Psoriasis is characterized by accumulation of immunostimulatory and Th1/Th17 cell-polarizing myeloid dendritic cells

CCR6 as a possible therapeutic target in psoriasis

IMPORTANCE OF THE FIELD

Psoriasis is a common, chronic autoimmune disease of the skin. Despite a number of effective treatments, new therapies are needed with enhanced efficacy, safety and convenience. Chemokine receptors are GPCRs that control leukocyte trafficking, and like other GPCRs, are good potential drug targets. The chemokine receptor CCR6 is expressed on the T(H)17 subset of CD4(+) T cells, which produces IL-17A/F, IL-22, TNF-alpha and other cytokines, and which has been implicated in the pathogenesis of psoriasis. CCR6 and its ligand, CCL20/MIP-3alpha, are highly expressed in psoriatic skin and CCR6 is necessary for the pathology induced in a mouse model of psoriasis-like inflammation.

AREAS COVERED IN THIS REVIEW

This review summarizes the evidence for the importance of the IL-23/T(H)17 axis, and in particular CCR6 and CCL20 in psoriasis, dating from 2000 to the present, and discusses the possibility of inhibiting CCR6 as a treatment for the disease.

WHAT THE READER WILL GAIN

The review informs the reader of the current thinking on the mechanisms of inflammation in psoriasis and the possible roles for CCR6 (and CCL20) in disease pathogenesis.

TAKE HOME MESSAGE

We conclude that CCR6 should be investigated as a potential therapeutic target in psoriasis.

Tolerogenic dendritic cells in autoimmune diseases: crucial players in induction and prevention of autoimmunity

The immune system has evolved to coordinate responses against numerous invading pathogens and simultaneously remain silent facing self-antigens and those derived from commensal organisms. But, if both processes are not maintained in strict balance, a potential threat can emerge due to the risk of chronic inflammation and/or autoimmunity development. Therefore, there is a negative immune regulation where tolerogenic dendritic cells (tDCs) participate actively. Under steady-state conditions, tDC are notably involved in the elimination of autoreactive T cells at the thymus, and in the control of T cells specific to self and harmless antigens in the periphery. But in the presence of foreign antigens in an inflammatory milieu, dendritic cells (DCs) mature and induce T cells activation and their migration to B cell areas to assist in antibody production. Additionally, there are other factors such as infections, anti tumoral immune responses, trauma-mediated disruption, etc. that may induce alterations in the balance between tolerogenic and immunogenic functions of DCs and instigate the development of autoimmune diseases (ADs). Therefore, in recent years, DCs have emerged as therapeutic targets to control of ADs. Diverse strategies in vitro and/or in animal models of ADs have explored the tolerogenic functions of DCs and demonstrated their feasibility to prevent or control an autoimmune process, but still leaving a void in their application in clinical assays. The purpose of this paper is to give a general overview of the current literature on the significance of tDCs in tolerance maintenance to self and innocuous antigens, the most relevant alterations involved in the pathophysiology of ADs, the cellular and molecular mechanisms involved in their tolerogenic function and the current strategies used to exploit their tolerogenic potential.

The relation of interleukin 17 (IL-17) and IL-23 to Th1/Th2 cytokines and disease activity in systemic lupus erythematosus

OBJECTIVE

Interleukin 17 (IL-17) was recently linked to pathogenesis of systemic lupus erythematosus (SLE), but its relation to disease activity has not been well characterized. We examined the relation between serum levels of Th17 (IL-17, IL-23), Th1 (IL-12, interferon-γ), Th2 (IL-10, IL-6, IL-4) cytokines and disease activity in patients with SLE.

METHODS

Serum cytokines were measured by enzyme linked immunosorbent assays. Disease activity was determined by SLE disease activity index (SLEDAI), anti-dsDNA antibody, and C3 and C4 levels.

RESULTS

Serum levels of IL-17 (p < 0.001), IL-6 (p = 0.006) and IL-10 (p < 0.001) were higher in SLE patients (n = 70) compared to healthy controls (n = 36). Higher serum IL-23 level was found in patients with active disease with cutaneous manifestations (p = 0.004) and serositis (p = 0.04) compared to those without. Serum IL-17 level above the detection limit was more frequently found in patients who had active lupus nephritis (11/23, 47.8%) (p = 0.002), nonrenal active disease (9/15, 60%) (p = 0.001), and inactive lupus (21/32, 65.6%) (p < 0.001) compared to healthy controls (0%). Serum IL-17 levels were otherwise comparable between these 3 groups of patients and were not related to SLEDAI, glomerular filtration rate, activity or chronicity score and ISN/RPS criteria class among patients with active lupus nephritis. There was no significant correlation between serum IL-17/IL-23 and Th1 or Th2 cytokine levels.

CONCLUSION

SLE patients had higher serum IL-17 levels than healthy controls. Elevated serum IL-23 was found in patients with inflammatory manifestations including cutaneous involvement and serositis. The lack of correlation between Th17, Th1, and Th2 cytokines suggested independent regulatory mechanisms for these cytokines.

