Epidermal Th22 and Tc17 cells form a localized disease memory in clinically healed psoriasis

The role of IL 23 in the treatment of psoriasis

INTRODUCTION

The IL-23/IL-17 axis is currently considered to be crucial in the pathogenesis of psoriasis. Human IL-23 is primarily produced by antigen-presenting cells and induces and maintains differentiation of Th17 cells and Th22 cells, a primary cellular source of proinflammatory cytokines such as IL-17 and IL-22, which mediate the epidermal hyperplasia, keratinocyte immune activation and tissue inflammation inherent in psoriasis. Agents that target the p40 subunit common to both IL-12 and IL-23 have shown robust clinical activity, but selectivity for IL-23p19 could offer advantages in efficacy and safety with respect to anti-p40 blockade. Areas covered: Relevant references regarding the role of the IL-23/IL-17 pathway in the pathogenesis of psoriasis/psoriatic arthritis and clinical trials with IL-23p40 and IL-23p19 blocking agents were obtained through a literature search in MEDLINE/Pubmed for articles published until November 2016. Moreover, ongoing registered clinical trials (RCTs) of moderate-to-severe psoriasis and psoriatic arthritis were searched through clinicaltrials.gov website, and a manual search was made for pertinent communications at the 2016 American Academy of Dermatology and European Academy of Dermatology and Venereology meetings. Expert commentary: There are potential advantages in selective blockade of the IL23-specific p19 subunit with respect to distal blockade of IL-17A or its receptor. Acting upstream in the IL-23/IL-17 cytokine pathway is likely to reduce the expression of multiple pro-inflammatory cytokines acting on keratinocytes -including IL-17F, IL-21 and IL-22-, in addition to IL-17A. On the other hand, safety data thus far suggest that these drugs might be devoid of some adverse effects of IL-17A blockade that seem to be class related, such as mucocutaneous Candida infections or triggering or worsening of inflammatory bowel disease. Specific IL-23p19 blockade with high-affinity monoclonal antibodies seems to be able to induce long-term remissions of the activity in psoriasis and might eventually represent a paradigm change in the treatment of psoriasis. The results of phase III and comparative head-to-head trials with these agents are eagerly awaited.

Understanding memory CD8+ T cells

Memory CD8+ T cells were originally thought to exist as two populations (effector and central memory). In recent years, a third population called resident memory T cells has been discovered and further to this these populations are being divided into different subtypes. Understanding the function and developmental pathways of memory CD8+ T cells is key to developing effective therapies against cancer and infectious diseases. Here we have reviewed what is currently known about all three subsets of memory CD8+ T populations and as to how each population was originally discovered and the developmental pathways of each subpopulation. Each memory population appears to play a distinct role in adaptive immune responses but we are still a long way from understanding how the populations are generated and what roles they play in protection against invading pathogens and if they contribute to the pathogenesis of inflammatory diseases.

Blood to skin recirculation of CD4+ memory T cells associates with cutaneous and systemic manifestations of psoriatic disease

Blood to skin recirculation could play a role in the pathogenesis of psoriasis. To investigate this possibility we dissected the phenotype of circulating T cells in psoriasis patients, calculated the correlation the clinical parameters of the disease and performed a parallel bioinformatics analysis of gene expression data in psoriatic skin. We found that circulating CCR6⁺ CD4⁺ T_EM and T_EFF cells significantly correlated with systemic inflammation. Conversely, the percentage of CXCR3⁺ CD4⁺ T_EM cells negatively correlated with the severity of the cutaneous disease. Importantly CLA⁺ CD4⁺ T_CM cells expressing CCR6⁺ or CCR4⁺CXCR3⁺ negatively correlated with psoriasis severity suggesting recruitment to the skin compartment. This assumption was reinforced by gene expression data showing marked increase of CCR7 and CLA-encoding gene SELPLG expression in psoriatic skin and strong association of their expression. The data enlightens a role for CD4⁺ T cells trafficking between blood and skin in cutaneous and systemic manifestations of psoriasis.

Resident memory T cells in mouse and human

Recent researches are revealing the importance of a new subset of memory T cells called resident memory T cells (T_RM^s). Once they enter the tissues according to their tissue-homing receptors, TRMs do not go back to circulation and stay in the same tissues for a long time. These T cells are defined as expressing CD69 and/or CD103, and are known to show strong effector functions. It is considered that T_RM^s have an important role against infection in barrier tissues such as GI tract, skin, respiratory system and reproductive tract. Furthermore, recent reports indicate their roles in organ-specific chronic inflammatory disorders, autoimmune disorders and tumor immunology even in non-barrier tissues such as central nerve system, lymphatic tissue, liver, kidney, pancreas and joint. Here in this session, the author organized what have been known about T_RM both in mouse and human, including the development, functional activities and relation of T_RM to disease manifestation, for the detailed understanding of this fraction.

Th22 Cells Form a Distinct Th Lineage from Th17 Cells In Vitro with Unique Transcriptional Properties and Tbet-Dependent Th1 Plasticity

Th22 cells are a major source of IL-22 and have been found at sites of infection and in a range of inflammatory diseases. However, their molecular characteristics and functional roles remain largely unknown because of our inability to generate and isolate pure populations. We developed a novel Th22 differentiation assay and generated dual IL-22/IL-17A reporter mice to isolate and compare pure populations of cultured Th22 and Th17 cells. Il17a fate-mapping and transcriptional profiling provide evidence that these Th22 cells have never expressed IL-17A, suggesting that they are potentially a distinct cell lineage from Th17 cells under in vitro culture conditions. Interestingly, Th22 cells also expressed granzymes, IL-13, and increased levels of Tbet. Using transcription factor-deficient cells, we demonstrate that RORγt and Tbet act as positive and negative regulators of Th22 differentiation, respectively. Furthermore, under Th1 culture conditions in vitro, as well as in an IFN-γ-rich inflammatory environment in vivo, Th22 cells displayed marked plasticity toward IFN-γ production. Th22 cells also displayed plasticity under Th2 conditions in vitro by upregulating IL-13 expression. Our work has identified conditions to generate and characterize Th22 cells in vitro. Further, it provides evidence that Th22 cells develop independently of the Th17 lineage, while demonstrating plasticity toward both Th1- and Th2-type cells.

