OX40 ligand and OX40 are increased in atopic dermatitis lesions but do not correlate with clinical severity

The Central Roles of Keratinocytes in Coordinating Skin Immunity

The function of keratinocytes (KCs) to form a barrier and produce cytokines is well-known, but recent progress has revealed many different roles for KCs in regulation of skin immunity. In this review, we provide an update on the current understanding of how KCs communicate with microbes, immunocytes, neurons, and other cells to form an effective immune barrier. We catalog the large list of genes and metabolites of KCs that participate in host defense and discuss the mechanisms of immune crosstalk, addressing how KCs simultaneously form a physical barrier, communicate with fibroblasts, and control immune signals. Overall, the signals sent and received by KCs are an exciting group of therapeutic targets to explore in the treatment of dermatologic disorders.

[Monoclonal antibodies for inflammatory, autoimmune and oncological skin diseases]

In 1997 rituximab, a genetically engineered chimeric monoclonal antibody (mAb) targeting CD20 expressed on B cells was approved for treatment of non-Hodgkin's lymphoma. Since then, pharmacological improvements combined with increased knowledge on the immunopathogenesis of diseases led to the development of specific mAb targeting different antigens (e.g., interleukins or transmembrane receptors). This approach reshaped the therapeutic methodology in many fields, including dermatology. Nowadays, the treatment of frequent and possibly impairing inflammatory disorders such as psoriasis, atopic dermatitis or hidradenitis suppurativa have different mAbs approved for both adult and pediatric patients. This class of drugs often shows a more favorable outcome and a better safety profile than routine immunosuppressants, such as steroids and steroid-sparing substances. For many years mAbs also represented a pillar of oncological treatment for severe diseases such as malignant melanoma or Merkel cell carcinoma. This review summarizes the current knowledge on already approved and promising new mAbs for the treatment of inflammatory and oncological skin diseases.

The role of OX40 ligand/OX40 axis signalling in atopic dermatitis

Atopic dermatitis (AD) is a heterogeneous inflammatory condition involving multiple immune pathways mediated by pathogenic T cells. OX40 ligand (OX40L) and OX40 are costimulatory immune checkpoint molecules that regulate effector and memory T-cell activity and promote sustained immune responses in multiple immunological pathways, including T helper (Th)2, Th1, Th17 and Th22. As such, OX40L/OX40 signalling between antigen-presenting cells (APCs) and activated T cells postantigen recognition promotes pathogenic T-cell proliferation and survival. Under inflammatory conditions, OX40L is upregulated on APCs, enhancing the magnitude of antigen-specific T-cell responses and secretion of proinflammatory cytokines. In AD, OX40L/OX40 signalling contributes to the amplification and chronic persistence of T-cell-mediated inflammation. Recent therapeutic success in clinical trials has highlighted the importance of the OX40L/OX40 axis as a promising target for the treatment of AD. Here, we discuss the many factors that are involved in the expression of OX40L and OX40, including the cytokine milieu, antigen presentation, the inflammatory environment in AD, and the therapeutic direction influenced by this costimulatory pathway.

The Role of OX40-OX40L Axis in the Pathogenesis of Atopic Dermatitis

OX40 is a co-stimulatory immune checkpoint molecule that promotes the activation and the effector function of T lymphocytes through interaction with its ligand (OX40L) on antigen-presenting cells. OX40-OX40L axis plays a crucial role in Th1 and Th2 cell expansion, particularly during the late phases or long-lasting response. Atopic dermatitis is characterized by an immune dysregulation of Th2 activity and by an overproduction of proinflammatory cytokines such as interleukin (IL)-4 and IL-13. Other molecules involved in its pathogenesis include thymic stromal lymphopoietin, IL-33, and IL-25, which contribute to the promotion of OX40L expression on dendritic cells. Lesional skin in atopic dermatitis exhibits a higher level of OX40L+-presenting cells compared with other dermatologic diseases or normal skin. Recent clinical trials using antagonizing anti-OX40 or anti-OX40L antibodies have shown symptom improvement and cutaneous manifestation alleviation in patients with atopic dermatitis. These findings suggest the relevance of the OX40-OX40L axis in atopic dermatitis pathogenesis.

