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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., How mutations in the microbial receptor NOD2 induce Blau syndrome in humans and related uveitis is unclear. Here the authors show, using Nod2-deficient mice and experimental uveitis, that Nod2 negatively regulates T cell activation and transcription of autoimmunity-related genes to suppress Th17 responses and uveitis.

Background Nod-like receptors (NLRs) are critical to innate immune activation and induction of adaptive T cell responses. Yet, their role in autoinflammatory diseases of the central nervous system (CNS) remains incompletely defined. The NLR, Nlrp12, has been reported to both inhibit and promote neuroinflammation in an animal model of multiple sclerosis (experimental autoimmune encephalomyelitis, EAE), where its T cell-specific role has been investigated. Uveitis resulting from autoimmunity of the neuroretina, an extension of the CNS, involves a breach in immune privilege and entry of T cells into the eye. Here, we examined the contribution of Nlrp12 in a T cell-mediated model of uveitis, experimental autoimmune uveitis (EAU). Methods Mice were immunized with interphotoreceptor retinoid-binding protein peptide 1–20 (IRBP1–20) emulsified in Complete Freund’s adjuvant, CFA. Uveitis was evaluated by clinical and histopathological scoring, and comparisons were made in WT vs. Nlrp12−/− mice, lymphopenic Rag1−/− mice reconstituted with WT vs. Nlrp12−/− CD4+ T cells, or among bone marrow (BM) chimeric mice. Antigen-specific Th-effector responses were evaluated by ELISA and intracellular cytokine staining. Cellular composition of uveitic eyes from WT or Nlrp12−/− mice was compared using flow cytometry. Expression of Nlrp12 and of cytokines/chemokines within the neuroretina was evaluated by immunoblotting and quantitative PCR. Results Nlrp12−/− mice developed exacerbated uveitis characterized by extensive vasculitis, chorioretinal infiltrates and photoreceptor damage. Nlrp12 was dispensable for T cell priming and differentiation of peripheral Th1 or Th17 cells, and uveitis in immunodeficient mice reconstituted with either Nlrp12−/− or WT T cells was similar. Collectively, this ruled out T cells as the source of Nlrp12-mediated protection to EAU. Uveitic Nlrp12−/− eyes had more pronounced myeloid cell accumulation than uveitic WT eyes. Transplantation of Nlrp12−/− BM resulted in increased susceptibility to EAU regardless of host genotype, but interestingly, a non-hematopoietic origin for Nlrp12 function was also observed. Indeed, Nlrp12 was found to be constitutively expressed in the neuroretina, where it suppressed chemokine/cytokine induction. Conclusions Our data identify a combinatorial role for Nlrp12 in dampening autoimmunity of the neuroretina. These findings could provide a pathway for development of therapies for uveitis and potentially other autoinflammatory/autoimmune diseases of the CNS.

Spondylarthritis (SpA) refers to a group of autoimmune diseases characterized by inflammation of the spine (spondylitis) and joints (arthritis) including ankylosing spondylitis and psoriatic arthritis. Genetic studies suggest that autoreactive Th17 cells drive SpA pathogenesis and in support IL-17 blockade in the clinic moderates symptoms. Although Th17 responses appear to be key in driving symptomatic disease, less is understood of the underlying innate cellular mechanisms that contribute to the initiation of pathogenic T cells. Upon analysis of SpA patient cell blood count data (1,497 events) we discovered a positive correlation between the absolute number of neutrophils and disease severity. Thus, we sought to determine how dysregulated neutrophil responses might control autoreactive Th17 responses using an experimental model of SpA (SKG mice). SKG mice have a point mutation in Zap70 resulting in autoreactive Th17 cells that cause arthritis and spondylitis. When SKG splenocyte cultures were treated with monoclonal antibodies to CD3 and simultaneously co-incubated with autologous neutrophils for 72h we detected increased T cell activation status (CD69 expression) and production of IL-17 but not IFNγ compared to media only (no neutrophils) controls. Neutrophil-deplete SKG mice had reduced autoreactive Th17 responses and delayed onset of arthritis compared to neutrophil-replete controls, supporting a role for neutrophils in promoting autoreactive Th17 responses and the induction of disease. In conclusion our data reveal a role for neutrophils in pathogenesis of SpA, indicating that neutrophil modulating drugs could be considered as a future treatment strategy for SpA. Supported by grants from VA (CDA-2 IK2BX004523 and Merit I01BX002180) and NIH (R01 EY025250)

We recently discovered a role for Nod2 within T cells in controlling Th17-immunity, such that deletion of Nod2 exacerbated experimental autoimmune arthritis and uveitis. Protection against opportunistic Candida albicans infection relies on intact Th17-responses. Thus, we considered whether the T cell intrinsic Nod2 might control antifungal Th17 responses at the cost of increasing host susceptibility to autoimmunity. Nod2−/− mice infected with 105 (LD50) Candida albicans had increased survival and reduced fungal burden in the kidney within 24–72 h post-infection, suggesting a critical role for Nod2 in C. albicans immunity. Rag−/− mice reconstituted with Nod2fl/fl/CD4-cre CD4+ T cells and infected with C. albicans had decreased fungal burden compared to control CD4-Cre T cell recipients, and IL-17 depletion reverted the phenotype. After 48h infection, Nod2fl/fl/CD4-cre CD4+ T cells in the kidney had increased activation (CD69), increased proportion of T effector cells, and decreased Tregs compared to controls, suggesting endogenous Nod2 negatively regulates fungal-triggered Teff/Th17 cell responses. We next asked how Nod2 might function in SKG mice that are genetically susceptible to arthritis. Whereas Nod2−/− SKG mice developed an exacerbated form of arthritis compared to Nod2+/+ SKG controls, these same mice cleared C. albicans infection better than Nod2+/+ SKG mice. Cumulatively our data indicate a critical role for T cell intrinsic Nod2 in antifungal Th17 immunity. Given these studies we posit that human NOD2 genetic variants may offer enhanced ability to fight fungal infection via a T cell intrinsic mechanism, at the cost of triggering autoimmunity. Supported by grants from VA (CDA-2 IK2BX004523 and Merit I01BX002180) and NIH (R01 EY025250).

Children with mutations in the nucleotide binding domain of NOD2 cause the monogenetic inflammatory disease Blau Syndrome, which is characterized by dermatitis, arthritis and uveitis. NOD2 is a well-known microbial sensor important in anti-bacterial immunity. However, the mechanism by which mutated NOD2 causes non-infectious inflammation in Blau is unknown. We recently reported a novel function of Nod2 as a central regulator of T cell homeostasis and as a negative regulator of autoreactive Th17 responses in experimental autoimmune uveitis (EAU) and arthritis. Here, we examined the effect of Blau mutations on T cell function and EAU using Blau knock-in mice carrying the most common Blau-mutation R314Q (corresponding to R334Q in humans) and Blau patient cells. We found that CD4+ T cells from Blau patients and Blau mice, produced increased IL-17 but decreased IFNγ following in vitro TCR-activation compared to control patients and WT mice, respectively. Blau mice developed worsened EAU compared to WT controls, which was accompanied by increased autoreactive (retina-specific) Th17 cells within the eye. Lymphocyte-deplete Rag1−/− mice reconstituted with Blau CD4+ T cells developed worse EAU than WT T cell recipients, indicating that CD4+ T cells expressing Blau-specific Nod2 mutations are sufficient to cause exacerbated EAU. Cumulatively, these data reveal a previously unconsidered role for Th17 cells in Blau Syndrome, and provide new T cell-targeted therapeutic avenues to treat this disease. Supported by grants from VA (CDA-2 IK2BX004523 and Merit I01BX002180) and NIH (R01 EY025250).

