KLK6 expression in skin induces PAR1-mediated psoriasiform dermatitis and inflammatory joint disease

Kallikrein-related peptidase 6 (KLK6) is a secreted serine protease hypothesized to promote inflammation via cleavage of protease-activated receptor 1 (PAR1) and PAR2. KLK6 levels are elevated in multiple inflammatory and autoimmune conditions, but no definitive role in pathogenesis has been established. Here, we show that skin-targeted overexpression of KLK6 causes generalized, severe psoriasiform dermatitis with spontaneous development of debilitating psoriatic arthritis-like joint disease. The psoriatic skin and joint phenotypes are reversed by normalization of skin KLK6 levels and attenuated following genetic elimination of PAR1 but not PAR2. Conservation of this regulatory pathway was confirmed in human psoriasis using vorapaxar, an FDA-approved PAR1 antagonist, on explanted lesional skin from patients with psoriasis. Beyond defining a critical role for KLK6/PAR1 signaling in promoting psoriasis, our results demonstrate that KLK6/PAR1-mediated inflammation in the skin alone is sufficient to drive inflammatory joint disease. Further, we identify PAR1 as a promising cytokine-independent target in therapy of psoriasis and psoriatic arthritis.

THU0079 THE MICROBIOME OF NEW-ONSET RHEUMATOID ARTHRITIS (NORA) PATIENTS DRIVES TLR4-DEPENDENT TH17 RESPONSES

Background:

Intestinal microbiota plays a prominent role in shaping the T cell immune response. Increasing evidence suggests that the gut microbiota is perturbed in patients with RA, and a variety of animal models demonstrated involvement of (mouse) microbiota in arthritis development. This underlines the necessity of understanding whether and how indigenous human NORA-associated microbiota may trigger RA.

Objectives:

To comprehensively investigate the intestinal mucosa cytokine production and DC, T and B cell responses to human gut microbiota associated with new-onset RA.

Methods:

We utilizedin vitrocultures of mucosal-like DCs (differentiated from bone marrow cells) and primary splenic DCs, as well asex vivocultures of healthy human intestinal biopsies, cultured in the presence of heat-killed fecal microbiota from either NORA or control donors. Furthermore, we performed studies in humanized mice carrying intestinal NORA microbiota, to study the effect on immune response during homeostasis and upon joint inflammation during collagen-induced arthritis (CIA).

Results:

In 24h DC cultures, NORA fecal microbiota more potently induced the expression of co-stimulatory molecules CD40 and CD80, and this enhanced DC maturation was partially mediated through TLR4 as demonstrated using the TLR4 antagonist TAK242. Interestingly, HC and NORA fecal microbiota differentially induced IL-12 and IL-6 production, with significantly enhanced IL-6 and reduced IL-12 secretion by the NORA microbiome. Furthermore, inex vivocultures of human ileum biopsies, the production of IL-1 and IL-33, as well as IL-23/Th17 cytokines IL-23, IL-22, and GM-CSF, were significantly increased by NORA-derived microbiome. Interestingly, in the small intestine lamina propria (SILP) of NORA-colonized mice, we observed enhanced Th17 polarization, increased innate GM-CSF expression and higher B cell CD40 and IgA levels during homeostasis. To study whether colonization with HC and NORA microbiota alters arthritis development, humanized mice and controls (mock, autologous, HC and NORA microbiota) were used in a CIA experiment. Macroscopic scoring of the arthritis severity at weekly intervals demonstrated that arthritis severity was significantly enhanced in NORA-colonized mice compared to HC-colonization and mock controls.

Conclusion:

Our data reveal that NORA microbiota, in addition to the previously described Th17 differentiation, induce higher levels of GM-CSF and B cell IgA in LP and have increased potential to aggravate arthritis through the activation of TLR4.

References:

[1]Scher et al., eLife 2013; Maeda Y et al., Arthritis & rheumatology 2016; Zhang X et al., Nature medicine 2015; Chen J et al., Genome Med 2016

Disclosure of Interests:

Marije Koenders: None declared, Heather Evans-Marin: None declared, Joyce Aarts: None declared, Parvathy Girija: None declared, Rebecca Rogier: None declared, Sergei Koralov: None declared, Julia Manasson: None declared, Peter van der Kraan: None declared, Shahla Abdollahi-Roodsaz: None declared, Jose Scher Consultant of: Novartis, Janssen, UCB, Sanofi.

Correction: Supplementation of diet with non-digestible oligosaccharides alters the intestinal microbiota, but not arthritis development, in IL-1 receptor antagonist deficient mice

[This corrects the article DOI: 10.1371/journal.pone.0219366.].

Microbiota-Dependent Involvement of Th17 Cells in Murine Models of Inflammatory Arthritis

Objective

Intestinal microbiota are associated with the development of inflammatory arthritis. The aim of this study was to dissect intestinal mucosal immune responses in the preclinical phase of arthritis and determine whether the presence of Th17 cells, beyond involvement of the cytokine interleukin‐17 (IL‐17), is required for arthritis development, and whether the involvement of Th17 cells in arthritis depends on the composition of the host microbiota.

Methods

Mucosal T cell production of IL‐17, interferon‐γ, tumor necrosis factor α (TNFα), IL‐22, and granulocyte–macrophage colony‐stimulating factor (GM‐CSF) was analyzed by flow cytometry and Luminex assay before arthritis onset in mice immunized to develop collagen‐induced arthritis (CIA). Pathogenic features of arthritis in mice with CIA and mice with antigen‐induced arthritis were compared between Th17 cell–deficient (CD4‐Cre⁺Rorc^flox/flox) and Th17 cell–sufficient (CD4‐Cre⁻Rorc^flox/flox) mice. In addition, the impact of intestinal microbiota on the Th17 cell dependence of CIA was assessed.

Results

Lamina propria CD4 T cells were activated before the onset of arthritis in mice with CIA, with marked up‐regulation of several cytokines, including IL‐17A, TNFα, and GM‐CSF. CD4‐Cre⁺Rorc^flox/flox mice showed a specific reduction in intestinal mucosal levels of Th17 cells and partially reduced levels of IL‐17–producing CD8 T cells. However, total levels of IL‐17A, mostly produced by γδ T cells and neutrophils, were unaffected. The severity of arthritis was significantly reduced in Th17 cell–deficient mice, suggesting that Th17 cells have additional, IL‐17A–independent roles in inflammatory arthritis. Accordingly, antigen‐stimulated T cells from Th17 cell–deficient mice produced less IL‐17A, IL‐17F, and GM‐CSF. Importantly, the dependence of CIA on the involvement of Th17 cells was mitigated in the presence of an alternative microbiome.

