Interleukin-17 and interferon-gamma synergize in the enhancement of proinflammatory cytokine production by human keratinocytes

Keratin 17 as a therapeutic target for the treatment of psoriasis

Keratin 17 (K17) is the only ectopically expressed keratin in psoriatic lesional epidermis. This review focuses mainly on reports that have addressed the mechanism of K17 up-regulation and its biological role in psoriasis. In addition to IFN-γ, IL-17A and IL-22, which are derived from Th17 and Th22 cells, could up-regulate K17 mRNA and protein levels in keratinocytes in a dose-dependent manner. Moreover, these effects are partially blocked with STAT1- and STAT3-specific inhibitors, as well as small interfering RNA (siRNA) targeting STAT1 and STAT3. On the other hand, the HLA DRB1*04 and/or *07 positive patients show significant T cell responses to two peptides from K17 protein selected on the basis of predicted HLA DRB1*04 and/or *07 bindings. One peptide contains the ALEEAN sequence, while the other peptide has an amino acid sequence that has not been previously reported. Analysis of these processes led us to propose the existence of a K17/T cells/cytokine autoimmune loop, in which ectopically expressed K17 impacts on the maintenance of psoriasis by activating autoreactive T cells. Furthermore, it has been found that altered peptide ligands, which are produced through single alanine residue substitutions at a critical TCR contact position, abolish the T cell proliferation and IFN-γ production induced by K17 pathogenic peptides. K17-specific antisense ODNs and RNAi suppress K17 mRNA and protein expression in psoriatic skin in vivo, which coincides with marked clinical and histological improvement. These findings highlight K17 as an attractive target for novel therapies aimed at curtailing psoriasis driven by chronic inflammation.

The roles of cells and cytokines in the pathogenesis of psoriasis

Psoriasis is considered an immune chronic disease in which T cells are accepted as important. Nowadays, it is believed that psoriasis is most likely a T helper (Th)1/Th17 induced inflammatory disease. However, some other cells, such as endothelial cells, dendritic cells, monocytic cells, neutrophils, keratinocytes, and several cytokines, appear to have, at different stages of the disease, an important role in its pathogenesis. For instance, the response to psoriasis therapy is dependent not only on the inactivation of Th1 and Th17 immune responses but also on the inactivation of dendritic cell products. Moreover, interleukin (IL)-23 deregulation appears to be an independent factor in the pathogenesis of psoriasis. Indeed, currently, the IL-23/Th17 axis is believed to be crucial in psoriasis pathogenesis, and its inhibition appears to be important for therapeutic achievement. This review presents the roles and interactions of cells and cytokines that are related to psoriasis pathogenesis.

Antimicrobial peptides in the pathogenesis of psoriasis

One characteristic abnormality of lesional skin in psoriasis is the excessive production of antimicrobial peptides and proteins (AMPs). AMPs typically are small (12-50 amino acids), have positive charge and amphipathic structure, and are found in all living organisms including mammals, insects, plants and invertebrates. These peptides are best known for their integral role in killing pathogenic microorganisms; however, in vertebrates, they are also capable of modifying host inflammatory responses by a variety of mechanisms. In psoriatic lesions, many AMPs are highly expressed, and especially the associations between psoriasis and cathelicidin, β-defensins or S100 proteins have been well studied. Among them, a cathelicidin peptide, LL-37, has been highlighted as a modulator of psoriasis development in recent years. AMPs had been thought to worsen psoriatic lesions but recent evidence has also suggested the possibility that the induction of AMPs expression might improve aspects of the disease. Further investigations are needed to uncover a previously underappreciated role for AMPs in modulating the immune response in psoriasis, and to improve disease without the risks of systemic immunosuppressive approaches.

Immune checkpoints in central nervous system autoimmunity

A number of autoimmune diseases, including multiple sclerosis, are mediated by self-reactive T cells that have escaped the deletional mechanisms of central tolerance. Usually, these T cells are kept at bay through peripheral tolerance mechanisms, including regulation through coinhibitory receptors and suppression by regulatory T cells. However, if these mechanisms fail, self-reactive T cells are activated and autoimmune responses ensue. This review outlines how the coinhibitory receptors CTLA-4 (cytotoxic T-lymphocyte antigen-4), PD-1 (programed death-1), Tim-3 (T-cell immunoglobulin- and mucin domain-containing molecule 3), and TIGIT (T-cell immunoreceptor with immunoglobulin and ITIM domains) act at different checkpoints to inhibit autoreactive T cells and suppress the development of central nervous system autoimmunity. Loss of each of these receptors predisposes to autoimmunity, indicating a non-redundant role in maintaining peripheral tolerance. At the same time, their functional patterns seem to overlap to a large degree. Therefore, we propose that only the concerted action of a combination of inhibitory receptors is able to maintain peripheral tolerance and prevent autoimmunity.

Compartmentalized expression of Th1 and Th17 cytokines in pediatric inflammatory bowel diseases

BACKGROUND

Interleukin (IL)-23, IL-17A, IL-17F, and interferon-gamma (IFN-γ) are important mediators of inflammatory colitis and are potential therapeutic targets in inflammatory bowel disease (IBD). Their expression profile in the different parts of normal noninflammatory intestine is unclear and their changes during pathology have not yet been addressed in pediatric IBD patients.

METHODS

We quantified the transcriptional expression of IL-23, IL-12, IL-17A, IL-17F, IL-6, and IL-10 in healthy, noninflammatory duodenum, ileum, and colon and in inflamed and noninflamed biopsies of pediatric patients with Crohn's disease (CD) and ulcerative colitis (UC).

RESULTS

In healthy tissue, expression of IL-17A is highest in the ileum, with IFN-γ expression lowest in the colon. Compared to healthy sections, CD patients displayed increased IL-12p35 and IFN-γ levels in noninflamed ileum and colon, respectively. Modifications of cytokine expression between noninflamed and inflamed tissues was characterized by increased IL-17A in UC colon, IFN-γ in CD colon, and IL-17A, IFN-γ and IL-6 in CD ileum. Elevated IL-17A levels were positively correlated with IFN-γ in both inflammatory CD and UC but IL-17A and IFN-γ were correlated with IL-23p19 in CD ileum only.

CONCLUSIONS

The expression of Th1 and Th17 cytokines varies along the intestine, indicating local specific regulation mechanisms. However, the cytokine expression patterns in the same tissue depends on the pathology, with a Th1 or a Th17 profile in the colon of CD and UC patients, respectively, and a Th1/Th17 profile in the ileum of CD patients. This indicates overlapping but distinct immune mechanisms driving intestinal inflammation in these two pathologies.

