IL-4 gene therapy for collagen arthritis suppresses synovial IL-17 and osteoprotegerin ligand and prevents bone erosion

Attenuation of collagen induced arthritis via suppression on Th17 response by activating cholinergic anti-inflammatory pathway with nicotine

The cholinergic anti-inflammatory pathway can inhibit the inflammation of collagen induced arthritis (CIA), a mouse model of rheumatoid arthritis (RA). However, the immunologic mechanisms that provide a therapeutic effect against the auto-inflammatory disease are not yet elucidated. The present study explores the effect of cholinergic anti-inflammatory pathway on CD4+ T cell responses in CIA. Forty DBA/1 mice were divided into 4 groups: a control group, a CIA group, a vagotomy group, and a nicotine group. The degree of arthritis was measured by arthritis score and hematoxylin and eosin. ELISA was used to detect the serum concentration of IFN-γ, IL-4 and IL-17A. Flow cytometry was used to detect the cytokines and transcription factors (TFs) (the TFs of Th1, Th2, and Th17 cells are T-bet, RORγτ and GATA3 respectively) in the spleen. Immunohistochemistry was used to analyze RORγτ expression in the joint synovium. Arthritis in the nicotine group was significantly lightened compared with that in the CIA group and in the vagotomy group. Nicotine attenuated Th17 lineage by reducing IL-17A production and RORγτ expression. The expressions of IL-4 and GATA3 were increased in the same setting. However, the expressions of IFN-γ and T-bet had no difference between the nicotine and the CIA group. Nicotine may induce a shift to the Th2 lineage and improve the Th1/Th2 imbalance. Activating the cholinergic anti-inflammatory pathway with nicotine can inhibit Th17 cell responses and may improve the Th1/Th2 imbalance in CIA, providing a new justification for its application in the treatment of 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.

Th17 Cells in Immunopathogenesis and treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by the sequestration of various leukocyte subpopulations within both the developing pannus and synovial space. The chronic nature of this disease results in inflammation of multiple joints, with subsequent destruction of the joint cartilage and erosion of bone. Identification of T helper (Th)17 cells led to breaking the dichotomy of the Th1/Th2 axis in immunopathogenesis of autoimmune diseases such as RA, and its experimental model, collagen-induced arthritis (CIA). Th17 cells produce cytokines, including interleukin (IL)-17, IL-6, IL-21, IL-22 and tumor necrosis factor (TNF)-α, with pro-inflammatory effects, which appear to have a role in immunopathogenesis of RA. Regarding the wide ranging production of pro-inflammatory cytokines and chemokines by Th17 cells, it is expected that Th17 cell could be a potent pathogenic factor in disease immunopathophysiology. Thus the identification of effector mechanisms used by Th17 cells in induction of disease lesions may open new prospects for designing a new therapeutic strategy for treatment of RA.

Serum levels of IL-17, IL-4, and INFγ in Serbian patients with early rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic, systemic, inflammatory disease with autoimmune etiology, characterized by synovial inflammation and destruction of joint cartilage and bone. There are controversial data about the profile of interleukin-17 (IL-17A), interleukin-4 (IL-4), and interferon-gamma (INFγ), indicating in some studies the key role of IL-17, while in others the Th1 cytokines.

MATERIALS AND METHODS

Serum samples of 31 early RA patients were evaluated for erythrocytes sedimentation rate (ESR), rheumatoid factor (RF), C-reactive protein (CRP), anti-cyclic citrullinated peptide antibodies (anti-CCP), and for the tested cytokines (IL-17A, IL-4, and INFγ). Disease activity score (DAS28) calculation was done for all patients. Control serum samples were obtained from 29 healthy volunteers.

RESULTS

The levels of tested cytokines were significantly higher (IL-17A, p < 0.001; INFγ, p < 0.001; IL-4, p < 0.01) in patients with early RA, compared to the healthy controls. In early RA patients, a strong correlation of serum IL-17A was found with DAS28, ESR, and CRP. Also, significant negative correlation was found between serum INFγ levels and the DAS28 score, indicating that INFγ may play a key role in maintaining immune homeostasis in patients with RA.

CONCLUSION

The mean serum IL-17A levels in patients with early RA, corresponded with the disease activity and severity. This might highlight the usefulness of the serum IL-17A level in defining the activity and predictive patterns, for aggressive disease therapy, and it might express specific therapeutically targets.

Prediction of IL4 inducing peptides

The secretion of Interleukin-4 (IL4) is the characteristic of T-helper 2 responses. IL4 is a cytokine produced by CD4+ T cells in response to helminthes and other extracellular parasites. It has a critical role in guiding antibody class switching, hematopoiesis and inflammation, and the development of appropriate effector T-cell responses. In this study, it is the first time an attempt has been made to understand whether it is possible to predict IL4 inducing peptides. The data set used in this study comprises 904 experimentally validated IL4 inducing and 742 noninducing MHC class II binders. Our analysis revealed that certain types of residues are preferred at certain positions in IL4 inducing peptides. It was also observed that IL4 inducing and noninducing epitopes differ in compositional and motif pattern. Based on our analysis we developed classification models where the hybrid method of amino acid pairs and motif information performed the best with maximum accuracy of 75.76% and MCC of 0.51. These results indicate that it is possible to predict IL4 inducing peptides with reasonable precession. These models would be useful in designing the peptides that may induce desired Th2 response.

The enigmatic cytokine oncostatin m and roles in disease

Oncostatin M is a secreted cytokine involved in homeostasis and in diseases involving chronic inflammation. It is a member of the gp130 family of cytokines that have pleiotropic functions in differentiation, cell proliferation, and hematopoetic, immunologic, and inflammatory networks. However, Oncostatin M also has activities novel to mediators of this cytokine family and others and may have fundamental roles in mechanisms of inflammation in pathology. Studies have explored Oncostatin M functions in cancer, bone metabolism, liver regeneration, and conditions with chronic inflammation including rheumatoid arthritis, lung and skin inflammatory disease, atherosclerosis, and cardiovascular disease. This paper will review Oncostatin M biology in a historical fashion and focus on its unique activities, in vitro and in vivo, that differentiate it from other cytokines and inspire further study or consideration in therapeutic approaches.