Role of immune-regulatory cells in skin pathology

The skin harbors a complex and unique immune system that protects against various pathologies, such as infection and cancer. Although many of the mechanisms of immune activation in the skin have been investigated, it is likewise important to uncover the immune-regulatory components that limit effective immunity or prevent autoimmunity. Several cell populations are involved in this immune-regulatory function, including CD4+ T cells that coexpress the transcription factor Foxp3, known as Tregs, and cells with immune-regulatory function known as myeloid-derived suppressor cells (MDSCs). This review focuses on the role that immune-regulatory cells, such as MDSCs and Tregs, play in cutaneous pathology, such as malignancy, psoriasis, dermatitis, burn wounds, and transplantation. Although their depletion may serve to augment immunity, expansion of these cells may be used to suppress excessive immune reactions. These cells are attractive, therapeutic targets for various conditions and thus, deserve further exploration.

Subcutaneous allergen immunotherapy restores human dendritic cell innate immune function

BACKGROUND

We recently reported that human blood dendritic cells from allergic subjects have impaired IFN-alpha production following toll-like receptor 9 (TLR9)-dependent innate immune stimulation. It is not known how subcutaneous allergen immunotherapy (SCIT) affects dendritic cell immune responses.

OBJECTIVE

The aim of this study is to determine how SCIT affects human dendritic cell function.

METHODS

Peripheral blood mononuclear cell (PBMC) and plasmacytoid dendritic cells (pDCs) were isolated from the blood of seven dust mite allergic subjects at baseline and upon reaching a standard SCIT maintenance dose that included dust mite and other aeroallergens. Cells were stimulated with various adaptive and innate immune receptor stimuli, or media alone for 20 h with secreted cytokine levels determined by ELISA. A portion of the cells were used to measure intracellular signalling proteins by flow cytometry. Humoral immune responses were measured from plasma.

RESULTS

SCIT resulted in a threefold increase in PBMC production of IFN-alpha in response to CpG at 100 nM (P=0.015) and at 500 nM (P=0.015), n=7. The predominant cell type known to produce IFN-alpha in response to CpG (CpG ODN-2216) and other TLR9 agonists is the pDC. As expected, a robust innate immune response from isolated pDCs was re-established among allergic subjects undergoing SCIT resulting in a fivefold increase in IFN-alpha production in response to CpG at 500 nM (P=0.046), n=7. In contrast, IL-6 production was unaffected by SCIT (P=0.468). Consistent with published reports, IgG4 blocking antibody increased 10-fold with SCIT (P=0.031), n=7. There was no significant increase in the frequency of pDCs or the expression of TLR9 that would account for the rise in IFN-alpha production.

CONCLUSIONS

Allergen immunotherapy increases dendritic cell TLR9-mediated innate immune function, which has previously been shown to be impaired at baseline in allergic subjects.

A subpopulation of CD163-positive macrophages is classically activated in psoriasis

Macrophages are important cells of the innate immune system, and their study is essential to gain greater understanding of the inflammatory nature of psoriasis. We used immunohistochemistry and double-label immunofluorescence to characterize CD163(+) macrophages in psoriasis. Dermal macrophages were increased in psoriasis compared with normal skin and were identified by CD163, RFD7, CD68, lysosomal-associated membrane protein 2 (LAMP2), stabilin-1, and macrophage receptor with collagenous structure (MARCO). CD163(+) macrophages expressed C-lectins CD206/macrophage mannose receptor and CD209/DC-SIGN, as well as costimulatory molecules CD86 and CD40. They did not express mature dendritic cell (DC) markers CD208/DC-lysosomal-associated membrane glycoprotein, CD205/DEC205, or CD83. Microarray analysis of in vitro-derived macrophages treated with IFN-γ showed that many of the genes upregulated in macrophages were found in psoriasis, including STAT1, CXCL9, Mx1, and HLA-DR. CD163(+) macrophages produced inflammatory molecules IL-23p19 and IL-12/23p40 as well as tumor necrosis factor (TNF) and inducible nitric oxide synthase (iNOS). These data show that CD163 is a superior marker of macrophages, and identifies a subpopulation of "classically activated" macrophages in psoriasis. We conclude that macrophages are likely to contribute to the pathogenic inflammation in psoriasis, a prototypical T helper 1 (Th1) and Th17 disease, by releasing key inflammatory products.

Effective narrow-band UVB radiation therapy suppresses the IL-23/IL-17 axis in normalized psoriasis plaques

Narrow-band UVB radiation (NB-UVB) therapy offers a well-established treatment modality for psoriasis. However, despite the common use of this form of treatment, the mechanism of action of NB-UVB is not well understood. We studied a group of 14 patients with moderate-to-severe psoriasis treated with carefully titrated and monitored NB-UVB for 6 weeks. Lesional plaques were classified as normalized (n=8) or nonresponsive (n=6) based on their histological improvement and normalization. We characterized lesional myeloid dendritic cells (DCs) and T cells and their inflammatory mediators using immunohistochemistry and real-time PCR. NB-UVB suppressed multiple parameters of the IL-23/IL-17 pathway in normalized plaques, but not in nonresponsive plaques. NB-UVB decreased the numbers of CD11c(+) DCs, specifically CD1c(-)CD11c(+) "inflammatory" DCs, and their products, IL-20, inducible nitric oxide synthase, IL-12/23p40, and IL-23p19. Furthermore, effective NB-UVB suppressed IL-17 and IL-22 mRNAs, which strongly correlated with lesion resolution. Therefore, in addition to its known role in suppressing IFN-γ production, NB-UVB radiation therapy can also target the IL-17 pathway to resolve psoriatic inflammation.JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article, please go to http://www.nature.com/jid/journalclub.