IL-17 downregulates filaggrin and affects keratinocyte expression of genes associated with cellular adhesion

Atopic eczema and psoriasis are common skin diseases. While it is well established that the pathogenesis of these diseases varies, both are characterized by impairment in epidermal barrier function and abnormal IL-17 expression in the skin and peripheral blood. Recent findings indicated that filaggrin is essential during barrier formation and its insufficiency underlies the pathogenesis of atopic eczema. Filaggrin downregulation has also been reported in psoriasis. It is clear that Th1/Th2 bias influences expression of the protein, but an analysis of the effects of interleukin-17 (IL-17) on the expression of the protein and profilaggrin-processing enzymes has not yet been reported. In addition, the effect of the cytokine on components of functional epidermal barrier, tight junctions and adhesion/desmosomal proteins, has not been elucidated. Keratinocytes were exposed to interleukin-17A, and microarray analysis was performed. Filaggrin protein level was assessed by western blot. We have observed a significant decrease in profilaggrin mRNA level in interleukin-17A-exposed cultures (P = 0.008). Expression of processing enzymes was also altered, indicating an indirect effect of the cytokine on filaggrin production/degradation. Moreover, expression of many genes involved in cellular adhesion was also decreased. A significant downregulation of filaggrin at the protein level was detected by western blot in immortal and primary keratinocytes. Gene ontology analysis indicated changes in keratinization, epidermal differentiation and formation of the cornified envelope. We conclude that IL-17A downregulates the expression of filaggrin and genes important for cellular adhesion which could affect epidermal barrier formation. This effect potentially contributes to barrier dysfunction and could become a possible therapeutic target.

Mnk Kinases in Cytokine Signaling and Regulation of Cytokine Responses

The kinases Mnk1 and Mnk2 are activated downstream of the p38 MAPK and MEK/ERK signaling pathways. Extensive work over the years has shown that these kinases control phosphorylation of the eukaryotic initiation factor 4E (eIF4E) and regulate engagement of other effector elements, including hnRNPA1 and PSF. Mnk kinases are ubiquitously expressed and play critical roles in signaling for various cytokine receptors, while there is emerging evidence that they have important functions as mediators of pro-inflammatory cytokine production. In this review the mechanisms of activation of MNK pathways by cytokine receptors are addressed and their roles in diverse cytokine-dependent biological processes are reviewed. The clinical-translational implications of such work and the relevance of future development of specific MNK inhibitors for the treatment of malignancies and auto-immune disorders are discussed.

IL-17/IL-17 receptor system in autoimmune disease: mechanisms and therapeutic potential

IL-17 (interleukin-17), a hallmark cytokine of Th17 (T-helper 17) cells, plays critical roles in host defence against bacterial and fungal infections, as well as in the pathogenesis of autoimmune diseases. The present review focuses on current knowledge of the regulation, functional mechanisms and targeting strategies of IL-17 in the context of inflammatory autoimmune diseases. Evidence shows that IL-17 is highly up-regulated at sites of inflammatory tissues of autoimmune diseases and amplifies the inflammation through synergy with other cytokines, such as TNF (tumour necrosis factor) α. Although IL-17 was originally thought to be produced mainly by Th17 cells, a newly defined T-cell subset with a specific differentiation programme and tight regulation, several other cell types (especially innate immune cells) are also found as important sources for IL-17 production. Although IL-17 activates common downstream signalling, including NF-κB (nuclear factor κB), MAPKs (mitogen-activated protein kinases), C/EBPs (CCAAT/enhancer-binding proteins) and mRNA stability, the immediate receptor signalling has been shown to be quite unique and tightly regulated. Mouse genetic studies have demonstrated a critical role for IL-17 in the pathogenesis of variety of inflammatory autoimmune diseases, such as RA (rheumatoid arthritis) and MS (multiple sclerosis). Importantly, promising results have been shown in initial clinical trials of monoclonal antibodies against IL-17 or its receptor (IL-17R) to block IL-17-mediated function in treating autoimmune patients with psoriasis, RA and MS. Therefore targeting IL-17/IL-17R, IL-17-producing pathways or IL-17-mediated signalling pathways can be considered for future therapy in autoimmune diseases.

Transplantation of adipose-derived mesenchymal stem cells into a murine model of passive chronic immune thrombocytopenia

BACKGROUND

Immune thrombocytopenia (ITP) is a bleeding disorder characterized by antibody-opsonized platelets (PLTs) being prematurely destroyed by macrophages in the reticuloendothelial system. T helper (Th) cells and different Th cytokines play an important role in the pathophysiology of ITP. As immunomodulators, adipose-derived mesenchymal stem cells (ADSCs) regulate Th cells and show therapeutic effects in autoimmune diseases. However, it is not clear how ADSCs affect ITP. In this study, we explored the specific effects of ADSCs on ITP in mice.

STUDY DESIGN AND METHODS

BALB/c mice were randomly divided into three groups: normal controls, ITP controls, and ITP with ADSC transplantation. PLT levels were monitored by an automatic blood cell counter, and the cytokines interferon-γ (IFN-γ); interleukin (IL)-2, -4, -10, and -17; and transforming growth factor-β1 (TGF-β1) were analyzed by enzyme-linked immunosorbent assays.

RESULTS

Compared to the untreated ITP mice, the PLT level of the ITP mice significantly increased after ADSC treatment. In the ADSC group, IFN-γ, IL-2, and IL-17 significantly decreased, while IL-4, IL-10, and TGF-β1 increased.

CONCLUSION

These findings constitute the first experimental evidence that ADSCs are efficacious in improving PLT levels and reducing the related Th cytokines mediating proinflammatory response in ITP mice, which may provide a scientific basis for using ADSCs as a new therapy for ITP.

Response to ustekinumab in a patient with both severe psoriasis and hypertrophic cutaneous lupus

Psoriasis is an autoimmune inflammatory disease that has recently been treated with a novel treatment, ustekinumab, a human monoclonal antibody that targets the Th17 pathway. Discoid lupus is a subset of chronic cutaneous lupus erythematosus. Recent studies have suggested the Th17 pathway may be involved in cutaneous lupus. We present a case of a 41-year-old man with both severe psoriasis and hypertrophic discoid lupus treated with ustekinumab. After three doses of 45 mg subcutaneous injections at day 1, week 4, and week 16, his psoriasis plaques cleared and his hypertrophic discoid lupus plaques showed moderate improvement. Following a fourth dose of 90 mg his lupus plaques showed marked improvement. Ustekinumab may be a promising therapy for this and other forms of cutaneous lupus.

Kojic acid-induced IL-6 production in human keratinocytes plays a role in its anti-melanogenic activity in skin

BACKGROUND

Kojic acid is a fungal metabolite widely used in medicinal and cosmetic formulations as a skin-lightening agent based on its de-pigmenting activity. Although in human clinical studies kojic acid has been shown to be effective in the treatment of hyper-pigmentation disorders such as melasma, the reasons for its apparent lack of anti-melanogenic activity in cultured mammalian melanocytes are unclear.

OBJECTIVES

This study was aimed to elucidate pharmacological mechanisms of the in vivo anti-melanogenic activity of kojic acid in human skin.