Demonstration of Tissue Resident Memory CD8 T Cells in Insulitic Lesions in Adult Patients with Recent-Onset Type 1 Diabetes

Subtypes of CD8+ T cells in insulitic lesions in biopsy specimens from six subjects with recent-onset type 1 diabetes (T1D) and six nondiabetic matched controls were analyzed using simultaneous multicolor immunofluorescence. Also, insulitic islets based on accumulation of CD3+ T cells were microdissected with laser-capture microscopy, and gene transcripts associated with inflammation and autoimmunity were analyzed. We found a substantial proportion, 43%, of the CD8+ T cells in the insulitic lesions to display a tissue resident memory T cell (TRM) (CD8+CD69+CD103+) phenotype in T1D subjects. Most TRM cells were located in the insulitic lesion in the endocrine-exocrine interface. TRM cells were also sporadically found in islets of control subjects. Moreover, gene expression analysis showed a lack of active transcription of genes associated with acute inflammatory or cytotoxic T-cell responses. We present evidence that a substantial proportion of T cells in insulitic lesions of recent-onset T1D patients are TRM cells and not classic cytotoxic CD8+ T cells. Our findings highlight the need for further analysis of the T cells involved in insulitis to elucidate their role in the etiology of T1D.

Survival of tissue-resident memory T cells requires exogenous lipid uptake and metabolism

Tissue-resident memory T (T_RM) cells persist indefinitely in epithelial barrier tissues and protect the host against pathogens. However, the biological pathways that enable the long-term survival of T_RM cells are obscure. Here we show that mouse CD8⁺ T_RM cells generated by viral infection of the skin differentially express high levels of several molecules that mediate lipid uptake and intracellular transport, including fatty-acid-binding proteins 4 and 5 (FABP4 and FABP5). We further show that T-cell-specific deficiency of Fabp4 and Fabp5 (Fabp4/Fabp5) impairs exogenous free fatty acid (FFA) uptake by CD8⁺ T_RM cells and greatly reduces their long-term survival in vivo, while having no effect on the survival of central memory T (T_CM) cells in lymph nodes. In vitro, CD8⁺ T_RM cells, but not CD8⁺ T_CM cells, demonstrated increased mitochondrial oxidative metabolism in the presence of exogenous FFAs; this increase was not seen in Fabp4/Fabp5 double-knockout CD8⁺ T_RM cells. The persistence of CD8⁺ T_RM cells in the skin was strongly diminished by inhibition of mitochondrial FFA β-oxidation in vivo. Moreover, skin CD8⁺ T_RM cells that lacked Fabp4/Fabp5 were less effective at protecting mice from cutaneous viral infection, and lung Fabp4/Fabp5 double-knockout CD8⁺ T_RM cells generated by skin vaccinia virus (VACV) infection were less effective at protecting mice from a lethal pulmonary challenge with VACV. Consistent with the mouse data, increased FABP4 and FABP5 expression and enhanced extracellular FFA uptake were also demonstrated in human CD8⁺ T_RM cells in normal and psoriatic skin. These results suggest that FABP4 and FABP5 have a critical role in the maintenance, longevity and function of CD8⁺ T_RM cells, and suggest that CD8⁺ T_RM cells use exogenous FFAs and their oxidative metabolism to persist in tissue and to mediate protective immunity.

CD49a Expression Defines Tissue-Resident CD8+ T Cells Poised for Cytotoxic Function in Human Skin

Tissue-resident memory T (Trm) cells form a heterogeneous population that provides localized protection against pathogens. Here, we identify CD49a as a marker that differentiates CD8⁺ Trm cells on a compartmental and functional basis. In human skin epithelia, CD8⁺CD49a⁺ Trm cells produced interferon-γ, whereas CD8⁺CD49a⁻ Trm cells produced interleukin-17 (IL-17). In addition, CD8⁺CD49a⁺ Trm cells from healthy skin rapidly induced the expression of the effector molecules perforin and granzyme B when stimulated with IL-15, thereby promoting a strong cytotoxic response. In skin from patients with vitiligo, where melanocytes are eradicated locally, CD8⁺CD49a⁺ Trm cells that constitutively expressed perforin and granzyme B accumulated both in the epidermis and dermis. Conversely, CD8⁺CD49a^– Trm cells from psoriasis lesions predominantly generated IL-17 responses that promote local inflammation in this skin disease. Overall, CD49a expression delineates CD8⁺ Trm cell specialization in human epithelial barriers and correlates with the effector cell balance found in distinct inflammatory skin diseases.

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CD49a expression marks CD8⁺ Trm cells poised for IFN-γ production in human skin

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IL-15 drives potent cytotoxic capacity in CD49a⁺ Trm cells

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IL-17 is preferentially produced by CD49a⁻ CD8⁺ Trm cells in the skin

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CD49a⁺ versus CD49^- Trm cell functional dichotomy is preserved in vitiligo and psoriasis

Peripheral Tc17 and Tc17/Interferon-γ Cells are Increased and Associated with Lung Function in Patients with Chronic Obstructive Pulmonary Disease

Background:

Chronic obstructive pulmonary disease (COPD) is characterized by progressive loss of lung function and local and systemic inflammation, in which CD8⁺ T-cells are believed to play a key role. Activated CD8⁺ T-cells differentiate into distinct subpopulations, including interferon-γ (IFN-γ)-producing Tc1 and interleukin (IL)-17-producing Tc17 cells. Recent evidence indicates that Tc17 cells exhibit considerable plasticity and may convert into IL-17/IFN-γ-double producing (Tc17/IFN-γ) cells when driven by inflammatory conditions. The aim of this study was to investigate the Tc17/IFN-γ subpopulation in peripheral blood of patients with COPD and to evaluate their potential roles in this disease.

