DNA hypomethylation leads to cGAS-induced autoinflammation in the epidermis.

DNA methylation is a fundamental epigenetic modification, important across biological processes. The maintenance methyltransferase DNMT1 is essential for lineage differentiation during development, but its functions in tissue homeostasis are incompletely understood. We show that epidermis-specific DNMT1 deletion severely disrupts epidermal structure and homeostasis, initiating a massive innate immune response and infiltration of immune cells. Mechanistically, DNA hypomethylation in keratinocytes triggered transposon derepression, mitotic defects, and formation of micronuclei. DNA release into the cytosol of DNMT1-deficient keratinocytes activated signaling through cGAS and STING, thus triggering inflammation. Our findings show that disruption of a key epigenetic mark directly impacts immune and tissue homeostasis, and potentially impacts our understanding of autoinflammatory diseases and cancer immunotherapy.

Deficiency in IL-17-committed Vγ4(+) γδ T cells in a spontaneous Sox13-mutant CD45.1(+) congenic mouse substrain provides protection from dermatitis.

Interleukin 17 (IL-17)-committed γδ T cells (γδT17 cells) participate in many immune responses, but their developmental requirements and subset specific functions remain poorly understood. Here we report that a commonly used CD45.1(+) congenic C57BL/6 mouse substrain is characterized by selective deficiency in Vγ4(+) γδT17 cells. This trait was due to a spontaneous mutation in the gene encoding the transcription factor Sox13 that caused an intrinsic defect in development of those cells in the neonatal thymus. The γδT17 cells migrated from skin to lymph nodes at low rates. In a model of psoriasis-like dermatitis, the Vγ4(+) γδT17 cell subset expanded considerably in lymph nodes and homed to inflamed skin. Sox13-mutant mice were protected from psoriasis-like skin changes, which identified a role for Sox13-dependent γδT17 cells in this inflammatory condition.

Cutaneous immunosurveillance and regulation of inflammation by group 2 innate lymphoid cells.

Type 2 immunity is critical for defense against cutaneous infections but also underlies the development of allergic skin diseases. We report the identification in normal mouse dermis of an abundant, phenotypically unique group 2 innate lymphoid cell (ILC2) subset that depended on interleukin 7 (IL-7) and constitutively produced IL-13. Intravital multiphoton microscopy showed that dermal ILC2 cells specifically interacted with mast cells, whose function was suppressed by IL-13. Treatment of mice deficient in recombination-activating gene 1 (Rag1(-/-)) with IL-2 resulted in the population expansion of activated, IL-5-producing dermal ILC2 cells, which led to spontaneous dermatitis characterized by eosinophil infiltrates and activated mast cells. Our data show that ILC2 cells have both pro- and anti-inflammatory properties and identify a previously unknown interactive pathway between two innate populations of cells of the immune system linked to type 2 immunity and allergic diseases.

Immune checkpoint inhibitors unleash pathogenic immune responses against the microbiota.

Immune checkpoint inhibitors (ICIs) are essential components of the cancer therapeutic armamentarium. While ICIs have demonstrated remarkable clinical responses, they can be accompanied by immune-related adverse events (irAEs). These inflammatory side effects are of unclear etiology and impact virtually all organ systems, with the most common being sites colonized by the microbiota such as the skin and gastrointestinal tract. Here, we establish a mouse model of commensal bacteria-driven skin irAEs and demonstrate that immune checkpoint inhibition unleashes commensal-specific inflammatory T cell responses. These aberrant responses were dependent on production of IL-17 by commensal-specific T cells and induced pathology that recapitulated the cutaneous inflammation seen in patients treated with ICIs. Importantly, aberrant T cell responses unleashed by ICIs were sufficient to perpetuate inflammatory memory responses to the microbiota months following the cessation of treatment. Altogether, we have established a mouse model of skin irAEs and reveal that ICIs unleash aberrant immune responses against skin commensals, with long-lasting inflammatory consequences.

Mitochondrial DNA variants and microbiota: An experimental strategy to identify novel therapeutic potential in chronic inflammatory diseases.