METHODS

A primary human melanocyte and keratinocyte co-culture system was used to evaluate whether kojic-acid-induced changes in keratinocytes were associated with anti-melanogenic activities in melanocytes. The cytokine secretion profiles in response to kojic acid were analyzed.

RESULTS

Kojic acid increased interleukin (IL)-6 and IL-8 production in melanocyte/keratinocyte co-cultures; however, IL-6 directly inhibited melanogenesis whereas IL-8 did not. In melanocyte monocultures, kojic acid did not increase IL-6 production whereas in keratinocyte monocultures it significantly up-regulated IL-6 gene and protein expression. Therefore, the up-regulation of IL-6 in melanocyte/keratinocyte co-cultures seems to be originated from kojic acid-induced changes in keratinocytes. Anti-IL-6 antibody treatment antagonized the anti-melanogenic effect of kojic acid on the co-cultures.

CONCLUSIONS

The pharmacological mechanism of kojic acid to explain clinically effective anti-melanogenic activity on hyper-pigmented skin is associated with the kojic acid-induced IL-6 production in keratinocytes. The cross-talk between melanocytes and keratinocytes should be determined in future studies on the pharmacological mechanisms of clinically effective dermatological drugs acting on the epidermis.

Critical role of the interleukin-23/T-helper 17 cell axis in the pathogenesis of psoriasis

Psoriasis is an inflammatory disease with dynamic interactions between the immune system and the skin. Recent studies have demonstrated that the interleukin (IL)-23/T-helper (Th)17 cell axis plays an important role in the pathogenesis of psoriasis. Here, the biology and function of Th17 cells as well as the crucial role of IL-23 in the context of the Th17 cell-dependent chronic inflammation in psoriatic skins are reviewed. Recent study about the role of the IL-23/Th17 axis in the pathogenesis of psoriasis-like lesions in K5.Stat3C transgenic mice is also discussed. This model mouse for psoriasis not only verifies the therapeutic efficacies of biologics that specifically target the IL-23/Th17 axis, but also clarifies the pathogenesis of psoriasis.

Low-dose rituximab in adult patients with idiopathic autoimmune hemolytic anemia: clinical efficacy and biologic studies

This prospective study investigated the efficacy, safety, and response duration of low-dose rituximab (100 mg fixed dose for 4 weekly infusions) together with a short course of steroids as first- or second-line therapy in 23 patients with primary autoimmune hemolytic anemia (AIHA). The overall response was 82.6% at month +2, and subsequently stabilized to ∼ 90% at months +6 and +12; the response was better in warm autoimmune hemolytic anemia (WAIHA; overall response, 100% at all time points) than in cold hemagglutinin disease (CHD; average, 60%); the relapse-free survival was 100% for WAIHA at +6 and +12 months versus 89% and 59% in CHD, respectively, and the estimated relapse-free survival at 2 years was 81% and 40% for the warm and cold forms, respectively. The risk of relapse was higher in CHD and in patients with a longer interval between diagnosis and enrollment. Steroid administration was reduced both as cumulative dose (∼ 50%) and duration compared with the patient's past history. Treatment was well tolerated and no adverse events or infections were recorded; retreatment was also effective. The clinical response was correlated with amelioration biologic markers such as cytokine production (IFN-γ, IL-12, TNF-α, and IL-17), suggesting that low-dose rituximab exerts an immunomodulating activity. This study is registered at www.clinicaltrials.gov as NCT01345708.

Mnk Kinases in Cytokine Signaling and Regulation of Cytokine Responses

The kinases Mnk1 and Mnk2 are activated downstream of the p38 MAPK and MEK/ERK signaling pathways. Extensive work over the years has shown that these kinases control phosphorylation of the eukaryotic initiation factor 4E (eIF4E) and regulate engagement of other effector elements, including hnRNPA1 and PSF. Mnk kinases are ubiquitously expressed and play critical roles in signaling for various cytokine receptors, while there is emerging evidence that they have important functions as mediators of pro-inflammatory cytokine production. In this review the mechanisms of activation of MNK pathways by cytokine receptors are addressed and their roles in diverse cytokine-dependent biological processes are reviewed. The clinical-translational implications of such work and the relevance of future development of specific MNK inhibitors for the treatment of malignancies and auto-immune disorders are discussed.

Interleukin-17- and protease-activated receptor 2-mediated production of CXCL1 and CXCL8 modulated by cyclosporine A, vitamin D3 and glucocorticoids in human keratinocytes

Protease-activated receptor 2 (PAR2) is a G protein-coupled receptor which mediates a variety of functions in the skin including cutaneous inflammation. SLIGKV-NH(2) , an agonist peptide for PAR2, enhanced the interleukin (IL)-17-induced production of two CXC chemokines, CXCL1 (GRO-α) and CXCL8 (IL-8), in normal human epidermal keratinocytes (NHEK) in a concentration-dependent manner. The enhanced production of those chemokines was suppressed by a PAR2-specific siRNA. The SLIGKV-NH(2) -induced production of both CXCL1 and CXCL8 was markedly reduced by cyclosporine A. The enhanced production of CXCL1 was suppressed by 1α, 24R-dihydroxyvitamin D(3) , an active form of vitamin D(3) , and weakly by glucocorticoids, dexamethasone and clobetasol propionate, whereas production of CXCL8 was not altered by any of those receptor agonists. In psoriatic skin, the thickened upper spinous layer of the epidermis was positive for PAR2 protein and the expression of the IL17A mRNA was increased. These results suggest that the IL-17-induced pro-inflammatory reaction is enhanced by the activation of PAR2 in keratinocytes, and that the effect of PAR2 is differentially modulated by cyclosporine A, the active form of vitamin D(3) and glucocorticoids.

IL-22, but not IL-17, dominant environment in cutaneous T-cell lymphoma

PURPOSE

Both patients with cutaneous T-cell lymphoma (CTCL) and those with atopic dermatitis (AD) have pruritus, T(H)2-biased T cells, and a tendency to have bacterial infections, suggesting a common pathologic basis for these two diseases. Recently, interleukin (IL)-22-producing T cells were reported in skin of patients with AD. In this study, we investigated expression levels of T(H)22- and T(H)17-related molecules in lesional skin and sera isolated from patients with CTCL.

EXPERIMENTAL DESIGN

Skin biopsies and sera were collected from patients with CTCL or psoriasis and from healthy volunteers. Protein and mRNA expression levels of IL-22, IL-17A, IL-17F, IL-23p19, IL-10, IL-4, CCL20, CCR6, IL-8, and IL-20 were examined in lesional tissue and a subset of these molecules in sera. Phosphorylation of STAT3 was also assessed in lesional skin of CTCL and psoriasis by immunohistochemistry.