Conclusion

These data from murine models suggest that activation of mucosal immunity precedes the development of arthritis, and also that Th17 cells have a microbiota‐dependent role in arthritis. Therefore, a microbiome‐guided stratification of patients might improve the efficacy of Th17‐targeted therapies.

Supplementation of diet with non-digestible oligosaccharides alters the intestinal microbiota, but not arthritis development, in IL-1 receptor antagonist deficient mice

The intestinal microbiome is perturbed in patients with new-onset and chronic autoimmune inflammatory arthritis. Recent studies in mouse models suggest that development and progression of autoimmune arthritis is highly affected by the intestinal microbiome. This makes modulation of the intestinal microbiota an interesting novel approach to suppress inflammatory arthritis. Prebiotics, defined as non-digestible carbohydrates that selectively stimulate the growth and activity of beneficial microorganisms, provide a relatively non-invasive approach to modulate the intestinal microbiota. The aim of this study was to assess the therapeutic potential of dietary supplementation with a prebiotic mixture of 90% short-chain galacto-oligosaccharides and 10% long-chain fructo-oligosaccharides (scGOS/lcFOS) in experimental arthritis in mice. We here show that dietary supplementation with scGOS/lcFOS has a pronounced effect on the composition of the fecal microbiota. Interestingly, the genera Enterococcus and Clostridium were markedly decreased by scGOS/lcFOS dietary supplementation. In contrast, the family Lachnospiraceae and the genus Lactobacillus, both associated with healthy microbiota, increased in mice receiving scGOS/lcFOS diet. However, the scGOS/lcFOS induced alterations of the intestinal microbiota did not induce significant effects on the intestinal and systemic T helper cell subsets and were not sufficient to reproducibly suppress arthritis in mice. As expected, we did observe a significant increase in the bone mineral density in mice upon dietary supplementation with scGOS/lcFOS for 8 weeks. Altogether, this study suggests that dietary scGOS/lcFOS supplementation is able to promote presumably healthy gut microbiota and improve bone mineral density, but not inflammation, in arthritis-prone mice.

Alteration of the intestinal microbiome characterizes preclinical inflammatory arthritis in mice and its modulation attenuates established arthritis

Perturbations of the intestinal microbiome have been observed in patients with new-onset and chronic autoimmune inflammatory arthritis. However, it is currently unknown whether these alterations precede the development of arthritis or are rather a consequence of disease. Modulation of intestinal microbiota by oral antibiotics or germ-free condition can prevent arthritis in mice. Yet, the therapeutic potential of modulation of the microbiota after the onset of arthritis is not well characterized. We here show that the intestinal microbial community undergoes marked changes in the preclinical phase of collagen induced arthritis (CIA). The abundance of the phylum Bacteroidetes, specifically families S24-7 and Bacteroidaceae was reduced, whereas Firmicutes and Proteobacteria, such as Ruminococcaceae, Lachnospiraceae and Desulfovibrinocaceae, were expanded during the immune-priming phase of arthritis. In addition, we found that the abundance of lamina propria Th17, but not Th1, cells is highly correlated with the severity of arthritis. Elimination of the intestinal microbiota during established arthritis specifically reduced intestinal Th17 cells and attenuated arthritis. These effects were associated with reduced serum amyloid A expression in ileum and synovial tissue. Our observations suggest that intestinal microbiota perturbations precede arthritis, and that modulation of the intestinal microbiota after the onset of arthritis may offer therapeutic opportunities.

Aberrant intestinal microbiota due to IL-1 receptor antagonist deficiency promotes IL-17- and TLR4-dependent arthritis

BACKGROUND

Perturbation of commensal intestinal microbiota has been associated with several autoimmune diseases. Mice deficient in interleukin-1 receptor antagonist (Il1rn ^-/- mice) spontaneously develop autoimmune arthritis and are susceptible to other autoimmune diseases such as psoriasis, diabetes, and encephalomyelitis; however, the mechanisms of increased susceptibility to these autoimmune phenotypes are poorly understood. We investigated the role of interleukin-1 receptor antagonist (IL-1Ra) in regulation of commensal intestinal microbiota, and assessed the involvement of microbiota subsets and innate and adaptive mucosal immune responses that underlie the development of spontaneous arthritis in Il1rn ^-/- mice.

RESULTS

Using high-throughput 16S rRNA gene sequencing, we show that IL-1Ra critically maintains the diversity and regulates the composition of intestinal microbiota in mice. IL-1Ra deficiency reduced the intestinal microbial diversity and richness, and caused specific taxonomic alterations characterized by overrepresented Helicobacter and underrepresented Ruminococcus and Prevotella. Notably, the aberrant intestinal microbiota in IL1rn ^-/- mice specifically potentiated IL-17 production by intestinal lamina propria (LP) lymphocytes and skewed the LP T cell balance in favor of T helper 17 (Th17) cells, an effect transferable to WT mice by fecal microbiota. Importantly, LP Th17 cell expansion and the development of spontaneous autoimmune arthritis in IL1rn ^-/- mice were attenuated under germ-free condition. Selective antibiotic treatment revealed that tobramycin-induced alterations of commensal intestinal microbiota, i.e., reduced Helicobacter, Flexispira, Clostridium, and Dehalobacterium, suppressed arthritis in IL1rn ^-/- mice. The arthritis phenotype in IL1rn ^-/- mice was previously shown to depend on Toll-like receptor 4 (TLR4). Using the ablation of both IL-1Ra and TLR4, we here show that the aberrations in the IL1rn ^-/- microbiota are partly TLR4-dependent. We further identify a role for TLR4 activation in the intestinal lamina propria production of IL-17 and cytokines involved in Th17 differentiation preceding the onset of arthritis.

CONCLUSIONS

These findings identify a critical role for IL1Ra in maintaining the natural diversity and composition of intestinal microbiota, and suggest a role for TLR4 in mucosal Th17 cell induction associated with the development of autoimmune disease in mice.

The lung microbiota in early rheumatoid arthritis and autoimmunity

BACKGROUND

Airway abnormalities and lung tissue citrullination are found in both rheumatoid arthritis (RA) patients and individuals at-risk for disease development. This suggests the possibility that the lung could be a site of autoimmunity generation in RA, perhaps in response to microbiota changes. We therefore sought to test whether the RA lung microbiome contains distinct taxonomic features associated with local and/or systemic autoimmunity.

