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

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.

Phenotype of Innate Immune Cells in Uveitis Associated with Axial Spondyloarthritis- and Juvenile Idiopathic Arthritis-associated Uveitis

Purpose: To analyze circulating immune cells in patients with anterior uveitis (AU) associated to axial spondyloarthritis (SpA), or juvenile idiopathic arthritis (JIA).Methods: Venous blood samples were collected from healthy controls (n = 16), and either SpA (n = 19) or JIA (n = 23) patients with associated anterior uveitis (AU) during active flare, or after ≥3 months of inactivity. Frequencies of CD56⁺, MHC-I⁺, and S100A9⁺ monocytes, CCR7⁺ dendritic cells, CD56^+dim natural killer (NK) cells and CD3⁺CD56^bright T-cells were analyzed via flow cytometry. Serum S100A8/A9 levels were determined via ELISA.Results: SpA patients showed a reduced frequency of CD56^+dim NK cells during uveitis activity, a constitutively activated monocyte phenotype, and elevated S100A8/A9 serum levels. In contrast, JIAU patients showed elevated frequencies of CD56⁺ monocytes and CCR7⁺ DC.Conclusion: Phenotype of peripheral immune cells differ between patients, probably contributing to different courses of acute onset AU in SpA and insidious onset AU in JIAU patients.Abbreviations: AU: anterior uveitis, AR: arthritis, JIA: juvenile idiopathic arthritis, SpA: axial spondyloarthritis.

The eye in spondyloarthritis✰

Acute anterior uveitis is the most common extra-articular clinical manifestation of spondyloarthropathy. Rheumatologists should be aware of uveitis, know how it presents, understand the differential diagnosis of uveitis and arthritis, and be familiar with the role of systemic medications in the treatment or prevention of uveitis.

The microbiome and HLA-B27-associated acute anterior uveitis

Acute anterior uveitis (AAU) and the spondyloarthritis (SpA) subtypes ankylosing spondylitis, reactive arthritis and psoriatic arthritis are among the inflammatory diseases affected by the biology of the intestinal microbiome. In this Review, the relationship between AAU, SpA and the microbiome is discussed, with a focus on the major SpA risk gene HLA-B*27 and how it is associated with both intestinal tolerance and the loss of ocular immune privilege that can accompany AAU. We provide four potential mechanisms to account for how dysbiosis, barrier function and immune response contribute to the development of ocular inflammation and the pathogenesis of AAU. Finally, potential therapeutic avenues to target the microbiota for the clinical management of AAU and SpA are outlined.

Can nano-hydroxyapatite permeate the oral mucosa? A histological study using three-dimensional tissue models

Nano-hydroxyapatite is used in oral care products worldwide. But there is little evidence yet whether nano-hydroxyapatite can enter systemic tissues via the oral epithelium. We investigated histologically the ability of two types of nano-hydroxyapatite, SKM-1 and Mi-HAP, to permeate oral epithelium both with and without a stratum corneum, using two types of three-dimensional reconstituted human oral epithelium, SkinEthic HGE and SkinEthic HOE respectively with and without a stratum corneum. Both types of nano-hydroxyapatite formed aggregates in solution, but both aggregates and primary particles were much larger for SKM-1 than for Mi-HAP. Samples of each tissue model were exposed to SKM-1 and Mi-HAP for 24 h at concentrations ranging from 1,000 to 50,000 ppm. After treatment, paraffin sections from the samples were stained with Dahl or Von Kossa stains. We also used OsteoSense 680EX, a fluorescent imaging agent, to test for the presence of HAP in paraffin tissue sections for the first time. Our results for both types of nano-hydroxyapatite showed that the nanoparticles did not penetrate the stratum corneum in SkinEthic HGE samples and penetrated only the outermost layer of cells in SkinEthic HOE samples without stratum corneum, and no permeation into the deeper layers of the epithelium in either tissue model was observed. In the non-cornified model, OsteoSense 680EX staining confirmed the presence of nano-hydroxyapatite particles in both the cytoplasm and extracellular matrix of outermost cells, but not in the deeper layers. Our results suggest that the stratum corneum may act as a barrier to penetration of nano-hydroxyapatite into the oral epithelium. Moreover, since oral epithelial cell turnover is around 5–7 days, superficial cells of the non-keratinized mucosa in which nanoparticles are taken up are likely to be deciduated within that time frame. Our findings suggest that nano-hydroxyapatite is unlikely to enter systemic tissues via intact oral epithelium.