Methods:

Peripheral blood samples were collected from 15 never-smokers, 23 smokers with normal lung function, and 25 patients with COPD (Global Initiative for Chronic Obstructive Lung Disease 2–4). Proportions of the IL-17/IFN-γ-double expressing subpopulation were assessed using flow cytometry. Plasma concentrations of cytokines favoring Tc17/IFN-γ differentiation were measured by enzyme-linked immunosorbent assay.

Results:

Patients with COPD had higher proportions of Tc17 cells and Tc17/IFN-γ cells in the peripheral blood than smokers and never-smokers. The plasticity of Tc17 cells was higher than that of Th17 cells. The percentages of Tc17 cells and Tc17/IFN-γ cells showed negative correlations with forced expiratory volume in 1 s % predicted value (r = −0.418, P = 0.03; r = −0.596, P = 0.002, respectively). The plasma concentrations of IL-6, transforming growth factor-β1, and IL-12 were significantly higher in patients with COPD compared with smokers and never-smokers.

Conclusions:

Peripheral Tc17 cells are increased and more likely to convert to Tc17/IFN-γ cells in COPD, suggesting that Tc17 cell plasticity may be involved in persistent inflammation of the disease.

Dynamic Changes in Resident and Infiltrating Epidermal Dendritic Cells in Active and Resolved Psoriasis

Epidermal Langerhans cells (LCs) are spatially separated from dermal dendritic cells (DCs) in healthy human skin. In active psoriasis, maintained by local production of IL-23 and IL-17, inflammatory DCs infiltrate both skin compartments. Here we show that CCR2⁺ epidermal DCs (eDCs) were confined to lesional psoriasis and phenotypically distinct from dermal DCs. The eDCs exceeded the number of LCs and displayed high expression of genes involved in neutrophil recruitment and the activation of keratinocytes and T cells. Resident LCs responded to toll-like receptor 4 and toll-like receptor 7/8 activation with increased IL-23 production, whereas eDCs additionally produced IL-1β together with IL-23 and tumor necrosis factor. Psoriasis typically recur in fixed skin lesions. eDCs were absent from resolved psoriasis. Instead, LCs from anti-tumor necrosis factor-treated lesions retained high IL23A expression and responded to toll-like receptor stimulation by producing IL-23. Our results reveal phenotypic and functional properties of eDCs and resident LCs in different clinical phases of psoriasis, and the capacity of these cells to amplify the epidermal microenvironment through the secretion of IL-17 polarizing cytokines.

Comparative study of isolation, expansion and characterization of epithelial cells

BACKGROUND AIMS

The human epithelial cells (EPCs) have been identified as the essential element for the regeneration of skin construct for burns, wounds and various tissue engineer-based products.

METHODS

In this study, the isolation, expansion and characterization of EPCs from various sources such as juvenile foreskin (JSK), buccal mucosa (BM), penile skin (PS) and urothelium (UR) in serum-free and xeno-free EpiLife media were evaluated.

RESULTS

The growth kinetics study revealed that EPCs from JSK and BM had notably higher growth rates compared with the others. Overall, the EPCs from all sources retained basic morphological characteristics and the functional characteristics such as Pan Cytokeratin (AE1/AE3). In addition, the cryopreservation stability of EPCs was accessed for post-thaw viability and found to be greater than 80% at 1 year of storage, but demonstrated reduced cell recovery (51%) at the second year in fetal bovine serum-free cryopreservation media.

CONCLUSIONS

Our result suggests that the EPCs from four cell sources can be grown in feeder-free, serum-free and xeno-free systems using commercially available EpiLife medium without losing epithelial cell characteristics even after passage 4. However, its suitability for clinical application must be accessed by preclinical and clinical studies.

Decreased expression of IL-27 in moderate-to-severe psoriasis and its anti-inflammation role in imiquimod-induced psoriasis-like mouse model

BACKGROUND

Psoriasis is a high-incident T-cell-mediated autoimmune disease mainly affecting the skin. Interleukin (IL)-27 is a novel member of the IL-6/IL-12 cytokine family, which plays a versatile role in the differentiation and function of distinct T cell subsets. Previous studies uncovered that IL-27 promoted the onset of psoriasis through enhancing the differentiation of T helper (Th) 1 cells. However, the role of IL-27 in other psoriasis-related Th lineages, especially Th17 cells, remains elusive.

OBJECTS

The study aimed to investigate the role of IL-27 in the progression of psoriasis and its underlying mechanisms, particularly its influence on Th1 and Th17.

METHODS

IL-27 and IL-27 receptor α (IL-27Rα) expressions in normal and lesional skin were determined by immunohistochemistry and western blot analysis. Serum levels of IL-27 and IL-10 were measured by ELISA. Expression levels of IL-27 and IL-27 receptor (IL-27R) mRNA in the skin tissue and peripheral blood mononuclear cells (PBMC) were assessed by quantitative polymerase chain reaction (PCR) analysis. To explore the function of IL-27 in vivo, we used imiquimod (IMQ)-induced psoriasis mouse model. We treated mice with IL-27 or its antagonist, evaluated disease severity and detected the cytokine secretion from splenic CD4+ T cells by flow cytometric analysis and the expression levels of IL-17 and IFN-γ in serum and skin lesion.