METHODS

16S rRNA gene high-throughput sequencing was utilized to compare the bacterial community composition of bronchoalveolar lavage fluid (BAL) in patients with early, disease-modifying anti-rheumatic drugs (DMARD)-naïve RA, patients with lung sarcoidosis, and healthy control subjects. Samples were further assessed for the presence and levels of anti-citrullinated peptide antibodies (including fine specificities) in both BAL and serum.

RESULTS

The BAL microbiota of RA patients was significantly less diverse and abundant when compared to healthy controls, but similar to sarcoidosis patients. This distal airway dysbiosis was attributed to the reduced presence of several genus (i.e., Actynomyces and Burkhordelia) as well as reported periodontopathic taxa, including Treponema, Prevotella, and Porphyromonas. While multiple clades correlated with local and systemic levels of autoantibodies, the genus Pseudonocardia and various related OTUs were the only taxa overrepresented in RA BAL and correlated with higher disease activity and erosions.

CONCLUSIONS

Distal airway dysbiosis is present in untreated early RA and similar to that detected in sarcoidosis lung inflammation. This community perturbation, which correlates with local and systemic autoimmune/inflammatory changes, may potentially drive initiation of RA in a proportion of cases.

S100A8/A9, a potent serum and molecular imaging biomarker for synovial inflammation and joint destruction in seronegative experimental arthritis

Background

Seronegative joint diseases are characterized by a lack of well-defined biomarkers since autoantibodies are not elevated. Calprotectin (S100A8/A9) is a damage-associated molecular pattern (DAMP) which is released by activated phagocytes, and high levels are found in seronegative arthritides. In this study, we investigated the biomarker potential of systemic and local levels of these S100 proteins to assess joint inflammation and joint destruction in an experimental model for seronegative arthritis.

Methods

Serum levels of S100A8/A9 and various cytokines were monitored during disease development in interleukin-1 receptor antagonist (IL-1Ra)^–/– mice using ELISA and multiplex bead-based immunoassay, and were correlated to macroscopic and microscopic parameters for joint inflammation, bone erosion, and cartilage damage. Local expression of S100A8 and S100A9 and matrix metalloproteinase (MMP)-mediated cartilage damage in the ankle joints were investigated by immunohistochemistry. In addition, local S100A8 and activated MMPs were monitored in vivo by optical imaging using anti-S100A8-Cy7 and AF489-Cy5.5, a specific tracer for activated MMPs.

Results

Serum levels of S100A8/A9 were significantly increased in IL-1Ra^–/– mice and correlated with macroscopic joint swelling and histological inflammation, while serum levels of pro-inflammatory cytokines did not correlate with joint swelling. In addition, early serum S100A8/A9 levels were prognostic for disease outcome at a later stage. The increased serum S100A8/A9 levels were reflected by an increased expression of S100A8 and S100A9 within the ankle joint, as visualized by molecular imaging. Next to inflammatory processes, serum S100A8/A9 also correlated with histological parameters for bone erosion and cartilage damage. In addition, arthritic IL-1Ra^–/– mice with increased synovial S100A8 and S100A9 expression showed increased cartilage damage that coincided with MMP-mediated neoepitope expression and in vivo imaging of activated MMPs.

Conclusions

Expression of S100A8 and S100A9 in IL-1Ra^–/– mice strongly correlates with synovial inflammation, bone erosion, and cartilage damage, underlining the potential of S100A8/A9 as a systemic and local biomarker in seronegative arthritis not only for assessing inflammation but also for assessing severity of inflammatory joint destruction.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1121-z) contains supplementary material, which is available to authorized users.

Intestinal Monocyte-Derived Macrophages Control Commensal-Specific Th17 Responses

Generation of different CD4 T cell responses to commensal and pathogenic bacteria is crucial for maintaining a healthy gut environment, but the associated cellular mechanisms are poorly understood. Dendritic cells (DCs) and macrophages (Mfs) integrate microbial signals and direct adaptive immunity. Although the role of DCs in initiating T cell responses is well appreciated, how Mfs contribute to the generation of CD4 T cell responses to intestinal microbes is unclear. Th17 cells are critical for mucosal immune protection and at steady state are induced by commensal bacteria, such as segmented filamentous bacteria (SFB). Here, we examined the roles of mucosal DCs and Mfs in Th17 induction by SFB in vivo. We show that Mfs, and not conventional CD103(+) DCs, are essential for the generation of SFB-specific Th17 responses. Thus, Mfs drive mucosal T cell responses to certain commensal bacteria.

Recognition of Coxiella burnetii by toll-like receptors and nucleotide-binding oligomerization domain-like receptors

BACKGROUND

Infection with Coxiella burnetii can lead to acute and chronic Q fever. Toll-like receptor 1 (TLR1), TLR2, TLR4, TLR6, nucleotide-binding oligomerization domain receptor 1 (NOD1), NOD2, and the mitogen-activated protein kinases are central in the innate immune response against microorganisms, but little is known about their role in the recognition of C. burnetii in humans.

METHODS

Human peripheral blood mononuclear cells (PBMCs) were stimulated with C. burnetii Nine Mile and the Dutch outbreak isolate C. burnetii 3262. TLRs were inhibited using specific antibodies or antagonists. Additionally, the influence of human polymorphisms in TLRs and Nod-like receptors (NLRs) on C. burnetii-induced cytokine production was assessed.

RESULTS

Inhibition of TLR2, p38, JNK, and ERK led to decreased cytokine responses in C. burnetii-stimulated human PBMCs. Humans with polymorphisms in TLR1 and NOD2 had reduced cytokine production, compared with humans with wild-type genotypes, after stimulation. Interestingly, polymorphisms in TLR6 led to decreased cytokine production after C. burnetii 3262 stimulation but not after C. burnetii Nine Mile stimulation.

CONCLUSIONS

The TLR1/TLR2 heterodimer and NOD2 are important recognition receptors for the induction of cytokine responses against C. burnetii in humans. Furthermore, an interesting finding was the divergent recognition of C. burnetii Nine Mile and C. burnetii 3262.

Interleukin-21 receptor deficiency increases the initial toll-like receptor 2 response but protects against joint pathology by reducing Th1 and Th17 cells during streptococcal cell wall arthritis

OBJECTIVE

The cytokine interleukin-21 (IL-21) can have both proinflammatory and immunosuppressive effects. The purpose of this study was to investigate the potential dual role of IL-21 in experimental arthritis in relation to Th17 cells.

METHODS

Antigen-induced arthritis (AIA) and chronic streptococcal cell wall (SCW) arthritis were induced in IL-21 receptor-deficient (IL-21R(-/-) ) and wild-type mice. Knee joints, synovial tissue, and serum were analyzed for arthritis pathology and inflammatory markers.