Orientia tsutsugamushi is an obligately intracellular bacterium and the etiological agent of scrub typhus. The lung is a major target organ of infection, displaying type 1-skewed proinflammatory responses. Lung injury and acute respiratory distress syndrome are common complications of severe scrub typhus; yet, their underlying mechanisms remain unclear. In this study, we investigated whether the C-type lectin receptor (CLR) Mincle contributes to immune recognition and dysregulation. Following lethal infection in mice, we performed pulmonary differential expression analysis with NanoString. Of 671 genes examined, we found 312 significantly expressed genes at the terminal phase of disease. Mincle (Clec4e) was among the top 5 greatest up-regulated genes, accompanied with its signaling partners, type 1-skewing chemokines (Cxcr3, Ccr5, and their ligands), as well as Il27. To validate the role of Mincle in scrub typhus, we exposed murine bone marrow-derived macrophages (MΦ) to live or inactivated O. tsutsugamushi and analyzed a panel of CLRs and proinflammatory markers via qRT-PCR. We found that while heat-killed bacteria stimulated transitory Mincle expression, live bacteria generated a robust response in MΦ, which was validated by indirect immunofluorescence and western blot. Notably, infection had limited impact on other tested CLRs or TLRs. Sustained proinflammatory gene expression in MΦ (Cxcl9, Ccl2, Ccl5, Nos2, Il27) was induced by live, but not inactivated, bacteria; infected Mincle-/- MΦ significantly reduced proinflammatory responses compared with WT cells. Together, this study provides the first evidence for a selective expression of Mincle in sensing O. tsutsugamushi and suggests a potential role of Mincle- and IL-27-related pathways in host responses to severe infection. Additionally, it provides novel insight into innate immune recognition of this poorly studied bacterium., Author summary Scrub typhus is a life-threatening disease caused by the bacterium Orientia tsutsugamushi. Severe disease often involves the lung, where diffuse alveolar damage can lead to significant morbidity and mortality. It is thought that dysregulated immune responses contribute to the development of severe disease; however, it remains unknown as to how the immune system senses and responds to O. tsutsugamushi. In this study, we used a lethal mouse model of scrub typhus, along with cultured macrophages and neutrophils, to examine immune sensors and inflammatory responses which may be involved during infection. We found that O. tsutsugamushi selectively stimulated the C-type lectin receptor Mincle in the lungs of infected mice, which was accompanied by increased markers of proinflammatory and type 1-responses. We also found that macrophages treated with live or inactivated bacteria increased Mincle expression alongside type 1 and M1 proinflammatory markers, some of which were markedly decreased in Mincle-/- cells. Activation of Mincle and its associated inflammatory profile by both live and inactivated O. tsutsugamushi may generate an overzealous immune response that contributes to acute tissue damage. This study provides novel insight into immune recognition of O. tsutsugamushi and a new framework for evaluating immune dysregulation in scrub typhus.

Caspase recruitment domain-containing protein 9 (Card9) promotes anti-fungal immunity following C-type lectin receptor Dectin-1 activation by b-glucans. CARD9 has also been implicated in the pathogenesis of T cell-mediated inflammatory diseases including rheumatoid arthritis and ankylosing spondylitis, but how Card9 controls non-infectious inflammation is poorly understood. Using genetically susceptible SKG mice that develop b-glucan (zymosan)-induced, Th17-mediated autoimmune arthritis and spondylitis we found that Card9-deficiency (Card9−/− SKG mice) conferred complete protection from disease. Card9 promoted arthritis via a Dectin-1-mediated mechanism, as the Dectin-1-specific ligand (curdlan) induced disease and bacterial/fungal ligands specific for Dectin-2 or Mincle did not. At 8 weeks post-zymosan Th17 cells and neutrophils were dramatically reduced in Card9−/− SKG mouse joints, indicating an interplay between Card9, neutrophils and Th17 cells in promoting arthritis. Importantly, pre-arthritic Card9−/− SKG mice had reduced neutrophils in lavage fluid 4 hours post-zymosan compared to SKG mice, but no changes in dendritic cells or macrophages. Lavage fluid neutrophils from Card9−/− SKG mice had similar Dectin-1 expression to SKG mice, yet decreased activation (retention of CD62L) and degranulation of primary (CD63) and secondary (CD66b). Akin to Card9−/− SKG mice, neutrophil-deplete SKG mice had decreased Th17 cells and delayed arthritis onset, supporting a pathogenic function for neutrophils in induction of arthritis. These data suggest that Card9 functions downstream of Dectin-1 to promote pathogenic neutrophil responses necessary to induce Th17-mediated arthritis and spondylitis.

Nucleotide-binding oligomerization domain-containing protein 2 (Nod2) is a pattern recognition receptor known to promote anti-bacterial immunity yet its function in fungal disease is less understood. Here we sought to investigate the role of Nod2 in regulating fungal infection. Our results demonstrate that Nod2−/− mice infected with 105 (LD50) Candida albicans had increased survival and reduced kidney pathology compared to WT mice, indicating an important role for Nod2-deficiency in protection against infection. In corroboration, Nod2−/− mice had increased fungal clearance in the kidney within 24–72 h post-infection. T cell-deficient Rag−/− or Nod2−/− Rag−/− mice infected with C. albicans had similar fungal burdens, indicating a cellular role for Nod2 outside of innate and non-hematopoietic cells. In support, Nod2−/− mouse kidneys had increased frequencies of CD4+ T cells 48h post-infection, indicating a potential protective function for Nod2−/− T cells. To evaluate a putative T cell-intrinsic function of Nod2 we infected Rag1−/− mice reconstituted with CD4+ T cells from conditional knockout mice deficient in Nod2 in CD4+ T cells (Nod2fl/fl/CD4-cre) or control mice (CD4-cre). Mice harboring CD4+ T cells from Nod2fl/fl/CD4-cre mice had decreased fungal burden within 48 h and increased Th17 cells in the kidneys akin to the global Nod2−/− mice. Protection conferred by Nod2-deficient CD4+ T cells was abrogated by neutralization of IL-17, indicating the functional importance of the Nod2/IL-17 response in CD4+ T cells in C. albicans pathogenesis. Cumulatively, our data suggest that in opposition to the known protective role of Nod2 in bacterial infections, T cell-intrinsic Nod2 promotes fungal infection.