OX40 in the Pathogenesis of Atopic Dermatitis-A New Therapeutic Target

Atopic dermatitis (AD) is a chronic, heterogeneous, inflammatory disease characterized by skin lesions, pruritus, and pain. Patients with moderate-to-severe AD experience chronic symptoms, intensified by unpredictable flares, and often have comorbidities and secondary complications, which can result in significant clinical burden that impacts the patient's overall quality of life. The complex interplay of immune dysregulation and skin barrier disruption drives AD pathogenesis, of which T-cell-dependent inflammation plays a critical role in patients with AD. Despite new targeted therapies, many patients with moderate-to-severe AD fail to achieve or sustain their individual treatment goals and/or may not be suitable for or tolerate these therapies. There remains a need for a novel, efficacious, well-tolerated therapeutic option that can deliver durable benefits across a heterogeneous AD patient population. Expression of OX40 [tumor necrosis factor receptor superfamily, member 4 (TNFRSF4)], a prominent T-cell co-stimulatory molecule, and its ligand [OX40L; tumor necrosis factor superfamily, member 4 (TNFSF4)] is increased in AD. As the OX40 pathway is critical for expansion, differentiation, and survival of effector and memory T cells, its targeting might be a promising therapeutic approach to provide sustained inhibition of pathogenic T cells and associated inflammation and broad disease control. Antibodies against OX40 [rocatinlimab (AMG 451/KHK4083) and telazorlimab (GBR 830)] or OX40L [amlitelimab (KY1005)] have shown promising results in early-phase clinical studies of moderate-to-severe AD, highlighting the importance of OX40 signaling as a new therapeutic target in AD.

Atopic Dermatitis Itch: Scratching for an Explanation

Chronic pruritus is a cardinal symptom of atopic dermatitis (AD). The mechanisms underlying atopic itch involve intricate crosstalk among skin, immune components, and neural components. In this review, we explore these mechanisms, focusing on key players and interactions that induce and exacerbate itch. We discuss the similarities and differences between pruritus and pain in patients with AD as well as the relationship between pruritus and factors such as sweat and the skin microbiome. Furthermore, we explore novel targets that could provide significant itch relief in these patients as well as exciting future research directions to better understand atopic pruritus in darker skin types.

T cell co-stimulatory and co-inhibitory pathways in atopic dermatitis

The use of immune checkpoint inhibitors (ICIs) targeting the T cell inhibitory pathways has revolutionized cancer treatment. However, ICIs might induce progressive atopic dermatitis (AD) by affecting T cell reactivation. The critical role of T cells in AD pathogenesis is widely known. T cell co-signaling pathways regulate T cell activation, where co-signaling molecules are essential for determining the magnitude of the T cell response to antigens. Given the increasing use of ICIs in cancer treatment, a timely overview of the role of T cell co-signaling molecules in AD is required. In this review, we emphasize the importance of these molecules involved in AD pathogenesis. We also discuss the potential of targeting T cell co-signaling pathways to treat AD and present the unresolved issues and existing limitations. A better understanding of the T cell co-signaling pathways would aid investigation of the mechanism, prognosis evaluation, and treatment of AD.

Sequential Increase in Complement Factor I, iC3b, and Cells Expressing CD11b or CD14 in Cutaneous Vasculitis

Mast cells contribute to the pathogenesis of cutaneous vasculitis through complement C3 that is cleaved to C3b and then to iC3b by complement factor I. The receptor of iC3b, CD11b, is expressed on neutrophils and monocytes and CD14 on monocytes. Their role in vasculitis is obscure. In this study, frozen skin biopsies from the nonlesional skin, initial petechial lesion, and palpable purpura lesion from 10 patients with immunocomplex-mediated small vessel vasculitis were studied immunohistochemically for complement factor I, iC3b, CD11b, and CD14. Peripheral blood mononuclear cells from 5 healthy subjects were used to study cell migration and cytokine secretion. Already, the nonlesional skin revealed marked immunostaining of complement factor I, iC3b, CD11b, and CD14, and their expression increased sequentially in initial petechial and palpable purpura lesions. Mast cell C3c correlated to iC3b, and both of them correlated to CD11b⁺ and CD14⁺ cells, in the nonlesional skin. The stimulation of mononuclear cells with 0.01-0.1 μg/ml iC3b induced cell migration in the transwell assay. C3a stimulated slightly interleukin-8 secretion, whereas 1 μg/ml iC3b inhibited it slightly, in 4/5 subjects. In conclusion, the C3-C3b-iC3b axis is activated already in the early vasculitis lesion leading to progressive accumulation of CD11b⁺ and CD14⁺ cells.