Re-evaluating the role of vitamin D in the periodontium

The importance of vitamin D in maintaining skeletal health via the regulation of calcium has long been recognized as a critical function of this secosteroid. An abundance of literature shows an association between oral bone mineral density and some measure of systemic osteoporosis and suggests that osteoporosis/low bone mass may be a risk factor for periodontal disease. Recently, nonskeletal functions of vitamin D have gained notoriety for several reasons. Many cells that are not associated with calcium homeostasis have been demonstrated to possess membrane receptors for vitamin D. These include activated T and B lymphocytes, and skin, placenta, pancreas, prostate and colon cancer cells. In addition, vitamin D "insufficiency" is a worldwide epidemic and epidemiologic evidence has linked this condition to multiple chronic health problems, including cardiovascular and autoimmune diseases, hypertension and a variety of cancers. Interestingly, there is mounting evidence connecting diminished serum levels of vitamin D with increased gingival inflammation and supporting the concept of "continual vitamin D sufficiency" in maintaining periodontal health. The ability of vitamin D to regulate both the innate and the adaptive components of the host response may play an important role in this process. This review will examine the skeletal and nonskeletal functions of vitamin D, and explore its potential role in protecting the periodontium as well as in regulating periodontal wound healing.

Osteoclast precursors in murine bone marrow express CD27 and are impeded in osteoclast development by CD70 on activated immune cells

Osteoclasts (OCs) are bone-resorbing cells that are formed from hematopoietic precursors. OCs ordinarily maintain bone homeostasis, but they can also cause major pathology in autoimmune and inflammatory diseases. Under homeostatic conditions, receptor activator of nuclear factor kappa-B (RANK) ligand on osteoblasts drives OC differentiation by interaction with its receptor RANK on OC precursors. During chronic immune activation, RANK ligand on activated immune cells likewise drives pathogenic OC differentiation. We here report that the related TNF family member CD70 and its receptor CD27 can also mediate cross-talk between immune cells and OC precursors. We identified CD27 on a rare population (0.3%) of B220(-)c-Kit(+)CD115(+)CD11b(low) cells in the mouse bone marrow (BM) that are highly enriched for osteoclastogenic potential. We dissected this population into CD27(high) common precursors of OC, dendritic cells (DCs) and macrophages and CD27(low/neg) downstream precursors that could differentiate into OC and macrophages, but not DC. In a recombinant mouse model of chronic immune activation, sustained CD27/CD70 interactions caused an accumulation of OC precursors and a reduction in OC activity. These events were due to a CD27/CD70-dependent inhibition of OC differentiation from the OC precursors by BM-infiltrating, CD70(+)-activated immune cells. DC numbers in BM and spleen were increased, suggesting a skewing of the OC precursors toward DC differentiation. The impediment in OC differentiation culminated in a high trabecular bone mass pathology. Mice additionally presented anemia, leukopenia, and splenomegaly. Thus, under conditions of constitutive CD70 expression reflecting chronic immune activation, the CD27/CD70 system inhibits OC differentiation and favors DC differentiation.

Chinese Herbal Formula Huo-Luo-Xiao-Ling Dan Protects against Bone Damage in Adjuvant Arthritis by Modulating the Mediators of Bone Remodeling

Huo-luo-xiao-ling dan (HLXL) is an herbal mixture that has long been used in traditional Chinese medicine for the treatment of rheumatoid arthritis (RA) and other inflammatory disorders. Despite the availability of potent conventionally used drugs for RA, their limited efficacy in a proportion of patients coupled with their high cost and severe adverse effects has necessitated the search for novel therapeutics for this debilitating disease. Further, the control of both inflammation and bone damage is essential for effective management of arthritis. The aim of our study was to evaluate the efficacy of HLXL against arthritic bone damage in adjuvant arthritis (AA) model of RA. Our results show that HLXL treatment suppressed inflammatory arthritis and reduced bone and cartilage damage in the joints of arthritic Lewis rats. HLXL-induced protection against bone damage was mediated primarily via inhibition of mediators of osteoclastic bone remodeling (e.g., receptor activator of nuclear factor kappa-B ligand; RANKL), skewing of RANKL/osteoprotegerin (OPG) ratio in favor of antiosteoclastic activity, reduction in the number of osteoclasts in the arthrodial joint's bone, and inhibition of cytokine production and MMP activity. Our results suggest that HLXL might offer a promising alternative/adjunct treatment for both inflammation and bone damage in RA.

Mediators of inflammation-induced bone damage in arthritis and their control by herbal products

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation of the synovial joints leading to bone and cartilage damage. Untreated inflammatory arthritis can result in severe deformities and disability. The use of anti-inflammatory agents and biologics has been the mainstay of treatment of RA. However, the prolonged use of such agents may lead to severe adverse reactions. In addition, many of these drugs are quite expensive. These limitations have necessitated the search for newer therapeutic agents for RA. Natural plant products offer a promising resource for potential antiarthritic agents. We describe here the cellular and soluble mediators of inflammation-induced bone damage (osteoimmunology) in arthritis. We also elaborate upon various herbal products that possess antiarthritic activity, particularly mentioning the specific target molecules. As the use of natural product supplements by RA patients is increasing, this paper presents timely and useful information about the mechanism of action of promising herbal products that can inhibit the progression of inflammation and bone damage in the course of arthritis.

Local effect of IL-4 delivery on polyethylene particle induced osteolysis in the murine calvarium

Wear particles generated with use of total joint replacements incite a chronic macrophage-mediated inflammatory reaction, which leads to implant failure. Macrophage activation may be polarized into two states, with an M1 proinflammatory state dominating an alternatively activated M2 anti-inflammatory state. We hypothesized that IL-4, an activator of M2 macrophages, could modulate polyethylene (PE) particle-induced osteolysis in an experimental murine model. Four animal groups included (a) calvarial saline injection with harvest at 14 days (b) single calvarial injection of PE particles subcutaneously (SC) without IL-4 (c) PE particles placed as in (b), then IL-4 given SC for 14 consecutive days and (d) PE particles as in (b) then IL-4 beginning 7 days after particle injection for 7 days. The calvarial bone volume to total tissue volume was measured using microCT and histomorphometry. Calvaria were cultured for 24 h to assess release of RANKL, OPG, TNF-α, and IL-1ra and isolation and identification of M1 and M2 specific proteins. MicroCT and histomorphometric analysis showed that bone loss was significantly decreased following IL-4 administration to PE treated calvaria for both 7 and 14 days. Western blot analysis showed an increased M1/M2 ratio in the PE treated calvaria, which decreased with addition of IL-4. Cytokine analysis showed that the RANKL/OPG ratio and TNF-α/IL-1ra ratio decreased in PE-treated calvaria following IL-4 addition for 14 days. IL-4 delivery mitigated PE particle-induced osteolysis through macrophage polarization. Modulation of macrophage polarization is a potential treatment strategy for wear particle induced periprosthetic osteolysis.