Summary Uveitis (intraocular inflammation) is a leading cause of loss of vision. Although its aetiology is largely speculative, it is thought to arise from complex genetic–environmental interactions that break immune tolerance to generate eye-specific autoreactive T cells. Experimental autoimmune uveitis (EAU), induced by immunization with the ocular antigen, interphotoreceptor retinoid binding protein (IRBP), in combination with mycobacteria-containing complete Freund's adjuvant (CFA), has many clinical and histopathological features of human posterior uveitis. Studies in EAU have focused on defining pathogenic CD4+ T cell effector responses, such as those of T helper type 17 (Th17) cells, but the innate receptor pathways precipitating development of autoreactive, eye-specific T cells remain poorly defined. In this study, we found that fungal-derived antigens possess autoimmune uveitis-promoting function akin to CFA in conventional EAU. The capacity of commensal fungi such as Candida albicans or Saccharomyces cerevisae to promote IRBP-triggered EAU was mediated by Card9. Because Card9 is an essential signalling molecule of a subgroup of C-type lectin receptors (CLRs) important in host defence, we evaluated further the proximal Card9-activating CLRs. Using single receptor-deficient mice we identified Dectin-2, but not Mincle or Dectin-1, as a predominant mediator of fungal-promoted uveitis. Conversely, Dectin-2 activation by α-mannan reproduced the uveitic phenotype of EAU sufficiently, in a process mediated by the Card9-coupled signalling axis and interleukin (IL)-17 production. Taken together, this report relates the potential of the Dectin-2/Card9-coupled pathway in ocular autoimmunity. Not only does it contribute to understanding of how innate immune receptors orchestrate T cell-mediated autoimmunity, it also reveals a previously unappreciated ability of fungal-derived signals to promote autoimmunity.

Arthritis in a genetically susceptible SKG strain of mice models a theoretical paradigm wherein autoimmune arthritis arises because of interplay between preexisting autoreactive T cells and environmental stimuli. SKG mice have a point mutation in ZAP-70 that results in attenuated TCR signaling, altered thymic selection, and spontaneous production of autoreactive T cells that cause arthritis following exposure to microbial β-glucans. In this study, we identify Nod2, an innate immune receptor, as a critical suppressor of arthritis in SKG mice. SKG mice deficient in Nod2 (Nod2−/−SKG) developed a dramatically exacerbated form of arthritis, which was independent of sex and microbiota, but required the skg mutation in T cells. Worsened arthritis in Nod2−/−SKG mice was accompanied by expansion of Th17 cells, which to some measure coproduced TNF, GM-CSF, and IL-22, along with elevated IL-17A levels within joint synovial fluid. Importantly, neutralization of IL-17A mitigated arthritis in Nod2−/−SKG mice, indicating that Nod2-mediated protection occurs through suppression of the Th17 response. Nod2 deficiency did not alter regulatory T cell development or function. Instead, Nod2 deficiency resulted in an enhanced fundamental ability of SKG CD4+ T cells (from naive mice) to produce increased levels of IL-17 and to passively transfer arthritis to lymphopenic recipients on a single-cell level. These data reveal a previously unconsidered role for T cell–intrinsic Nod2 as an endogenous negative regulator of Th17 responses and arthritogenic T cells. Based on our findings, future studies aimed at understanding a negative regulatory function of Nod2 within autoreactive T cells could provide novel therapeutic strategies for treatment of patients with arthritis.

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.

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.

Background/aim Peptidoglycan (PGN) recognition proteins (PGLYRPs) are innate immune molecules that recognise bacterial cell wall PGN, and participate in several inflammatory diseases such as arthritis. We sought to elucidate the contribution of PGLYRPs in murine uveitis (intraocular inflammatory disease) elicited by PGN, and the extent to which systemically administered PGN alters uveitis compared with arthritis versus locally triggered ocular responses. Methods Mice deficient for PGLYRP-2, PGLYRP-3 or PGLYRP-4 were administered PGN by an intraperitoneal or intraocular injection. Arthritis was assessed by near-infrared imaging and histopathology, while uveitis was measured by intravital videomicroscopy and histopathology. Results Systemic PGN exposure predisposed to arthritis through a PGLYRP-2 dependent mechanism. By contrast, systemic PGN exposure did not predispose to uveitis, and PGLYRP-2 deficiency had no impact on the development the uveitis. When PGN was administered locally, a robust uveitis ensued, which occurred independently of PGLYRP-2. Regardless of whether PGN was administered systemically or locally, neither PGLYRP-3 nor PGLYRP-4 deficiency significantly altered ocular inflammation compared with wild-type control animals. Conclusions Our findings highlight the complexity of PGLYRPs and how PGLYRP-2 may use different molecular pathways in the joints versus eyes. Collectively, our results support a non-essential or redundant role for PGLYRPs-2, -3, -4 in uveitis.

Uveitis, which occurs in association with systemic immunological diseases, presents a considerable medical challenge because of incomplete understanding of its pathogenesis. The signals that initiate T cells to target the eye, which may be of infectious or noninfectious origin, are poorly understood. Experimental autoimmune uveoretinitis (EAU) develops in mice immunized with the endogenous retinal protein interphotoreceptor retinoid binding protein in the presence of the adjuvant CFA. EAU manifests as posterior ocular inflammation consisting of vasculitis, granulomas, retinal damage, and invasion of self-reactive T cells, which are key clinical features of human uveitis. Our studies uncover Card9 as a critical genetic determinant for EAU. Card9 was responsible for Th17 polarization and Th17-associated Ag-specific responses, but not Th1-associated responses. Nonetheless, Card9 expression was essential for accumulation of both lineages within the eye. Consistent with its recently identified role as an intracellular signaling mediator for C-type lectin receptors (CLRs), a Card9-dependent transcriptional response in the neuroretina was observed involving genes encoding the CLRs Dectin-1, Dectin-2, and Mincle. Genetic deletion of these individual CLRs revealed an essential role for Mincle. Mincle activation was sufficient to generate the EAU phenotype, and this required activation of both Syk and Card9. In contrast, Dectin-1 contributed minimally and a possible repressive role was shown for Dectin-2. These findings extend our understanding of CLRs in autoimmune uveitis. The newly identified role of Mincle and Syk/Card9-coupled signaling axis in autoimmune uveitis could provide novel targets for treatment of patients with ocular inflammatory disease.