The Role of Co-Signaling Molecules in Psoriasis and Their Implications for Targeted Treatment

Psoriasis is a chronic, systemic immune-mediated inflammatory disease manifesting in the skin, joint or both. Co-signaling molecules are essential for determining the magnitude of the T cell response to the antigen. According to the function of co-signaling molecules, they can be divided into co-stimulatory molecules and co-inhibitory molecules. The role of co-signaling molecules in psoriasis is recognized, mainly including the co-stimulatory molecules CD28, CD40, OX40, CD27, DR3, LFA-1, and LFA-3 and the co-inhibitory molecules CTLA-4, PD-1, and TIM-3. They impact the pathological process of psoriasis by modulating the immune strength of T cells, regulating the production of cytokines or the differentiation of Tregs. In recent years, immunotherapies targeting co-signaling molecules have made significant progress and shown broad application prospects in psoriasis. This review aims to outline the possible role of co-signaling molecules in the pathogenesis of psoriasis and their potential application for the treatment of psoriasis.

OX40L-OX40 Signaling in Atopic Dermatitis

OX40 is one of the co-stimulatory molecules expressed on T cells, and it is engaged by OX40L, primarily expressed on professional antigen-presenting cells such as dendritic cells. The OX40L-OX40 axis is involved in the sustained activation and expansion of effector T and effector memory T cells, but it is not active in naïve and resting memory T cells. Ligation of OX40 by OX40L accelerates both T helper 1 (Th1) and T helper 2 (Th2) effector cell differentiation. Recent therapeutic success in clinical trials highlights the importance of the OX40L-OX40 axis as a promising target for the treatment of atopic dermatitis.

A deep dive into UV-based phototherapy: Mechanisms of action and emerging molecular targets in inflammation and cancer

UV-based phototherapy (including psoralen plus UVA (PUVA), UVB and UVA1) has a long, successful history in the management of numerous cutaneous disorders. Photoresponsive diseases are etiologically diverse, but most involve disturbances in local (and occasionally systemic) inflammatory cells and/or abnormalities in keratinocytes that trigger inflammation. UV-based phototherapy works by regulating the inflammatory component and inducing apoptosis of pathogenic cells. This results in a fascinating and complex network of simultaneous events-immediate transcriptional changes in keratinocytes, immune cells, and pigment cells; the emergence of apoptotic bodies; and the trafficking of antigen-presenting cells in skin-that quickly transform the microenvironment of UV-exposed skin. Molecular elements in this system of UV recognition and response include chromophores, metabolic byproducts, innate immune receptors, neurotransmitters and mediators such as chemokines and cytokines, antimicrobial peptides, and platelet activating factor (PAF) and PAF-like molecules that simultaneously shape the immunomodulatory effects of UV and their interplay with the microbiota of the skin and beyond. Phototherapy's key effects-proapoptotic, immunomodulatory, antipruritic, antifibrotic, propigmentary, and pro-prebiotic-promote clinical improvement in various skin diseases such as psoriasis, atopic dermatitis (AD), graft-versus-host disease (GvHD), vitiligo, scleroderma, and cutaneous T-cell lymphoma (CTCL) as well as prevention of polymorphic light eruption (PLE). As understanding of phototherapy improves, new therapies (UV- and non-UV-based) are being developed that will modify regulatory T-cells (Treg), interact with (resident) memory T-cells and /or utilize agonists and antagonists as well as antibodies targeting soluble molecules such as cytokines and chemokines, transcription factors, and a variety of membrane-associated receptors.

New and Emerging Biologics for Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease that is characterized by complex pathophysiology involving both skin barrier dysfunction and aberrant type 2 inflammation/immune responses. AD can be a debilitating condition that drastically impairs quality of life, especially in patients with moderate-to-severe disease. Currently, topical therapies such as corticosteroids and non-steroidal immunomodulatory therapy provide limited efficacy for patients with moderate-to-severe AD; limitations include inadequate response, cutaneous toxicity from overuse, and poor tolerance due to stinging and burning. Historically, the development of targeted therapies has been challenging due to the complex and multifaceted etiology of AD. Recent progress in understanding the immunopathology of AD reinforces the development of newly targeted therapeutics. The successful launch of dupilumab, a monoclonal antibody targeting the interleukin (IL)-4α receptor subunit, for AD in 2017 spurred the development of a number of biologics targeting novel cytokine and receptor targets that are now in phase II and III of development. This review aims to explore the rationale behind these novel biological therapies and to summarize current clinical studies of these agents.