The Eyes Have it: A Rheumatologist's View of Uveitis

Uveitis is defined as intraocular inflammation. It is an extraarticular manifestation of many forms of joint disease, which include spondyloarthritis, juvenile idiopathic arthritis, and Behçet's disease. Rheumatologists may be asked to consult on the ophthalmologic care of patients with uveitis in order to identify an associated systemic illness. Diagnoses such as spondyloarthritis, sarcoidosis, and interstitial nephritis with uveitis are frequently overlooked by referring ophthalmologists. Alternatively, rheumatologists may be asked to help manage the patient's immunosuppression, including biologic therapy, which can be required to treat a subset of patients with uveitis. This review is intended to provide rheumatologists with the necessary information to facilitate collaboration in the comanagement of patients with uveitis.

Investigation of the relationship between the onset of arthritis and uveitis in genetically predisposed SKG mice

Introduction

Systemic rheumatic conditions are often accompanied by intraocular inflammatory disease (termed uveitis). Despite the frequent manifestation of uveitis with arthritis, very little is understood of the underlying mechanisms that mediate the eye’s susceptibility to disease. The genetically susceptible SKG mouse strain develops arthritis that arises from an inherent mutation that disrupts T-cell antigen receptor signal transduction and thymic selection. The ensuing T-cell–mediated disease is further modulated through exposure to microbial triggers. The purpose of this study was to elucidate how a genetically determined shift in the T-cell repertoire toward self-reactive T cells that drive arthritis influences uveitis in SKG mice.

Methods

SKG mice (BALB/c mice that harbor the W163C point mutation in zeta-chain-associated protein kinase 70 [i.e., ZAP-70]) were housed under arthritis-resistant, specific pathogen–free conditions. Arthritis was induced by intraperitoneal injection with fungal glucans (zymosan or curdlan). Arthritis onset and severity were evaluated by clinical scoring, histopathology and infrared imaging within the joints. Periocular traits involving blepharoconjunctivitis were evaluated by clinical scoring and histology. Eyes were evaluated for signs of anterior uveitis using intravital videomicroscopy to document cell-trafficking responses within the iris vasculature and stroma and by histology to detect inflammatory infiltrate and tissue damage within the anterior and posterior eye segments.

Results

Exposure to zymosan resulted in the predicted arthritic, sexually dimorphic phenotype in SKG mice. The eyes of SKG mice exhibited episodic intravascular cellular responses to zymosan or curdlan as indicated by significant increases in leukocyte–endothelium interactions akin to ocular vasculitis. However, despite the significant increase in early cell-trafficking responses, cellular infiltration into the iris stroma was not observed and histopathological signs indicative of a sustained uveitis were absent. Instead, eyes of SKG mice developed blepharoconjunctivitis that coincided with arthritis and exhibited sexual dimorphism.

Conclusions

This study underscores the complexity surrounding the pathogenesis of uveitis and its relationship with arthritis. The findings suggest that distinct mechanisms exist by which pathogenic autoimmune T cells target the eyes versus joints, which likely involves the environmental context but nonetheless should be taken into account in the identification and development of effective therapies for each organ.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0725-z) contains supplementary material, which is available to authorized users.

All-Trans Retinoic Acid Improves the Effects of Bone Marrow-Derived Mesenchymal Stem Cells on the Treatment of Ankylosing Spondylitis: An In Vitro Study

Previous studies have demonstrated the immunosuppressive effects of both all-trans retinoic acid (ATRA) and mesenchymal stem cells (MSCs). The present study aimed to assess the immunoregulatory effects of ATRA on MSCs in the treatment of ankylosing spondylitis (AS). Bone marrow-derived MSCs from healthy donors were pretreated with ATRA and cocultured with CD3/28-activated peripheral blood mononuclear cells (PBMCs) derived from AS patients. Frequencies of Th17 and regulatory T (Treg) cells were analyzed using flow cytometry. The secretion and the mRNA level of key cytokines were measured with cytometric bead array and quantitative real-time PCR, respectively. ATRA pretreatment increased interleukin-6 (IL-6) secretion of MSCs. Th17 and Treg subset populations were increased and reduced by ATRA-pretreated MSCs, respectively. ATRA-pretreated MSCs significantly decreased not only the vital pathogenic cytokine in AS, tumor necrosis factor-α (TNF-α), but also AS-boosting factors interleukin-17 (IL-17A) and interferon-γ (IFN-γ). These results indicated that IL-6 may be a potential protective factor in AS and highlighted the promising role of ATRA in improving the efficacy of MSC-based treatment of AS.