OBJECTIVE—The spondyloarthropathies (such as ankylosing spondylitis) are multi-system inflammatory diseases that frequently result in uveitis, or intra-ocular eye inflammation. Despite the common co-occurrence of uveitis with arthritis, there has been no explanation for the eye’s susceptibility to inflammation. Using an innovative intravital videomicroscopic approach, we discovered the co-existence of uveitis with axial and peripheral joint inflammation in mice immunized with cartilage proteoglycan (PG). Here, we elucidate the characteristics of uveitis and test the impact of IFNγ deficiency on the eye versus the joint and spine. METHODS—Female, TCR-Tg or IFNγ knock-out crossed to TCR-Tg mice were immunized with PG. Uveitis was assessed by intravital videomicroscopy and histology. The clinical and histopathologic severity of arthritis and spondylitis were evaluated. Bone remodeling process within the spine was assessed by whole-body NIR imaging. Immunoblotting and immunofluorescence staining were used to examine expression of PG and ADAMTS-5 along with examination of the cellular composition of uveitic eyes. RESULTS—PG neo-epitopes along with the aggrecanase, ADAMTS-5, are present in the eye as they are the joint. Anterior uveitis develops in response to PG immunization. The cellular infiltrate consists mainly of neutrophils and eosinophils. Unexpectedly, IFNγ deficiency markedly exacerbates uveitis while ameliorating joint and spine disease, indicating divergent mechanisms that drive diseases in the eye versus joints and spine. CONCLUSIONS—This is the first detailed description of a murine disease model wherein uveitis coincides with arthritis and spondylitis. Our observations provide great opportunity to understand the pathogenesis of a relatively common but poorly understood disease. Many immune-mediated inflammatory diseases including systemic lupus erythematosus (SLE), rheumatoid arthritis, Sjogren’s syndrome, Wegener’s granulomatosis

Innate immune receptors such as the nucleotide-binding domain, leucine-rich repeat-containing (NBD-LRR) receptors, referred to as NLRs, are known to serve as a critical component of host defense. However, their participation in inflammatory responses within immune privileged sites such as the brain and eye is less understood. The potential importance of NLRs in regulation of inflammation within these particular sites is further underscored by their association with autoinflammatory disorders, wherein localized inflammation can occur within the brain or eye as neuroinflammation or uveitis, respectively. Many NLRs are expressed within the brain and eye and in this review, we discuss their roles in the inflammation of the central nervous system (CNS) and uveitis.

Activation of pattern recognition receptors (PRR) may contribute to arthritis. Here, we elucidated the role of NOD2, a genetic cause of inflammatory arthritis, and several other PRR in a murine model of inflammatory arthritis.The roles of CR3, TLR2, MyD88, NOD1, NOD2, Dectin-1 and Dectin-2 were tested in vivo in arthritis elicited by intra-articular injections of zymosan, the fungal cell wall components curdlan, laminarin and mannan, and the bacterial cell wall peptidoglycan.Dectin-1, and to a lesser extent Dectin-2, contributed to arthritis. TLR2, MyD88 and CR3 played non-essential roles. Observations based on injection of curdlan, laminarin or mannan supported the dominant role of the Dectin-1 pathway in the joint. We demonstrated differential roles for NOD1 and NOD2 and identified NOD2 as a novel and essential mediator of zymosan-induced arthritis.Together, Dectin-1 and NOD2 are critical, sentinel receptors in the arthritogenic effects of zymosan. Our data identify a novel role for NOD2 during inflammatory responses within joints.

Nod2 is a pattern recognition receptor known for its role in antimicrobial immunity. Intriguingly, NOD2 appears to have a role outside of infection, as a single point mutation in this molecule leads to 100% incidence of an inflammatory arthritis called Blau Syndrome. Here we investigate the role of Nod2 in regulation of arthritogenic CD4+ T cells in SKG mice. SKG mice have a mutation in ZAP-70 that results in altered thymic selection and spontaneous production of arthritogenic T cells. Nod2−/− SKG mice have exacerbated arthritis and increased numbers of CD4+IL-17+ (Th17) cells that co-produce TNF and GM-CSF compared to SKG mice. Additionally, Nod2−/− SKG mice have augmented levels of IL-17A in their joint synovial fluid. Exacerbated disease in Nod2−/− SKG mice is independent of sex or SKG-mediated dysbiosis as shown by co-housing studies, but dependent on the skg-mutation. Naïve (non-arthritic) Nod2−/− SKG mice have similar numbers of conventional CD4+ T cells with unaltered Treg frequency or function compared to SKG mice. However, CD4+ T cells isolated from naïve Nod2−/− SKG mice produce increased levels of pro-inflammatory cytokines (IL-17, IFNγ) in response to TCR-dependent or -independent stimulus. Furthermore, transfer of CD4+ T cells isolated from naïve Nod2−/−SKG mice into lymphopenic (Nude) recipients results in worsened arthritis compared to an analogous transfer of SKG-CD4+ T cells. These data suggest a previously unappreciated function of Nod2 as a negative regulator of the proinflammatory capacity and pathogenesis of autoreactive CD4+ T cells in SKG mice. Understanding how Nod2 participates in immune tolerance mechanisms will contribute to our knowledge of the pathophysiology of autoimmunity and arthritis.

Nucleotide-binding and oligomerization domain 2 (NOD2) is an intracellular a protein involved in innate immunity and linked to chronic inflammatory diseases in humans. Further characterization of the full spectrum of proteins capable of binding to NOD2 may provide new insights into its normal functioning as well as the mechanisms by which mutated forms cause disease. Using a proteomics approach to study human THP-1 cells, we have identified 2’-5’-oligoadenylate synthetase type 2 (OAS2), a dsRNA binding protein involved in the pathway that activates RNase-L, as a new binding partner for NOD2. The interaction was confirmed using over-expression of OAS2 and NOD2 in HEK cells. Further confirmation was obtained by detecting NOD2 in immunoprecipitates of endogenous OAS2 in THP-1 cells. Finally, over-expression of NOD2 in THP-1 cells led to enhanced RNase-L activity in cells treated with poly(I:C), a mimic of double-stranded RNA virus infection. These data indicate connectivity in pathways involved in innate immunity to bacteria and viruses and suggest a regulatory role whereby NOD2 enhances the function of RNase-L.

In addition to its role in innate immunity, nucleotide oligomerization domain 2 (NOD2) has been shown to play a suppressive role in models of colitis. Notably, mutations in NOD2 cause the inherited granulomatous disease of the joints called Blau syndrome, thereby linking NOD2 with joint disease as well. However, the role of NOD2 in joint inflammation has not been clarified. We demonstrate here that NOD2 is functional within the mouse joint and promotes inflammation, as locally or systemically administered muramyl dipeptide (MDP; the NOD2 agonist) resulted in significant joint inflammation that was abolished in NOD2-deficient mice. We then sought to investigate the role of NOD2 in a mouse model of inflammatory arthritis dependent on adaptive immunity using TCR-transgenic mice whose T cells recognized the dominant epitope of proteoglycan (PG). Mice immunized with PG in the presence of MDP developed a more severe inflammatory arthritis and histopathology within the joints. Antigen-specific activation of splenocytes was enhanced by MDP with respect to IFN-γ production, which would be consistent with the Th1-mediated disease in vivo. Intriguingly, NOD2 deficiency did not alter the PG-induced arthritis, indicating that NOD2 does not play an essential role in this model of joint disease when it is not activated by MDP. In conclusion, we demonstrate that in a model of inflammatory arthritis dependent on T and B cell priming, NOD2 activation potentiates disease. However, the absence of NOD2 does not alter the course of inflammatory arthritis, in contrast to models of intestinal inflammation.