Brucella abortus-infected macrophages modulate T lymphocytes to promote osteoclastogenesis via IL-17

The pathogenic mechanisms of bone loss caused by Brucella species have not been completely deciphered. Although T lymphocytes (LTs) are considered important to control infection, the mechanism of Brucella-induced T-cell responses to immunopathological features is not known. We present in vitro and in vivo evidence showing that Brucella abortus-induced inflammatory response leads to the activation of LTs, which further promote osteoclastogenesis. Pre-activated murine LTs treated with culture supernatant from macrophages infected with B. abortus induced bone marrow-derived monocytes (BMMs) to undergo osteoclastogenesis. Furthermore, osteoclastogenesis was mediated by CD4(+) T cells. Although B. abortus-activated T cells actively secreted the pro-osteoclastogenic cytokines RANKL and IL-17, osteoclastogenesis depended on IL-17, because osteoclast generation induced by Brucella-activated T cells was completely abrogated when these cells were cultured with BMMs from IL-17 receptor knockout mice. Neutralization experiments indicated that IL-6, generated by Brucella infection, induced the production of pro-osteoclastogenic IL-17 from LTs. By using BMMs from tumor necrosis factor receptor p55 knockout mice, we also demonstrated that IL-17 indirectly induced osteoclastogenesis through the induction of tumor necrosis factor-α from osteoclast precursors. Finally, extensive and widespread osteoclastogenesis was observed in the knee joints of mice injected with Brucella-activated T cells. Our results indicate that activated T cells, elicited by B. abortus-infected macrophages and influenced by the inflammatory milieu, promote the generation of osteoclasts, leading to bone loss.

Elevated serum level of type-2 cytokine and low IL-17 in first episode psychosis and schizophrenia in relapse

Schizophrenia is chronic and debilitating mental disorder. In broad spectrum of possible causes or contributing factors, immune system and cytokines were investigated in the onset and development of schizophrenia. The aim of our study was to analyze the serum concentrations of type-1 cytokines: TNF-α, IFN-γ, type-2 cytokines: IL-4, IL-10, type-17 cytokine: IL-17 and regulatory cytokines: TGF-β, IL-27, IL-6, in drug-naive patients with First Episode Psychosis - FEP (n = 88) and Schizophrenia in relapse - SC in relapse patients (n = 45), comparing to healthy controls (n = 36). Also, we attempted to determine potential correlation between cytokine levels and/or cytokine ratios with clinical parameters, such as severity of illness, positive, negative and general psychopathology. Our results showed decreased levels of IL-17 (p = 0.018), demonstrating that type-17 response is blunted in psychotic episode. Increased levels of IL-4 (p = 0.033) showed that type-2 response is overweight in psychotic episode. Also, levels of IL-4 in serum of SC in relapse patients were higher than controls (p < 0.0005) and patient with FEP (p = 0.003). This alteration was accompanied with increase in production of TGF-β in psychotic patients (p = 0.009) and also in FEP (p < 0.0005) and SC in relapse (p < 0.0005). Analysis showed that TGF-β can be a valuable marker for psychosis. The presence of enhanced anti-inflammatory/immunosuppressive activity in schizophrenia may be an attempt to counteract or limit ongoing pro-inflammatory processes and downregulating chronic inflammation. Finally we have documented decreased levels of IL-17 and IL-17/TGF-β ratio in these types of psychotic patients, suggesting the new aspects of schizophrenia pathophysiology.

Correlation analyses of clinical and molecular findings identify candidate biological pathways in systemic juvenile idiopathic arthritis

BACKGROUND

Clinicians have long appreciated the distinct phenotype of systemic juvenile idiopathic arthritis (SJIA) compared to polyarticular juvenile idiopathic arthritis (POLY). We hypothesized that gene expression profiles of peripheral blood mononuclear cells (PBMC) from children with each disease would reveal distinct biological pathways when analyzed for significant associations with elevations in two markers of JIA activity, erythrocyte sedimentation rate (ESR) and number of affected joints (joint count, JC).

METHODS

PBMC RNA from SJIA and POLY patients was profiled by kinetic PCR to analyze expression of 181 genes, selected for relevance to immune response pathways. Pearson correlation and Student's t-test analyses were performed to identify transcripts significantly associated with clinical parameters (ESR and JC) in SJIA or POLY samples. These transcripts were used to find related biological pathways.

RESULTS

Combining Pearson and t-test analyses, we found 91 ESR-related and 92 JC-related genes in SJIA. For POLY, 20 ESR-related and 0 JC-related genes were found. Using Ingenuity Systems Pathways Analysis, we identified SJIA ESR-related and JC-related pathways. The two sets of pathways are strongly correlated. In contrast, there is a weaker correlation between SJIA and POLY ESR-related pathways. Notably, distinct biological processes were found to correlate with JC in samples from the earlier systemic plus arthritic phase (SAF) of SJIA compared to samples from the later arthritis-predominant phase (AF). Within the SJIA SAF group, IL-10 expression was related to JC, whereas lack of IL-4 appeared to characterize the chronic arthritis (AF) subgroup.

CONCLUSIONS

The strong correlation between pathways implicated in elevations of both ESR and JC in SJIA argues that the systemic and arthritic components of the disease are related mechanistically. Inflammatory pathways in SJIA are distinct from those in POLY course JIA, consistent with differences in clinically appreciated target organs. The limited number of ESR-related SJIA genes that also are associated with elevations of ESR in POLY implies that the SJIA associations are specific for SJIA, at least to some degree. The distinct pathways associated with arthritis in early and late SJIA raise the possibility that different immunobiology underlies arthritis over the course of SJIA.