Uveitis in spondyloarthritis including psoriatic arthritis, ankylosing spondylitis, and inflammatory bowel disease

Uveitis is a common complication of spondyloarthritis. The "phenotype" of the uveitis characteristic of ankylosing spondylitis (sudden onset, anterior, unilateral, recurrent, more often male) may differ from the phenotype often seen with either psoriatic arthritis or inflammatory bowel disease (insidious onset, anterior and intermediate, bilateral, chronic, and/or more often female). The frequency of uveitis is also much greater in association with ankylosing spondylitis than with either inflammatory bowel disease or psoriasis. Uveitis may affect the choice of therapy and can rarely be a complication of therapy. Uveitis and arthritis also co-exist in several animal models.

Blau syndrome-associated Nod2 mutation alters expression of full-length NOD2 and limits responses to muramyl dipeptide in knock-in mice

The biochemical mechanism by which mutations in nucleotide-binding oligomerization domain containing 2 (NOD2) cause Blau syndrome is unknown. Several studies have examined the effect of mutations associated with Blau syndrome in vitro, but none has looked at the implication of the mutations in vivo. To test the hypothesis that mutated NOD2 causes alterations in signaling pathways downstream of NOD2, we created a Nod2 knock-in mouse carrying the most common mutation seen in Blau syndrome, R314Q (corresponding to R334Q in humans). The endogenous regulatory elements of mouse Nod2 were unaltered. R314Q mice showed reduced cytokine production in response to i.p. and intravitreal muramyl dipeptide (MDP). Macrophages from R314Q mice showed reduced NF-κB and IL-6 responses, blunted phosphorylation of MAPKs, and deficient ubiquitination of receptor-interacting protein 2 in response to MDP. R314Q mice expressed a truncated 80-kDa form of NOD2 that was most likely generated by a posttranslational event because there was no evidence for a stop codon or alternative splicing event. Human macrophages from two patients with Blau syndrome also showed a reduction of both cytokine production and phosphorylation of p38 in response to MDP, indicating that both R314Q mice and cells from patients with Blau syndrome show reduced responses to MDP. These data indicate that the R314Q mutation when studied with the Nod2 endogenous regulatory elements left intact is associated with marked structural and biochemical changes that are significantly different from those observed from studies of the mutation using overexpression, transient transfection systems.

Aberrant interleukin-1 signalling does not increase susceptibility of mice to NOD2-dependent uveitis

BACKGROUND

NOD2 is the genetic cause of Blau syndrome, an autoinflammatory disease that manifests as coincident uveitis and arthritis. Since dysregulation of IL-1 signalling is considered a pathogenic mechanism in a number of related autoinflammatory conditions, we examined the extent to which unimpeded interleukin (IL)-1 signalling influences NOD2-dependent inflammation of the eye versus the joint.

METHODS

Mice deficient for IL-1R antagonist (IL-1Ra) were administered the NOD2 agonist muramyl dipeptide (MDP) by systemic (intraperitoneal) or local (intraocular and/or intra-articular) injections. NOD2-deficient mice received an intraocular injection of recombinant IL-1β. Uveitis was evaluated by intravital videomicroscopy and histopathology, and arthritis was assessed by near-infrared imaging and histopathology. Ocular levels of IL-1α, IL-1β and IL-1Ra were quantified by enzyme-linked immunosorbent assay.

RESULTS

IL-1Ra deficiency did not render mice more responsive to systemic exposure of MDP. Despite the increased production of IL-1R agonists IL-1α and IL-1β in response to intraocular injection of MDP, deficiency in IL-1Ra did not predispose mice to MDP-triggered uveitis, albeit intravascular cell rolling and adherence were exacerbated. NOD2 expression was dispensable for the potential of IL-1 to elicit uveitis. However, we find that IL-1Ra does play an important protective role in arthritis induced locally by MDP injection in the joint.

CONCLUSIONS

Our findings highlight the complexity of NOD2 activation and IL-1 signalling effects that can be compounded by local environmental factors of the target organ. These observations may impact how we understand the molecular mechanisms by which NOD2 influences inflammation of the eye versus joint, and consequently, treatment options for uveitis versus arthritis.

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.