RESULTS

During AIA and chronic SCW arthritis, IL-21R deficiency protected against severe inflammation and joint destruction. This was accompanied by suppressed serum IgG1 levels and antigen-specific T cell responses. Levels of IL-17 were reduced during AIA, and synovial lymphocytes isolated during SCW arthritis for flow cytometry demonstrated that mainly IL-17+ interferon-γ (IFNγ)-positive T cells were reduced in IL-21R(-/-) mice. However, during the acute phases of SCW arthritis, significantly higher joint swelling scores were observed, consistent with enhanced tumor necrosis factor and IL-6 expression. Interestingly, IL-21R(-/-) mice were significantly less capable of up-regulating suppressor of cytokine signaling 1 (SOCS-1) and SOCS-3 messenger RNA. IL-21 stimulation also affected the Toll-like receptor 2 (TLR-2)/caspase recruitment domain 15 response to SCW fragments in vitro, indicating that impaired SOCS regulation in the absence of IL-21 signaling might contribute to the increased local activation during SCW arthritis.

CONCLUSION

In contrast to the proinflammatory role of IL-21 in adaptive immunity, which drives IL-17+IFN+ cells and joint pathology during chronic experimental arthritis, IL-21 also has an important immunosuppressive role, presumably by inhibiting TLR signaling via SOCS-1 and SOCS-3. If this dual role of IL-21 in various immune processes is present in human disease, it could make IL-21 a difficult therapeutic target in rheumatoid arthritis.

Periodontal pathogens directly promote autoimmune experimental arthritis by inducing a TLR2- and IL-1-driven Th17 response

Increasing epidemiologic evidence supports a link between periodontitis and rheumatoid arthritis. The actual involvement of periodontitis in the pathogenesis of rheumatoid arthritis and the underlying mechanisms remain, however, poorly understood. We investigated the influence of concomitant periodontitis on clinical and histopathologic characteristics of T cell-mediated experimental arthritis and evaluated modulation of type II collagen (CII)-reactive Th cell phenotype as a potential mechanism. Repeated oral inoculations of periodontal pathogens Porphyromonas gingivalis and Prevotella nigrescens induced periodontitis in mice, as evidenced by alveolar bone resorption. Interestingly, concurrent periodontitis induced by both bacteria significantly aggravated the severity of collagen-induced arthritis. Exacerbation of arthritis was characterized by increased arthritic bone erosion, whereas cartilage damage remained unaffected. Both P. gingivalis and P. nigrescens skewed the CII-specific T cell response in lymph nodes draining arthritic joints toward the Th17 phenotype without affecting Th1. Importantly, the levels of IL-17 induced by periodontal pathogens in CII-specific T cells directly correlated with the intensity of arthritic bone erosion, suggesting relevance in pathology. Furthermore, IL-17 production was significantly correlated with periodontal disease-induced IL-6 in lymph node cell cultures. The effects of the two bacteria diverged in that P. nigrescens, in contrast to P. gingivalis, suppressed the joint-protective type 2 cytokines, including IL-4. Further in vitro studies showed that the Th17 induction strongly depended on TLR2 expression on APCs and was highly promoted by IL-1. Our data provide evidence of the involvement of periodontitis in the pathogenesis of T cell-driven arthritis through induction of Ag-specific Th17 response.

Toll-like receptor 2 controls acute immune complex-driven arthritis in mice by regulating the inhibitory Fcγ receptor IIB

OBJECTIVE

Previous studies have demonstrated a protective role of Toll-like receptor 2 (TLR-2) and a proinflammatory function of TLR-4 during chronic T cell-driven arthritis. The involvement of TLRs in T cell-independent arthritic processes, however, remains unclear. This study was undertaken to determine the functional significance of TLR-2 and TLR-4 in T cell-independent immune complex-driven arthritis.

METHODS

Serum-transfer arthritis was induced in wild-type and TLR-deficient mice by intraperitoneal injections of arthritogenic K/BxN mouse serum. Arthritis was assessed macroscopically and by histologic analysis. The influence of TLR-2 on macrophage cytokine profile, Fcγ receptor (FcγR) expression, and response to immune complexes was determined.

RESULTS

While TLR-4, unexpectedly, did not play any significant role, TLR-2 deficiency accelerated the onset and markedly increased the severity of acute immune complex-driven arthritis in mice. TLR-2 deficiency resulted in a substantial increase in joint inflammation, bone erosion, and cartilage pathology, indicating a protective function of TLR-2 in passive FcγR-driven disease. Ex vivo study of the macrophage inflammatory phenotype revealed increased production of tumor necrosis factor α (TNFα) and interleukin-6 (IL-6) despite similar levels of IL-10, along with a significant increase in FcγR-specific response, in TLR-2-/- mouse macrophages early in the disease. Although distinct FcγR messenger RNA expression was not affected, cell surface protein expression of the inhibitory FcγRIIB in TLR-2-/- naive primary macrophages was specifically diminished, resulting in a higher proinflammatory response. Accordingly, TLR-2 stimulation specifically up-regulated FcγRIIB, but not the activating FcγR, on macrophages.

CONCLUSION

TLR-2 regulates acute immune complex-driven arthritis by controlling macrophage FcγR response. Our findings indicate that the protective role of TLR-2 is extended beyond its previously described role in promoting Treg cells during T cell-mediated arthritis.

Therapeutic efficacy of Tyro3, Axl, and Mer tyrosine kinase agonists in collagen-induced arthritis

OBJECTIVE

Hyperactivation of innate immunity by Toll-like receptors (TLRs) can contribute to the development of autoinflammatory or autoimmune diseases. This study evaluated the activation of Tyro3, Axl, Mer (TAM) receptors, physiologic negative regulators of TLRs, by their agonists, growth arrest-specific protein 6 (GAS-6) and protein S, in the prevention of collagen-induced arthritis (CIA).

METHODS

Adenoviruses overexpressing GAS-6 and protein S were injected intravenously or intraarticularly into mice during CIA. Splenic T helper cell subsets from intravenously injected mice were studied by flow cytometry, and the knee joints of mice injected intravenously and intraarticularly were assessed histologically. Synovium from mice injected intraarticularly was evaluated for cytokine and suppressor of cytokine signaling (SOCS) expression.