RESULTS

IL-22, IL-10, IL-4, CCL20, and CCR6 mRNA and protein levels, but not IL-17A, IL-17F, IL-23p19, IL-8, or IL-20, were significantly elevated in lesional skin of CTCL. Phosphorylation of STAT3 was detected in epidermis of CTCL skin. Moreover, serum IL-22, IL-10, and CCL20 levels were increased in CTCL and correlated with disease severity.

CONCLUSIONS

Our results suggest that IL-22 is important in establishing the tumor microenvironment for CTCL. Enhanced expression of CCL20 may explain epidermal hyperplasia and migration of CCR6(+) cells, such as Langerhans cells, into lesional skin. Relatively low expression of IL-17 may explain the lack of neutrophils in lesions of CTCL, which correlates with bacterial infections that commonly occur in skin affected by CTCL.

Psoriasis

Psoriasis is a common relapsing and remitting immune-mediated inflammatory disease that affects the skin and joints. This review focuses on current immunogenetic concepts, key cellular players, and axes of cytokines that are thought to contribute to disease pathogenesis. We highlight potential therapeutic targets and give an overview of the currently used immune-targeted therapies.

Staphylococcal-associated molecular patterns enhance expression of immune defense genes induced by IL-17 in mammary epithelial cells

Interleukin-17A (IL-17A) and IL-17F have been shown to mediate a crucial crosstalk between the immune system and various epithelial tissues, stimulating various defensive mechanisms to bacterial infections. A number of studies have characterized the response to IL-17A and IL-17F of epithelial cells from airways, intestine, and skin, but not from the mammary gland. To evaluate the potential contribution of IL-17 to the immune defense of the mammary gland, we analyzed the effects of recombinant bovine IL-17A and IL-17F on primary bovine mammary epithelial cells (MEC) by quantitative PCR and ELISA. We found expression (mRNA) of the two components of the IL-17 receptor complex, IL-17RA and IL-17RC, in mammary tissue and MEC in vitro. The expression of a number of genes encoding cytokines, chemokines and proteins endowed with antibacterial activities was increased by IL-17A, and to a lesser extent by IL-17F, but the magnitude of responses was modest. As expected, responses were augmented by the combination of IL-17A or IL-17F with TNF-α. Interestingly, responses of a few of the tested genes, such as IL8, CCL20, iNOS, and CfB, were augmented by the combination of IL-17A with staphylococcal lipoteichoic acid or muramyl dipeptide, bacterial agonists of the innate immune system. This can be interpreted as indicating that IL-17A and IL-17F are tailored to exert their full potential in a septic environment. MEC responses were characterized by the expression of chemokines targeting not only neutrophils (CXCL3 and CXCL8) but also mononuclear leucocytes (CCL2, CCL20). Production of IL-6 was low and the inflammatory cytokines TNF-α and IL-1β were expressed (mRNA) but proteins were not secreted. Altogether, our results suggest that IL-17A and IL-17F have a potential to modulate the mammary gland immune response to mastitis-causing pathogens.

Platelet-activating factor induces Th17 cell differentiation

Th17 cells have been implicated in a number of inflammatory and autoimmune diseases. The phospholipid mediator platelet-activating factor (PAF) is found in increased concentrations in inflammatory lesions and has been shown to induce IL-6 production. We investigated whether PAF could affect the development of Th17 cells. Picomolar concentrations of PAF induced IL-23, IL-6, and IL-1β expression in monocyte-derived Langerhans cells (LCs) and in keratinocytes. Moreover, when LC were pretreated with PAF and then cocultured with anti-CD3- and anti-CD28-activated T cells, the latter developed a Th17 phenotype, with a significant increase in the expression of the transcriptional regulator RORγt and enhanced expression of IL-17, IL-21, and IL-22. PAF-induced Th17 development was prevented by the PAF receptor antagonist WEB2086 and by neutralizing antibodies to IL-23 and IL-6R. This may constitute a previously unknown stimulus for the development and persistence of inflammatory processes that could be amenable to pharmacologic intervention.

Reduced expression of transforming growth factor-β1 and correlated elevation of interleukin-17 and interferon-γ in pediatric patients with chronic primary immune thrombocytopenia (ITP)

BACKGROUND

Dysregulated T helper (Th) cells are considered important in the pathophysiology of chronic primary immune thrombocytopenia (ITP). The present study investigated whether levels of Th cytokines in pediatric patients with chronic ITP were different compared with healthy controls.

PROCEDURES

Fifty-seven pediatric patients with chronic ITP and 28 healthy controls were enrolled. Patients were divided into three groups based on their platelet counts at the time of the study: (i) active disease <50 × 10(9) /l (n = 23), (ii) stable disease 50-150 × 10(9) /l (n = 23), and (iii) in remission >150 × 10(9) /l (n = 11). Plasma concentration of Th1 [interferon gamma (INF-γ), interleukin 2 (IL-2)], Th2 (IL-4, IL-10), Th3 [transforming growth factor-β1 (TGF-β1)], and Th17 (IL-17) cytokines were investigated by enzyme-linked immunosorbent assay.

RESULTS

IFN-γ was increased in patients with active (P < 0.001) and stable disease (P = 0.026) when compared with controls. The IL-17 level was significantly higher in all of the 3 patient groups. In addition, there was a positive correlation between IL-17 and IFN-γ levels in chronic ITP patients (r = 0.640, P < 0.001). Reduced TGF-β1 expression was observed in patients with active (P < 0.001) and stable disease (P = 0.001) in comparison with controls. Moreover, TGF-β1 level in patients was positively correlated with the platelet count (r = 0.355, P = 0.007).

CONCLUSIONS

Elevation of IL-17 and IFN-γ may be an important dysregulation of cellular immunity in pediatric patients with chronic ITP. The disease activity is associated with reduced production of TGF-β1.

IL-17 receptor and its functional significance in psoriatic arthritis

To delineate the functional significance of IL-17 Receptor (IL-17RA) and characterize the IL-17 producing T cell (Th17) subpopulation in psoriatic arthritis (PsA). Mononuclear cells from blood and synovial fluid (SF) were obtained from PsA (n=20), rheumatoid arthritis (RA, n=20) and osteoarthritis (OA, n=20) patients. Synoviocytes (FLS) were isolated from the synovium of RA (n=5), PsA (n=5) and OA (n=5) patients. IL-17RA expression in FLS was identified by western blotting (WB) and flowcytometry. T lymphocytes derived from the SF of these patients were studied to identify and phenotype the Th17 cells. The functional significance of IL-17RA was determined by evaluating its regulatory role on the production of proinflammatory cytokines and endopeptidase. IL-17RA expression was found to be significantly higher in FLS of RA (15.7%±4.9) and PsA (4.5%±0.9) in comparison to OA (1.14%±0.9). Western blot analyses showed that the relative intensity (RI) of IL-17RA protein was higher in RA and PsA compared to OA (Fisher exact, P<0.01). A significant enrichment of IL-17-producing CD4+ T cells (7.9%±2.8) was observed in the SF of PsA patients compared to that of OA patients (P<.001). Compared to OA-FLS, recombinant IL-17 induced higher levels of IL-6, IL-8, and MMP-3 production in PsA-FLS. Blockage of IL-17RA with an anti-IL-17RA antibody inhibited the production of IL-6, IL-8, and MMP-3. This is the first report to demonstrate the functional significance of IL-17RA in PsA. Results of this study support the hypothesis that IL-17RA blocking antibodies have the potential to be a therapeutic option for psoriatic arthritis.