IL-4 inhibits TNF-α-mediated osteoclast formation by inhibition of RANKL expression in TNF-α-activated stromal cells and direct inhibition of TNF-α-activated osteoclast precursors via a T-cell-independent mechanism in vivo

It has been reported that osteoclastogenesis is induced by tumor necrosis factor (TNF)-α. Interleukin (IL)-4 is the most important cytokine involved in humoral immunity. However, no studies have investigated the effect of IL-4 on TNF-α-mediated osteoclast formation in vivo. In this study, we investigated the effect of IL-4 on TNF-α-mediated osteoclast formation in vivo. TNF-α was administered with and without IL-4 into the supracalvariae of mice. The number of osteoclasts and the levels of mRNA for cathepsin K and tartrate-resistant acid phosphate, both osteoclast markers, in mice administered TNF-α and IL-4 were lower than those in mice administered TNF-α alone. The level of tartrate-resistant acid phosphatase form 5b (TRACP5b) as a marker of bone resorption in mice administered both TNF-α and IL-4 was also lower. We showed that IL-4 inhibited TNF-α-mediated osteoclast formation in osteoclast precursors in vitro. Expression of receptor activator of NF-κB ligand (RANKL) in TNF-α-activated stromal cells was also inhibited. Furthermore, we investigated whether IL-4 had effects on both stromal cells and osteoclast precursors in TNF-α-mediated osteoclast formation in vivo. Using mice whose stromal cells and osteoclast precursors were chimeric for the presence of TNF receptors, IL-4 inhibited TNF-α-mediated osteoclast formation in the presence of TNF-α-responsive stromal cells, and TNF-α-responsive osteoclast precursors in vivo. IL-4 also inhibited TNF-α-induced RANKL expression in the presence of TNF-α-responsive stromal cells in vivo. This event is dependent on p38 inhibition in vitro. Additionally, IL-4 inhibited TNF-α-mediated osteoclast formation in T cell-depleted mice. In summary, we conclude that IL-4 inhibited TNF-α-mediated osteoclast formation by inhibiting expression of RANKL in TNF-α-activated stromal cells, and directly inhibited TNF-α-activated osteoclast precursors in vivo via a T cell-independent mechanism.

Effect of locally administered Syk siRNA on allergen-induced arthritis and asthma

New approaches for the treatment of inflammatory disorders such as rheumatic arthritis (RA) and inflammatory lung disease (asthma) are needed because a significant population of patients do not experience sustained relief with currently available therapies. The tyrosine kinase Syk plays a crucial role in inflammatory signaling pathways and has gained much attention as a potential target for treatment of inflammatory disorders. We have shown that our Syk siRNA injected directly into limb joints of arthritic mice, diminishes joint swelling and reduces levels of Syk kinase and inflammatory cytokines in joint tissue. Further, our Syk siRNA, administered via nasal instillation, inhibits recruitment of inflammatory cells to the bronchoalveolar fluid of allergen-sensitized mice. We propose that targeting Syk via localized application of Syk siRNA provides an opportunity for specific knockdown of Syk kinase with minimal potential for systemic effects.

Celastrus and its bioactive celastrol protect against bone damage in autoimmune arthritis by modulating osteoimmune cross-talk

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by bone erosion and cartilage destruction in the joints. Many of the conventional antiarthritic drugs are effective in suppressing inflammation, but they do not offer protection against bone damage. Furthermore, the prolonged use of these drugs is associated with severe adverse reactions. Thus, new therapeutic agents that can control both inflammation and bone damage but with minimal side effects are sought. Celastrus is a Chinese herb that has been used for centuries in folk medicine for the treatment of various inflammatory diseases. However, its utility for protection against inflammation-induced bone damage in arthritis and the mechanisms involved therein have not been examined. We tested celastrus and its bioactive component celastrol for this attribute in the adjuvant-induced arthritis model of RA. The treatment of arthritic rats with celastrus/celastrol suppressed inflammatory arthritis and reduced bone and cartilage damage in the joints as demonstrated by histology and bone histomorphometry. The protective effects against bone damage are mediated primarily via the inhibition of defined mediators of osteoclastic bone remodeling (e.g. receptor activator of nuclear factor-κB ligand (RANKL)), the deviation of RANKL/osteoprotegerin ratio in favor of antiosteoclastic activity, and the reduction in osteoclast numbers. Furthermore, both the upstream inducers (proinflammatory cytokines) and the downstream effectors (MMP-9) of the osteoclastogenic mediators were altered. Thus, celastrus and celastrol controlled inflammation-induced bone damage by modulating the osteoimmune cross-talk. These natural products deserve further consideration and evaluation as adjuncts to conventional therapy for RA.

Impaired IL-17 signaling pathway contributes to the increased collagen expression in scleroderma fibroblasts

Among IL-17 families, IL-17A and IL-17F share amino acid sequence similarity and bind to IL-17R type A. IL-17 signaling is implicated in the pathogenesis of various autoimmune diseases, but its role in the regulatory mechanism of extracellular matrix expression and its contribution to the phenotype of systemic sclerosis (SSc) both remain to be elucidated. This study revealed that IL-17A expression was significantly increased in the involved skin and sera of SSc patients, whereas the IL-17F levels did not increase. In contrast, the expression of IL-17R type A in SSc fibroblasts significantly decreased in comparison with that in normal fibroblasts, due to the intrinsic TGF-β1 activation in these cell types. Moreover, IL-17A, not IL-17F, reduced the protein expression of α1(I) collagen and connective tissue growth factor. miR-129-5p, one of the downregulated microRNAs in SSc fibroblasts, increased due to IL-17A and mediated the α1(I) collagen reduction. These results suggest that IL-17A signaling, not IL-17F, has an antifibrogenic effect via the upregulation of miR-129-5p and the downregulation of connective tissue growth factor and α1(I) collagen. IL-17A signaling is suppressed due to the downregulation of the receptor by the intrinsic activation of TGF-β1 in SSc fibroblasts, which may amplify the increased collagen accumulation and fibrosis characteristic of SSc. Increased IL-17A levels in the sera and involved skin of SSc may be due to negative feedback. Clarifying the novel regulatory mechanisms of fibrosis by the cytokine network consisting of TGF-β and IL-17A may lead to a new therapeutic approach for this disease.

Interleukin-4 inhibits RANKL-induced NFATc1 expression via STAT6: a novel mechanism mediating its blockade of osteoclastogenesis

Interleukin-4 (IL-4) is an important immune regulatory protein that possesses potent anti-osteoclastogenic properties, and does so via the transcription factor STAT6. Previous studies have shown that IL-4 selectively blocks RANKL-induced activation of NF-κB and mitogen-activated protein kinase (MAPK) pathway molecules, suggesting that the cytokine arrests osteoclastogenesis by blockade of these signaling cascades. However, the fact that the inhibitory effect on these pathways requires prolonged IL-4 pretreatment, and that the cytokine fails to exert an anti-osteoclastogenic effect after short-term pre-exposure of RANKL to osteoclast precursors, suggests that an additional, more immediate mechanism may also be involved. In this study, we found that simultaneous exposure of IL-4 did not alter RANKL-dependent activation of NF-κB or MAPKs, whereas the cytokine did block RANKL-induced nuclear factor activated T cells c1 (NFATc1), a master osteoclastogenic transcription factor. This inhibitory effect of IL-4 required STAT6, consistent with its functional role in osteoclastogenesis. In addition, the cytokine also partially impaired RANKL-stimulated bone resorption. Furthermore, IL-4 suppressed expression of RANKL-induced osteoclast specific genes in a STAT6-dependent manner, but failed to do so when osteoclast precursors were pre-exposed to RANKL. Thus, we provide the first evidence that IL-4 inhibits osteoclast formation by inhibiting RANKL induction of NFATc1 via STAT6 as an early event, in addition to its suppression of other signaling pathways. The inhibitory effect is ultimately regulated at the gene expression transcriptional level.

