IL-17 induces an expanded range of downstream genes in reconstituted human epidermis model.

BACKGROUND: IL-17 is the defining cytokine of the Th17, Tc17, and γδ T cell populations that plays a critical role in mediating inflammation and autoimmunity. Psoriasis vulgaris is an inflammatory skin disease mediated by Th1 and Th17 cytokines with relevant contributions of IFN-γ, TNF-α, and IL-17. Despite the pivotal role IL-17 plays in psoriasis, and in contrast to the other key mediators involved in the psoriasis cytokine cascade that are capable of inducing broad effects on keratinocytes, IL-17 was demonstrated to regulate the expression of a limited number of genes in monolayer keratinocytes cultured in vitro. METHODOLOGY/PRINCIPAL FINDINGS: Given the clinical efficacy of anti-IL-17 agents is associated with an impressive reduction in a large set of inflammatory genes, we sought a full-thickness skin model that more closely resemble in vivo epidermal architecture. Using a reconstructed human epidermis (RHE), IL-17 was able to upregulate 419 gene probes and downregulate 216 gene probes. As possible explanation for the increased gene induction in the RHE model is that C/CAAT-enhancer-binding proteins (C/EBP) -ß, the transcription factor regulating IL-17-responsive genes, is expressed preferentially in differentiated keratinocytes. CONCLUSIONS/SIGNIFICANCE: The genes identified in IL-17-treated RHE are likely relevant to the IL-17 effects in psoriasis, since ixekizumab (anti-IL-17A agent) strongly suppressed the "RHE" genes in psoriasis patients treated in vivo with this IL-17 antagonist.

Contrasting pathogenesis of atopic dermatitis and psoriasis--part I: clinical and pathologic concepts.

Atopic dermatitis and psoriasis are 2 of the most common inflammatory skin diseases. They are similar in that they are complex inherited diseases involving genes that encode immune components and structural proteins that regulate differentiation of epidermal cells. Each disease is characterized by proliferation of epidermal keratinocytes and abnormal cornification or terminal differentiation in the epidermis; skin lesions contain immune infiltrates of T cells, dendritic cells, and other types of leukocytes. We review similarities between the diseases and differences in epidermal barrier defects and immune cells. We also propose mechanisms of pathogenesis based on differences in the balance of immune cell subsets that could cause the phenotypes that distinguish these diseases. The first part of this 2-part review focuses on the clinical and pathologic features of the diseases; the second part discusses differences in immune cell subsets between atopic dermatitis and psoriasis and recent therapeutic strategies.

Contrasting pathogenesis of atopic dermatitis and psoriasis--part II: immune cell subsets and therapeutic concepts.

Atopic dermatitis (AD) and psoriasis are among the most common inflammatory skin diseases. In the first part of this 2-part review, we discussed the similarities and differences between AD and psoriasis with respect to clinical features and pathology. The diseases are characterized by infiltration of skin lesions by large numbers of inflammatory cells; the second part of this review focuses on immune cell subsets that distinguish each disease and the therapeutic strategies that might be used or developed based on this information. We discuss the interactions among different populations of immune cells that ultimately create the complex inflammatory phenotype of AD and compare these with psoriasis. Therapeutic strategies have been developed for psoriasis based on the cytokine network that promotes inflammation in this disease. Antibodies against IL-12 and IL-23p40 antibody and antagonists of TNF are used to treat patients with psoriasis, and studies are underway to test specific antagonists of IL-23, IL-17, IL-17 receptor, IL-20, and IL-22. We discuss how these therapeutic approaches might be applied to AD.

Anti-cytokine therapies for psoriasis.

Current approaches for the treatment of psoriasis with anti-cytokine therapies involve the blockade of TNF-α, or the p40 sub-unit of IL-12 and IL-23. However, the field is currently evolving to test more selective antagonists, such as anti-IL-23p19, IL-17 and other inflammatory cytokines. Here we discuss our current understanding of dendritic cell and T cell subsets that are relevant in psoriasis, and the pharmacologic strategies that temper their activity in this disease.

Integrative responses to IL-17 and TNF-α in human keratinocytes account for key inflammatory pathogenic circuits in psoriasis.