RESULTS

Protein S significantly reduced ankle joint swelling when overexpressed systemically. Further analysis of knee joints revealed a moderate reduction in pathologic changes in the joint and a significant reduction in the number of splenic Th1 cells when protein S was overexpressed systemically. Local overexpression of GAS-6 decreased joint inflammation and joint pathology. Protein S treatment showed a similar trend of protection. Consistently, GAS-6 and protein S reduced cytokine production in the synovium. Moreover, levels of messenger RNA for interleukin-12 (IL-12) and IL-23 were reduced by GAS-6 and protein S treatment, with a corresponding decrease in the production of interferon-γ and IL-17. TAM ligand overexpression was associated with an increase in SOCS-3 levels, which likely contributed to the amelioration of arthritis.

CONCLUSION

This study provides the first evidence that TAM receptor stimulation by GAS-6 and protein S can be used to ameliorate arthritis when applied systemically or locally. TAM receptor stimulation limits proinflammatory signaling and adaptive immunity. This pathway provides a novel strategy by which to combat rheumatoid arthritis.

Toll-like receptor 4 in bone marrow-derived cells as well as tissue-resident cells participate in aggravating autoimmune destructive arthritis

OBJECTIVE

A prominent role of Toll-like receptor 4 (TLR4) in arthritis is emerging. TLR4 is functional in immune cells and stromal cells. The aim was to investigate the involvement of TLR4 in bone marrow (BM)-derived and resident cells in arthritis.

METHODS

Reciprocal sex-mismatched BM transplantation was performed between IL-1Ra(-/-)TLR4(+/+) and IL-1Ra(-/-)TLR4(-/-) double knockout animals in Balb/c background. Arthritis was assessed macroscopically and by histopathology. Immunity was evaluated by splenic cytokine production and flow cytometry in draining lymph node (DLN) cells.

RESULTS

Arthritis progression was reduced to a similar extent in animals lacking TLR4 on BM-derived, resident cells or both. Histology revealed that joint inflammation was partially TLR4-dependent in either BM-derived or resident cells. TLR4 plays an additive role in BM-derived and resident cells in promoting cartilage erosion. By contrast, TLR4 was equally important in BM-derived and resident cells in mediating bone erosion. Systemically, TLR4 in both BM-derived and resident cells contributed to IL-17 production by splenic T-cells, whereas in the DLNs of arthritic joints this was not the case. Interestingly, in DLN, the dominant cells producing IL-17 were CD4 negative, and cell numbers were determined by TLR4 in the BM-derived cells.

CONCLUSIONS

TLR4 is necessary in both BM-derived and resident cells for full-blown joint swelling, inflammation and bone erosion. Furthermore, TLR4 on BM-derived and tissue-resident cells show an additive effect in cartilage destruction. Interestingly, TLR4 on BM-derived and tissue-resident cells are both required for IL-17 production in spleen, but only in BM-derived cells in DLN.

Alarmins S100A8 and S100A9 elicit a catabolic effect in human osteoarthritic chondrocytes that is dependent on Toll-like receptor 4

OBJECTIVE

S100A8 and S100A9 are two Ca(2+) binding proteins classified as damage-associated molecular patterns or alarmins that are found in high amounts in the synovial fluid of osteoarthritis (OA) patients. The purpose of this study was to investigate whether S100A8 and/or S100A9 can interact with chondrocytes from OA patients to increase catabolic mediators.

METHODS

Using immunohistochemistry, we stained for S100A8 and S100A9 protein, matrix metalloproteinases (MMPs), and a cartilage-breakdown epitope specific for MMPs (VDIPEN) in cartilage from OA donors. Isolated chondrocytes or explants from OA and non-OA donors were stimulated with S100A8 and/or S100A9. Messenger RNA and protein levels of MMPs, cytokines, and cartilage matrix molecules were determined with quantitative reverse transcription-polymerase chain reaction and Luminex techniques, respectively. For receptor blocking studies, specific inhibitors for Toll-like receptor 4 (TLR-4), receptor for advanced glycation end products (RAGE), and carboxylated glycans were used.

RESULTS

In cartilage from OA patients, the expression of S100A8 and S100A9 protein close to chondrocytes was associated with proteoglycan depletion and expression of MMP-1, MMP-3, and VDIPEN. Stimulation of chondrocytes with S100A8 and S100A9 caused a strong up-regulation of catabolic markers (MMPs 1, 3, 9, and 13, interleukin-6 [IL-6], IL-8, and monocyte chemotactic protein 1) and down-regulation of anabolic markers (aggrecan and type II collagen), thereby favoring cartilage breakdown. Blocking TLR-4, but not carboxylated glycans or RAGE, inhibited the S100 effect. The catabolic S100 effect was significantly more pronounced in chondrocytes from OA patients as compared to those from non-OA patients, possibly due to higher TLR-4 expression.

CONCLUSION

S100A8 and S100A9 have a catabolic effect on human chondrocytes that is TLR-4 dependent. OA chondrocytes are more sensitive than normal chondrocytes to S100 stimulation.

T cell lessons from the rheumatoid arthritis synovium SCID mouse model: CD3-rich synovium lacks response to CTLA-4Ig but is successfully treated by interleukin-17 neutralization

OBJECTIVE

To provide an intermediate step between classic arthritis models and clinical trials, the rheumatoid arthritis (RA) synovium SCID mouse model is a valuable tool for use during preclinical research. We undertook this study to investigate the validity of this humanized mouse model using anti-tumor necrosis factor (anti-TNF) and anti-interleukin-1 (anti-IL-1) treatment and to investigate the direct effect of T cells- and B cell-related therapies on the transplanted RA synovial tissue.

METHODS

CB17/SCID mice were engrafted with human RA synovial tissue and systemically treated with anti-TNF, anti-IL-1, anti-IL-17, CTLA-4Ig, anti-CD20, or isotype control antibodies.

RESULTS

Validation of the model with anti-TNF treatment significantly reduced serum cytokine levels and decreased histologic inflammation, whereas anti-IL-1 therapy did not show any effect on the RA synovial grafts. In mice engrafted with B cell-rich synovial tissue, anti-CD20 treatment showed clear therapeutic effects. Surprisingly, CTLA-4Ig treatment did not show any effects in this transplantation model, despite prescreening of the synovial tissue for the presence of CD3+ T cells and the costimulatory molecules CD80 and CD86. In contrast, great therapeutic potential was observed for anti-IL-17 treatment, but only when CD3+ T cells were abundantly present in the RA synovial tissue.

CONCLUSION

This human RA synovium SCID mouse model enabled us to show that CTLA-4Ig lacks direct effects on T cell activation processes in the synovial tissue. Further evidence was obtained that IL-17 might indeed be an interesting therapeutic target in RA patients with CD3-rich synovial tissue. Further characterization of the RA patients' individual synovial profiles is of great importance for achieving tailored therapy.