We previously demonstrated that mice carrying natural mtDNA variants of the FVB/NJ strain (m.7778 G>T in the mt-Atp8 gene in mitochondrial complex V), namely C57BL/6 J-mtFVB/NJ (B6-mtFVB), exhibited (i) partial protection from experimental skin inflammatory diseases in an anti-murine type VII collagen antibody-induced skin inflammation model and psoriasiform dermatitis model; (ii) significantly altered metabolites, including short-chain fatty acids, according to targeted metabolomics of liver, skin and lymph node samples; and (iii) a differential composition of the gut microbiota according to bacterial 16 S rRNA gene sequencing of stool samples compared to wild-type C57BL/6 J (B6) mice. To further dissect these disease-contributing factors, we induced an experimental antibody-induced skin inflammatory disease in gnotobiotic mice. We performed shotgun metagenomic sequencing of caecum contents and untargeted metabolomics of liver, CD4+ T cell, and caecum content samples from conventional B6-mtFVB and B6 mice. We identified D-glucosamine as a candidate mediator that ameliorated disease severity in experimental antibody-induced skin inflammation by modulating immune cell function in T cells, neutrophils and macrophages. Because mice carrying mtDNA variants of the FVB/NJ strain show differential disease susceptibility to a wide range of experimental diseases, including diet-induced atherosclerosis in low-density lipoprotein receptor knockout mice and collagen antibody-induced arthritis in DBA/1 J mice, this experimental approach is valuable for identifying novel therapeutic options for skin inflammatory conditions and other chronic inflammatory diseases to which mice carrying specific mtDNA variants show differential susceptibility.

Insights into the cellular basis of skin inflammation in systemic autoimmune rheumatic diseases from single-cell technologies.

Cutaneous inflammation is a common feature of several systemic autoimmune rheumatic diseases (SARDs) including systemic lupus erythematosus (SLE), undifferentiated connective tissue disease (UCTD), mixed connective tissue disease (MCTD) and dermatomyositis (DM) but is less common in other SARDs such as primary Sjögren's syndrome (pSS). It is important to understand whether the pathophysiological processes underlying skin inflammation are different or shared between SARDs to develop targeted therapies. This review will discuss commonalities and differences between inflammatory skin disease in SARDs focusing on histopathology and describe newer insights obtained from single-cell technologies.

Microbiota instruct IL-17A-producing innate lymphoid cells to promote skin inflammation in cutaneous leishmaniasis.

Innate lymphoid cells (ILCs) comprise a heterogeneous population of immune cells that maintain barrier function and can initiate a protective or pathological immune response upon infection. Here we show the involvement of IL-17A-producing ILCs in microbiota-driven immunopathology in cutaneous leishmaniasis. IL-17A-producing ILCs were RORγt+ and were enriched in Leishmania major infected skin, and topical colonization with Staphylococcus epidermidis before L. major infection exacerbated the skin inflammatory responses and IL-17A-producing RORγt+ ILC accumulation without impacting type 1 immune responses. IL-17A responses in ILCs were directed by Batf3 dependent CD103+ dendritic cells and IL-23. Moreover, experiments using Rag1-/- mice established that IL-17A+ ILCs were sufficient in driving the inflammatory responses as depletion of ILCs or neutralization of IL-17A diminished the microbiota mediated immunopathology. Taken together, this study indicates that the skin microbiota promotes RORγt+ IL-17A-producing ILCs, which augment the skin inflammation in cutaneous leishmaniasis.

The enzyme Cyp26b1 mediates inhibition of mast cell activation by fibroblasts to maintain skin-barrier homeostasis.

Mast cells (MCs) mature locally, thus possessing tissue-dependent phenotypes for their critical roles in both protective immunity against pathogens and the development of allergy or inflammation. We previously reported that MCs highly express P2X7, a receptor for extracellular ATP, in the colon but not in the skin. The ATP-P2X7 pathway induces MC activation and consequently exacerbates the inflammation. Here, we identified the mechanisms by which P2X7 expression on MCs is reduced by fibroblasts in the skin, but not in the other tissues. The retinoic-acid-degrading enzyme Cyp26b1 is highly expressed in skin fibroblasts, and its inhibition resulted in the upregulation of P2X7 on MCs. We also noted the increased expression of P2X7 on skin MCs and consequent P2X7- and MC-dependent dermatitis (so-called retinoid dermatitis) in the presence of excessive amounts of retinoic acid. These results demonstrate a unique skin-barrier homeostatic network operating through Cyp26b1-mediated inhibition of ATP-dependent MC activation by fibroblasts.