IUPAC glossary of terms used in immunotoxicology (IUPAC Recommendations 2012)

The primary objective of this “Glossary of Terms Used in Immunotoxicology” is to give clear definitions for those who contribute to studies relevant to immunotoxicology but are not themselves immunologists. This applies especially to chemists who need to understand the literature of immunology without recourse to a multiplicity of other glossaries or dictionaries. The glossary includes terms related to basic and clinical immunology insofar as they are necessary for a self-contained document, and particularly terms related to diagnosing, measuring, and understanding effects of substances on the immune system. The glossary consists of about 1200 terms as primary alphabetical entries, and Annexes of common abbreviations, examples of chemicals with known effects on the immune system, autoantibodies in autoimmune disease, and therapeutic agents used in autoimmune disease and cancer. The authors hope that among the groups who will find this glossary helpful, in addition to chemists, are toxicologists, pharmacologists, medical practitioners, risk assessors, and regulatory authorities. In particular, it should facilitate the worldwide use of chemistry in relation to occupational and environmental risk assessment.

Macrophage-elicited osteoclastogenesis in response to Brucella abortus infection requires TLR2/MyD88-dependent TNF-α production

Osteoarticular complications are common in human brucellosis, but the pathogenic mechanisms involved are largely unknown. In this manuscript, we described an immune mechanism for inflammatory bone loss in response to infection by Brucella abortus. We established a requirement for MyD88 and TLR2 in TNF-α-elicited osteoclastogenesis in response to B. abortus infection. CS from macrophages infected with B. abortus induced BMM to undergo osteoclastogenesis. Although B. abortus-infected macrophages actively secreted IL-1β, IL-6, and TNF-α, osteoclastogenesis depended on TNF-α, as CS from B. abortus-infected macrophages failed to induce osteoclastogenesis in BMM from TNFRp55⁻/⁻ mice. CS from B. abortus-stimulated MyD88⁻/⁻ and TLR2⁻/⁻ macrophages failed to express TNF-α, and these CS induced no osteoclast formation compared with that of the WT or TLR4⁻/⁻ macrophages. Omp19, a B. abortus lipoprotein model, recapitulated the cytokine production and subsequent osteoclastogenesis induced by the whole bacterium. All phenomena were corroborated using human monocytes, indicating that this mechanism could play a role in human osteoarticular brucellosis. Our results indicate that B. abortus, through its lipoproteins, may be involved in bone resorption through the pathological induction of osteoclastogenesis.

Interleukin-4 (IL-4) and IL-13 suppress excessive neutrophil infiltration and hepatocyte damage during acute murine schistosomiasis japonica

Due to the importance of neutrophils and proinflammatory cytokines in schistosomal liver damage, we analyzed the mechanisms underlying neutrophil and proinflammatory responses in murine schistosomiasis japonica. We found that granulomatous inflammation around parasite eggs in the liver was greater in Schistosoma japonicum-infected IL-4-/- IL-13-/- (double-knockout [DKO]) mice than in infected wild-type (WT) mice at 6 weeks, but not at 8 weeks, postinfection, suggesting the importance of Th2 responses in these typical hepatic lesions. Infected DKO mice also showed increased neutrophil infiltration accompanying more severe pathology, as shown by the enhanced necrosis of hepatocytes. This was not likely due to a Th1/Th2 imbalance, because there was no detectable increase in gamma interferon (IFN-γ) production in these DKO mice. mRNA expression of interleukin-17A (IL-17A), proinflammatory cytokines, and the neutrophil chemoattractant CXCL2 in liver was higher in infected DKO mice than in WT mice. However, in IL-4-/- IL-13-/- IL-17A-/- (triple-knockout [TKO]) mice, the absence of IL-17A was associated with only marginal differences in schistosomal liver damage, suggesting that IL-17A is only partially responsible for neutrophil-driven hepatic damage. Furthermore, the expression of mRNAs encoding proinflammatory cytokines was not under the control of IL-17A in TKO mice. These findings indicate that IL-4 and IL-13 suppress excessive neutrophil recruitment, proinflammatory cytokine production, and hepatic damage during the acute stage of S. japonicum infection, suggesting that neutrophils and proinflammatory cytokines are mainly responsible for hepatocyte damage during acute murine schistosomiasis japonica. However, neutrophil induction and the production of proinflammatory cytokines were not due solely to IL-17A.

Time course of changes in inflammatory markers during a 6-mo exercise intervention in sedentary middle-aged men: a randomized-controlled trial

Regular exercise may improve systemic markers of chronic inflammation, but direct evidence and dose-response information is lacking. The objective of this study was to examine the effect and time course of changes in markers of chronic inflammation in response to progressive exercise training (and subsequent detraining). Forty-one sedentary men 45-64 yr of age completed either a progressive 24-wk exercise intervention or control followed by short-term removal of the intervention (2-wk detraining). Serum IL-6 fell by -0.4 pg/ml (SD 0.6) after 12 wk and responded to moderate-intensity exercise. Serum alanine aminotransferase (ALT) activity fell -7 U/l (SD 11) at 24 wk although there was no evidence of any change by week 12 (and therefore ALT required more vigorous-intensity activity and/or a more prolonged intervention). The effect on IL-6 was lost after 2-wk detraining whereas the change in ALT was retained. The temporal fall and rise in IL-6 with training and subsequent detraining in men with high IL-6 at baseline provided a retrospective opportunity to examine parallel genomic changes in peripheral mononuclear cells. A subset of 53 probes was differentially regulated by at least twofold after training with 31 of these changes being lost after detraining (n = 6). IL-6 responded quickly to the carefully monitored exercise intervention (within weeks) and required only moderate-intensity exercise, whereas ALT took longer to change and/or required more vigorous-intensity exercise. Further work is required to determine whether any of the genes that temporally changed in parallel with changes in IL-6 are a cause or consequence of this response.

