ deficiency markedly exacerbated uveitis while ameliorating joint and spine disease, indicating divergent mechanisms that drive diseases in the eye versus the joints and spine.

CONCLUSION

This study provides the first detailed description of a murine disease model in which uveitis coincides with arthritis and spondylitis. Our observations provide a great opportunity for understanding the pathogenesis of a relatively common but poorly understood disease.

Neutralization of IL-17 ameliorates uveitis but damages photoreceptors in a murine model of spondyloarthritis

Introduction

Uveitis, or intraocular inflammatory disease, is a frequent extra-articular manifestation of several forms of arthritis. Despite the frequent co-occurrence of uveitis and arthritis, little is understood of the eye's predisposition to this disease. We recently described a previously unreported uveitis in a murine model of spondyloarthropathy triggered by autoimmunity to aggrecan, a prominent proteoglycan (PG) macromolecule in cartilage. In contrast to the joint and spine, wherein interferon-gamma (IFNγ) deficiency reduced disease, IFNγ deficiency worsened uveitis. Given the regulatory role of IFNγ on the Th17 response and the current focus of anti-interleukin-17 therapeutics in patients with uveitis and spondyloarthritis, we sought to determine the extent to which interleukin (IL)-17 mediates uveitis in the absence of IFNγ.

Methods

Antigen specific T cell cytokine production was measured in splenocyte cultures using multiplex-ELISA. Transgenic (Tg) mice expressing the T cell receptor (TCR) recognizing the dominant arthritogenic epitope in the G1 domain of PG (TCR-Tg), also lacking IFNγ, were immunized with PG. Mice were then systemically administered an anti-IL-17 neutralizing antibody. The onset and severity of peripheral arthritis was evaluated by clinical scoring criteria and histology. Uveitis was assessed using intravital videomicroscopy, which visualizes leukocyte trafficking within the vasculature and tissue of the iris, and by histology.

Results

TCR-Tg splenocytes stimulated in vitro with recombinant G1 peptide demonstrated exacerbated production of cytokines, such as macrophage inflammatory protein (MIP)-1α, MIP-1β, IL-1β, and most notably IL-17A as a consequence of IFNγ deficiency. In vivo, IL-17 inhibition prevented the component of PG-induced arthritis that occurs independently of IFNγ. Blockade of IL-17 ameliorated the ongoing leukocyte trafficking responses within the iris vasculature and tissue, which coincided with reduced infiltration of leukocytes within the anterior and posterior eye segments. However, the anti-IL-17 treatment resulted in unanticipated photoreceptor toxicity.

Conclusions

These data support a protective, regulatory role for IFNγ in suppression of IL-17-mediated intraocular disease and to a lesser extent, joint disease. The unanticipated photoreceptor toxicity raises some caution regarding the use of anti-IL-17 therapeutics until the mechanism of this potential effect is determined.

PD-L1(hi) retinal pigment epithelium (RPE) cells elicited by inflammatory cytokines induce regulatory activity in uveitogenic T cells

We previously reported that after exposure to inflammatory cytokines, such as IL-17 and IFN-γ, RPE cells express increased amounts of suppressor of cytokine signaling, leading to general suppression of the inflammatory response. Here, we demonstrate that RPE cells expressed increased levels of PD-L1 in response to IL-17, IFN-γ, or Poly I:C. These PD-L1(hi) RPE cells inhibited the pathogenic activities of IRBP-specific T cells, which usually induced uveitis when injected into naïve mice (EAU). The suppressed pathogenicity of these uveitogenic T cells after exposure to PD-L1(hi) RPE cells could be partially reversed by anti-PD-L1 antibodies. Nevertheless, IRBP-specific T cells pre-exposed to PD-L1(hi) RPE cells displayed substantial suppressor activity, which strongly inhibited the activation of fresh IRBP-Teffs in response to subsequent antigenic challenge and when transferred into naïve mice, inhibited the induction of EAU by IRBP-Teff transfer. These findings suggest that inflammatory cytokine-triggered up-regulation of PD-L1 on RPE constitutes a critical factor for inducing infiltrated uveitogenic T cells with regulatory activities, which may accelerate the natural resolution of T cell-mediated intraocular inflammation.

Aquaporin expression in blood-retinal barrier cells during experimental autoimmune uveitis

PURPOSE

Blood-retinal barrier (BRB) breakdown and retinal edema are major complications of autoimmune uveitis and could be related to deregulation of aquaporin (AQP) expression. We have therefore evaluated the expression of AQP1 and AQP4 on BRB cells during experimental autoimmune uveitis (EAU) in mice.

METHODS

C57Bl6 mice were immunized with interphotoreceptor retinoid-binding protein (IRBP) peptide 1-16. The disease was graded clinically, and double immunolabeling using glial fibrillary acidic protein (GFAP; a marker of disease activity) and AQP1 or AQP4 antibodies was performed at day 28. AQP1 expression was also investigated in mouse retinal pigment epithelium (RPE) cells (B6-RPE07 cell line) by reverse transcriptase PCR and western blot under basal and tumor necrosis factor alpha (TNF-alpha)-stimulated conditions.