Background: Uveitis is often associated with a systemic inflammatory disease such as ankylosing spondylitis. Our understanding of the eye’s susceptibility to immune-mediated uveitis as in the apparent absence of infection has been limited by a relative lack of experimental models. Here we sought to assess whether ocular inflammation occurs in a previously described murine model of proteoglycan-induced spondylitis, wherein mice develop progressive spondylitis, sacroiliitis and peripheral arthritis – features common to the clinical presentations of ankylosing spondylitis. Methods: Using intravital microscopy we examined the ocular inflammatory response after the onset of arthritis in mice that overexpressed the T cell receptor (TCR) specific for a dominant arthritogenic epitope of cartilage proteoglycan [TCR-Tg (transgenic) mice] or BALB/c controls. Results: Immunized TCR-Tg mice showed a significant increase in the number of rolling and adhering cells within the iris vasculature compared to adjuvant control mice. Cellular infiltration within the iris tissue, as assessed by intravital microscopy and histology, was also increased. Our initial temporal analysis has revealed that immunized TCR-Tg mice show a significant increase in intravascular inflammation by 2 weeks after immunization, but it diminishes at 4 weeks after immunization. Conclusions: Although these data are preliminary, this model has the potential to clarify the mechanisms accounting for the coexistence of eye and sacroiliac inflammation as occurs in patients with ankylosing spondylitis.

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.

xCorticotropin-releasing hormone (CRH) is a central mediator in the response to stress, coordinating behavioral, autonomic and neuroendocrine activation. CRH overproduction is implicated in several affective disorders, including major depression, panic-anxiety disorder and anorexia-diseases also associated with altered immune function. We investigated the link between CRH overdrive and immune function using CRH transgenic mice. Following immunization, CRH transgenic mice fail to form germinal centers; chronic glucocorticoid administration recapitulates this effect in wild-type mice. Regulation of germinal centers by glucocorticoids appears to be mediated, in part, through effects on follicular dendritic cells (FDC), providing a novel mechanism by which CRH dysregulation may significantly impair humoral immune responses. (C) 2004 Elsevier B.V. All rights reserved.

Summary Background Molecular mechanisms of neuroprotection that lead to ischaemic tolerance are incompletely understood. Identification of genes involved in the process would provide insight into cell survival and therapeutic approaches for stroke. We developed a mouse model of neuroprotection in stroke and did gene expression profiling to identify potential neuroprotective genes and their associated pathways. Methods Eight mice per condition were subjected to occlusion of the middle cerebral artery for 15 min (preconditioning), 60 min (injurious ischaemia), or preconditioning followed 72 h later by injurious ischaemia. RNA was extracted from the cortical regions of the ischaemic and non-ischaemic hemispheres. Three pools per condition were generated, and RNA was hybridised to oligonucleotide microarrays for comparison of ischaemic and non-ischaemic hemispheres. Real-time PCR and western blots were used to validate results. Follow-up experiments were done to address the biological relevance of findings. Findings Microarray analysis revealed changes in gene expression with little overlap among the conditions of injurious ischaemia, ischaemic preconditioning, or both. Injurious ischaemia induced upregulation of gene expression; 49 (86%) of 57 genes regulated showed increased expression in the ischaemic hemisphere. By contrast, preconditioning followed by injurious ischaemia resulted in pronounced downregulation; 47 (77%) of 61 regulated genes showed lower expression. Preconditioning resulted in transcriptional changes involved in suppression of metabolic pathways and immune responses, reduction of ion-channel activity, and decreased blood coagulation. Interpretation Preconditioning reprogrammes the response to ischaemic injury. Similar changes reported by others support an evolutionarily conserved endogenous response to decreased blood flow and oxygen limitation such as seen during hibernation.

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.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.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.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.

Ellen J Lee1,2 and Holly L Rosenzweig1,2,3* 1Department of Ophthalmology, Oregon Health & Science University, Portland, OR, USA 2VA Medical Center, Portland, OR, USA 3Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, OR, USA *Corresponding author: Holly L. Rosenzweig, PhD, VA Medical Center, 3710 SW US, Veterans Hospital Rd. Bldg 103, Room E-221A, Mail stop: VA RD E-mail: rosenzwh@ohsu.edu

Rheumatoid arthritis remains a major public health concern, estimated to affect 1.5 million adults in the U.S. However, the etiology and underlying immunological mechanisms of this disease remain largely speculative. SKG mice harbor a spontaneous mutation in ZAP-70 and develop arthritogenic T cells, leading to chronic, self-sustained joint destruction. Arthritis in SKG mice replicates a current theoretical paradigm that environmental factors, including microbes, activate preexisting autoreactive T cells in genetically predisposed individuals to cause disease. Currently, the mechanisms by which innate immune receptors augment T cell activation as well as disease onset and progression are not understood. Here we sought to characterize the role of the intracellular pattern recognition molecule, NOD2, in disease pathology. Using NIR-spectroscopy and clinical scoring methods we determined that SKG mice lacking NOD2 develop markedly worse arthritis when triggered by fungal associated molecules, including curdlan and zymosan, as compared to SKG/NOD2+/+ mice. Intracellular cytokine staining showed no difference between Th17 and Th1 cytokine production by CD4+ and CD8+ T cell splenocytes between genotypes. Importantly, neutralization of IL-17A reduced disease severity in SKG/NOD2−/− mice to levels of disease exhibited by SKG/NOD2+/+, suggesting IL-17A as the prominent worsening factor in SKG/NOD2−/− mice. Our data suggest that NOD2 serves a protective role against autoimmune arthritis, in part due to regulation of IL-17A. Thus, understanding how microbial recognition pathways like NOD2 factor into the induction and pathology of arthritis is key to the development of effective a therapy.

We recently identified the innate receptor Mincle, a C-type lectin receptor (CLR) that signals through Syk and Card9, as essential in induction of ocular autoimmunity, using experimental autoimmune uveitis (EAU). Now, we further delineate molecular and cellular factors involved in orchestrating this Mincle-dependent mechanism. EAU is typically induced by immunization with interphotoreceptor retinoid-binding protein (IRBP) in CFA and then evaluated by fundus imaging and histology. When the synthetic Mincle agonist TDB (trehalose-6-6′-dibehenate) was used in lieu of CFA, TDB-immunized mice developed uveitis (p

BackgroundUveitis, or inflammatory eye disease, is a common extra-articular manifestation of many systemic autoinflammatory diseases involving the joints. Anakinra (recombinant interleukin (IL)-1 receptor antagonist (Ra)) is an effective therapy in several arthritic diseases; yet, few studies have investigated the extent to which IL-1 signalling or IL-1Ra influences the onset and/or severity of uveitis.ObjectiveTo seek possible links between arthritis and uveitis pathogenesis related to IL-1 signalling.MethodsThe eyes of IL-1Ra-deficient BALB/c mice were monitored histologically and by intravital videomicroscopy to determine if uveitis developed along with the expected spontaneous arthritis in ankles and knees. Expression levels of IL-1R and its negative regulators (IL-1Ra, IL-1RII, IL-1RAcP and single Ig IL-1R-related molecule) in eye and joint tissues were compared. Differences in uveitis induced by intraocular injection of lipopolysaccharide (LPS) in mice lacking IL-1R or IL-1Ra were assessed.ResultsDeficiency in IL-1Ra predisposes to spontaneous arthritis, which is exacerbated by previous systemic LPS exposure. The eye, however, does not develop inflammatory disease despite the progressive arthritis or LPS exposure. Organ-specific expression patterns for IL-1Ra and negative regulators of IL-1 activity were observed that appear to predict predisposition to inflammation in each location in IL-1Ra knockout mice. The eye is extremely sensitive to locally administered LPS, and IL-1Ra deficiency markedly exacerbates the resulting uveitis.ConclusionThis study demonstrates that IL-1Ra plays an important role in suppressing local responses in eyes injected with LPS and that there is discordance between murine eyes and joints in the extent to which IL-1Ra protects against spontaneous inflammation.