Induction of regulatory Tr1 cells and inhibition of T(H)17 cells by IL-27

Accumulating evidence indicates that IL-27, a member of the IL-12 family of cytokines, alleviates the severity of autoimmune diseases in both mice and men. The IL-27-induced activation of signal transducer and activator of transcription (Stat)1 and Stat3 promotes the generation of IL-10- producing type 1 regulatory T (Tr1) cells that inhibit effector T cells. In addition, IL-27 also suppresses the development of pathogenic IL-17-producing CD4(+) T cells (T(H)17) cells suggesting that pharmacological manipulations of IL-27 signaling pathway could be exploited therapeutically in regulating tissue inflammation. Here, we review how IL-27 controls inflammation through the regulation of Tr1 and T(H)17 responses.

CD4+ T cell depletion changes the cytokine environment from a TH1/TH2 response to a TC17-like response in a murine model of atopic dermatitis

Atopic dermatitis (AD) is a common inflammatory skin disease often associated with co-morbidities including allergic hypersensitivity. We have studied induced AD-like disease in NC/Nga mice using the hapten FITC. Following FITC-treatment the NC/Nga mice develop AD-like skin lesions in regard to the histopathological and immunological changes. Consistent with AD in humans the number of CD4(+) T cells within the blood and draining lymph nodes increases considerably. To evaluate the contribution of T(H) cells on disease development we examined the effect of CD4 depletion. Following CD4 depletion the mice still develop AD-like skin lesions characterized by e.g. increased epidermal proliferation, hyperkeratosis and cellular infiltrate, however, the underlying immunological mechanisms change. CD4 depletion results in increased IL-17A and IL-22 production, which traditionally are associated with T(H)17 cells. Using confocal microscopy, we demonstrate that epidermal CD8(+) cells are positive for IL-17A, indicating that these cells are T(C)17 cells, the cytotoxic T cell counterpart to T(H)17 cells. In conclusion, we show that NC/Nga mice develop AD-like disease following CD4 depletion. This is mirrored by an increased production of IL-17A, which we suggest are produced by T(C)17 cells. These findings support that CD8(+) T cells can play a role in AD.

Clinical and immunological responses in ocular demodecosis

The purpose of this study was to investigate clinical and immunological responses to Demodex on the ocular surface. Thirteen eyes in 10 patients with Demodex blepharitis and chronic ocular surface disorders were included in this study and treated by lid scrubbing with tea tree oil for the eradication of Demodex. We evaluated ocular surface manifestations and Demodex counts, and analyzed IL-1β, IL-5, IL-7, IL-12, IL-13, IL-17, granulocyte colony-stimulating factor, and macrophage inflammatory protein-1β in tear samples before and after the treatment. All patients exhibited ocular surface manifestations including corneal nodular opacity, peripheral corneal vascularization, refractory corneal erosion and infiltration, or chronic conjunctival inflammatory signs before treatment. After treatment, Demodex was nearly eradicated, tear concentrations of IL-1β and IL-17 were significantly reduced and substantial clinical improvement was observed in all patients. In conclusion, we believe that Demodex plays an aggravating role in inflammatory ocular surface disorders.

Evolving insights in the pathogenesis and therapy of cutaneous T-cell lymphoma (mycosis fungoides and Sezary syndrome)

Cutaneous T-cell lymphomas (CTCL) are a heterogeneous group of malignancies derived from skin-homing T cells. The most common forms of CTCL are Mycosis Fungoides (MF) and Sezary Syndrome (SS). Accurate diagnosis remains a challenge due to the heterogeneity of presentation and the lack of highly characteristic immunophenotypical and genetic markers. Over the past decade molecular studies have improved our understanding of the biology of CTCL. The identification of gene expression differences between normal and malignant T-cells has led to promising new diagnostic and prognostic biomarkers that now need validation to be incorporated into clinical practice. These biomarkers may also provide insight into the mechanism of development of CTCL. Additionally, treatment options have expanded with the approval of new agents, such as histone deacetylase inhibitors. A better understanding of the cell biology, immunology and genetics underlying the development and progression of CTCL will allow the design of more rational treatment strategies for these malignancies. This review summarizes the clinical epidemiology, staging and natural history of MF and SS; discusses the immunopathogenesis of MF and the functional role of the malignant T-cells; and reviews the latest advances in MF and SS treatment.

IL-17A upregulates keratin 17 expression in keratinocytes through STAT1- and STAT3-dependent mechanisms

Psoriasis, an immunological skin disease, is characterized by epidermal hyperproliferation, chronic inflammation, and an accumulation of infiltrating T cells. IL-17A is a key cytokine that has a critical role in the pathogenesis of psoriasis. Keratin 17 (K17) is strongly expressed in psoriatic lesions but not in normal skin. Thus, K17 expression is regarded as a hallmark of psoriasis. We previously reported that the K17/T cells/cytokine autoimmune loop was involved in psoriasis. However, the relationship between IL-17A and K17 has yet to be determined. In the present study, IL-17A-induced K17 expression was confirmed in cultured keratinocytes in both mRNA and protein levels. In addition, increased K17 expression was found in the epidermis of IL-17A-injected mouse skin. The regulatory mechanism of K17 expression was further investigated. We found that both the signal transducer and activator of transcription (STAT) 1 and STAT3 pathways were involved in the upregulation of K17 expression induced by IL-17A, and that such regulation could be partially suppressed by STAT1 or STAT3 small interfering RNA and inhibitor. Our data suggest that IL-17A can upregulate K17 expression in keratinocytes in a dose-dependent manner through STAT1- and STAT3-dependent mechanisms. The results indicate that IL-17A might be an important cytokine in the K17/T cells/cytokine autoimmune loop associated with psoriasis.

IL-17-expressing cells as a potential therapeutic target for treatment of immunological disorders

IL-17 is a multifunctional cytokine produced by activated CD4+ and CD8+ lymphocytes as well as stimulated unconventional Tγδ and natural killer T cells. IL-17 induces expression of chemokines, proinflammatory cytokines and metalloproteinases, thereby stimulating the inflammation and chemotaxis of neutrophils. Elevation of proinflammatory cytokines is associated with asthma and autoimmune disorders, such as multiple sclerosis, rheumatoid arthritis and psoriasis. Although the role of IL-17 in these disorders is not always easy to define, extensive research has demonstrated an aggravating influence of IL-17 in some animal models. Thus, the development of therapeutics to reduce IL-17 levels is a promising strategy for ameliorating inflammatory diseases. This review briefly summarizes recent knowledge about stimulants and intracellular signaling pathways that induce development and maturation of IL-17-expressing cells. Its positive and negative roles on disease progression and its importance in vaccine-induced memory are also discussed. Finally, recent literature describing potential therapeutic approaches for targeting IL-17 is presented.