8-methoxypsoralen plus ultraviolet A therapy acts via inhibition of the IL-23/Th17 axis and induction of Foxp3+ regulatory T cells involving CTLA4 signaling in a psoriasis-like skin disorder

To elucidate the molecular action of 8-methoxypsoralen plus UVA (PUVA), a standard dermatological therapy, we used K5.hTGF-beta1 transgenic mice exhibiting a skin phenotype and cytokine abnormalities with strong similarities to human psoriasis. We observed that impaired function of CD4+CD25+ regulatory T cells (Tregs) and increased cytokine levels of the IL-23/Th17 pathway were responsible for the psoriatic phenotype in this mouse model. Treatment of K5.hTGF-beta1 transgenic mice with PUVA suppressed the IL-23/Th17 pathway, Th1 milieu, as well as transcription factors STAT3 and orphan nuclear receptor RORgammat. PUVA induced the Th2 pathway and IL-10-producing CD4+CD25+Foxp3+Tregs with disease-suppressive activity that was abolished by anti-CTLA4 mAb treatment. These findings were paralleled by macroscopic and microscopic clearance of the diseased murine skin. Anti-IL-17 mAb treatment also diminished the psoriatic phenotype of the mice. This indicated that both induced Tregs involving CTLA4 signaling and inhibition of the IL-23/Th17 axis are central for the therapeutic action of PUVA.

Identification of TNF-related apoptosis-inducing ligand and other molecules that distinguish inflammatory from resident dendritic cells in patients with psoriasis

BACKGROUND

Previous work has identified CD11c(+)CD1c(-) dendritic cells (DCs) as the major "inflammatory" dermal DC population in patients with psoriasis vulgaris and CD1c(+) DCs as the "resident" cutaneous DC population.

OBJECTIVE

We sought to further define molecular differences between these 2 myeloid dermal DC populations.

METHODS

Inflammatory and resident DCs were single-cell sorted from lesional skin biopsy specimens of patients with psoriasis, and the transcriptome of CD11c(+)CD1c(-) versus CD1c(+) DCs was determined. Results were confirmed with RT-PCR, flow cytometry, immunohistochemistry, and double-labeled immunofluorescence. Human keratinocytes were cultured for functional studies.

RESULTS

TNF-related apoptosis-inducing ligand (TRAIL), Toll-like receptors 1 and 2, S100A12/ENRAGE, CD32, and many other inflammatory products were differentially expressed in inflammatory DCs compared with resident DCs. Flow cytometry and immunofluorescence confirmed higher protein expression on CD1c(-) versus CD1c(+) DCs. TRAIL receptors, death receptor 4, and decoy receptor 2 were expressed in keratinocytes and dermal cells. In vitro culture of keratinocytes with TRAIL induced CCL20 chemokine.

CONCLUSIONS

CD11c(+)CD1c(-) inflammatory DCs in psoriatic lesional skin express a wide range of inflammatory molecules compared with skin-resident CD1c(+) DCs. Some molecules made by inflammatory DCs, including TRAIL, could have direct effects on keratinocytes or other skin cell types to promote disease pathogenesis.

Circulating Th17, Th22, and Th1 cells are increased in psoriasis

Th17, Th22, and Th1 cells are detected in psoriatic skin lesions and implicated in psoriasis pathogenesis, but inflammatory T cell numbers in blood, as well as the relative importance of each cell type, is unclear. Using 7-color flow cytometry, circulating Th17, Th22, and Th1 cells were quantified in 21 untreated psoriatics and 17 healthy individuals. CCR6 was the best cell surface marker for IL-17A+ cells when compared with IL-23R or CD161. CCR6+, IL-17A+, IL-22+, CCR6+IL-17A+, CCR6+IL-22+, CCR6+tumor necrosis factor-alpha+, IL-17A+IFN-gamma-, IL-17A+IL-22+IFN-gamma-, and IL-17A+IL-22-IFN-gamma- cells were increased in psoriatics (all values P<0.001), indicating elevations in circulating Th17 cells, using multiple criteria to define these cells. Th22 (IL-17A-IL-22+IFN-gamma-, P<0.05) and Th1 (IL-17A-IFN-gamma+, P<0.05) cells were also increased in psoriatics, but to a lesser extent. Inhibition of either NF-kappaB or STAT3 in vitro blocked cytokine production by both Th17 and Th1 cells. Circulating levels of Th17 and Th1 cells decreased in a subset of five psoriasis patients serially evaluated following induction therapy with infliximab. In summary, elevated numbers of circulating inflammatory T cells may contribute to cutaneous inflammation and systemic inflammatory disease that occurs in individuals with psoriasis.

Foxp3+ regulatory T cells and related cytokines differentially expressed in plaque vs. guttate psoriasis vulgaris

BACKGROUND

Differences in the number of Foxp3+ regulatory T cells (Tregs) in lesional skin and peripheral blood and their functioning in plaque vs. guttate psoriasis have not been reported.

OBJECTIVES

To investigate whether there is a differential expression of Foxp3+ Tregs and a differential regulation of inflammatory cytokines in plaque vs. guttate psoriasis vulgaris.