In vertebrates, the innate and adaptive immune systems have evolved seamlessly to protect the host by rapidly responding to danger signals, eliminating pathogens and creating immunological memory as well as immunological tolerance to self. The innate immune system harnesses receptors that recognize conserved pathogen patterns and alongside the more specific recognition systems and memory of adaptive immunity, their interplay is evidenced by respective roles during generation and regulation of immune responses. The hallmark of adaptive immunity which requires engagement of innate immunity is an ability to discriminate between self and non-self (and eventually between pathogen and symbiont) as well as peripheral control mechanisms maintaining immunological health and appropriate responses. Loss of control mechanisms and/or regulation of either the adaptive or the innate immune system lead to autoimmunity and autoinflammation respectively. Although autoimmune pathways have been largely studied to date in the context of development of non-infectious intraocular inflammation, the recruitment and activation of innate immunity is required for full expression of the varied phenotypes of non-infectious uveitis. Since autoimmunity and autoinflammation implicate different molecular pathways, even though some convergence occurs, increasing our understanding of their respective roles in the development of uveitis will highlight treatment targets and influence our understanding of immune mechanisms operative in other retinal diseases. Herein, we extrapolate from the basic mechanisms of activation and control of innate and adaptive immunity to how autoinflammatory and autoimmune pathways contribute to disease development in non-infectious uveitis patients.

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.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.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.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.

The inflammasome complex involving caspase-1 and nucleotide-binding domain, leucine-rich repeat containing protein (NLRP)3, also known as NALP3 or cryopyrin is important for host responses to microbial pathogens and several autoinflammatory diseases. We investigated the extent to which NLRP3 and caspase-1 control ocular interleukin (IL)-1β production and severity of uveitis (intraocular inflammatory disease) in an established, acute inflammatory uveitis model, endotoxin-induced uveitis (EIU).Expression of NLRP3, its adaptor molecule ASC, also known as PYCARD (PYD and CARD domain containing), and caspase-1 were examined by immunoblotting. IL-1β production was measured by enzyme-linked immunosorbent assay (ELISA). Using knockout mice, roles for caspase-1 and NLRP3 were examined in uveitis induced by intraocular injection of Escherichia coli lipopolysaccharide (LPS).NLRP3, ASC, and caspase-1 proteins are constitutively expressed in eye tissue. During EIU, IL-1β protein production increases; this requires the presence of both caspase-1 and NLRP3. However, severity of EIU is not altered by deficiency in either caspase-1 or NLRP3, as assessed by both intravital microscopy and histology.These data identify the importance of the NLRP3 inflammasome for IL-1β production in the eye, yet indicate that its participation in EIU is nonessential.

PURPOSE. A marked cellular infiltrate has been observed when endotoxin (lipopolysaccharide [LPS]) is injected into the mouse eye, but systemically injected LPS does not produce a comparable effect. Several hypotheses were tested to reconcile this discordance. METHODS. BALB/c mice were injected intravitreally (ivt) or intraperitoneally (ip) with Escherichia coli LPS. Uveitis was assessed by traditional and intravital microscopy. Cytokine levels in the eye, plasma, or spleen were measured by single or multiplex ELISA assays. RESULTS. The eye's higher sensitivity was confirmed to local LPS exposure, as 250 ng ivt LPS produced a brisk leukocytic infiltrate whereas ip injection of 100 μg LPS did not. The hypothesis was tested that the lack of a cellular infiltrate after ip LPS is explained by less induction of cytokines in the eye, but surprisingly, ip LPS resulted in comparable cytokine levels to ivt LPS. The hypothesis was disproved that the eye's sensitivity to local LPS is due to lack of expression of intracellular inhibitors of LPS such as A20, IRAK-M, or SARM. Finally, the hypothesis that systemic LPS inhibits diapedesis was tested by injection of LPS ip and ivt simultaneously, a strategy that did not significantly reduce leukocyte rolling or sticking in iris vessels but blocked the cellular infiltrate normally seen with ivt LPS. CONCLUSIONS. Systemic and local LPS exposures produce discordant effects within the murine eye. The hypothesis that systemic LPS desensitizes leukocytes to the stimuli responsible for transmigration offers a plausible explanation for this discordance.

The NOD-like receptor family (NLR) plays a critical role in innate immunity. The members of the NLR family share many functional and structural characteristics and are thought to cooperate with Toll-like receptors (TLRs) in host defense. While much of the focus has been on the role of TLRs and their involvement in autoinflammatory diseases such as arthritis, the NLR family is emerging as an important participant in inflammation—perhaps even more so than TLRs in light of the association of the many NLR family members and inflammatory diseases (1, 2). One NLR family member in particular, NOD2 (also known as NLRC2 or CARD15), plays an important role in the health and function of diathrodial joints as evidenced by the fact that a single amino acid change in NOD2 causes Blau syndrome (3), which is characterized by inflammatory arthritis, uveitis and dermatitis (4, 5). In addition, most patients previously diagnosed with early onset sarcoidosis have been shown to have a mutation in the nucleotide oligomerization domain (NOD) of NOD2 (6). As such, understanding the function of NOD2 in the joints could clarify the pathogenesis of Blau syndrome and quite possibly other more common forms of arthritis. NOD2 plays an important role in bacterial infections. It is understood that NOD2 functions as an intracellular sensor of muramyl dipeptide (MDP) (7-9), which is a breakdown product of peptidoglycan (PGN)—an ubiquitous component of bacterial cell walls. Once activated NOD2 plays a role in the induction of signal transduction pathways involving the kinase, RIP2, the transcription factor, NF-κB, and CARD9 and MAP kinases (10-13). Cross-talk between NOD2 and several different TLRs, including TLR2, has been observed, further linking TLR and NLR functioning and perhaps regulation. In some settings NOD2 amplifies the function of TLRs since suboptimal concentrations of specific TLR ligands and MDP delivered simultaneously can produce synergistic cytokine responses (14-17). Conversely, in models of colitis, activation of NOD2 by MDP has ability to suppress inflammation triggered by TLR activation (18). Interestingly, different polymorphisms in NOD2 increase the risk for developing Crohn's disease, a chronic inflammatory disorder of the intestinal tract (6). Mouse models of colitis support a negative regulatory role of NOD2 in intestinal inflammation and mice deficient in NOD2 have lost this negative regulatory function, making them prone to murine colitis when TLR2 is activated in the gut (18-20). Despite our understanding of the cellular function of NOD2, whether NOD2 exerts a similar regulatory capacity in the joint is far from understood. We have previously demonstrated that NOD2 deficiency did not alter a T-cell dependent model of chronic and sterile arthritis induced by immunization with the cartilage component proteoglycan (21). However, our finding that MDP activation of NOD2 exacerbated proteoglycan-induced disease prompted us to explore the role of NOD2 in an acute model of inflammatory arthritis triggered by innate immunity. Evidence demonstrating expression of NOD2 within joint tissue (22, 23) along with the presence of bacterial cell wall components such as PGN and MDP within the joints of patients with rheumatoid arthritis (RA) (23, 24) would support the notion that bacterial components could directly activate NOD2 within the joints themselves to trigger local inflammation. In order to gain insight into this question, we have studied arthritis induced following intra-articular injection of two TLR2 ligands, peptidoglycan (PGN) and synthetic lipopeptide, N, palmityol(S)-[2,3-bis(palmitoyloxy)-(2Rs)-propyl]Cys-Ser-Lys4 (Pam3CSK4), along with muramyl dipeptide (MDP), a breakdown product of PGN that is sensed by NOD2. Using mice deficient in TLR2 and NOD2, we have explored the functioning of these proteins in acute inflammatory arthritis.