The interleukin-17 cytokine family: critical players in host defence and inflammatory diseases

The interleukin-17 (IL-17) cytokines, IL-17A to IL-17F, are emerging as critical players in host defence responses and inflammatory diseases. Substantial data support the role of these proteins in innate and adaptive immunity. Of these family members, IL-17A, IL-17F and IL-17E have been the best studied. Both IL-17A and IL-17F contribute to the host response to extracellular bacteria and fungi, and IL-17E has been shown to play a role in parasitic infections. In addition, numerous pre-clinical and clinical studies link these proteins to the pathogenesis of inflammatory diseases, and a number of therapeutic programmes targeting these family members are in clinical development. This review will highlight the cellular sources, receptors/target cells, and role in inflammation of these and the less-characterized family members, IL-17B, IL-17C and IL-17D.

From the bench to the clinic: New aspects on immunoregulation by vitamin D analogs

The skin is a vital organ that plays a crucial role in defending us from pathogens. Multiple players from the innate and adaptive immune system are involved, such as neutrophils, dendritic cells, lymphocytes and antimicrobial peptides. Chronic inflammatory skin diseases can be mediated by inflammatory T cells and their interactions with other cells in the skin. Vitamin D is generated in the skin upon sun exposure and has a variety of effects. Vitamin D and its analogs have been used with success in treating mild to moderate T cell-mediated skin diseases, but how they mediate the beneficial effects is not well understood. In the recent years, emerging evidence is rising that vitamin D analogs and its modulation on the immune system plays a major role. It has been shown that vitamin D analogs can induce the generation of regulatory T cells, which are able to suppress proliferation and alter the function of inflammatory T cells. This may help explain the therapeutic effects that are observed and at the same time give hope that in combination with other therapy or used alone, vitamin D analogs may be helpful when treating more severe forms of the diseases.

Foxp3+ regulatory T cells of psoriasis patients easily differentiate into IL-17A-producing cells and are found in lesional skin

Psoriasis is an autoimmune-related chronic inflammatory skin disease that is strongly associated with IL-23 and T helper-17 (Th17) effector cytokines. In addition, CD4+CD25(high) regulatory T-cell (Treg) function appeared to be impaired in psoriasis. CD4+CD25(high)Foxp3+ Tregs are typically considered inhibitors of autoimmune responses. However, under proinflammatory conditions, Tregs can differentiate into inflammation-associated Th17 cells--a paradigm shift, with as yet largely unknown consequences for human disease initiation or progression. Th17 cells are highly proinflammatory T cells that are characterized by IL-17A and IL-22 production and expression of the transcription factor retinoic acid-related orphan receptor γt (RORγt). We here show that Tregs of patients with severe psoriasis, as compared with those of healthy controls, have an enhanced propensity to differentiate into IL-17A-producing cells on ex vivo stimulation. This enhanced Treg differentiation was linked to unexpectedly high RORγt levels and enhanced loss of Foxp3. Notably, IL-23 boosted this Treg differentiation process particularly in patients with psoriasis but less so in controls. IL-23 further reduced Foxp3 expression while leaving the high RORγt levels unaffected. The histone/protein deacetylase inhibitor, Trichostatin-A, prevented Th17 differentiation of Tregs in psoriasis patients. Importantly, IL-17A+/Foxp3+/CD4+ triple-positive cells were present in skin lesions of patients with severe psoriasis. These data stress the clinical relevance of Treg differentiation for the perpetuation of chronic inflammatory disease and may pave novel ways for immunotherapy.

Platelet-activating factor blockade inhibits the T-helper type 17 cell pathway and suppresses psoriasis-like skin disease in K5.hTGF-β1 transgenic mice

Platelet-activating factor (PAF), a potent biolipid mediator, is involved in a variety of cellular transduction pathways and plays a prominent role in inducing inflammation in different organs. We used K5.hTGF-β1 transgenic mice, which exhibit an inflammatory skin disorder and molecular and cytokine abnormalities with strong similarities to human psoriasis, to study the pathogenic role of PAF. We found that injecting PAF into the skin of transgenic mice led to inflammation and accelerated manifestation of the psoriatic phenotype by a local effect. In contrast, injecting mice with PAF receptor antagonist PCA-4248 lowered the PAF level (most likely by depressing an autocrine loop) and neutrophil, CD68(+) cell (monocyte/macrophage), and CD3(+) T-cell accumulation in the skin and blocked progression of the psoriasis-like phenotype. This effect of PAF blockade was specific and similar to that of psoralen-UV-A and was paralleled by a decrease in abnormally elevated mRNA and/or protein levels of T-helper type 17 cell-related cytokines IL-17A, IL-17F, IL-23, IL-12A, and IL-6 and its transcription factor signal transducer and activator of transcription 3. In contrast, PCA-4248 treatment up-regulated mRNA levels of cyclooxygenase-2 and IL-10 in dorsal skin and release of IL-10 in serum and skin. Interfering with PAF may offer the opportunity to develop novel therapeutic strategies for inflammatory psoriasis and associated comorbidities, including metabolic syndrome and atherosclerosis, in which the IL-17 axis may be involved.

Interleukin-17A differentially modulates BCG induction of cytokine production in human blood macrophages

The pathogenesis of Mtb depends in part on cytokine cross-regulation between macrophages and T cells in host immunity. Th17 cells produce IL-17A to induce granuloma formation and to restrict mycobacterial dissemination. IL-17A also mediates cytokine responses induced by proinflammatory cytokines such as TNF-α. Our previous results showed that BCG induces IL-6, IL-10, and TNF-α via activity of protein kinases, including dsRNA-activated serine/threonine protein kinase and glycogen synthase kinase-3 in primary human monocytes. Therefore, we investigated whether IL-17A, upon its induction by BCG, plays an additional role to aid the production of downstream proinflammatory cytokines in macrophages. Here, we showed that IL-17A enhanced IL-6 mRNA and protein levels inducible by BCG in a time- and dose-dependent manner, whereas it had no effect on IL-10 and TNF-α production. We also demonstrated that IL-17A activated the phosphorylation of ERK1/2 triggered by BCG. With the use of a specific chemical inhibitor of a MAPK/ERK-activating kinase (MEK1/2), we confirmed the correlation between the enhanced ERK1/2 activation and augmented IL-6 production. Additionally, we revealed that IL-17A acts in concert with BCG-induced TNF-α to enhance the level of IL-6 synthesis. Taken together, our results suggest a significant role of IL-17A to serve as a modulator of cytokine expression in innate immune response during mycobacterial infection.