RESULTS

The expression levels of IL-27 and IL-27Rα were significantly reduced in the moderate-to-severe psoriatic lesions, along with a consistent decrease in serum IL-27 levels, compared with those of healthy control subjects. Moreover, subcutaneous administration of IL-27 recombinant protein lessened severity of IMQ-induced psoriasis-like cutaneous lesions, whereas IL-27p28 antagonist exaggerated the disease severity. Further analysis revealed that IL-27 significantly repressed IL-17 secretion from CD4+ T lymphocytes. Also administration of IL-27 decreased IL-17A level while IL-27p28 antagonist increased IL-17A level in serum and psoriasis-like lesion in the IMQ-treated mice.

CONCLUSION

Our results suggest that IL-27 might predominantly play a protective role in the pathogenesis of psoriasis through abrogating Th17 differentiation. The potential therapeutic benefit of harnessing IL-27 in treating psoriasis awaits future investigation.

Potential role of IL-17-producing CD4/CD8 double negative αβ T cells in psoriatic skin inflammation in a TPA-induced STAT3C transgenic mouse model

BACKGROUND

Psoriasis is one of the most common immune-mediated chronic inflammatory skin disorders and is accompanied by erythematous scaly plaques. There is growing evidence that the IL-23/Th17 axis plays a critical role in development of the disease. It was recently shown that in addition to CD4⁺ Th17 cells, various IL-17-producing cell subsets such as CD8⁺ Tc17 cells, dermal γδ T cells, and innate lymphoid cells are also involved in the development of psoriatic inflammation in humans.

OBJECTIVE

To investigate which subsets of IL-17-producing cells are involved in psoriasis-like skin inflammation in a TPA (tumor promoter 12-O-tetradecanoylphorbol-13-acetate)-induced K14.Stat3C mouse model.

METHOD

Skin-infiltrating cells were isolated from inflamed lesions of TPA-treated K14.Stat3C transgenic mice, and analyzed for IL-17 producing cell subsets by flow cytometry.

RESULTS

We observed significantly increased numbers of IL-17-producing CD4⁺ T cells, CD8⁺ T cells and dermal γδ T cells in TPA-induced skin lesions of K14.Stat3C mice. Additionally, we found that another IL-17-producing T cell subset, αβ-TCR⁺ CD4CD8 double negative T cells (DN αβ T cells), was also increased in lesional skin. These IL-17-producing DN αβ T cells are NK1.1 negative, suggesting they are not natural killer T cells or mucosal associated invariant T cells. As well as other IL-17-producing cells, DN αβ T cells in the inflamed skin can also respond to IL-23 stimulation to produce IL-17. It is also suggested that DN αβ T cells may express retinoic acid-related orphan receptor gamma t and CC chemokine receptor 6.

CONCLUSION

In TPA-induced lesional skin of K14.Stat3C mice, IL-17-producing CD4⁺ Th17 cells, CD8⁺ Tc17 cells, dermal γδ T cells and TCR^- cells probably containing ILCs all participated in skin inflammation, which is similar to human clinical psoriatic features. Furthermore, we showed for the first time the possibility that an IL-17-producing DN αβ T cell subset is also involved in psoriatic inflammation.

Expanding the List of Dysregulated Immunosuppressive Cells in Psoriasis

Traditionally, myeloid-derived suppressor cells (MDSC) have been studied in regard to their increased numbers of circulating cells in cancer patients. Recent research efforts have also increased awareness of MDSC in non-malignant inflammatory diseases, including asthma, inflammatory bowel disease, and arthritis. Psoriasis can now be added to the growing list of inflammatory disorders with an MDSC component. Cao et al. report increased numbers of monocytic myeloid-derived suppressor cells (Mo-MDSC) in psoriasis patients and examine the implication of dysregulated Mo-MDSC function. Cao et al. describe psoriatic Mo-MDSC that produce increased IL-23, IL-1b, and CCL4 cytokines compared to Mo-MDSC from healthy controls. These results complement previous research demonstrating psoriatic Mo-MDSC are unable to suppress autologous and heterologous CD8 T-cell proliferations, display decreased expression levels of PD-1 as well as PD-L1, and fail to produce effective immuno-competent regulatory T cells (Tregs). Cao et al. also identify the unique expression of the surface protein DC-HIL on psoriatic Mo-MDSC. The expanded population of DC-HIL(+) Mo-MDSC in psoriasis patients, however, display inferior suppressive capabilities compared to DC-HIL(+) Mo-MDSC found in melanoma patients, suggesting contextual signaling as a potential contributing factor to Mo-MDSC function.

T Helper Cell Subsets in Clinical Manifestations of Psoriasis

Psoriasis is a chronic inflammatory skin disease, which is associated with systemic inflammation and comorbidities, such as psoriatic arthritis and cardiovascular diseases. The autoimmune nature of psoriasis has been established only recently, conferring a central role to epidermal CD8 T cells recognizing self-epitopes in the initial phase of the disease. Different subsets of helper cells have also been reported as key players in the psoriasis pathogenesis. Here, we reviewed the knowledge on the role of each subset in the psoriatic cascade and in the different clinical manifestations of the disease. We will discuss the role of Th1 and Th17 cells in the initiation and in the amplification phase of cutaneous inflammation. Moreover, we will discuss the recently proposed role of tissue resident Th22 cells in disease memory in sites of recurrent psoriasis and the possible involvement of Th9 cells. Finally, we will discuss the hypothesis of a link between T helper cell subsets recirculating from the skin and the systemic manifestations of psoriasis.