PURPOSE NOD1 plays an important role in host defense and recognizes the minimal component of bacterial cell walls, meso-diaminopimelic acid (iE-DAP). Polymorphisms in NOD1 are associated with autoinflammatory diseases characterized by uveitis such as Crohn's disease and sarcoidosis. NOD1 is homologous to NOD2, which is responsible for an autosomal dominant form of uveitis. Nonetheless, the role of NOD1 in intraocular inflammation has not been explored. The induction of uveitis by iE-DAP in mice and the potential contribution of interleukin (IL)-1beta were investigated. METHODS BALB/c mice or mice deficient in caspase-1 or IL-1R1 and their congenic controls were injected intravitreally with iE-DAP or saline. The time course, dose response, and contribution of IL-1beta to ocular inflammation were quantified by intravital video microscopy, histology, and immunohistochemistry. NOD1 and IL-1beta were measured in eye tissue by immunoblotting and ELISA. RESULTS NOD1 protein is expressed in the eye and promotes ocular inflammation in a dose- and time-dependent fashion. The authors previously defined the role of IL-1beta in NOD2 uveitis and tested whether NOD1 and NOD2 used similar mechanisms. Treatment with iE-DAP significantly increased IL-1beta, which was caspase-1 dependent. However, in contrast to NOD2, caspase-1 and IL-1R1 were essential mediators of iE-DAP-induced uveitis, suggesting that NOD1 and NOD2 induce ocular inflammation by distinct mechanisms involving IL-1beta. CONCLUSIONS These findings demonstrate that NOD1 is expressed within the eye and that its activation results in uveitis in an IL-1beta-dependent mechanism. Characterizing the differences between NOD1 and NOD2 responses may provide insight into the pathogenesis of uveitis.

Nucleotide-binding and oligomerization domain 2 (NOD2) belongs to the emerging Nod-like receptor (NLR) family considered important in innate immunity. Mutations in NOD2 cause Blau syndrome, an inherited inflammation of eye, joints, and skin. Mutations in a homologous region of another NLR member, NALP3, cause autoinflammation, wherein IL-1β plays a critical role. Here, we tested the hypothesis that IL-1β is a downstream mediator of NOD2-dependent ocular inflammation. We used a mouse model of NOD2-dependent ocular inflammation induced by muramyl dipeptide (MDP), the minimal bacterial motif sensed by NOD2. We report that MDP-induced ocular inflammation generates IL-1β and IL-18 within the eye in a NOD2- and caspase-1-dependent manner. Surprisingly, two critical measures of ocular inflammation, leukocyte rolling and leukocyte intravascular adherence, appear to be completely independent of IL-1 signaling effects, as caspase-1 and IL-1R1-deficient mice still developed ocular inflammation in response to MDP. In contrast to the eye, a diminished neutrophil response was observed in an in vivo model of MDP-induced peritonitis in caspase-1-deficient mice, suggesting that IL-1β is not essential in NOD2-dependent ocular inflammation, but it is involved, in part, in systemic inflammation triggered by NOD2 activation. This disparity may be influenced by IL-1R antagonist (IL-1Ra), as we observed differential IL-1Ra levels in the eye versus plasma at baseline levels and in response to MDP treatment. This report reveals a new in vivo function of NOD2 within the eye yet importantly, distinguishes NOD2-dependent from NALP3-dependent inflammation, as ocular inflammation in mice occurred independently of IL-1β.

Lipopolysaccharide (LPS) preconditioning provides neuroprotection against subsequent cerebral ischemic injury. Tumor necrosis factor-alpha (TNFalpha) is protective in LPS-induced preconditioning yet exacerbates neuronal injury in ischemia. Here, we define dual roles of TNFalpha in LPS-induced ischemic tolerance in a murine model of stroke and in primary neuronal cultures in vitro, and show that the cytotoxic effects of TNFalpha are attenuated by LPS preconditioning. We show that LPS preconditioning significantly increases circulating levels of TNFalpha before middle cerebral artery occlusion in mice and show that TNFalpha is required to establish subsequent neuroprotection against ischemia, as mice lacking TNFalpha are not protected from ischemic injury by LPS preconditioning. After stroke, LPS preconditioned mice have a significant reduction in the levels of TNFalpha (approximately threefold) and the proximal TNFalpha signaling molecules, neuronal TNF-receptor 1 (TNFR1), and TNFR-associated death domain (TRADD). Soluble TNFR1 (s-TNFR1) levels were significantly increased after stroke in LPS-preconditioned mice (approximately 2.5-fold), which may neutralize the effect of TNFalpha and reduce TNFalpha-mediated injury in ischemia. Importantly, LPS-preconditioned mice show marked resistance to brain injury caused by intracerebral administration of exogenous TNFalpha after stroke. We establish an in vitro model of LPS preconditioning in primary cortical neuronal cultures and show that LPS preconditioning causes significant protection against injurious TNFalpha in the setting of ischemia. Our studies suggest that TNFalpha is a twin-edged sword in the setting of stroke: TNFalpha upregulation is needed to establish LPS-induced tolerance before ischemia, whereas suppression of TNFalpha signaling during ischemia confers neuroprotection after LPS preconditioning.

Osteopontin (OPN) is a secreted extracellular phosphoprotein involved in diverse biologic functions, including inflammation, cell migration, and antiapoptotic processes. Here we investigate the neuroprotective potential of OPN to reduce cell death using both in vitro and in vivo models of ischemia. We show that incubation of cortical neuron cultures with OPN protects against cell death from oxygen and glucose deprivation. The effect of OPN depends on the Arg–Gly–Asp (RGD)-containing motif as the protective effect of OPN in vitro was blocked by an RGD-containing hexapeptide, which prevents integrin receptors binding to their ligands. Osteopontin treatment of cortical neuron cultures caused an increase in Akt and p42/p44 MAPK phosphorylation, which is consistent with OPN-inducing neuroprotection via the activation of these protein kinases. Indeed, the protective effect of OPN was reduced by inhibiting the activation of Akt and p42/p44 MAPK using LY294002 and U0126, respectively. The protective effect of OPN was also blocked by the protein synthesis inhibitor cycloheximide, suggesting that the neuroprotective effect of OPN required new protein synthesis. Finally, intracerebral ventricular administration of OPN caused a marked reduction in infarct size after transient middle cerebral artery occlusion in a murine stroke model. These data suggest that OPN is a potent neuroprotectant against ischemic injury.