Murine insulin growth factor-like (IGFL) and human IGFL1 proteins are induced in inflammatory skin conditions and bind to a novel tumor necrosis factor receptor family member, IGFLR1

Psoriasis is a human skin condition characterized by epidermal hyperproliferation and infiltration of multiple leukocyte populations. In characterizing a novel insulin growth factor (IGF)-like (IGFL) gene in mice (mIGFL), we found transcripts of this gene to be most highly expressed in skin with enhanced expression in models of skin wounding and psoriatic-like inflammation. A possible functional ortholog in humans, IGFL1, was uniquely and significantly induced in psoriatic skin samples. In vitro IGFL1 expression was up-regulated in cultured primary keratinocytes stimulated with tumor necrosis factor α but not by other psoriasis-associated cytokines. Finally, using a secreted and transmembrane protein library, we discovered high affinity interactions between human IGFL1 and mIGFL and the TMEM149 ectodomain. TMEM149 (renamed here as IGFLR1) is an uncharacterized gene with structural similarity to the tumor necrosis factor receptor family. Our studies demonstrate that IGFLR1 is expressed primarily on the surface of mouse T cells. The connection between mIGFL and IGFLR1 receptor suggests mIGFL may influence T cell biology within inflammatory skin conditions.

IL-21 promotes skin recruitment of CD4(+) cells and drives IFN-γ-dependent epidermal hyperplasia

Psoriasis is a chronic inflammatory disorder of the skin characterized by epidermal hyperplasia and infiltration of leukocytes into the dermis and epidermis. T cell-derived cytokines, such as IFN-γ and IL-17A, play a major role in the psoriasis-associated epidermal hyperplasia, even though factors/mechanisms that regulate the production of these cytokines are not fully understood. We have recently shown that IL-21 is synthesized in excess in psoriatic skin lesions and causes epidermal hyperplasia when injected intradermally in mice. Moreover, in the human psoriasis SCID mouse model, neutralization of IL-21 reduces both skin thickening and expression of inflammatory molecules, thus supporting the pathogenic role of IL-21 in psoriasis. However, the basic mechanism by which IL-21 promotes skin pathology remains unknown. In this study, we show that CD4(+) cells accumulate early in the dermis of IL-21-treated mice and mediate the development of epidermal hyperplasia. Indeed, IL-21 fails to induce skin damage in RAG1-deficient mice and CD4(+) cell-depleted wild-type mice. The majority of CD4(+) cells infiltrating the dermis of IL-21-treated mice express IFN-γ and, to a lesser extent, IL-17A. Studies in cytokine knockout mice show that IFN-γ, but not IL-17A, is necessary for IL-21-induced epidermal hyperplasia. Finally, we demonstrate that IFN-γ-producing CD4(+) cells infiltrating the human psoriatic plaque express IL-21R, and abrogation of IL-21 signals reduces IFN-γ expression in cultures of psoriatic CD4(+) cells. Data indicate that IL-21 induces an IFN-γ-dependent pathogenic response in vivo, thus contributing to elucidate a mechanism by which IL-21 sustains skin-damaging inflammation.

Structure and function of interleukin-17 family cytokines

The recently identified interleukin-17 (IL-17) cytokines family, which comprises six members in mammals (IL-17A-F), plays essential roles in the host immunity against infectious diseases and chronic inflammatory diseases. The three-dimensional structures containing IL-17A or IL-17F have become available and revealed the unique structural features of IL-17s as well as their receptors. Molecular modeling in this review shows that IL-17s may adopt a "cysteine knot" fold commonly seen in nerve growth factor (NGF) and other neurotrophins. Further modeling analysis unmasks a signature interaction feature of the IL-17F/IL-17RA complex, where a small loop of IL-17RA slots into the deep groove of the interface of IL-17F homodimer. This is quite different from the interaction between the best known four-helix cytokines and their cognate receptors. On the other hand, structure of IL-17A and its monoclonal antibody (CAT-2200) shows that, albeit that the antigenic epitope of IL-17A resides outside of the IL-17A homodimer interface, its physical proximity to the receptor binding groove may explain that antibody blockage would be achieved by interfering with the ligand-receptor interaction. This review is to summarize the advance in understanding the structure and function of IL-17 family cytokines, focusing mainly on IL-17A, IL-17F and IL-17E, in the hope of gaining better knowledge of immunotherapeutic strategies against various inflammatory diseases.

Role of TH-17 cells in rheumatic and other autoimmune diseases

In humans multiple pathways can induce TH-17 cell differentiation, whereas in mice this process is mostly modulated by IL-6 and TGF-β. IL-17 produced by TH-17 cells has been associated with a number of inflammatory autoimmune diseases including psoriasis, systemic lupus erythematosus, inflammatory bowel disease, multiple sclerosis, and rheumatoid arthritis. In this review, we have primarily focused on the role of TH-17 cells/IL-17 in the pathogenesis of rheumatoid arthritis and experimental arthritis. The potential role of TH-17 cells in rheumatoid arthritis progression has been demonstrated by correlating the percent TH-17 cells or levels of IL-17 with rheumatoid arthritis disease activity score and C-reactive protein levels. Further, previous studies suggest that IL-17 mediated vascularization may lay the foundation for rheumatoid arthritis joint neutrophil and monocyte recruitment as well as cartilage and bone destruction. The profound role of IL-17 in the pathogenesis of experimental arthritis may be due to its synergistic effect with TNF-α and IL-1β. Although the initial clinical trial employing anti-IL-17 antibody has been promising for rheumatoid arthritis, future studies in humans will shed more light on how anti-IL-17 therapy affects rheumatoid arthritis and other autoimmune disease pathogenesis.

Role of endothelial chemokines and their receptors during inflammation

Chemokines are a large group of small cytokines known for their chemotactic ability to regulate the recruitment of leukocytes to sites of inflammation. This occurs through the binding of chemokines to their receptors located on the leukocyte that results in cellular changes such as actin rearrangement and cell shape, which allow for the migration of the leukocyte. In addition to regulating leukocyte function, it is now becoming apparent that other nonhematopoetic cells, such as smooth muscle cells and endothelial cells, can also be regulated by chemokines. Studies within the past 10 years has demonstrated the presence of various chemokine receptors on endothelial cells as well as the ability of chemokines to activate these receptors resulting in various cellular responses including migration, proliferation, and cellular activation. The purpose of this review is to highlight the research that has been done to date demonstrating the important role for chemokines in regulating endothelial function during various inflammatory conditions associated with angiogenesis, homeostasis, and leukocyte transmigration. This review will focus specifically on the role of the endothelium in mediating chemokine effects associated with wound healing, atherosclerosis, and autoimmune diseases, conditions where leukocyte recruitment and angiogenesis play a major role. Recent progress in the development and implementation of therapeutics agents against these small molecules, or their receptors, will also be addressed.