The role of OX40L and ICAM-1 in the stability of coronary atherosclerotic plaques and their relationship with sudden coronary death

Background

Coronary heart disease is related to sudden death caused by multi-factors and a major threat to human health.This study explores the role of OX40L and ICAM-1 in the stability of coronary plaques and their relationship with sudden coronary death.

Methods

A total of 118 human coronary arteries with different degrees of atherosclerosis and/or sudden coronary death comprised the experimental group and 28 healthy subjects constituted the control group were isolated from patients. The experimental group was subdivided based on whether the cause of death was sudden coronary death and whether it was accompanied by thrombosis, plaque rupture, plaque outflow and other secondary changes: group I: patients with coronary atherosclerosis but not sudden coronary death, group II: sudden coronary death without any of the secondary changes mentioned above, group III: sudden coronary death with coronary artery atherosclerotic lesions accompanied by either of the above secondary changes. The histological structure of the coronary artery was observed under a light microscope after routine HE staining, and the related indexes of atherosclerotic plaque lesions were assessed by image analysis software. The expressions of OX40L and ICAM-1 were detected by real-time quantitative PCR (RT-PCR), immunohistochemistry (IHC) and Western blotting, and the correlations between the expressions and the stability of coronary atherosclerotic plaque and sudden coronary death were analyzed.

Results

(1) The expression of OX40L protein in the control group and the three experimental groups showed an increasing trend, and the difference between groups was statistically significant (P < 0.05). (2) The expression of the ICAM-1 protein in the control group and the three experimental groups showed a statistically significant (P < 0.05) increasing trend. (3) The expression of OX40L and ICAM-1 mRNAs increased in the control and the three experimental groups and the difference was statistically significant (P < 0.05).

Conclusion

The expression of OX40L and ICAM-1 proteins and mRNAs is positively correlated with the stability of coronary atherosclerotic plaque and sudden coronary death.

Statins can suppress DC-mediated Th2 responses through the repression of OX40-ligand and CCL17 expression

DCs and epithelial cell-derived thymic stromal lymphopoietin (TSLP) have pivotal roles in allergic inflammation. TSLP stimulates myeloid DCs to express OX40-ligand (OX40L) and CCL17, which trigger and maintain Th2 cell responses. We have previously shown that statins, which are HMG-CoA reductase inhibitors, have the ability to suppress type I IFN production by plasmacytoid DCs. Here, we extended our previous work to examine the immunomodulatory effect of statins on allergic responses, particularly the TSLP-dependent Th2 pathway induced by myeloid DCs. We found that treatment of TSLP-stimulated DCs with either pitavastatin or simvastatin suppressed both the DC-mediated inflammatory Th2 cell differentiation and CRTH2+ CD4+ memory Th2 cell expansion and also repressed the expressions of OX40L and CCL17 by DCs. These inhibitory effects of statins were mimicked by treatment with either a geranylgeranyl-transferase inhibitor or Rho-kinase inhibitor and were counteracted by the addition of mevalonate, suggesting that statins induce geranylgeranylated Rho inactivation through a mevalonate-dependent pathway. We also found that statins inhibited the expressions of phosphorylated STA6 and NF-κB-p50 in TSLP-stimulated DCs. This study identified a specific ability of statins to control DC-mediated Th2 responses, suggesting their therapeutic potential for treating allergic diseases.

New treatments for atopic dermatitis targeting beyond IL-4/IL-13 cytokines

OBJECTIVE

Atopic dermatitis (AD) is an increasingly common inflammatory skin disease undergoing significant revolution in recent years. New data on disease pathogenesis advanced the developments of novel therapeutics, mainly for patients with moderate to severe conditions, for whom treatment options have been largely insufficient for many years.

DATA SOURCES

Review of recent studies investigating systemic treatments for AD.

STUDY SELECTIONS

Relevant literature concerning novel therapeutics for AD beyond targeted monoclonal antibodies antagonizing selectively interleukin (IL)-4 or IL-13 was obtained from a PubMed and clinicaltrials.gov search and summarized.