Destructive role of myeloid differentiation factor 88 and protective role of TRIF in interleukin-17-dependent arthritis in mice

OBJECTIVE

Increasing evidence indicates the involvement of Toll-like receptors (TLRs) in the progression of arthritis; however, the contribution of the two signaling pathways used by TLRs, which are mediated by myeloid differentiation factor 88 (MyD88) and TRIF, remains unclear. The objective of this study was to investigate the specific roles of MyD88 and TRIF in chronic experimental arthritis and the accompanying adaptive immune responses.

METHODS

Chronic arthritis was induced in wild-type, MyD88(-/-) , and Trif(lps2) (TRIF(-/-) ) mice by repetitive intraarticular injections of streptococcal cell wall (SCW) fragments. SCW-specific T cell and B cell responses, joint swelling, and histopathologic changes were analyzed during chronic arthritis.

RESULTS

Both MyD88 and TRIF pathways contributed to antigen-specific T cell proliferation and antibody production, with the MyD88 pathway playing the dominant role. The severity of joint swelling and synovial inflammation, as well as the histopathologic damage to cartilage and bone, was strongly dependent on MyD88 signaling, whereas TRIF was redundant. MyD88 signaling was critical for the development of pathogenic T cell response (i.e., interleukin-17 [IL-17] production) in response to SCW antigen. Interestingly, when the T cell-dependent phase was prolonged, TRIF signaling appeared to down-regulate bone erosion, an effect accompanied by an inhibitory effect on IL-17 production.

CONCLUSION

This study reveals a central role of MyD88 and a counterregulatory function of TRIF in T cell-driven arthritis. The findings provide a rationale for a pathway-specific interference in order to block the pathogenic features and to preserve or stimulate the beneficial aspects of TLR signaling.

S100A8 enhances osteoclastic bone resorption in vitro through activation of Toll-like receptor 4: implications for bone destruction in murine antigen-induced arthritis

OBJECTIVE

Rheumatoid arthritis, which is associated with elevated levels of S100A8 and S100A9, is characterized by severe bone erosions caused by enhanced osteoclast formation and activity. The aim of the present study was to investigate the role of S100A8 and S100A9 in osteoclastic bone destruction in murine antigen-induced arthritis (AIA).

METHODS

Bone destruction was analyzed in the arthritic knee joints of S100A9-deficient mice in which S100A8 protein expression was also lacking, and in wild-type (WT) controls. Osteoclast precursors from S100A9-deficient and WT mice were differentiated into osteoclasts in vitro. Additionally, precursors were stimulated with S100A8, S100A9, or S100A8/A9 during osteoclastogenesis. Receptor involvement was investigated using an anti-receptor for advanced glycation end products (anti-RAGE)-blocking antibody, soluble RAGE, or Toll-like receptor 4 (TLR-4)-deficient osteoclast precursors. The formation of osteoclasts and actin rings, the regulation of osteoclast markers, and bone resorption were analyzed.

RESULTS

Bone erosions and cathepsin K staining were significantly suppressed in S100A9-deficient mice after AIA induction. However, osteoclast precursors from S100A9-deficient mice developed normally into functional osteoclasts, which excludes a role for intrinsic S100A8/A9. In contrast to the results observed with S100A9 and S100A8/A9, the addition of S100A8 during osteoclastogenesis resulted in stimulation of osteoclast formation in conjunction with enhanced actin ring formation and increased bone resorption. Analysis of the putative receptor for S100A8 in osteoclastogenesis revealed that osteoclast differentiation and function could not be inhibited by blocking RAGE, whereas the increase in osteoclast numbers and enhanced bone resorption were completely abrogated using TLR-4-deficient osteoclast precursors.

CONCLUSION

These results demonstrate that S100A8 stimulated osteoclast formation and activity and suggest that both S100A8 and TLR-4 are important factors in mediating osteoclastic bone destruction in experimental arthritis.

Trapped in a vicious loop: Toll-like receptors sustain the spontaneous cytokine production by rheumatoid synovium

Synovial tissue of patients with rheumatoid arthritis (RA) spontaneously produces several cytokines, of which a fundamental role in joint inflammation and destruction has been established. However, the factors sustaining this phenomenon remain poorly understood. In a recent report, blockade of Toll-like receptor 2 (TLR2) was found to inhibit the spontaneous release of inflammatory cytokines by intact RA synovial explant cultures. Adding to the recent evidence implicating other TLRs (in particular, TLR4), this observation highlights the potential of TLRs as therapeutic targets to suppress the local production of multiple cytokines and to control the chronic inflammatory loop in RA.

Toll-like receptor 4 signalling is specifically TGF-beta-activated kinase 1 independent in synovial fibroblasts

OBJECTIVE

Activated synovial fibroblasts are key players in the pathogenesis of RA by driving inflammation and joint destruction. Numerous molecules including cytokines and Toll-like receptor (TLR) ligands induce pro-inflammatory signalling and gene expression through a hierarchical network of kinases. Upstream mitogen-activated protein kinase kinase kinases (MAP3Ks) represent an attractive target for RA treatment. In this study, we sought to determine the role of the MAP3K TGF-β-activated kinase 1 (TAK1) in cytokine and TLR-mediated signalling.

METHODS

TAK1 activity was inhibited using either a small molecule inhibitor or lentivirally overexpressed kinase-inactive TAK1-K63W mutant in murine embryonic and human dermal and synovial fibroblasts. Fibroblasts were stimulated with IL-1, TNF, TLR2 or TLR4 agonists and responses were evaluated using transcriptional reporters, western blotting and analysis of gene expression of collagenases (MMP3 and MMP13), cytokines (IL-1β and IL-6) and chemokines (IL-8 and MCP-1).

RESULTS

TAK1 inhibition abrogated cytokine- and TLR-induced nuclear factor-κB (NF-κB) and Saa3-promoter reporter activation in murine and human dermal fibroblasts. In synovial fibroblasts, TAK1 regulated IL-1 and TNF-mediated NF-κB, but not Saa3-promoter reporter activation. Inducible mRNA expression of cytokines, collagenases and chemokines, except MCP-1, was TAK1 dependent for IL-1, TNF and TLR2 signalling. Unexpectedly, TLR4-mediated NF-κB reporter activation and inducible mRNA expression was fully TAK1 independent. Accordingly, NF-κB p65 and p38 MAPK phosphorylation was unaffected by TAK1 inhibition.

CONCLUSION

In general, TAK1 crucially regulates IL-1 and TNF signalling in fibroblasts. Interestingly, TLR4 signalling is specifically TAK1 independent in synovial fibroblasts. Consequently, therapeutic TAK1 inhibition in arthropathies may not dampen the damage-associated molecular pattern-mediated TLR4 activation of synovial fibroblasts.