T-helper 17 cell: A distinctive cell in liver diseases

T-helper (Th)17 cells, a new population of effector CD4(+) T cells, are characterized by the secretion of interleukin (IL)-17. It has been demonstrated that Th17 cells are distinct from Th1 and Th2 cells; they play important roles in the pathogenesis of numerous inflammatory and autoimmune diseases; and are closely related to host defense, tumorigenesis and transplant rejection. Moreover, it has been found that these cells have a close and intricate connection with the regulatory T cells, which play an important role in maintaining self-tolerance and down-tuning immune responses. In the present review, we find that they are significantly elevated in various kinds of liver diseases including liver autoimmunity and inflammatory diseases, alcoholic liver disease and hepatocellular carcinoma.

Induction of tolerogenic lung CD4+ T cells by local treatment with a pSTAT-3 and pSTAT-5 inhibitor ameliorated experimental allergic asthma

Signal transducer and activator of transcription (STAT)-3 inhibitors play an important role in regulating immune responses. Galiellalactone (GL) is a fungal secondary metabolite known to interfere with the binding of phosphorylated signal transducer and activator of transcription (pSTAT)-3 as well of pSTAT-6 dimers to their target DNA in vitro. Intra nasal delivery of 50 μg GL into the lung of naive Balb/c mice induced FoxP3 expression locally and IL-10 production and IL-12p40 in RNA expression in the airways in vivo. In a murine model of allergic asthma, GL significantly suppressed the cardinal features of asthma, such as airway hyperresponsiveness, eosinophilia and mucus production, after sensitization and subsequent challenge with ovalbumin (OVA). These changes resulted in induction of IL-12p70 and IL-10 production by lung CD11c(+) dendritic cells (DCs) accompanied by an increase of IL-3 receptor α chain and indoleamine-2,3-dioxygenase expression in these cells. Furthermore, GL inhibited IL-4 production in T-bet-deficient CD4(+) T cells and down-regulated the suppressor of cytokine signaling-3 (SOCS-3), also in the absence of STAT-3 in T cells, in the lung in a murine model of asthma. In addition, we found reduced amounts of pSTAT-5 in the lung of GL-treated mice that correlated with decreased release of IL-2 by lung OVA-specific CD4(+) T cells after treatment with GL in vitro also in the absence of T-bet. Thus, GL treatment in vivo and in vitro emerges as a novel therapeutic approach for allergic asthma by modulating lung DC phenotype and function resulting in a protective response via CD4(+)FoxP3(+) regulatory T cells locally.

1α,25-Dihydroxyvitamin D3 and all-trans retinoic acid synergistically inhibit the differentiation and expansion of Th17 cells

1α,25-Dihydroxyvitamin D(3) (1,25D3), the active form of vitamin D(3), is an immunoregulatory hormone with beneficial effects on Th1 cell-mediated inflammatory diseases. Although IL-17-producing CD4(+) T helper (Th17) cells have been recently identified as novel effector cells, the immunomodulating effects of 1,25D3 on Th17 cells have not been well defined. We confirmed here that 1,25D3 inhibited the generation of Th17 cells in vitro. Interestingly, 1,25D3 synergistically suppressed the generation of Th17 cells by the combination with all-trans retinoic acid (ATRA). 1,25D3 and ATRA suppressed the development of allergen-induced contact hypersensitivity (CHS) in a mouse ear swelling model. In addition, we found that 1,25D3 and ATRA significantly inhibited the development of human Th17 cells from both naïve and memory human CD4(+) T cells. 1,25D3 and ATRA effectively suppressed mRNA expressions of IL-1R1, IL-21R, IL-23R, RORC, and AHR in human T cells. ATRA further suppressed IL-6R, whereas 1,25D3 did not. Finally, we found that 1,25D3 and ATRA remarkably blocked IL-22 as well as IL-17 mRNA expression in human memory CD4(+) T cells. Thus, we initially reveal that 1,25D3 and ATRA have synergistic effects on the generation of Th17 cells, suggesting that the combination with ATRA would provide a promising novel therapy for Th17 cell-related immune diseases including skin inflammation.

Overrepresentation of IL-17A and IL-22 producing CD8 T cells in lesional skin suggests their involvement in the pathogenesis of psoriasis

BACKGROUND

Although recent studies indicate a crucial role for IL-17A and IL-22 producing T cells in the pathogenesis of psoriasis, limited information is available on their frequency and heterogeneity and their distribution in skin in situ.

METHODOLOGY/PRINCIPAL FINDINGS

By spectral imaging analysis of double-stained skin sections we demonstrated that IL-17 was mainly expressed by mast cells and neutrophils and IL-22 by macrophages and dendritic cells. Only an occasional IL-17(pos), but no IL-22(pos) T cell could be detected in psoriatic skin, whereas neither of these cytokines was expressed by T cells in normal skin. However, examination of in vitro-activated T cells by flow cytometry revealed that substantial percentages of skin-derived CD4 and CD8 T cells were able to produce IL-17A alone or together with IL-22 (i.e. Th17 and Tc17, respectively) or to produce IL-22 in absence of IL-17A and IFN-γ (i.e. Th22 and Tc22, respectively). Remarkably, a significant proportional rise in Tc17 and Tc22 cells, but not in Th17 and Th22 cells, was found in T cells isolated from psoriatic versus normal skin. Interestingly, we found IL-22 single-producers in many skin-derived IL-17A(pos) CD4 and CD8 T cell clones, suggesting that in vivo IL-22 single-producers may arise from IL-17A(pos) T cells as well.

CONCLUSIONS/SIGNIFICANCE

The increased presence of Tc17 and Tc22 cells in lesional psoriatic skin suggests that these types of CD8 T cells play a significant role in the pathogenesis of psoriasis. As part of the skin-derived IL-17A(pos) CD4 and CD8 T clones developed into IL-22 single-producers, this demonstrates plasticity in their cytokine production profile and suggests a developmental relationship between Th17 and Th22 cells and between Tc17 and Tc22 cells.

Effector and regulatory T-cell subsets in autoimmunity and tissue inflammation

Many autoimmune diseases are driven by self-reactive T helper cells. Until recently, organ-specific autoimmune diseases were primarily associated with Th1 cells but not Th2 cells. However, the discovery of a number of new effector T-cell subsets, like Th17 and Th9 cells, and regulatory T cells, like Tregs and Tr1 cells, has changed the way we view and understand autoimmunity at cellular and molecular levels. In recent years, IL-17-producing Th17 cells have emerged as major players in autoimmunity. The complicated relationship between Th1 and Th17 cells, as well as the intricate balance between Tregs and Th17 cells, provides a basis for understanding the immunological mechanisms that induce and regulate autoimmunity. Here, we give an overview of the interplay between different effector T-cell subsets and regulatory T-cell subsets, and how they contribute to the development of autoimmunity and tissue inflammation.