Targeting IL-17 and Th17 cells in rheumatoid arthritis

Identification of interleukin-17 (IL-17) as a powerful proinflammatory cytokine and the recent recognition of a T-helper cell subset that secretes it have focused attention on the role of IL-17 and Th17 cells in rheumatoid arthritis (RA) and other immune-mediated diseases. While understanding of its role in RA is still evolving, evidence from both animal models and human systems provides a compelling rationale for therapeutic targeting of IL-17 in RA. Both direct and indirect approaches to accomplish this are feasible. Mechanistic studies in the context of clinical trials will be required to understand why some strategies may be preferable from the perspectives of efficacy and safety.

[Role of Th17 cells in rheumatoid arthritis]

Th17 cells are the newly described subset of the CD4(+) T lymphocytes. Activated Th17 cells are characterized by their ability to produce IL-17A and other pro-inflammatory cytokines. IL-17A regulates immune function through its cell-surface receptor expressed on epithelial-and endothelial cells, fibroblasts and leukocytes by promoting neutrophil recruitment and releasing further pro-inflammatory mediators. Failures of the susceptible balance of the immunoregulation may lead to unchecked immune response and autoimmune diseases. The central role of Th17 cells and cytokines produced by Th17 cells were confirmed in a wide variety of human autoimmune diseases, including rheumatoid arthritis. Recently Th17 cells and its cytokines come into the focus of immunological research as potential therapeutic targets.

Interleukin-23 promotes Th17 differentiation by inhibiting T-bet and FoxP3 and is required for elevation of interleukin-22, but not interleukin-21, in autoimmune experimental arthritis

OBJECTIVE

To examine the role of interleukin-23 (IL-23) in subgroup polarization of IL-17A-positive and/or interferon-gamma (IFNgamma)-positive T cells in autoimmune disease-prone DBA/1 mice with and without collagen-induced arthritis.

METHODS

A magnetic-activated cell sorting system was used to isolate CD4+ T cells from the spleen of naive and type II collagen (CII)-immunized DBA/1 mice. These CD4+ T cells were stimulated in vitro under Th0, Th1, or different Th17 culture conditions. Intracellular staining for IL-17A and IFNgamma was evaluated by flow cytometry. In addition, Th17 cytokines and T helper-specific transcription factors were analyzed by enzyme-linked immunosorbent assay and/or quantitative polymerase chain reaction.

RESULTS

In CD4+ T cells from naive DBA/1 mice, IL-23 alone hardly induced retinoic acid-related orphan receptor gammat (RORgammat), Th17 polarization, and Th17 cytokines, but it inhibited T-bet expression. In contrast, transforming growth factor beta1 (TGFbeta1)/IL-6 was a potent inducer of RORgammat, RORalpha, IL-17A, IL-17F, IL-21, and FoxP3 in these cells. In contrast to TGFbeta1/IL-6, IL-23 was critical for the induction of IL-22 in CD4+ T cells from both naive and CII-immunized DBA/1 mice. Consistent with these findings, IL-23 showed a more pronounced induction of the IL-17A+IFNgamma- subset in CD4+ T cells from CII-immunized mice. However, in CD4+ T cells from naive mice, IL-23 significantly increased the TGFbeta1/IL-6-induced Th17 polarization, including elevated levels of IL-17A and IL-17F and decreased expression of T-bet and FoxP3. Of note, the IL-23-induced increase in IL-17A and IL-17F levels was prevented in T-bet-deficient mice.

CONCLUSION

IL-23 promotes Th17 differentiation by inhibiting T-bet and FoxP3 and is required for elevation of IL-22, but not IL-21, levels in autoimmune arthritis. These data indicate different mechanisms for IL-23 and TGFbeta1/IL-6 at the transcription factor level during Th17 differentiation in autoimmune experimental arthritis.

1,25-dihydroxyvitamin D3 modulates Th17 polarization and interleukin-22 expression by memory T cells from patients with early rheumatoid arthritis

OBJECTIVE

To examine the immunologic mechanism by which 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) may prevent corticosteroid-induced osteoporosis in patients with early rheumatoid arthritis (RA), with a focus on T cell biology.

METHODS

Peripheral blood mononuclear cells (PBMCs) and CD4+CD45RO+ (memory) and CD4+CD45RO- (non-memory) T cells separated by fluorescence-activated cell sorting (FACS) from treatment-naive patients with early RA were stimulated with anti-CD3/anti-CD28 in the absence or presence of various concentrations of 1,25(OH)(2)D(3), dexamethasone (DEX), and 1,25(OH)(2)D(3) and DEX combined. Levels of T cell cytokines were determined by enzyme-linked immunosorbent assay and flow cytometry.

RESULTS

The presence of 1,25(OH)(2)D(3) reduced interleukin-17A (IL-17A) and interferon-gamma levels and increased IL-4 levels in stimulated PBMCs from treatment-naive patients with early RA. In addition, 1,25(OH)(2)D(3) had favorable effects on tumor necrosis factor alpha (TNFalpha):IL-4 and IL-17A:IL-4 ratios and prevented the unfavorable effects of DEX on these ratios. Enhanced percentages of IL-17A- and IL-22-expressing CD4+ T cells and IL-17A-expressing memory T cells were observed in PBMCs from treatment-naive patients with early RA as compared with healthy controls. Of note, we found no difference in the percentage of CD45RO+ and CD45RO- cells between these 2 groups. Interestingly, 1,25(OH)(2)D(3), in contrast to DEX, directly modulated human Th17 polarization, accompanied by suppression of IL-17A, IL-17F, TNFalpha, and IL-22 production by memory T cells sorted by FACS from patients with early RA.

CONCLUSION

These data indicate that 1,25(OH)(2)D(3) may contribute its bone-sparing effects in RA patients taking corticosteroids by the modulation of Th17 polarization, inhibition of Th17 cytokines, and stimulation of IL-4.

Protease-activated receptor 2 has pivotal roles in cellular mechanisms involved in experimental periodontitis

The tissue destruction seen in chronic periodontitis is commonly accepted to involve extensive upregulation of the host inflammatory response. Protease-activated receptor 2 (PAR-2)-null mice infected with Porphyromonas gingivalis did not display periodontal bone resorption in contrast to wild-type-infected and PAR-1-null-infected mice. Histological examination of tissues confirmed the lowered bone resorption in PAR-2-null mice and identified a substantial decrease in mast cells infiltrating the periodontal tissues of these mice. T cells from P. gingivalis-infected or immunized PAR-2-null mice proliferated less in response to antigen than those from wild-type animals. CD90 (Thy1.2) expression on CD4(+) and CD8(+) T-cell-receptor beta (TCRbeta) T cells was significantly (P < 0.001) decreased in antigen-immunized PAR-2-null mice compared to sham-immunized PAR-2-null mice; this was not observed in wild-type controls. T cells from infected or antigen-immunized PAR-2-null mice had a significantly different Th1/inflammatory cytokine profile from wild-type cells: in particular, gamma interferon, interleukins (interleukin-2, -3, and -17), granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor alpha demonstrated lower expression than wild-type controls. The absence of PAR-2 therefore appears to substantially decrease T-cell activation and the Th1/inflammatory response. Regulation of such proinflammatory mechanisms in T cells and mast cells by PAR-2 suggests a pivotal role in the pathogenesis of the disease.