Neisseria meningitidis lipid A mutant LPSs function as LPS antagonists in humans by inhibiting TLR 4-dependent cytokine production

Lipopolysaccharide is a major constituent of the outer membrane of Gram-negative bacteria and important in the induction of pro-inflammatory responses. Recently, novel LPS species derived from Neisseria meningitidis H44/76 by insertional inactivation of the lpxL1 and lpxL2 genes have been created with a lipid A portion consisting of five (penta-acylated lpxL1) or four (tetra-acylated lpxL2) fatty acids connected to the glucosamine backbone instead of six fatty acids in the wild-type LPS. We show that these mutant LPS-types are poor inducers of cytokines (tumor-necrosis factor-α, IL-1β, IL-10, IL-RA) in human mononuclear cells. Both penta- and tetra-acylated meningococcal LPSs were able to inhibit cytokine production by wild-type Escherichia coli or meningococcal LPS. Binding of FITC-labelled E. coli LPS TLR4 transfected Chinese hamster ovary (CHO) cells was inhibited by both mutant LPS-types. Experiments with CHO fibroblasts transfected with human CD14 and TLR4 showed that the antagonizing effect was dependent on the expression of human TLR4. In contrast to the situation in humans, lpxL1 LPS has agonistic activity for cytokine production in peritoneal macrophages of DBA mice, and exacerbated arthritis in murine collagen induced arthritis model. N. meningitidis lipid A mutant LPSs lpxL1 and lpxL2 function as LPS antagonists in humans by inhibiting TLR4-dependent cytokine production but have agonistic activity in mice.

R-spondin 1 protects against inflammatory bone damage during murine arthritis by modulating the Wnt pathway

OBJECTIVE

During the course of different musculoskeletal diseases, joints are progressively damaged by inflammatory, infectious, or mechanical stressors, leading to joint destruction and disability. While effective strategies to inhibit joint inflammation, such as targeted cytokine-blocking therapy, have been developed during the last decade, the molecular mechanisms of joint damage are still poorly understood. This study was undertaken to investigate the role of the Wnt pathway modulator R-Spondin 1 (RSpo1) in protecting bone and cartilage in a mouse model of arthritis.

METHODS

Tumor necrosis factor alpha (TNFalpha)-transgenic mice were treated with vehicle or Rspo1. Mice were evaluated for signs of arthritis, and histologic analysis of the hind paws was performed. Moreover, we determined the effect of Rspo1 on Wnt signaling activity and osteoprotegerin (OPG) expression in murine primary osteoblasts.

RESULTS

The secreted Wnt pathway modulator RSpo1 was highly effective in preserving the structural integrity of joints in a TNFalpha-transgenic mouse model of arthritis by protecting bone and cartilage from inflammation-related damage. RSpo1 antagonized the Wnt inhibitor Dkk-1 and modulated Wnt signaling in mouse mesenchymal cells. In osteoblasts, RSpo1 induced differentiation and expression of OPG, thereby inhibiting osteoclastogenesis in vitro. In vivo, RSpo1 promoted osteoblast differentiation and bone formation while blocking osteoclast development, thereby contributing to the integrity of joints during inflammatory arthritis.

CONCLUSION

Our results demonstrate the therapeutic potential of RSpo1 as an anabolic agent for the preservation of joint architecture.

A crucial role for tumor necrosis factor receptor 1 in synovial lining cells and the reticuloendothelial system in mediating experimental arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease that mainly affects synovial joints. Biologics directed against tumor-necrosis-factor (TNF)-alpha are efficacious in the treatment of RA. However, the role of TNF receptor-1 (TNFR1) in mediating the TNFalpha effects in RA has not been elucidated and conflicting data exist in experimental arthritis models. The objective is to investigate the role of TNFR1 in the synovial lining cells (SLC) and the reticuloendothelial system (RES) during experimental arthritis.

METHODS

Third generation of adenovirus serotype 5 were either injected locally in the knee joint cavity or systemically by intravenous injection into the retro-orbital venous sinus to specifically target SLC and RES, respectively. Transduction of organs was detected by immunohistochemistry of the eGFP transgene. An adenoviral vector containing a short hairpin (sh) RNA directed against TNFR1 (HpTNFR1) was constructed and functionally evaluated in vitro using a nuclear factor-kappaB (NF-kappaB) reporter assay and in vivo in streptococcal cell wall-induced arthritis (SCW) and collagen-induced arthritis (CIA). Adenoviruses were administered before onset of CIA, and the effect of TNFR1 targeting on the clinical development of arthritis, histology, quantitative polymerase chain reaction (qPCR), cytokine analyses and T-cell assays was evaluated.

RESULTS

Systemic delivery of Ad5.CMV-eGFP predominantly transduced the RES in liver and spleen. Local delivery transduced the synovium and not the RES in liver, spleen and draining lymph nodes. In vitro, HpTNFR1 reduced the TNFR1 mRNA expression by three-fold resulting in a 70% reduction of TNFalpha-induced NF-kappaB activation. Local treatment with HpTNFR1 markedly reduced mRNA and protein levels of interleukin (IL)-1beta and IL-6 in SLC during SCW arthritis and ameliorated CIA. Systemic targeting of TNFR1 in RES of liver and spleen by systemic delivery of Ad5 virus encoding for a small hairpin RNA against TNFR1 markedly ameliorated CIA and simultaneously reduced the mRNA expression of IL-1beta, IL-6 and Saa1 (75%), in the liver and that of Th1/2/17-specific transcription factors T-bet, GATA-3 and RORgammaT in the spleen. Flow cytometry confirmed that HpTNFR1 reduced the numbers of interferon (IFN)gamma (Th1)-, IL-4 (Th2)- and IL-17 (Th17)-producing cells in spleen.

CONCLUSIONS

TNFR1-mediated signaling in both synovial lining cells and the reticuloendothelial system independently played a major pro-inflammatory and immunoregulatory role in the development of experimental arthritis.

TLR2 promotes Th2/Th17 responses via TLR4 and TLR7/8 by abrogating the type I IFN amplification loop

TLR2 plays an important role in the removal of Gram-positive bacteria; contrastingly, it also appears to have important protective effects against unrestrained inflammation and subsequent organ injury during infection and autoimmunity. We hypothesized that TLR2 tunes the phenotype of dendritic cells (DCs) activated through other TLRs, thereby fulfilling a crucial role in the modulation of the immune response. TLR2 potently inhibited TLR4- and TLR7/8-induced cytokine production by human DCs. The inhibitory effect of TLR2 on the release of TNF-alpha but not of IL-12p70 was mediated by PI3K. TLR2 inhibits the production of IL-12p70 by dampening the type 1 IFN amplification loop. When DCs were triggered with the potent synergistic combination of LPS (TLR4) and R848 (TLR7/8) in conjunction with a TLR2 ligand, a clear shift to more Th2- and Th17-prone responses in the naive and memory T cell subpopulations was observed. This shift in T cell responses was inherent to the inability of TLR2-stimulated DCs to produce IL-12p70 and was dependent on the production of IL-1 and IL-6.