RESULTS

In both normal and EAU retina, AQP1 and AQP4 expression were restricted to the photoreceptor layer and to the Müller cells, respectively. Retinal endothelial cells never expressed AQP1. In vasculitis and intraretinal inflammatory infiltrates, decreased AQP1 expression was observed due to the loss of photoreceptors and the characteristic radial labeling of AQP4 was lost. On the other hand, no AQP4 expression was detected in RPE cells. AQP1 was strongly expressed by choroidal endothelial cells, rendering difficult the evaluation of AQP1 expression by RPE cells in vivo. No major differences were found between EAU and controls at this level. Interestingly, B6-RPE07 cells expressed AQP1 in vitro, and TNF-alpha downregulated AQP1 protein expression in those cells.

CONCLUSIONS

Changes in retinal expression of AQP1 and AQP4 during EAU were primarily due to inflammatory lesions, contrasting with major modulation of AQP expression in BRB detected in other models of BRB breakdown. However, our data showed that TNF-alpha treatment strongly modulates AQP1 expression in B6-RPE07 cells in vitro.

Retinal Astrocytes respond to IL-17 differently than Retinal Pigment Epithelial cells

IL-17+ T cells make up the majority of the infiltrating cells in the inflamed eye during the development of EAU. However, the role of IL-17 in ocular inflammation is poorly defined. Given that the primary target cells for IL-17 are parenchymal cells of the tissue, we investigated the in vitro effect of IL-17 on mouse RACs and RPE cells. Our results showed that although RACs and RPE cells expressed the IL-17R, RACs responded to IL-17 by producing increased amounts of proinflammatory cytokines and chemokines, leading to increased migration of granulocytes, whereas RPE cells responded to the same concentration of IL-17 by expressing increased levels of SOCS proteins, resulting in only limited production of proinflammatory cytokines and chemokines and an increased amount of suppressive cytokines, such as LIF. The combination of IL-17 and IFN-gamma had a synergistic effect on cell migration with RACs but an antagonistic effect with RPE. In addition, specific inhibitors of the PI3K/Akt signaling pathway completely blocked inflammatory cell migration induced by chemokines released by IL-17-stimulated RACs. Our results demonstrate that IL-17 can induce a pro- or anti-inflammatory effect in the eye, depending on the parenchymal cells stimulated.

Regulatory role of TLR ligands on the activation of autoreactive T cells by retinal astrocytes

PURPOSE

To determine whether Toll-like receptor (TLR) ligands regulate the activation of retinal astrocytes (RACs) and the possible role of RACs in the polarization of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells.

METHODS

TLR expression on RACs isolated from C57BL/6 mice was examined using real-time PCR and flow cytometry. The ability of RACs before or after treatment with TLR ligands to interact with T cells was assessed by measuring major histocompatibility complex class II and costimulatory molecule expression and cytokine production. The stimulatory effect of RACs, with or without TLR stimulation, on responder IRBP-specific T cells was examined by T-cell proliferation, cytokine production, and disease-inducing ability.

RESULTS

Cultured mouse RACs expressed TLR2, TLR3, and TLR4. Different TLR ligands had distinct stimulatory effects on RACs. PolyI:C (a TLR3 ligand) had the greatest effect in stimulating RACs to acquire antigen-presentation function, whereas BLP (a TLR2 ligand) had the lowest effect. TLR3 ligation increased the expression of MHC and costimulatory molecules and induced the production of IL-6, IL-12, and IL-23 by RACs. IRBP-specific T cells activated by polyI:C-treated RACs expanded vigorously, produced significant amounts of IFN-gamma and IL-17, and induced experimental autoimmune uveitis when injected into naive mice.

CONCLUSIONS

The stimulatory effect of RACs on autoreactive T cells is regulated by TLR ligands. TLR3 had a marked effect on the ability of RACs to promote the activation of Th1 and Th17 IRBP-specific T cells. Thus, exposure to microbial antigen(s) may alter susceptibility to autoimmune uveitis by promoting the activation of autoreactive T cells.

Anti-inflammatory role of IL-17 in experimental autoimmune uveitis

Previous studies have shown that IL-17 is a strong proinflammatory cytokine and that IL-17-producing autoreactive T cells play a major role in the pathogenesis of autoimmune diseases. In a previous study, we showed that injection of experimental autoimmune uveitis-susceptible mice with anti-IL-17 Abs blocked subsequent disease development. To determine whether administration of IL-17 to experimental autoimmune uveitis-susceptible Lewis rats and B10RIII mice injected with disease-inducing peptides enhanced disease susceptibility, we injected the recipient animals with various doses of human rIL-17 (hIL-17). Unexpectedly, the treated animals showed significant amelioration of disease; in addition, both the intensity of the autoreactive response and cytokine production by the autoreactive T cells induced by immunization with uveitogenic peptides were significantly decreased. Our results show that IL-17 has anti-inflammatory activity and that this cytokine can suppress the development of autoimmune disease.