Regulation of pathogenic IL-17 responses in collagen-induced arthritis: roles of endogenous interferon-gamma and IL-4

INTRODUCTION

Interleukin (IL)-17 plays an important role in the pathogenesis of rheumatoid arthritis and the mouse model collagen-induced arthritis (CIA). Interferon(IFN)-gamma and IL-4 have been shown to suppress Th17 development in vitro, but their potential immunoregulatory roles in vivo are uncertain. The goals of this study were to determine the relationship between Th17 responses and disease severity in CIA and to assess regulation of IL-17 by endogenous IFN-gamma and IL-4.

METHODS

DBA1/LacJ mice were immunized with type II collagen in complete Freund's adjuvant (CFA) to induce arthritis, and treated with neutralizing antibody to IFN-gamma and/or IL-4. Systemic IL-17, IFN-gamma, and IL-4 were measured in serum. At the peak of disease, cytokine production was measured by ELISA of supernatants from spleen, lymph node and paw cultures. Paws were also scored for histologic severity of arthritis.

RESULTS

Joint inflammation was associated with a higher ratio of systemic IL-17/IFN-gamma. Neutralization of IFN-gamma accelerated the course of CIA and was associated with increased IL-17 levels in the serum and joints. The IFN-gamma/IL-4/IL-17 responses in the lymphoid organ were distinct from such responses in the joints. Neutralization of IL-4 led to increased arthritis only in the absence of IFN-gamma and was associated with increased bone and cartilage damage without an increase in the levels of IL-17.

CONCLUSIONS

IL-4 and IFN-gamma both play protective roles in CIA, but through different mechanisms. Our data suggests that the absolute level of IL-17 is not the only determinant of joint inflammation. Instead, the balance of Th1, Th2 and Th17 cytokines control the immune events leading to joint inflammation.

Cytokines in chronic rheumatic diseases: is everything lack of homeostatic balance?

Biological systems have powerful inbuilt mechanisms of control intended to maintain homeostasis. Cytokines are no exception to this rule, and imbalance in cytokine activities may lead to inflammation with subsequent tissue and organ damage, altered function, and death. Balance is achieved through multiple, not mutually exclusive, mechanisms including the simultaneous production of agonist and antagonistic cytokines, expression of soluble receptors or membrane-bound nonsignaling receptors, priming and/or reprogramming of signaling, and uncoupling of ligand/receptor pairing from signal transduction. Insight into cytokine balance is leading to novel therapeutic approaches particularly in autoimmune conditions, which are intimately linked to a dysregulated cytokine production.

Lessons from animal models of arthritis over the past decade

This review summarizes the major developments in animal models of arthritis in the past decade. It focuses on novel transgenic models, addresses the involvement of cytokines and discusses novel findings in cartilage and bone erosion. It is clear that interest has been raised in the direct arthritogenic role of autoantibodies, apart from T cell involvement, and their interaction with cells through Fcgamma receptors. In addition, a role for IL-6 and IL-17 and Th17 cells seems apparent in most T cell-driven arthritis models, with environmental triggering through Toll-like receptors contributing to this process. Further insights into enzymes involved in cartilage proteoglycan loss in arthritis, as well as mediators regulating bone erosion and bone apposition, have been gained.

The role of T helper type 17 cells in inflammatory arthritis

While T cells have been implicated in the pathogenesis of inflammatory arthritis for more than three decades, the focus on the T helper type 17 (Th17) subset of CD4 T cells and their secreted cytokines, such as interleukin (IL)-17, is much more recent. Proinflammatory actions of IL-17 were first identified in the 1990s, but the delineation of a distinct Th17 subset in late 2005 has sparked great interest in the role of these cells in a broad range of immune-mediated diseases. This review summarizes current understanding of the role of Th17 cells and their products in both animal models of inflammatory arthritis and human immune-driven arthritides.

Human rheumatoid arthritis tissue production of IL-17A drives matrix and cartilage degradation: synergy with tumour necrosis factor-alpha, Oncostatin M and response to biologic therapies

INTRODUCTION

The aim of this study was to examine IL-17A in patients, following anti-TNF-alpha therapy and the effect of IL-17A on matrix turnover and cartilage degradation.

METHODS

IL-17A expression was examined by ELISA and immunohistology in the rheumatoid arthritis (RA) joints. RA whole synovial tissue explant (RA ST), primary synovial fibroblasts (RASFC), human cartilage and chondrocyte cultures were stimulated with IL-17A +/- TNF-alpha and Oncostatin M (OSM). Matrix metalloproteinase (MMP) and tissue inhibitor (TIMP-1) were assessed by ELISA and zymography. Cartilage proteoglycan release was assessed histologically by Safranin-O staining. Clinical parameters, IL-17A, MMP/TIMP were assessed in patients pre/post biologic therapy.

RESULTS

IL-17A levels were higher in RA vs osteoarthritis (OA)/normal joints (P < 0.05). IL-17A up-regulated MMP-1, -2, -9, and -13 in RA ST, RASFC, cartilage and chondrocyte cultures (P < 0.05). In combination with TNF-alpha and OSM, IL-17A shifted the MMP:TIMP-1 ratio in favor of matrix degradation (all P < 0.05). Cartilage proteoglycan depletion in response to IL-17A was mild; however, in combination with TNF-alpha or OSM showed almost complete proteoglycan depletion. Serum IL-17A was detected in 28% of patients commencing biologic therapy. IL-17A negative patients demonstrated reductions post therapy in serum MMP1/TIMP4, MMP3/TIMP1 and MMP3/TIMP4 ratios and an increase in CS846 (all P < 0.05). No significant changes were observed in IL-17A positive patients.

CONCLUSIONS

IL-17A is produced locally in the inflamed RA joint. IL-17A promotes matrix turnover and cartilage destruction, especially in the presence of other cytokines, mimicking the joint environment. IL-17A levels are modulated in vivo, following anti-TNF therapy, and may reflect changes in matrix turnover.