Local interleukin-1-driven joint pathology is dependent on toll-like receptor 4 activation

Toll-like receptors (TLRs) may contribute to the pathogenesis of chronic inflammatory destructive diseases through the recognition of endogenous ligands produced on either inflammation or degeneration of the extracellular matrix. The presence of endogenous TLR agonists has been reported in rheumatoid joints. In the present study, we investigated the significance of TLR2 and TLR4 activation by locally- produced endogenous ligands in the severity of joint inflammation and destruction. Local joint pathology independent of systemic immune activation was induced by overexpression of interleukin (IL)-1 and TNF in naive joints using adenoviral gene transfer. Here, we report that at certain doses, IL-1-induced local joint inflammation, cartilage proteoglycan depletion, and bone erosion are dependent on TLR4 activation, whereas TLR2 activation is not significantly involved. In comparison, tumor necrosis factor alpha-driven joint pathology seemed to be less dependent on TLR2 and TLR4. The severity of IL-1-induced bone erosion and irreversible cartilage destruction was markedly reduced in TLR4(-/-) mice, even though the degree of inflammation was similar, suggesting uncoupled processes. Furthermore, the expression of cathepsin K, a marker for osteoclast activity, induced by IL-1beta was dependent on TLR4. Overexpression of IL-1beta in the joint as well as ex vivo IL-1 stimulation of patellae provoked the release of endogenous TLR4 agonists capable of inducing TLR4-mediated cytokine production. These data emphasize the potential relevance of TLR4 activation in rheumatoid arthritis, particularly with respect to IL-1-mediated joint pathology.

Stimulation of chondrocyte-mediated cartilage destruction by S100A8 in experimental murine arthritis

OBJECTIVE

To investigate whether S100A8 is actively involved in matrix metalloproteinase (MMP)-mediated chondrocyte activation.

METHODS

S100A8 and S100A9 proteins were detected in inflamed knee joints from mice with various forms of murine arthritis, using immunolocalization. Murine chondrocyte cell line H4 was stimulated with proinflammatory cytokines or recombinant S100A8. Messenger RNA (mRNA) and protein levels were measured using reverse transcriptase-polymerase chain reaction and intracellular fluorescence-activated cell sorting (FACS). Breakdown of aggrecan on the pericellular surface of the chondrocytes was measured using VDIPEN and NITEGE antibodies and FACS, and breakdown in patellar cartilage was measured by immunolocalization.

RESULTS

S100A8 and S100A9 proteins were abundantly expressed in and around chondrocytes in inflamed knee joints after induction of antigen-induced arthritis or onset of spontaneous arthritis in interleukin-1 (IL-1) receptor antagonist-knockout mice. Stimulation of chondrocytes by the proinflammatory cytokines tumor necrosis factor alpha, IL-1beta, IL-17, and interferon-gamma caused strong up-regulation of S100A8 mRNA and protein levels and up-regulation to a lesser extent of S100A9 levels. Stimulation of chondrocytes with S100A8 induced significant up-regulation of MMP-2, MMP-3, MMP-9, MMP-13, ADAMTS-4, and ADAMTS-5 mRNA levels (up-regulated 4, 4, 3, 16, 8, and 4 times, respectively). VDIPEN and NITEGE neoepitopes were significantly elevated in a concentration-dependent manner in chondrocytes treated with 0.2, 1, or 5 microg/ml of S100A8. (VDIPEN levels were elevated 17%, 67%, and 108%, respectively, and NITEGE levels were elevated 8%, 33%, and 67%, respectively.) S100A8 significantly increased the effect of IL-1beta on MMP-3, MMP-13, and ADAMTS-5. Mouse patellae incubated with both IL-1beta and S100A8 had elevated levels of NITEGE within the cartilage matrix when compared with patellae incubated with IL-1beta or S100A8 alone.

CONCLUSION

These findings indicate that S100A8 and S100A9 are found in and around chondrocytes in experimental arthritis. S100A8 up-regulates and activates MMPs and aggrecanase-mediated pericellular matrix degradation.

Interleukin-1 drives pathogenic Th17 cells during spontaneous arthritis in interleukin-1 receptor antagonist-deficient mice

OBJECTIVE

Interleukin-1 receptor antagonist-deficient (IL-1Ra-/-) mice spontaneously develop an inflammatory and destructive arthritis due to unopposed excess IL-1 signaling. In this study, the role of Th17 cells and the effect of neutralization of IL-17, IL-1, and tumor necrosis factor alpha (TNFalpha) were investigated in this IL-1-driven murine arthritis model.

METHODS

T cells isolated from IL-1Ra-/- and wild-type (WT) mice were stained for IL-17 and interferon-gamma, with results assessed by fluorescence-activated cell sorting analysis. To investigate the contribution of IL-1 and IL-17 in further progression of arthritis in this model, mice were treated with neutralizing antibodies after the onset of arthritis.

RESULTS

Compared with WT mice, IL-1Ra-/- mice had similar levels of Th1 cells but clearly enhanced levels of Th17 cells; this increase in the number of Th17 cells was evident even before the onset of arthritis, in young, nonarthritic IL-1Ra-/- mice. The percentage of Th17 cells increased even more after the onset of arthritis and, similar to the serum levels and local messenger RNA levels of IL-17, the percentage of IL-17+ Th17 cells clearly correlated with the severity of arthritis. Anti-IL-17 treatment prevented any further increase in inflammation and bone erosion, whereas blocking of TNFalpha after the onset of arthritis had no effect. In contrast, neutralization of IL-1 resulted in a complete suppression of arthritis. Interestingly, this anti-IL-1 treatment also significantly reduced the percentage of IL-17+ Th17 cells in the draining lymph nodes of these arthritic mice.

CONCLUSION

Increased levels of Th17 cells can be detected in IL-1Ra-/- mice even preceding the onset of arthritis. In addition, the results of cytokine-blocking studies demonstrated that IL-17 contributes to the inflammation and bone erosion in this model, which suggests that IL-1 is the driving force behind the IL-17-producing Th17 cells.