METHODS

The number and the percentage of Foxp3+ cells in different phases of skin lesions of patients with plaque and guttate psoriasis vulgaris were assessed by immunohistochemical staining. The expression of Foxp3 and interleukin (IL)-17 protein in CD4 populations was measured by flow cytometry. Inflammatory cytokine production by transforming growth factor-beta1-induced Foxp3+ Tregs was assessed in an in vitro study. The cytokines in supernatant and serum were determined by enzyme-linked immunosorbent assay.

RESULTS

The percentage of Foxp3+ CD3+ cells in the papillary layer was higher than in the reticular layer of dermis and in epidermis (P < 0.05). The numbers of Foxp3+ Tregs in skin lesions and peripheral blood were higher in plaque than in guttate psoriasis, whereas the percentage of IL-17+ CD4+ cells was higher in guttate than in plaque psoriasis (P < 0.05). The numbers of Foxp3+ cells were positively correlated with the Psoriasis Severity Index score of skin lesions (P < 0.0001), and the percentages of Foxp3+ CD4+ cells in peripheral blood were positively correlated with the Psoriasis Area and Severity Index score of patients (P < 0.05). The inhibitory functions of Tregs to IL-17 and IL-6 in guttate psoriasis and to tumour necrosis factor-alpha in plaque psoriasis were deficient.

CONCLUSIONS

Differential expression and regulatory functioning for inflammatory cytokine production by Foxp3+ Tregs may imply a different immunopathogenesis for plaque and guttate psoriasis.

Natural killer cells in atopic and autoimmune diseases of the skin

Natural killer (NK) cells are best known for their ability to recognize and kill tumor cells and virally infected cells and for their ability to produce large amounts of some cytokines, such as IFN-gamma. Recent research has substantially expanded our view on the function of NK cells in the immune system in health and disease. In addition to the better-studied functions in cancer and autoimmunity, contributions from NK cells to allergies and various skin diseases have emerged. We briefly recount the traditional NK cell functions before focusing on their roles in atopic dermatitis, psoriasis, alopecia areata, and pemphigus vulgaris. Although this field is still developing, strong data are available that indicate NK cell involvement. In patients with allergic diseases, the production of T(H)2 cytokines by NK cells contributes to the known immune deviation. In patients with psoriasis, their pathophysiologic role seems to be especially the production of IFN-gamma. NK cell overactivation can be found in patients with alopecia areata and pemphigus vulgaris. Many details are still unclear; however, we believe that there is solid evidence that NK cells actively participate in a number of diseases that have not been traditionally linked to this type of lymphocyte.

Skin-resident T cells: the ups and downs of on site immunity

The cutaneous surface of a normal adult individual contains approximately 20 billion T cells, nearly twice the number present in the entire circulation. Recent studies have shown a role for these cells in both normal immunity and in inflammatory skin diseases such as psoriasis. Regulatory T cells protect against autoimmune reactions to self antigens and assist in the resolution of cutaneous inflammation. However, they can also shield tumors from immune detection, allow latent infections to persist and can dysfunction under the conditions present in inflammatory skin diseases. Th17 T cells protect organisms against extracellular pathogens but also have a key role in the pathogenesis of psoriasis. Evidence suggests that effector memory T cells produced during immune reactions survive and persist long term within the skin, providing local and rapid protection against pathogen reexposure. This review summarizes the current understanding of how skin-resident T cells contribute to normal and aberrant immunity in the skin.

Human Langerhans cells induce distinct IL-22-producing CD4+ T cells lacking IL-17 production

IL-22 is a cytokine that acts mainly on epithelial cells. In the skin, it mediates keratinocyte proliferation and epidermal hyperplasia and is thought to play a central role in inflammatory diseases with marked epidermal acanthosis, such as psoriasis. Although IL-22 was initially considered a Th17 cytokine, increasing evidence suggests that T helper cells can produce IL-22 even without IL-17 expression. In addition, we have shown the existence of this unique IL-22-producing T cell in normal skin and in the skin of psoriasis and atopic dermatitis patients. In the present study, we investigated the ability of cutaneous resident dendritic cells (DCs) to differentiate IL-22-producing cells. Using FACS, we isolated Langerhans cells (LCs; HLA-DR(+)CD207(+) cells) and dermal DCs (HLA-DR(hi)CD11c(+)BDCA-1(+) cells) from normal human epidermis and dermis, respectively. Both LCs and dermal DCs significantly induced IL-22-producing CD4(+) and CD8(+) T cells from peripheral blood T cells and naive CD4(+) T cells in mixed leukocyte reactions. LCs were more powerful in the induction of IL-22-producing cells than dermal DCs. Moreover, in vitro-generated LC-type DCs induced IL-22-producing cells more efficiently than monocyte-derived DCs. The induced IL-22 production was more correlated with IFN-gamma than IL-17. Surprisingly, the majority of IL-22-producing cells induced by LCs and dermal DCs lacked the expression of IL-17, IFN-gamma, and IL-4. Thus, LCs and dermal DCs preferentially induced helper T cells to produce only IL-22, possibly "Th22" cells. Our data indicate that cutaneous DCs, especially LCs, may control the generation of distinct IL-22 producing Th22 cells infiltrating into the skin.