Psoriasis is a complex inflammatory disease mediated by tumor necrosis factor (TNF)-α and cytokines secreted by specialized T-cell populations, e.g., IL-17, IL-22, and IFN-γ. The mechanisms by which innate and adaptive immune cytokines regulate inflammation in psoriasis are not completely understood. We sought to investigate the effects of TNF-α and IL-17 on keratinocyte (KC) gene profile, to identify genes that might be coregulated by these cytokines and determine how synergistically activated genes relate to the psoriasis transcriptome. Primary KCs were stimulated with IL-17 or TNF-α alone, or in combination. KC responses were assessed by gene array analysis, followed by reverse transcriptase-PCR confirmation for significant genes. We identified 160 genes that were synergistically upregulated by IL-17 and TNF-α, and 196 genes in which the two cytokines had at least an additive effect. Synergistically upregulated genes included some of the highest expressed genes in psoriatic skin with an impressive correlation between IL-17/TNF-α-induced genes and the psoriasis gene signature. KCs may be key drivers of pathogenic inflammation in psoriasis through integrating responses to TNF-α and IL-17. Our data predict that psoriasis therapy with either TNF or IL-17 antagonists will produce greater modulation of the synergistic/additive gene set, which consists of the most highly expressed genes in psoriasis skin lesions.

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.

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.

New insights in the immunologic basis of psoriasis.

Psoriasis vulgaris is a multifactorial heritable disease characterized by severe inflammation resulting in poorly differentiated, hyperproliferative keratinocytes. Recent advances in genetic analyses have implicated components regulating the interleukin (IL)-23 and nuclear factor-kappaB pathways as risk factors for psoriasis. These inflammatory pathways exhibit increased activity in skin lesions, and promote secretion of various cytokines, such as IL-17 and IL-22. Unrestrained, the activated inflammatory cytokine network in psoriasis may trigger a vicious cycle of inflammation and cellular proliferation that ultimately results in lesion formation. These advances in genetic analyses, together with the progress made in targeted biological therapy, pave the path to tailor treatment on the basis of an individual's genetic and immunologic profile.

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.

Broad defects in epidermal cornification in atopic dermatitis identified through genomic analysis.

BACKGROUND: Psoriasis and atopic dermatitis (AD) are common, complex inflammatory skin diseases. Both diseases display immune infiltrates in lesions and epidermal growth/differentiation alterations associated with a defective skin barrier. An incomplete understanding of differences between these diseases makes it difficult to compare human disease pathology to animal disease models. OBJECTIVE: To characterize differences between these diseases in expression of genes related to epidermal growth/differentiation and inflammatory circuits. METHODS: We performed genomic profiling of mRNA in chronic psoriasis (n = 15) and AD (n = 18) skin lesions compared with normal human skin (n = 15). RESULTS: As expected, clear disease classifications could be constructed on the basis of expected immune polarity (T(H)1, T(H)2, T(H)17) differences. However, even more striking differences were identified in epidermal differentiation programs that could be used for precise disease classifications. Although both psoriasis and AD skin lesions displayed regenerative epidermal hyperplasia, which is a general alteration in epidermal growth, keratinocyte terminal differentiation was differentially polarized. In AD, we found selective defects in expression of multiple genes encoding the cornified envelope, with the largest alteration in loricrin (expressed at 2% of the level of normal skin). At the ultrastructural level, the cornified envelope in AD was broadly defective with highly decreased compaction of corneocytes and reduced intercellular lipids. Hence, the entire keratinocyte terminal differentiation program (cytoplasmic compaction, cornification, and lipid release) is defective in AD, potentially underlying the immune differences. CONCLUSION: Our study shows that although alterations in barrier responses exist in both diseases, epidermal differentiation is differentially polarized, with major implications for primary disease pathogenesis.

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.

Self-peptides prolong survival in murine autoimmunity via reduced IL-2/IL-7-mediated STAT5 signaling, CD8 coreceptor, and V alpha 2 down-regulation.

Although the pathogenic role of B cells and CD4 T cells has been studied extensively, less is known about the role of CD8 T cells in autoimmunity and self-tolerance. To evaluate the role of CD8 T cells in autoimmunity and its modulation using self-peptides, we used mice expressing soluble OVA (sOVA) under control of the keratin-14 promoter. Spontaneous autoimmunity occurred when sOVA mice were crossed with OT-I mice, whose CD8 T cells carry a Valpha2/Vbeta5-transgenic TCR with specificity for the OVA(257-264) peptide. Eighty-three percent of OVA/OT-I mice died during the first 2 wk of life due to multiple organ inflammation. In contrast, preventive or therapeutic OVA(257-264) peptide injections induced a dose-dependent increase in survival. Healthy survivors exhibited reductions in peripheral CD8 T cells, CD8 coreceptor, and Valpha2 expression. Furthermore, CD8 T cells from healthy mice were anergic and could not be activated by exogenous IL-2. A block in IL-2/IL-7 signaling via the STAT5 pathway provided the basis for low surface expression of the CD8 coreceptor and failure of IL-2 to break CD8 T cell anergy. Thus, the soluble TCR ligand triggered multiple tolerance mechanisms in these sOVA/OT-I mice, making this treatment approach a potential paradigm for modulating human autoimmune diseases.