Memory T cells in cutaneous leishmaniasis

Leishmania causes a spectrum of diseases that range from self-healing to fatal infections. Control of leishmania is dependent upon generating CD4+ Th1 cells that produce IFNγ, leading to macrophage activation and killing of the intracellular parasites. Following resolution of the disease, short-lived effector T cells, as well as long-lived central memory T cells and skin resident memory T cells, are retained and able to mediate immunity to a secondary infection. However, there is no vaccine for leishmaniasis, and the drugs used to treat the disease can be toxic and ineffective. While a live infection generates immunity, a successful vaccine will depend upon generating memory T cells that can be maintained without the continued presence of parasites. Since both central memory and skin resident memory T cells are long-lived, they may be the appropriate targets for a leishmaniasis vaccine.

CD8(+) T cells in human autoimmune arthritis: the unusual suspects

CD8(+) T cells are key players in the body's defence against viral infections and cancer. To date, data on the role of CD8(+) T cells in autoimmune diseases have been scarce, especially when compared with the wealth of research on CD4(+) T cells. However, growing evidence suggests that CD8(+) T-cell homeostasis is impaired in human autoimmune diseases. The contribution of CD8(+) T cells to autoimmune arthritis is indicated by the close association of MHC class I polymorphisms with disease risk, as well as the correlation between CD8(+) T-cell phenotype and disease outcome. The heterogeneous phenotype, resistance to regulation and impaired regulatory function of CD8(+) T cells - especially at the target organ - might contribute to the persistence of autoimmune inflammation. Moreover, newly identified populations of tissue-resident CD8(+) T cells and their interaction with antigen-presenting cells might have a key role in disease pathology. In this Review, we assess the link between CD8(+) T cells, autoimmune arthritis and the basis of their homeostatic changes under inflammatory conditions. Improved insight into CD8(+) T cell-specific pathogenicity will be essential for a better understanding of autoimmune arthritis and the identification of new therapeutic targets.

Cutting Edge: Skin CCR10+ CD8+ T Cells Support Resident Regulatory T Cells through the B7.2/Receptor Axis To Regulate Local Immune Homeostasis and Response

Resident T cells in barrier tissues are important in protecting against foreign agents but can also contribute to inflammatory diseases if dysregulated. How T cell homeostasis is maintained in barrier tissues is still poorly understood. We report that resident CD8(+) T cells directly support maintenance of regulatory T cells (Tregs) in the skin to promote immune homeostasis. Impaired establishment of resident CD8(+) T cells caused by knockout of the skin-homing chemokine receptor CCR10 resulted in an altered balance of resident Tregs and CD4(+) effector T cells in the skin and overreactive inflammatory responses to cutaneous stimulations. Furthermore, B7.2 expressed on skin CD8(+) T cells supports the survival of Tregs, likely through interaction with its receptor CTLA-4, which is highly expressed on skin Tregs. Our findings provide novel insights into T cell homeostatic regulation in the skin and may improve our understanding of the pathobiology of tissue inflammatory diseases.

Recent advances in understanding psoriasis

T helper (Th) cells producing interleukin (IL)-17, IL-22, and tumor necrosis factor (TNF) form the key T cell population driving psoriasis pathogenesis. They orchestrate the inflammation in the skin that results in the proliferation of keratinocytes and endothelial cells. Besides Th17 cells, other immune cells that are capable of producing IL-17-associated cytokines participate in psoriatic inflammation. Recent advances in psoriasis research improved our understanding of the cellular and molecular players that are involved in Th17 pathology and inflammatory pathways in the skin. The inflammation-driving actions of TNF in psoriasis are already well known and antibodies against TNF are successful in the treatment of Th17-mediated psoriatic skin inflammation. A further key cytokine with potent IL-17-/IL-22-promoting properties is IL-23. Therapeutics directly neutralizing IL-23 or IL-17 itself are now extending the therapeutic spectrum of antipsoriatic agents and further developments are on the way. The enormous progress in psoriasis research allows us to control this Th17-mediated inflammatory skin disease in many patients.

A role for CCR5(+)CD4 T cells in cutaneous psoriasis and for CD103(+) CCR4(+) CD8 Teff cells in the associated systemic inflammation

Recent results have identified critical components of the T cell response involved in the initiation and amplification phases of psoriasis. However the link between T cell responses arising in the skin and the systemic inflammation associated with severe psoriasis is largely unknown. We hypothesized that specific subsets of memory T cells recirculating from the skin could play a role. We therefore dissected the circulating memory T cell compartment in patients by analyzing the TCM, TEM and Teff phenotype, the pattern of CCR4 and CCR5 chemokine receptor expression and the expression of the tissue homing molecule CD103. For each subset we calculated the correlation with the Psoriasis Area and Severity Index (PASI) and with the extent of systemic inflammation measured as serum level of the prototypic short pentraxin, C reactive protein (CRP). Validation was performed by comparison with gene expression data in psoriatic plaques. We found that circulating CD103(+)CCR4(+)CCR5(+) and CCR4(+)CCR6(-) CD8(+) Teff cells, were highly correlated with CRP levels as well as with the validated index PASI, reflecting a link between skin involvement and systemic inflammation in patients with severe psoriasis. In addition we observed a contraction of circulating CCR5(+) T cells in psoriasis patients, with a highly significant inverse correlation between CCR5(+)CD4 T cells and the PASI score. Increased expression of CCR5 and CCL5 genes in psoriatic skin lesions was consistent with an accumulation of CCR5(+) cells in psoriatic plaques indicating a role for CCR5/CCL5 axis in disease pathogenesis.