Increased Th17 cells are accompanied by FoxP3(+) Treg cell accumulation and correlated with psoriasis disease severity

Both T-helper 17 cells (Th17) and CD4(+)CD25(+) regulatory T cells (Treg) play important roles in the pathogenesis of psoriasis. However, the relationship between Th17 and Treg cells and their dynamic variations in psoriasis remain unclear. In this study, we found that both Th17 and FoxP3(+) Treg cells were increased in psoriasis patients both in the peripheral circulation and skin tissue lesions and were positively correlated with disease severity. The ratio of Th17 to Treg cells in skin tissue lesions was inversely correlated with PASI scores, while it was positively correlated with PASI scores in the circulation. IL-17 secretion by CD4(+) T cells was not regulated by Treg cells, even though Treg cells exhibited significant inhibition on CD4(+) T cells proliferation and IFN-gamma production. These findings provide new information regarding the association between Th17 and Treg cells, which will further our understanding of the pathogenesis of psoriasis.

Molecular pathophysiology of psoriasis and molecular targets of antipsoriatic therapy

Psoriasis is a chronic inflammatory skin disease characterised by elevated red scaly plaques on specific body sites. Histologically, the plaques are defined by epidermal hyperplasia, epidermal and dermal infiltration by leukocytes, and changes in the dermal microvasculature. Differentiation and activation are disturbed in lesional psoriatic keratinocytes, and the pool of proliferating keratinocytes is increased, which is accompanied by enhanced production of proinflammatory cytokines, adhesion molecules and antimicrobial peptides. These changes in psoriatic keratinocytes are caused by altered expression of genes associated with epidermal differentiation, and by activation of signalling pathways involving signal transducer and activator of transcription 3 (STAT3), type I interferon (IFN) and mitogen-activated protein kinase (MAPK). The number of T cells, and myeloid and plasmacytoid dendritic cells (DCs) is markedly increased in psoriatic lesions. Myeloid DCs produce interleukin (IL)-23, tumour necrosis factor (TNF)-alpha and inducible nitric oxide synthase (iNOS), which are crucial cytokines in the pathogenesis of psoriasis. IL-23 stimulates the secretion of IL-22 by T helper 17 cells, and IL-22 induces epidermal hyperplasia. The crosstalk between keratinocytes and leukocytes via their proinflammatory cytokines creates the vicious circle of chronic skin inflammation seen in psoriasis. This suggests that optimal treatment of psoriasis needs to target pathogenic pathways in both leukocytes and keratinocytes.

Effective treatment of psoriasis with etanercept is linked to suppression of IL-17 signaling, not immediate response TNF genes

BACKGROUND

TNF inhibitors have revolutionized the treatment of psoriasis vulgaris as well as psoriatic and rheumatoid arthritis and Crohn disease. Despite our understanding that these agents block TNF, their complex mechanism of action in disease resolution is still unclear.

OBJECTIVE

To analyze globally the genomic effects of TNF inhibition in patients with psoriasis, and to compare genomic profiles of patients who responded or did not respond to treatment.

METHODS

In a clinical trial using etanercept TNF inhibitor to treat psoriasis vulgaris (n = 15), Affymetrix gene arrays were used to analyze gene profiles in lesional skin at multiple time points during drug treatment (baseline and weeks 1, 2, 4, and 12) compared with nonlesional skin. Patients were stratified as responders (n = 11) or nonresponders (n = 4) on the basis of histologic disease resolution. Cluster analysis was used to define gene sets that were modulated with similar magnitude and velocity over time.

RESULTS

In responders, 4 clusters of downregulated genes and 3 clusters of upregulated genes were identified. Genes downmodulated most rapidly reflected direct inhibition of myeloid lineage immune genes. Upregulated genes included the stable dendritic cell population genes CD1c and CD207 (langerin). Comparison of responders and nonresponders revealed rapid downmodulation of innate IL-1beta and IL-8 sepsis cascade cytokines in both groups, but only responders downregulated IL-17 pathway genes to baseline levels.

CONCLUSION

Although both responders and nonresponders to etanercept inactivated sepsis cascade cytokines, response to etanercept is dependent on inactivation of myeloid dendritic cell genes and inactivation of the T(H)17 immune response.

Translational mini-review series on Th17 cells: function and regulation of human T helper 17 cells in health and disease

T helper (Th) cell have a central role in modulating immune responses. While Th1 and Th2 cells have long been known to regulate cellular and humoral immunity, Th17 cells have been identified only recently as a Th lineage that regulates inflammation via production of distinct cytokines such as interleukin (IL)-17. There is growing evidence that Th17 cells are pathological in many human diseases, leading to intense interest in defining their origins, functions and developing strategies to block their pathological effects. The cytokines that regulate Th17 differentiation have been the focus of much debate, due primarily to inconsistent findings from studies in humans. Evidence from human disease suggests that their in vivo development is driven by specialized antigen-presenting cells. Knowledge of how Th17 cells interact with other immune cells is limited, but recent data suggest that Th17 cells may not be subject to strict cellular regulation by T regulatory cells. Notably, Th17 cells and T regulatory cells appear to share common developmental pathways and both cell types retain significant plasticity. Herein, we will discuss the molecular and cellular regulation of Th17 cells with an emphasis on studies in humans.