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

BACKGROUND: Psoriasis and atopic dermatitis (AD) are common inflammatory skin diseases. An upregulated TH17/IL-23 pathway was demonstrated in psoriasis. Although potential involvement of TH17 T cells in AD was suggested during acute disease, the role of these cells in chronic AD remains unclear. OBJECTIVE: To examine differences in IL-23/TH17 signal between these diseases and establish relative frequencies of T-cell subsets in AD. METHODS: Skin biopsies and peripheral blood were collected from patients with chronic AD (n = 12) and psoriasis (n = 13). Relative frequencies of CD4+ and CD8+ T-cell subsets within these 2 compartments were examined by intracellular cytokine staining and flow cytometry. RESULTS: In peripheral blood, no significant difference was found in percentages of different T-cell subsets between these diseases. In contrast, psoriatic skin had significantly increased frequencies of TH1 and TH17 T cells compared with AD, whereas TH2 T cells were significantly elevated in AD. Distinct IL-22-producing CD4+ and CD8+ T-cell populations were significantly increased in AD skin compared with psoriasis. IL-22+CD8+ T-cell frequency correlated with AD disease severity. CONCLUSION: Our data established that T cells could independently express IL-22 even with low expression levels of IL-17. This argues for a functional specialization of T cells such that "T17" and "T22" T-cells may drive different features of epidermal pathology in inflammatory skin diseases, including induction of antimicrobial peptides for "T17" T cells and epidermal hyperplasia for "T22" T-cells. Given the clinical correlation with disease severity, further characterization of "T22" T cells is warranted, and may have future therapeutic implications.

New insights into the pathogenesis and genetics of psoriatic arthritis.

Psoriasis vulgaris and psoriatic arthritis (PsA) are inter-related heritable diseases. Psoriatic skin is characterized by hyperproliferative, poorly differentiated keratinocytes and severe inflammation. Psoriatic joints are characterized by highly inflamed synovia and entheses with focal erosions of cartilage and bone. Genetic analyses have uncovered risk factors shared by both psoriasis and PsA. Predisposition to psoriasis and PsA arising from common variation is most strongly conferred by the HLA class I region. Other genetic risk factors implicate the interleukin (IL)-23 pathway and the induction and regulation of type 17 T-helper cells in the pathogenesis of both diseases. Secretion of cytokines, such as IL-22 and IL-17, could result in the hyperproliferative phenotype of keratinocytes and potentially synoviocytes, leading to a vicious cycle of cellular proliferation and inflammation in both the skin and joints. In synovial tissue, disease-related cytokines could also promote osteoclast formation, resulting in bone erosion. The next step will be to identify genetic risk factors specifically associated with PsA. Although therapies that target tumor necrosis factor are often highly successful in the treatment of both diseases, genetic findings are likely to lead to the development of treatments tailored to an individual's genetic profile.

Low expression of the IL-23/Th17 pathway in atopic dermatitis compared to psoriasis.

The classical Th1/Th2 paradigm previously defining atopic dermatitis (AD) and psoriasis has recently been challenged with the discovery of Th17 T cells that synthesize IL-17 and IL-22. Although it is becoming evident that many Th1 diseases including psoriasis have a strong IL-17 signal, the importance of Th17 T cells in AD is still unclear. We examined and compared skin biopsies from AD and psoriasis patients by gene microarray, RT-PCR, immunohistochemistry, and immunofluorescence. We found a reduced genomic expression of IL-23, IL-17, and IFN-gamma in AD compared with psoriasis. To define the effects of IL-17 and IL-22 on keratinocytes, we performed gene array studies with cytokine-treated keratinocytes. We found lipocalin 2 and numerous other innate defense genes to be selectively induced in keratinocytes by IL-17. IFN-gamma had no effect on antimicrobial gene-expression in keratinocytes. In AD skin lesions, protein and mRNA expression of lipocalin 2 and other innate defense genes (hBD2, elafin, LL37) were reduced compared with psoriasis. Although AD has been framed by the Th1/Th2 paradigm as a Th2 polar disease, we present evidence that the IL-23/Th17 axis is largely absent, perhaps accounting for recurrent skin infections in this disease.