RESULTS

Multiple clinical trials of both nonspecific as well as specific agents revealed favorable outcomes in AD, including JAK inhibitors, a dual JAK/SYK inhibitor, a histamine H4R antagonist, antagonists of the TSLP/OX40L axis, an IL-22 inhibitor, and IL-33 and IL-17C antagonists. Importantly, negative trials were published as well (eg, phosphodiesterase 4 inhibitor, apremilast).

CONCLUSION

In this rapidly evolving field of AD treatments, a completely new treatment paradigm will be available in the near future.

Understanding the immune landscape in atopic dermatitis: The era of biologics and emerging therapeutic approaches

Atopic dermatitis (AD) is a chronic, systemic, inflammatory disease that affects the skin and is characterized by persistent itch and marked redness. AD is associated with an increased risk of skin infections and a reduced quality of life. Most AD treatment options to date were not designed to selectively target disease-causing pathways that have been established for this indication. Topical therapies have limited efficacy in moderate-to-severe disease, and systemic agents such as corticosteroids and immunosuppressants present with tolerability issues. Advances in the understanding of AD pathobiology have made possible a new generation of more disease-specific AD therapies. AD is characterized by the inappropriate activation of type 2 T helper (Th2) cells and type 2 innate lymphoid (ILC2) cells, with a predominant increase in type 2 cytokines in the skin, including interleukin (IL)-13 and IL-4. Both cytokines are implicated in tissue inflammation and epidermal barrier dysfunction, and monoclonal antibodies targeting each of these interleukins or their receptors are in clinical development in AD. In March 2017, dupilumab, a human anti-IL-4Rα antibody, became the first biologic to receive approval in the United States for the treatment of moderate-to-severe AD. The anti-IL-13 monoclonal antibodies lebrikizumab and tralokinumab, which bind different IL-13 epitopes with potentially different effects, are currently in advanced-stage trials. Here, we briefly review the underlying pathobiology of AD, the scientific basis for current AD targets, and summarize current clinical studies of these agents, including new research to develop both predictive and response biomarkers to further advance AD therapy in the era of precision medicine.

Hakemi M, Ghasemi R, Eskandari N. Correlation of OX40 ligand on B cells with serum total IgE and IL-4 levels by CD4+ T cells in allergic rhinitis

INTRODUCTION AND OBJECTIVES

Allergic rhinitis (AR) is a classic Th2-mediated disease, with important contributions to the pathology of interleukins 4, 5, and 13. The co-stimulatory molecule of OX40 and its ligand interaction participate in the immune response by regulation of Th1/Th2 cells balance. Considering the paucity of information on the relation between OX40 ligand (OX40L) and AR, this study aimed to examine its expression on B lymphocytes.

PATIENTS AND METHODS

This case-control study consisted of 20 AR patients and 20 healthy subjects. The serum level of total immunoglobulin E (IgE) was measured using the electro-chemiluminescence (ECL) technology. The percentage of B-lymphocytes expressing OX40L was assessed by flow cytometry. The amounts of IL-4 in CD4⁺ T cells culture supernatant was also measured by the enzyme-linked immunosorbent assay (ELISA).

RESULTS

OX40L expression on B lymphocytes of patients was significantly higher than the control group (44.32±19.21% vs. 2.79±2.48% respectively, p<0.001). In AR patients, OX40L expression correlated positively with the levels of serum total IgE and IL-4 produced by CD4⁺ T lymphocytes (p<0.01 - p<0.05) respectively.

CONCLUSIONS

Collectively, the findings of this work suggest that there is a relationship between the OX40L expression level on B lymphocytes and allergic markers such as IgE and IL-4 in patients with allergic rhinitis.

T-cell inhibitors for atopic dermatitis

The management of atopic dermatitis is changing with the development of novel biologic agents to target specific molecules in the inflammatory cascade. Following the ability of dupilumab has proved its ability to act on the interleukin 4 receptor in treating atopic dermatitis. Thymic stromal lymphopoietin monoclonal antibody (AMG157/MEDI9929) and OX40 blocking antibody (GBR 830) were developed by targeting the same pathway as dupilumab further upstream. The clinical data on the efficacy for these drugs are not yet known. There is some early evidence that AMG157/MEDI9929 attenuates most measures of allergen-induced asthmatic responses. However, there are no public data on its ability to treat atopic dermatitis. In a phase 2a study, GBR 830 showed at least a 50% reduction in the Eczema Area and Severity Index scores of 17 of 23 patients, but it was not sufficiently powered for identification of statistical differences between GBR 830 versus placebo. Although there is potential for these 2 drugs to greatly improve the management of severe atopic dermatitis, significant clinical trials have not yet been completed to prove efficacy, and there are not yet any available phase 3 clinical trials, which are needed to truly evaluate their efficacy in affecting T-cells.