Mechanisms of interleukin-22's beneficial effects in acute pancreatitis

Acute pancreatitis (AP) is a disorder characterized by parenchymal injury of the pancreas controlled by immune cell-mediated inflammation. AP remains a significant challenge in the clinic due to a lack of specific and effective treatment. Knowledge of the complex mechanisms that regulate the inflammatory response in AP is needed for the development of new approaches to treatment, since immune cell-derived inflammatory cytokines have been recognized to play critical roles in the pathogenesis of the disease. Recent studies have shown that interleukin (IL)-22, a cytokine secreted by leukocytes, when applied in the severe animal models of AP, protects against the inflammation-mediated acinar injury. In contrast, in a mild AP model, endogenous IL-22 has been found to be a predominantly anti-inflammatory mediator that inhibits inflammatory cell infiltration via the induction of Reg3 proteins in acinar cells, but does not protect against acinar injury in the early stage of AP. However, constitutively over-expressed IL-22 can prevent the initial acinar injury caused by excessive autophagy through the induction of the anti-autophagic proteins Bcl-2 and Bcl-XL. Thus IL-22 plays different roles in AP depending on the severity of the AP model. This review focuses on these recently reported findings for the purpose of better understanding IL-22's regulatory roles in AP which could help to develop a novel therapeutic strategy.

Tissue-resident memory T cells: local specialists in immune defence

T cells have crucial roles in protection against infection and cancer. Although the trafficking of memory T cells around the body is integral to their capacity to provide immune protection, studies have shown that specialization of some memory T cells into unique tissue-resident subsets gives the host enhanced regional immunity. In recent years, there has been considerable progress in our understanding of tissue-resident T cell development and function, revealing mechanisms for enhanced protective immunity that have the potential to influence rational vaccine design. This Review discusses the major advances and the emerging concepts in this field, summarizes what is known about the differentiation and the protective functions of tissue-resident memory T cells in different tissues in the body and highlights key unanswered questions.

Human skin is protected by four functionally and phenotypically discrete populations of resident and recirculating memory T cells

The skin of an adult human contains about 20 billion memory T cells. Epithelial barrier tissues are infiltrated by a combination of resident and recirculating T cells in mice, but the relative proportions and functional activities of resident versus recirculating T cells have not been evaluated in human skin. We discriminated resident from recirculating T cells in human-engrafted mice and lymphoma patients using alemtuzumab, a medication that depletes recirculating T cells from skin, and then analyzed these T cell populations in healthy human skin. All nonrecirculating resident memory T cells (TRM) expressed CD69, but most were CD4(+), CD103(-), and located in the dermis, in contrast to studies in mice. Both CD4(+) and CD8(+) CD103(+) TRM were enriched in the epidermis, had potent effector functions, and had a limited proliferative capacity compared to CD103(-) TRM. TRM of both types had more potent effector functions than recirculating T cells. We observed two distinct populations of recirculating T cells, CCR7(+)/L-selectin(+) central memory T cells (TCM) and CCR7(+)/L-selectin(-) T cells, which we term migratory memory T cells (TMM). Circulating skin-tropic TMM were intermediate in cytokine production between TCM and effector memory T cells. In patients with cutaneous T cell lymphoma, malignant TCM and TMM induced distinct inflammatory skin lesions, and TMM were depleted more slowly from skin after alemtuzumab, suggesting that TMM may recirculate more slowly. In summary, human skin is protected by four functionally distinct populations of T cells, two resident and two recirculating, with differing territories of migration and distinct functional activities.

Adverse cutaneous drug eruptions: current understanding

Adverse cutaneous drug reactions are recognized as being major health problems worldwide causing considerable costs for health care systems. Most adverse cutaneous drug reactions follow a benign course; however, up to 2% of all adverse cutaneous drug eruptions are severe and life-threatening. These include acute generalized exanthematous pustulosis (AGEP), drug reaction with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN). Physicians should be aware of specific red flags to rapidly identify these severe cutaneous drug eruptions and initiate appropriate treatment. Besides significant progress in clinical classification and treatment, recent studies have greatly enhanced our understanding in the pathophysiology of adverse cutaneous drug reactions. Genetic susceptibilities to certain drugs have been identified in SJS/TEN patients, viral reactivation in DRESS has been elucidated, and the discovery of tissue resident memory T cells helps to better understand the recurrent site-specific inflammation in patients with fixed drug eruption.

Resident memory T cells in human health and disease

Resident memory T cells are non-recirculating memory T cells that persist long-term in epithelial barrier tissues, including the gastrointestinal tract, lung, skin, and reproductive tract. Resident memory T cells persist in the absence of antigens, have impressive effector functions, and provide rapid on-site immune protection against known pathogens in peripheral tissues. A fundamentally distinct gene expression program differentiates resident memory T cells from circulating T cells. Although these cells likely evolved to provide rapid immune protection against pathogens, autoreactive, aberrantly activated, and malignant resident memory cells contribute to numerous human inflammatory diseases including mycosis fungoides and psoriasis. This review will discuss both the science and medicine of resident memory T cells, exploring how these cells contribute to healthy immune function and discussing what is known about how these cells contribute to human inflammatory and autoimmune diseases.

Human mast cells are major IL-22 producers in patients with psoriasis and atopic dermatitis

BACKGROUND

Psoriasis is a systemic inflammatory disease in which IL-17 and IL-22 levels are markedly increased in the skin and blood. The prevalent concept, using skin cells that are isolated from psoriatic plaques and examined after cell expansion and in vitro stimulation, is that IL-17 and IL-22 production essentially results from T cells and the rare type 3 innate lymphoid cells.

OBJECTIVE

We sought to examine the cellular source of IL-17A and IL-22 at the protein and transcriptional single-cell level immediately after ex vivo skin cell isolation from psoriatic plaques.

METHODS

Skin biopsy specimens were collected from patients with psoriasis, as well as from patients with atopic dermatitis. Cell suspensions were prepared by combining mild enzymatic digestion and mechanical dissociation and analyzed for cytokine expression without prior in vitro culture and stimulation. Expression of IL-17 and IL-22 was quantified at the protein and mRNA single-cell level by using flow cytometry.