IL-27 is a key regulator of IL-10 and IL-17 production by human CD4+ T cells

Although the physiologic pathways that control regulatory T cells (Foxp3-expressing regulatory T cells, IL-10-secreting Tr1 cells) and Th17 cells in rodents have been defined, the factors that control these differentiation pathways in humans are not well understood. In this study, we show that IL-27 promotes the differentiation of IL-10-secreting Tr1 cells while inhibiting Th17 generation and molecules associated with Th17 function. Furthermore, IL-27 inhibits IL-17-polarizing cytokines on dendritic cells, which in turn decrease IL-17 secretion from T cells. Our results demonstrate that IL-27 plays a key role in human T cells by promoting IL-10-secreting Tr1 cells and inhibiting Th17 cells and thus provides a dual regulatory mechanism to control autoimmunity and tissue inflammation.

Osteoimmunology: crosstalk between the immune and bone systems

INTRODUCTION

The interaction between the immune and skeletal systems has long been acknowledged, but investigation into rheumatoid arthritis (RA) as well as the various bone phenotypes found in immunocompromised gene-deficient mice has highlighted the importance of the dynamic interplay between the two systems. This has led to the recent emergence and subsequent rapid evolution of the field of osteoimmunology. BONE DESTRUCTION WITH ARTHRITIS AS A RANKL DISEASE: In the bone destruction associated with RA, IL-17-producing helper T cells (T(H)17) play a major role by inducing receptor activator of nuclear factor-kappaB ligand (RANKL). RANKL stimulates osteoclastogenesis through nuclear factor of activated T cells cytoplasmic 1 (NFATc1), which is well known as a crucial regulator of immunity.

NEW PLAYERS IN OSTEOIMMUNOLOGY

In addition to cellular interactions via cytokines, the immune and skeletal systems share various molecules, including transcription factors, signaling molecules, and membrane receptors.

CONCLUSION

The scope of osteoimmunology has grown to encompass a wide range of molecular and cellular interactions, the elucidation of which will provide a scientific basis for future therapeutic approaches to diseases of both the immune and skeletal systems.

Function and dysfunction of dendritic cells in autoimmune rheumatic diseases

Dendritic cells (DC) have been implicated both in initiation of immunity and in immune tolerance. The mechanisms whereby tolerogenic DC may induce and maintain peripheral tolerance include the generation or expansion of regulatory T cells (Treg) and the promotion of T-cell anergy or deletion. A wide spectrum of hematopoietic growth factors and cytokines are endowed with the ability to differentiate tolerogenic DC both in vitro and in vivo. Based on this knowledge, therapeutic vaccination with cytokine-modulated tolerogenic DC has been applied to animal models of autoimmune disorders. This article will review the current experimental evidence underpinning DC dysfunction in rheumatic autoimmune diseases and will discuss how the manipulation of DC and Treg number and function may control undesired T-cell responses.

Th17 cells in human disease

SUMMARY

Our understanding of the role of T cells in human disease is undergoing revision as a result of the discovery of T-helper 17 (Th17) cells, a unique CD4(+) T-cell subset characterized by production of interleukin-17 (IL-17). IL-17 is a highly inflammatory cytokine with robust effects on stromal cells in many tissues. Recent data in humans and mice suggest that Th17 cells play an important role in the pathogenesis of a diverse group of immune-mediated diseases, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma. Initial reports also propose a role for Th17 cells in tumorigenesis and transplant rejection. Important differences, as well as many similarities, are emerging when the biology of Th17 cells in the mouse is compared with corresponding phenomena in humans. As our understanding of human Th17 biology grows, the mechanisms underlying many diseases are becoming more apparent, resulting in a new appreciation for both previously known and more recently discovered cytokines, chemokines, and feedback mechanisms. Given the strong association between excessive Th17 activity and human disease, new therapeutic approaches targeting Th17 cells are highly promising, but the potential safety of such treatments may be limited by the role of these cells in normal host defenses against infection.

Th17 cells in human disease

SUMMARY

Our understanding of the role of T cells in human disease is undergoing revision as a result of the discovery of T-helper 17 (Th17) cells, a unique CD4(+) T-cell subset characterized by production of interleukin-17 (IL-17). IL-17 is a highly inflammatory cytokine with robust effects on stromal cells in many tissues. Recent data in humans and mice suggest that Th17 cells play an important role in the pathogenesis of a diverse group of immune-mediated diseases, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma. Initial reports also propose a role for Th17 cells in tumorigenesis and transplant rejection. Important differences, as well as many similarities, are emerging when the biology of Th17 cells in the mouse is compared with corresponding phenomena in humans. As our understanding of human Th17 biology grows, the mechanisms underlying many diseases are becoming more apparent, resulting in a new appreciation for both previously known and more recently discovered cytokines, chemokines, and feedback mechanisms. Given the strong association between excessive Th17 activity and human disease, new therapeutic approaches targeting Th17 cells are highly promising, but the potential safety of such treatments may be limited by the role of these cells in normal host defenses against infection.

IL-22-producing "T22" T cells account for upregulated IL-22 in atopic dermatitis despite reduced IL-17-producing TH17 T cells

BACKGROUND

Psoriasis and atopic dermatitis (AD) are common inflammatory skin diseases. An upregulated TH17/IL-23 pathway was demonstrated in psoriasis. Although potential involvement of TH17 T cells in AD was suggested during acute disease, the role of these cells in chronic AD remains unclear.

OBJECTIVE

To examine differences in IL-23/TH17 signal between these diseases and establish relative frequencies of T-cell subsets in AD.

METHODS

Skin biopsies and peripheral blood were collected from patients with chronic AD (n = 12) and psoriasis (n = 13). Relative frequencies of CD4+ and CD8+ T-cell subsets within these 2 compartments were examined by intracellular cytokine staining and flow cytometry.

RESULTS

In peripheral blood, no significant difference was found in percentages of different T-cell subsets between these diseases. In contrast, psoriatic skin had significantly increased frequencies of TH1 and TH17 T cells compared with AD, whereas TH2 T cells were significantly elevated in AD. Distinct IL-22-producing CD4+ and CD8+ T-cell populations were significantly increased in AD skin compared with psoriasis. IL-22+CD8+ T-cell frequency correlated with AD disease severity.

CONCLUSION

Our data established that T cells could independently express IL-22 even with low expression levels of IL-17. This argues for a functional specialization of T cells such that "T17" and "T22" T-cells may drive different features of epidermal pathology in inflammatory skin diseases, including induction of antimicrobial peptides for "T17" T cells and epidermal hyperplasia for "T22" T-cells. Given the clinical correlation with disease severity, further characterization of "T22" T cells is warranted, and may have future therapeutic implications.