Molecular dissection of psoriasis: integrating genetics and biology

Psoriasis is a common and debilitating disease of the skin, nails, and joints, with an acknowledged but complex genetic basis. Early genome-wide linkage studies of psoriasis focused on segregation of microsatellite markers in families; however, the only locus consistently identified resided in the major histocompatibility complex. Subsequently, several groups mapped this locus to the vicinity of HLA-C, and two groups have reported HLA-Cw6 itself to be the major susceptibility allele. More recently, the development of millions of single-nucleotide polymorphisms, coupled with the development of high-throughput genotyping platforms and a comprehensive map of human haplotypes, has made possible a genome-wide association approach using cases and controls rather than families. Taking advantage of these developments, we participated in a collaborative genome-wide association study of psoriasis involving thousands of cases and controls. Initial analysis of these data revealed and/or confirmed association between psoriasis and seven genetic loci-HLA-C, IL12B, IL23R, IL23A, IL4/IL13, TNFAIP3, and TNIP1-and ongoing studies are revealing additional loci. Here, we review the epidemiology, immunopathology, and genetics of psoriasis, and present a disease model integrating its genetics and immunology.

IL-17-producing CD8+ T lymphocytes from psoriasis skin plaques are cytotoxic effector cells that secrete Th17-related cytokines

IL-17-producing CD4+ T lymphocytes (Th17) are currently considered relevant participants in the pathogenesis of psoriasis skin lesions. However, little is known about the potential role of IL-17-producing CD8+ T cells, which are also present at the psoriatic plaque. We have addressed the functional characterization of this CD8+ subtype of T lymphocytes from psoriasis patients. Our results show that CD8+IL-17+ cells from psoriasis-inflamed skin tissue produce TNF-alpha and IFN-gamma (Th1-related cytokines) as well as IL-17, IL-21, and IL-22 (Th17-related cytokines) efficiently. A significant up-regulation of the RORC transcription factor is also observed. These cells are refractory to Tregs but show a proliferative response to anti-CD3/CD28 stimulation that is enhanced by IL-12 and IL-15. Blocking of TNF-alpha activity inhibits TCR-mediated activation and IL-17 production. CD8+IL-17+ T cells are cytotoxic cells that display TCR/CD3-mediated cytotoxic abilities to kill target cells. Thus, CD8+IL-17+ T cells share some key features with Th17 cells and exhibit remarkable differential abilities attributable to the CD8+ lineage of T lymphocytes, adding new insights into the functional resources of IL-17-producing cells from human epidermis that could be of potential interest to our understanding of the pathogenesis of psoriasis.

Angiogenesis drives psoriasis pathogenesis

Psoriasis pathogenesis is closely associated with disease-inducing Th1 and Th17 cells. Yet, several studies suggest that aberrant keratinocyte or endothelial cell signalling significantly contributes to disease manifestation. Histological hallmarks of psoriatic skin include the infiltration of multiple immune cells, keratinocyte proliferation and increased dermal vascularity. Formation of new blood vessels starts with early psoriatic changes and disappears with disease clearance. Several angiogenic mediators like vascular endothelial growth factor, hypoxia-inducible factors, angiopoietins and pro-angiogenic cytokines, such as tumour necrosis factor (TNF), interleukin (IL)-8 and IL-17, are up-regulated in psoriasis development. Contact- and mediator-dependent factors derived from keratinocytes, mast cells and immune cells may contribute to the strong blood vessel formation of psoriasis. New technologies and experimental models provide new insights into the role of angiogenesis in psoriasis pathogenesis. Interestingly, many therapies target not only immune cells, but also protein structures of endothelial cells. Here we summarize the role of pro-angiogenic factors in psoriasis development and discuss angiogenesis as a potential target of novel therapies.

Vitamin D analogs differentially control antimicrobial peptide/"alarmin" expression in psoriasis

Antimicrobial peptides (AMPs) are strongly expressed in lesional skin in psoriasis and play an important role as proinflammatory "alarmins" in this chronic skin disease. Vitamin D analogs like calcipotriol have antipsoriatic effects and might mediate this effect by changing AMP expression. In this study, keratinocytes in lesional psoriatic plaques showed decreased expression of the AMPs beta-defensin (HBD) 2 and HBD3 after topical treatment with calcipotriol. At the same time, calcipotriol normalized the proinflammatory cytokine milieu and decreased interleukin (IL)-17A, IL-17F and IL-8 transcript abundance in lesional psoriatic skin. In contrast, cathelicidin antimicrobial peptide expression was increased by calcipotriol while psoriasin expression remained unchanged. In cultured human epidermal keratinocytes the effect of different vitamin D analogs on the expression of AMPs was further analyzed. All vitamin D analogs tested blocked IL-17A induced HBD2 expression by increasing IkappaB-alpha protein and inhibition of NF-kappaB signaling. At the same time vitamin D analogs induced cathelicidin through activation of the vitamin D receptor and MEK/ERK signaling. These studies suggest that vitamin D analogs differentially alter AMP expression in lesional psoriatic skin and cultured keratinocytes. Balancing AMP "alarmin" expression might be a novel goal in treatment of chronic inflammatory skin diseases.