Phase I randomized study of KHK4083, an anti-OX40 monoclonal antibody, in patients with mild to moderate plaque psoriasis

Background

OX40 (CD134) is expressed in lesional but not healthy skin of patients with psoriasis. KHK4083 is a fully human monoclonal antibody against OX40.

Objective

The primary aim of this first‐in‐human phase 1 study was to determine the safety and tolerability of ascending single doses of KHK4083 in patients with mild to moderate plaque psoriasis. Secondary aims were to determine the pharmacokinetics and immunogenicity of KHK4083, and an exploratory objective was to assess clinical activity.

Methods

In phase 1a, single doses of KHK4083 0.003 and 0.001 mg/kg IV were administered open label in two cohorts (each n = 6). Phase 1b had a multicentre, randomized, double‐blind, placebo‐controlled, ascending single‐dose design in seven cohorts. Randomization was performed 3 : 1 to KHK4083 (n = 6) or placebo (n = 2) within each cohort. Ascending doses of KHK4083 were 0.03, 0.1, 0.3, 1.0, 3.0 and 10 mg/kg IV, and 1.0 mg/kg SC.

Results

There were no severe or serious adverse events (AEs), or discontinuations because of AEs. The most frequent treatment‐related AEs in the 55 patients who received KHK4083 were mild or moderate chills (9.1%), and infusion/injection site reactions (7.3%). No clinically meaningful or dose‐related changes from baseline in laboratory values, vital signs, ECG recordings or physical examinations were observed. Some KHK4083 recipients (10/54) developed anti‐KHK4083 antibodies following treatment. Mean elimination half‐life (t_1/2) increased with dose, maximum serum concentration increased in a dose‐proportional manner, and area under the serum concentration–time curve increased in a more than dose‐proportional manner with increasing IV dose. Absolute bioavailability following SC administration was 73%. There was some indication of improvement in Psoriasis Area Severity Index (PASI) and sPGA scores at the highest IV doses (1.0 and 10 mg/kg) and the SC dose (1.0 mg/kg). The largest PASI 50 response and improvement in sPGA score ≥2 occurred with KHK4083 1.0 mg/kg SC.

Conclusion

KHK4083 administration as a single dose up to 10 mg/kg IV or 1.0 mg/kg SC was generally safe and well tolerated in patients with mild to moderate plaque psoriasis with no dose‐limiting AEs.

Epidermal Expression of Filaggrin/Profilaggrin Is Decreased in Atopic Dermatitis: Reverse Association With Mast Cell Tryptase and IL-6 but Not With Clinical Severity

BACKGROUND

A decrease in filaggrin expression contributes to the pathogenesis of atopic dermatitis (AD) and can be modified by inflammatory factors.

OBJECTIVES

The aim of this study was to determine the correlation of (pro)filaggrin (filaggrin and profilaggrin) expression with clinical severity in AD and with mast cell (MC) tryptase, chymase, and IL-6.

METHODS

Punch biopsies were collected from 17 patients with moderate-to-severe AD and from 10 psoriatic patients. Atopic dermatitis severity was measured using different clinical parameters. (Pro)filaggrin, MC tryptase, chymase, and IL-6 were stained using immunohistochemical, enzymehistochemical, and sequential double-staining methods.

RESULTS

(Pro)filaggrin expression was lower in the lesional than in the nonlesional granular layer in AD and was correlated negatively with itch severity but not with other severity parameters. (Pro)filaggrin expression was also decreased in the psoriatic lesions. In AD, (pro)filaggrin expression correlated negatively with the number of tryptase MCs in the nonlesional granular layer and with IL-6 MCs in both the nonlesional and lesional granular layers.

CONCLUSION

(Pro)filaggrin expression is decreased in AD and is reversely associated with MC tryptase and IL-6. However, it does not associate with disease severity, and it was also decreased in psoriasis.