RESULTS

IL-22 is predominantly expressed by CD3(-)c-Kit(+) cells relative to CD3(+) T cells in lesional skin of patients with psoriasis and patients with atopic dermatitis. Strikingly, we identified c-Kit(+)FcεRI(+) mast cells as major IL-22 producers. The proportion of mast cells that produce IL-22 ranges from 20% to 80% in patients with psoriasis or those with atopic dermatitis. Skin mast cells express IL-22 and IL-17 mRNA. Conversely, IL-17-producing T cells outnumber IL-17-producing mast cells, which also express IL-17 receptor.

CONCLUSION

Human skin mast cells are previously unrecognized IL-22 producers. We further established that skin mast cells express IL-17. Thus mast cells might play an important role in the physiopathology of chronic inflammatory skin disorders.

CCL20 and IL22 Messenger RNA Expression After Adalimumab vs Methotrexate Treatment of Psoriasis: A Randomized Clinical Trial

IMPORTANCE

Methotrexate is a first-line systemic agent for treating of psoriasis, although its onset of effects is slower and overall it is less effective than tumor necrosis factor blockers.

OBJECTIVE

To differentiate the response of psoriatic disease to adalimumab and methotrexate sodium.

DESIGN, SETTING, AND PARTICIPANTS

Single-center, randomized, assessor-blind, 2-arm clinical trial of 30 patients from the outpatient dermatology center of Tufts Medical Center, enrolled from August 18, 2009, to October 11, 2011. Patients aged 18 to 85 years with chronic plaque-type psoriasis, a minimum Physician Global Assessment score of 3 (higher scores indicate more severe disease), and a psoriatic plaque of at least 2 cm were randomized in a 1:1 fashion to receive subcutaneous adalimumab or oral methotrexate. Skin biopsy specimens obtained at baseline and weeks 1, 2, 4, and 16 were given a histologic grade by blinded assessors to evaluate treatment response. Analyses were conducted from April 16, 2013, to January 5, 2015.

INTERVENTIONS

A 16-week course of subcutaneous adalimumab (40 mg every 2 weeks after a loading dose) or low-dosage oral methotrexate sodium (7.5-25 mg/wk).

MAIN OUTCOMES AND MEASURES

Changes in genomic, immunohistochemical, and messenger RNA (mRNA) profiles.

RESULTS

Methotrexate responders experienced significant downregulation of helper T-cell-related (T(H)1, T(H)17, and T(H)22) mRNA expression compared with methotrexate nonresponders. Comparisons among adalimumab-treated patients were limited by the number of nonresponders (n = 1). Between adalimumab and methotrexate responders, we found no significant differences in gene expression at any study point or in the expression of T-cell-related mRNA at week 16. Adalimumab responders demonstrated early downregulation of chemokine (C-C motif) ligand 20 (CCL20) mRNA (mean [SE] at week 2, -1.83 [0.52], P < .001; week 16, -3.55 [0.54], P < .001) compared with late downregulation for methotrexate responders (week 2, 0.02 [0.51], P = .96; week 16, -2.96 [0.51], P < .001). Similar differences were observed with interleukin 22 (IL22) mRNA showing early downregulation for adalimumab responders (week 2, -3.17 [1.00], P < .001; week 16, -3.58 [1.00], P < .001) compared with late downregulation for methotrexate responders (week 2, -0.44 [0.68], P = .64; week 16, -5.14 [0.68], P < .001). Analysis of variance findings for key mRNA and immunohistochemical marker expression over the study course were significant only for CCL20 (P = .03) and IL22 (P = .006) mRNA comparing adalimumab and methotrexate responders.

CONCLUSIONS AND RELEVANCE

Methotrexate is an immunomodulator with effects on helper T-cell signaling in psoriasis. Similar genomic and immunohistochemical response signatures and levels of mRNA downregulation at study completion among adalimumab and methotrexate responders suggest a disease-driven instead of therapeutic-driven pathway regulation. Adalimumab and methotrexate responses are differentiated by patterns of normalization of CCL20 and IL22 mRNA expression and may explain the varied onset and degree of clinical responses by each treatment.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00932113.

The emerging role of resident memory T cells in protective immunity and inflammatory disease

Over the past decade, it has become clear that there is an important subset of memory T cells that resides in tissues-tissue-resident memory T (TRM) cells. There is an emerging understanding that TRM cells have a role in human tissue-specific immune and inflammatory diseases. Furthermore, the nature of the molecular signals that maintain TRM cells in tissues is the subject of much investigation. In addition, whereas it is logical for TRM cells to be located in barrier tissues at interfaces with the environment, these cells have also been found in brain, kidney, joint and other non-barrier tissues in humans and mice. Given the biology and behavior of these cells, it is likely that they have a role in chronic relapsing and remitting diseases of both barrier and non-barrier tissues. In this Review we discuss recent insights into the biology of TRM cells with a particular focus on their roles in disease, both proven and putative.

Laser capture microdissection followed by next-generation sequencing identifies disease-related microRNAs in psoriatic skin that reflect systemic microRNA changes in psoriasis

Psoriasis is a systemic disease with cutaneous manifestations. MicroRNAs (miRNAs) are small non-coding RNA molecules that are differentially expressed in psoriatic skin; however, only few cell- and region-specific miRNAs have been identified in psoriatic lesions. We used laser capture microdissection (LCM) and next-generation sequencing (NGS) to study the specific miRNA expression profiles in the epidermis (Epi) and dermal inflammatory infiltrates (RD) of psoriatic skin (N = 6). We identified 24 deregulated miRNAs in the Epi and 37 deregulated miRNAs in the RD of psoriatic plaque compared with normal psoriatic skin (FCH > 2, FDR < 0.05). Interestingly, 9 of the 37 miRNAs in RD, including miR-193b and miR-223, were recently described as deregulated in circulating peripheral blood mononuclear cells (PBMCs) from patients with psoriasis. Using flow cytometry and qRT-PCR, we found that miR-193b and miR-223 were expressed in Th17 cells. In conclusion, we demonstrate that LCM combined with NGS provides a robust approach to explore the global miRNA expression in the epidermal and dermal compartments of psoriatic skin. Furthermore, our results indicate that the altered local miRNA changes seen in the RD are reflected in the circulating immune cells, suggesting that miRNAs may contribute to the pathogenesis of psoriasis.