Background and Purpose—Tolerance to ischemic brain injury is induced by several preconditioning stimuli, including lipopolysaccharide (LPS). A small dose of LPS given systemically confers ischemic protection in the brain, a process that appears to involve activation of an inflammatory response before ischemia. We postulated that LPS preconditioning modulates the cellular inflammatory response after cerebral ischemia, resulting in neuroprotection.Methods—Mice were treated with LPS (0.2 mg/kg) 48 hours before ischemia induced by transient middle cerebral artery occlusion (MCAO). The infarct was measured by 2,3,5-triphenyltetrazolium chloride staining. Microglia/macrophage responses after MCAO were assessed by immunofluorescence and flow cytometry. The effect of MCAO on white blood cells in the brain and peripheral circulation was measured by flow cytometry 48 hours after MCAO.Results—LPS preconditioning induced significant neuroprotection against MCAO. Administration of low-dose LPS before MCAO prevented the cellular inflammatory response in the brain and blood. Specifically, LPS preconditioning suppressed neutrophil infiltration into the brain and microglia/macrophage activation in the ischemic hemisphere, which was paralleled by suppressed monocyte activation in the peripheral blood.Conclusions—LPS preconditioning induces neuroprotection against ischemic brain injury in a mouse model of stroke. LPS preconditioning suppresses the cellular inflammatory response to ischemia in the brain and circulation. Diminished activation of cellular inflammatory responses that ordinarily exacerbate ischemic injury may contribute to neuroprotection induced by LPS preconditioning.

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.

The innate immune receptor NOD2 is a genetic cause of uveitis (Blau syndrome). Intriguingly, in the intestine where polymorphisms of NOD2 predispose to Crohn's disease, NOD2 reportedly suppresses inflammation triggered by the bacterial cell wall component, peptidoglycan (PGN). Whether NOD2 exerts a similar capacity in the regulation of ocular inflammation to PGN has not been explored.NOD2, NOD1, or MyD88 knockout (KO) mice and their wild-type (WT) controls were administered an intravitreal injection of PGN (a metabolite of which is the NOD2 agonist, muramyl dipeptide), or synthetic TLR2/1 and TLR2/6 agonists, Pam₃CSK4 and FSL-1. Ocular inflammation was assessed by intravital microscopy and histopathology. Cytokine production in eye tissue homogenates was measured by ELISA.PGN triggered uveitis in mice. This inflammation was abolished in the absence of the TLR signaling mediator MyD88. NOD2 exerted a negative regulatory role because PGN-triggered eye inflammation was exacerbated in NOD2 KO mice. Increased intravascular response coincided with enhanced leukocytes within the aqueous and vitreous humors. The enhanced susceptibility of NOD2 KO mice to PGN uveitis coincided with increased cytokine production of IL-12p40, IL-17, and IL-23 but not IL-12p70, TNFα, or IFNγ. NOD1 deficiency did not result in the same sensitivity to PGN. Ocular inflammation induced by synthetic TLR2 agonists required MyD88 but not NOD2 or NOD1.NOD2 may serve differential roles in the eye to promote inflammation while also tempering cell responses to PGN akin to what has been reported in colitis.

Introduction The major histocompatibility complex (H-2d) and non-major histocompatibility complex genetic backgrounds make the BALB/c strain highly susceptible to inflammatory arthritis and spondylitis. Although different BALB/c colonies develop proteoglycan-induced arthritis and proteoglycan-induced spondylitis in response to immunization with human cartilage proteoglycan, they show significant differences in disease penetrance despite being maintained by the same vendor at either the same or a different location. Methods BALB/c female mice (24 to 26 weeks old after 4 weeks of acclimatization) were immunized with a suboptimal dose of cartilage proteoglycan to explore even minute differences among 11 subcolonies purchased from five different vendors. In vitro-measured T-cell responses, and serum cytokines and (auto)antibodies were correlated with arthritis (and spondylitis) phenotypic scores. cDNA microarrays were also performed using spleen cells of naïve and immunized BALB/cJ and BALB/cByJ mice (both colonies from The Jackson Laboratory, Bar Harbor, ME, USA), which represent the two major BALB/c sublines. Results The 11 BALB/c colonies could be separated into high (n = 3), average (n = 6), and low (n = 2) responder groups based upon their arthritis scores. While the clinical phenotypes showed significant differences, only a few immune parameters correlated with clinical or histopathological abnormalities, and seemingly none of them affected differences found in altered clinical phenotypes (onset time, severity or incidence of arthritis, or severity and progression of spondylitis). Affymetrix assay (Affymetrix, Santa Clara, CA, USA) explored 77 differentially expressed genes (at a significant level, P < 0.05) between The Jackson Laboratory's BALB/cJ (original) and BALB/cByJ (transferred from the National Institutes of Health, Bethesda, MD, USA). Fourteen of the 77 differentially expressed genes had unknown function; 24 of 77 genes showed over twofold differences, and only 8 genes were induced by immunization, some in both colonies. Conclusions Using different subcolonies of the BALB/c strain, we can detect significant differences in arthritis phenotypes, single-nucleotide polymorphisms (SNPs), and a large number of differentially expressed genes, even in non-immunized animals. A number of the known genes (and SNPs) are associated with immune responses and/or arthritis in this genetically arthritis-prone murine strain, and a number of genes of as-yet-unknown function may affect or modify clinical phenotypes of arthritis and/or spondylitis.

NOD2 plays an important role in the recognition of intracellular bacteria through its ability to sense the components of bacterial peptidoglycan (PGN), namely muramyl dipeptide (MDP) and muramyl tripeptide (MTP). Specific mutations in the human NOD2 gene cause Blau syndrome, an autosomal dominant form of uveitis, arthritis, and dermatitis. As a first step toward understanding the role of NOD2 in the pathogenesis of uveitis, the authors developed a mouse model of MDP-dependent uveitis.BALB/c mice and mice deficient in L-selectin or NOD2 received intravitreal injection of MDP, MTP, or PGN. The intravascular response within the iris and cellular infiltration was quantified by intravital microscopy and histologic assessment.MDP induced an acute, ocular inflammatory response, wherein rolling and adhering leukocytes within the vasculature were significantly increased within 6 hours after MDP treatment. A minor increase in cellular infiltration occurred at 12 hours after MDP treatment. The adhesion molecule L-selectin participated in MDP-induced vascular inflammation because L-selectin knockout mice showed a significant decrease in the number of rolling cells. Importantly, NOD2 plays an essential role in ocular inflammation induced by MDP, as indicated by the fact that uveitis did not develop in Nod2 knockout mice in response to MDP. Nod2 knockout mice also showed abolished ocular inflammation in response to MTP but not to PGN treatment.These findings demonstrate a novel mouse model of uveitis, wherein NOD2 plays an essential role in inflammation induced by the minimal components of PGN. Thus, innate immune responses mediated by NOD2 may participate in the development of uveitis in response to bacterial products.