Osteopontin and the skin: multiple emerging roles in cutaneous biology and pathology

Osteopontin (OPN) is a glycoprotein expressed by various tissues and cells. The existence of variant forms of OPN as a secreted (sOPN) and intracellular (iOPN) protein and its modification through post-translational modification and proteolytic cleavage explain its broad range of functions. There is increasing knowledge which receptors OPN isoforms can bind to and which signaling pathways are activated to mediate different OPN functions. sOPN interacts with integrins and CD44, mediates cell adhesion, migration and tumor invasion, and has T helper 1 (Th1) cytokine functions and anti-apoptotic effects. iOPN has been described to regulate macrophage migration and interferon-alpha secretion in plasmacytoid dendritic cells. Both sOPN and iOPN, through complex functions for different dendritic cell subsets, participate in the regulation of Th cell lineages, among them Th17 cells. For skin disease, OPN from immune cells and tumor cells is of pathophysiological relevance. OPN is secreted in autoimmune diseases such as lupus erythematosus, and influences inflammation of immediate and delayed type allergies and granuloma formation. We describe that OPN is overexpressed in psoriasis and propose a model to study OPN function in psoriatic inflammation. Through cytokine functions, OPN supports immune responses against Mycobacteria and viruses such as herpes simplex virus. OPN is also implicated in skin tumor progression. Overexpression of OPN influences invasion and metastasis of melanoma and squamous cell carcinoma cells, and OPN expression in melanoma is a possible prognostic marker. As OPN protein preparations and anti-OPN antibodies may be available in the near future, in-depth knowledge of OPN functions may open new therapeutic approaches for skin diseases.

Immunopathogenesis of psoriasis: focus on natural killer T cells

Psoriasis is a common inflammatory skin disease triggered by dysregulated immune response and characterized by hyperproliferation and altered differentiation of keratinocytes. Formation of psoriatic lesions is thought to be elicited by the complex cellular and cytokine network arising from the pathogenic interactions between keratinocytes and components of innate and acquired immune system. Natural killer T (NKT) cells are a heterogenous T-cell lineage that has been implicated in the pathogenesis of various autoimmune diseases including psoriasis. Due to the numerous functions of NKT cells that link innate and adaptive immunity, their role in psoriasis is complex and still elusive. We summarize the currently available literature data on this issue and discuss the possible role of NKT cells in the immunopathogenesis of this autoimmune disease.

Myeloid dendritic cells from human cutaneous squamous cell carcinoma are poor stimulators of T-cell proliferation

To determine the phenotype and function of myeloid dendritic cells (DCs) from human cutaneous squamous-cell carcinoma (SCC), we studied their surface marker expression and allo-stimulatory potential ex vivo. There were abundant CD11c(+) myeloid DCs, as well as TNF and inducible nitric oxide synthase (iNOS)-producing DCs, in and around SCC tumor nests. Although myeloid DCs from SCC, adjacent non-tumor-bearing skin, and normal skin, were phenotypically similar by flow cytometry, and there was a pronounced genomic signature of mature DCs in SCC, they showed different T-cell stimulatory potential in an allogeneic mixed leukocyte reaction. Myeloid DCs from SCC were less potent stimulators of allogeneic T-cell proliferation than DCs from non-tumor-bearing skin. Culture with a DC-maturing cytokine cocktail (IL-1beta, IL-6, TNF-alpha, and PGE(2)) enhanced stimulatory potential in DCs from non-tumor-bearing skin, whereas SCC-associated DCs remained poor stimulators of T-cell proliferation. The microenvironment associated with SCC showed expression of TGF-beta, IL-10, and VEGF-A, factors capable of suppressing the DC function. These findings indicate that CD11c(+)/HLA-DR(hi) DCs from SCC are mature, but are not potent stimulators of T-cell proliferation compared with phenotypically similar DCs isolated from non-tumor-bearing skin. Identification of mechanisms responsible for suppression of tumor-associated DCs may provide insight into the evasion of immunosurveillance by SCC.

Dendritic cells in the pathogenesis of sarcoidosis

Sarcoidosis is a noncaseating granulomatous disease, likely of autoimmune etiology, that causes inflammation and tissue damage in multiple organs, most commonly the lung, but also skin, and lymph nodes. Reduced dendritic cell (DC) function in sarcoidosis peripheral blood compared with peripheral blood from control subjects suggests that blunted end organ cellular immunity may contribute to sarcoidosis pathogenesis. Successful treatment of sarcoidosis with tumor necrosis factor (TNF) inhibitors, which modulate DC maturation and migration, has also been reported. Together, these observations suggest that DCs may be important mediators of sarcoidosis immunology. This review focuses on the phenotype and function of DCs in the lung, skin, blood, and lymph node of patients with sarcoidosis. We conclude that DCs in end organs are phenotypically and functionally immature (anergic), while DCs in the lymph node are mature and polarize pathogenic Th1 T cells. The success of TNF inhibitors is thus likely secondary to inhibition of DC-mediated Th1 polarization in the lymph node.

The IL-23/Th17 axis in the immunopathogenesis of psoriasis

Abnormal production of inflammatory mediators is believed to play an important role in the pathogenesis of psoriasis. Emerging data, both in mice and in humans, put the spotlight on a new subset of T helper (Th) cells, in part characterized by their production of IL-17 and accordingly named Th17 cells. Here, we review the development, characterization, and function of human Th17 cells as well as the crucial role of IL-23 in the context of Th17-cell-dependent chronic inflammation in psoriasis. We further discuss recent clinical trials targeting the IL-23/Th17 axis in psoriasis.