Abnormal interactions between perifollicular mast cells and CD8+ T-cells may contribute to the pathogenesis of alopecia areata

Alopecia areata (AA) is a CD8+ T-cell dependent autoimmune disease of the hair follicle (HF) in which the collapse of HF immune privilege (IP) plays a key role. Mast cells (MCs) are crucial immunomodulatory cells implicated in the regulation of T cell-dependent immunity, IP, and hair growth. Therefore, we explored the role of MCs in AA pathogenesis, focusing on MC interactions with CD8+ T-cells in vivo, in both human and mouse skin with AA lesions. Quantitative (immuno-)histomorphometry revealed that the number, degranulation and proliferation of perifollicular MCs are significantly increased in human AA lesions compared to healthy or non-lesional control skin, most prominently in subacute AA. In AA patients, perifollicular MCs showed decreased TGFβ1 and IL-10 but increased tryptase immunoreactivity, suggesting that MCs switch from an immuno-inhibitory to a pro-inflammatory phenotype. This concept was supported by a decreased number of IL-10+ and PD-L1+ MCs, while OX40L+, CD30L+, 4–1BBL+ or ICAM-1+ MCs were increased in AA. Lesional AA-HFs also displayed significantly more peri- and intrafollicular- CD8+ T-cells as well as more physical MC/CD8+ T-cell contacts than healthy or non-lesional human control skin. During the interaction with CD8+ T-cells, AA MCs prominently expressed MHC class I and OX40L, and sometimes 4–1BBL or ICAM-1, suggesting that MC may present autoantigens to CD8+ T-cells and/or co-stimulatory signals. Abnormal MC numbers, activities, and interactions with CD8+ T-cells were also seen in the grafted C3H/HeJ mouse model of AA and in a new humanized mouse model for AA. These phenomenological in vivo data suggest the novel AA pathobiology concept that perifollicular MCs are skewed towards pro-inflammatory activities that facilitate cross-talk with CD8+ T-cells in this disease, thus contributing to triggering HF-IP collapse in AA. If confirmed, MCs and their CD8+ T-cell interactions could become a promising new therapeutic target in the future management of AA.

New era of biologic therapeutics in atopic dermatitis

INTRODUCTION

Atopic dermatitis (AD) is a common inflammatory skin disease regulated by genetic and environmental factors. Both skin barrier defects and aberrant immune responses are believed to drive cutaneous inflammation in AD. Existing therapies rely largely on allergen avoidance, emollients and topical and systemic immune-suppressants, some with significant toxicity and transient efficacy; no specific targeted therapies are in clinical use today. As our specific understanding of the immune and molecular pathways that cause different subsets of AD increases, a variety of experimental agents, particularly biologic agents that target pathogenic molecules bring the promise of safe and effective therapeutics for long-term use.

AREAS COVERED

This paper discusses the molecular pathways characterizing AD, the contributions of barrier and immune abnormalities to its pathogenesis, and development of new treatments that target key molecules in these pathways. In this review, we will discuss a variety of biologic therapies that are in development or in clinical trials for AD, perhaps revolutionizing treatment of this disease.

EXPERT OPINION

Biologic agents in moderate to severe AD offer promise for controlling a disease that currently lacks good and safe therapeutics posing a large unmet need. Unfortunately, existing treatments for AD aim to decrease cutaneous inflammation, but are not specific for the pathways driving this disease. An increasing understanding of the immune mechanisms underlying AD brings the promise of narrow targeted therapies as has occurred for psoriasis, another inflammatory skin disease, for which specific biologic agents have been demonstrated to both control the disease and prevent occurrence of new skin lesions. Although no biologic is yet approved for AD, these are exciting times for active therapeutic development in AD that might lead to revolutionary therapeutics for this disease.

Novel identified receptors on mast cells

Mast cells (MC) are major participants in the allergic reaction. In addition they possess immunomodulatory roles in the innate and adaptive immune reactions. Their functions are modulated through a number of activating and inhibitory receptors expressed on their surface. This review deals with some of the most recently described receptors, their expression patterns, ligand(s), signal transduction mechanisms, possible cross-talk with other receptors and, last but not least, regulatory functions that the MC can perform based on their receptor expression in health or in disease. Where the receptor role on MC is still not clear, evidences from other hematopoietic cells expressing them is provided as a possible insight for their function on MC. Suggested strategies to modulate these receptors’ activity for the purpose of therapeutic intervention are also discussed.