IL-17A-producing CD8(+)T cells as therapeutic targets in autoimmunity

INTRODUCTION

The involvement of IL-17-producing CD8(+)T cells (TC17) in various conditions, such as infection, cancer and autoimmune inflammation, has been documented in both humans and mice; however, TC17 cells have received only marginal attention.

AREAS COVERED

Here, we provide an overview of the cytokines, chemokines, and cytokine and chemokine receptors that characterize the murine and human TC17 cell phenotype. We also discuss signaling pathways, molecular interactions, and transcriptional and epigenetic events that contribute to TC17 differentiation and acquisition of effector functions. Heterogeneity and inherent phenotypic instability of TC17 cells were shown both in humans and murine models. Aberrant expression of TC17 cells was observed in many autoimmune conditions. Moreover, functional analysis demonstrated in vivo plasticity of TC17 cells may be a key feature of TC17 cell biology in autoimmune diseases.

EXPERT OPINION

Due to its important roles in inflammation and autoimmunity, TC17 cell pathway may have promise as a potential therapeutic target for autoimmune diseases. The strategies include the suppression of TC17 cell generation and migration and the blockade of TC17 cell instability and heterogeneity. TMP778 may open an avenue to novel therapeutic strategies.

Tc17 Cells in Immunity and Systemic Autoimmunity

Tc17 cells-a subset of CD8(+)T cells-have recently been identified that are characterized by the production of interleukin (IL)-17. Cytokines IL-6 and transforming growth factor-beta 1 (TGF-β1) and transcription factors signaling transducers and activators of transcription (STAT)3, retinoic acid receptor-related orphan nuclear receptor gamma (RORγt), and interferon regulatory factor (IRF)4 are necessary for differentiation of Tc17 cells, controlling expression of molecules essential for Tc17 cell trafficking and function. Current human researches have determined the significance of CD161 expression as either a marker of Tc17 cells or as an effector and regulator of Tc17 cell function. Noncytotoxic Tc17 cells possess a high plasticity to convert into IFN-γ producing cells, which exhibit strong cytotoxic activity. The importance of in vivo plasticity of Tc17 cells for the induction of autoimmune diseases has been demonstrated and Tc17 cells potentially represent novel therapeutic targets in autoimmune diseases. The involvement of interleukin (IL)-17-producing CD8(+)T cells (Tc17) in various conditions, such as infection, cancer, and autoimmune inflammation, has been documented in both humans and mice; however, Tc17 cells have received only marginal attention. Here, we provide an overview of the cytokines and chemokines that characterize the murine and human Tc17 cells. Moreover, we discuss signaling pathways, molecular interactions, and transcriptional events that contribute to Tc17 differentiation and acquisition of effector functions. Also considered is the basis of Tc17 cell plasticity toward the Tc1 lineage, and we suggest that in vivo plasticity of Tc17 cells may be a key feature of Tc17 cell biology in autoimmune diseases. Furthermore, current human researches have revealed that Tc17 cells are different than that in mice because all of them express CD161 and exclusively originate from CD161 precursors present in umbilical cord blood. Finally, we focus on the recent evidence for long-lived Tc17 memory cell populations in mouse models and humans, and their functional roles in mediating disease memory. Hopefully, the information obtained will benefit for developing novel therapeutic strategies.

Tissue-resident T cells: dynamic players in skin immunity

The skin is a large and complex organ that acts as a critical barrier protecting the body from pathogens in the environment. Numerous heterogeneous populations of immune cells are found within skin, including some that remain resident and others that can enter and exit the skin as part of their migration program. Pathogen-specific CD8⁺ T cells that persist in the epidermis following infection are a unique population of memory cells with important roles in immune surveillance and protective responses to reinfection. How these tissue-resident memory T cells form in the skin, the signals controlling their persistence and behavior, and the mechanisms by which they mediate local recall responses are just beginning to be elucidated. Here, we discuss recent progress in understanding the roles of these skin-resident T cells and also highlight some of the key unanswered questions that need addressing.

Mucosal resident memory CD4 T cells in protection and immunopathology

Tissue-resident memory T cells (TRM) comprise a newly defined subset, which comprises a major component of lymphocyte populations in diverse peripheral tissue sites, including mucosal tissues, barrier surfaces, and in other non-lymphoid and lymphoid sites in humans and mice. Many studies have focused on the role of CD8 TRM in protection; however, there is now accumulating evidence that CD4 TRM predominate in tissue sites, and are integral for in situ protective immunity, particularly in mucosal sites. New evidence suggests that mucosal CD4 TRM populations differentiate at tissue sites following the recruitment of effector T cells by local inflammation or infection. The resulting TRM populations are enriched in T-cell specificities associated with the inducing pathogen/antigen. This compartmentalization of memory T cells at specific tissue sites may provide an optimal design for future vaccination strategies. In addition, emerging evidence suggests that CD4 TRM may also play a role in immunoregulation and immunopathology, and therefore, targeting TRM may be a viable therapeutic approach to treat inflammatory diseases in mucosal sites. This review will summarize our current understanding of CD4 TRM in diverse tissues, with an emphasis on their role in protective immunity and the mechanisms by which these populations are established and maintained in diverse mucosal sites.