Cytokine-producing dendritic cells in the pathogenesis of inflammatory skin diseases

INTRODUCTION

Inflammatory skin diseases can be examined from many viewpoints. In this review, we consider three distinct cutaneous inflammatory diseases from the point of view of their major lesional dendritic cell (DC) subpopulations. The DC populations considered are Langerhans cells, myeloid DCs, and plasmacytoid DCs (pDCs), with specific attention to the presence and role of the inflammatory counterparts of these cells. From such a "dendritic cell-centric" focus, psoriasis, atopic dermatitis (AD), and cutaneous lupus erythematosus (CLE) are explored.

DISCUSSION

In psoriasis, there is a specific population of myeloid "inflammatory" DCs that appears to play an important pathogenic role, while pDCs have been recently implicated in the initiation of psoriatic lesions. In AD, Langerhans cells may be important during initiation, while "inflammatory dendritic epidermal cells" (IDECs) appear to be abundant in lesional epidermis and dermis and contribute to maintenance of AD. These IDECs may actually be analogous to the myeloid inflammatory DCs found in the epidermal and dermal compartments of the skin in psoriasis, although they express distinct surface markers and induce different T cell polarities as a result of different cytokine milieu in which they develop. CLE has been recently characterized as a type I IFN-mediated disease, and pDCs are integral to the pathogenesis of this disease.

CONCLUSION

Thus, these DC subpopulations and their products will be reviewed in the context of these three cutaneous diseases to provide clinico-pathophysiological correlations between the lesional DCs, their products, and the skin diseases.

Differential capability of human cutaneous dendritic cell subsets to initiate Th17 responses

Human skin-migratory dendritic cells (DCs) have the ability to prime and bias Th1 and Th2 CD4+ T lymphocytes. However, whether human cutaneous DCs are capable of initiating proinflammatory Th17 responses remains undetermined. We report that skin-migratory DCs stimulate allogeneic naive CD4+ T cells that differentiate simultaneously into two distinct effector Th17 and Th1 populations capable of homing to the skin, where they induce severe cutaneous damage. Skin-migratory Langerhans cells (smiLCs) were the main cutaneous DC subset capable of inducing Th17 responses dependent on the combined effects of IL-15 and stabilized IL-6, which resulted in IL-6 trans-signaling of naive CD4+ T cells. Different from smiLCs, purified skin-migratory dermal DCs did not synthesize IL-15 and were unable to bias Th17 responses. Nevertheless, these dermal DCs were capable of differentiating Th17 cells in mixed leukocyte cultures supplemented with IL-15 and stabilized IL-6. Overall, our data demonstrate that human epidermal smiLCs induce Th17 responses by mechanisms different from those previously described and highlight the need to target clinical treatments based on these variations.

[What's new in dermatological research?]

Medical literature is rich with new and relevant information, resulting from basic or applied research. Some strong arguments are presented in this document. Firstly, the discovery and role of a virus, the polyomavirus, in the development of Merkel tumours. It is a small virus with double bit DNA strand, coding for a oncoprotein. If the polyomavirus plays a causal role in the tumorigenesis, it acts by various mechanisms. The micro-RNAs represent an abundant class of small RNA not coding for proteins, but which control the gene expression coding for proteins on a post-transcriptional level. The first obvious sign of the role of the micro-RNAs in the inflammatory dermatoses appeared recently, in particular when these micro-RNAs associated with psoriasis and atopic dermatitis were identified through a broad genomic analysis of the expression of these micro-RNAs. A new giant virus strain sheltering another unknown tiny virus to date has just been discovered. This virus infinitely small called Sputnik enables to deteriorate a much larger virus baptized Mama, at the point of preventing it to manufacture normal viral particles and also preventing it from reproducing. This discovery raises a crucial question: Is Sputnik a new system of transfer of genes of a species of one virus to another? A group of blood cells expressing E-cadherin, the dot cells, found in the fetal blood of the dermis, contributes to tissue repair through the mechanisms of cellular differentiation and their action allows healing without scar. CD4+ T helper lymphocytes producing interleukin 17 (IL17) play a pathogenic part in atopic dermatitis. The genes of the beta defensins could be involved in the genetic susceptibility of the psoriatic disease. The autoimmune origin of the alopecia areata is supported by a great number of observations, the role of neuropeptides in the initiation of the autoimmunity during alopecia areata has just been demonstrated. The dendritic cells are cells presenting antigens which play a crucial role in the adaptive immunological response. It was shown that activation of the proliferation of the lymphocytes T after the migration of dendritic cells on the level of the lymphatic ganglion depended not on Langerhans cell, but of the dendritic cell. A new way appears to control the autoimmunity in the psoriasis and involves the plasmacytoid dendritic cells which are sensitized with the DNA itself when it is coupled with an antibacterial peptide. Mast cells express cathelicidin, which acts like an antibiotic with broad spectrum and influences the defence system of the epitheliums. We have perhaps found a new therapeutic target for rosacea by disclosing high rates of cathelicidin and a series of associated proteases in skin lesions. The sebocytes express antibacterial functional peptides deriving from cathelicidin which can have a bactericidal effect against P. Acnes. A vast genomic study in the androgenetic alopecia highlighted the existence of new loci localized on the 20p11 chromosome, associated with the risk of androgenetic alopecia. New alleles to determine the color of hair and the cutaneous pigmentation were identified. Two loci (IRF 4 and SLC24A4) are highly associated with the color of hair, like three other areas. The blue color of the eyes could be due to a change of an element located in gene HERC2 preventing of the expression of OCA2. Thus, many fields of dermatology were the object of research which opens new prospects for diagnosis and treatment.