Reactive Neutrophilic Dermatoses in Adult-Onset Immunodeficiency due to Interferon-Gamma Autoantibody and Their Associated Factors.

BACKGROUND: Adult-onset immunodeficiency (AOID) due to interferon-gamma autoantibody is a rare, acquired immunodeficiency disease. Reactive neutrophilic dermatoses (RND), predominantly Sweet syndrome (SS), and generalized pustular eruption have been reported repeatedly. OBJECTIVES: The aims of this study were to describe the cutaneous manifestations in AOID patients and determine the incidence of RND and associated factors using a larger population size than have been previously reported. METHODS: A retrospective chart review of all confirmed AOID cases in Chiang Mai University Hospital from January 2006 to June 2020 was conducted. The demographics and characteristics of RND including type, onset, and laboratory information in every episode of cutaneous manifestations were collected. Generalized estimating equations of binary logistic regression were used to determine the indicators of RND. RESULTS: A total of 146 patients with confirmed AOID were identified. Of these, 57 cases (39%) developed at least one episode of RND. Thirteen cases (23%) of the patients experienced RND twice during the follow-up period. All recurrence of RND displayed the same cutaneous phenotype, with the exception of 2 cases who had both SS and generalized pustular eruption. Finally, 49 episodes of SS and 22 episodes of generalized pustular eruption were included in the analysis. All patients with RND had concomitant active opportunistic infections, of which most were non-tuberculous mycobacterium (NTM) infection. NTM infection (prevalence odds ratio [POR] 2.87), lymphadenopathy (POR 3.30) as well as lower serum alkaline phosphatase (ALP) level (POR 0.71 for every 100-unit increment in ALP) were found to be significantly associated with RND occurrence. CONCLUSIONS: 39% of our AOID patients experienced RND once during the course of the disease. Notable factors associated with RND occurrence were concomitant NTM infection, lymphadenopathy, and lower level of ALP.

Leukotriene B4-driven neutrophil recruitment to the skin is essential for allergic skin inflammation.

Scratching triggers skin flares in atopic dermatitis. We demonstrate that scratching of human skin and tape stripping of mouse skin cause neutrophil influx. In mice, this influx was largely dependent on the generation of leukotriene B4 (LTB4) by neutrophils and their expression of the LTB4 receptor BLT1. Allergic skin inflammation in response to epicutaneous (EC) application of ovalbumin to tape-stripped skin was severely impaired in Ltb4r1(-/-) mice and required expression of BLT1 on both T cells and non-T cells. Cotransfer of wild-type (WT) neutrophils, but not neutrophils deficient in BLT1 or the LTB4-synthesizing enzyme LTA4H, restored the ability of WT CD4(+) effector T cells to transfer allergic skin inflammation to Ltb4r1(-/-) recipients. Pharmacologic blockade of LTB4 synthesis inhibited allergic skin inflammation elicited by cutaneous antigen challenge in previously EC-sensitized mice. Our results demonstrate that a neutrophil-T cell axis reliant on LTB4-BLT1 interaction is required for allergic skin inflammation.

Critical role for mast cells in interleukin-1ß-driven skin inflammation associated with an activating mutation in the nlrp3 protein.

Cryopyrin-associated periodic syndromes (CAPS) are caused by aberrant interleukin-1ß (IL-1ß) production induced by mutations in the NLRP3 protein in humans, but the mechanisms involved remain poorly understood. Using a mouse model, we show a role for the indigenous microbiota and mast cells (MCs) in skin disease associated with mutant Nlrp3 protein. Unlike normal cells, MCs expressing mutant Nlrp3 produced IL-1ß in response to lipopolysaccharide or tumor necrosis factor-α (TNF-α). In neonatal mice, the microbiota induced TNF-α and IL-1ß and promoted skin disease. MC deficiency greatly reduced disease in Nlrp3 mutant mice, and reconstitution of MC-deficient mice with mutant MCs restored skin disease, which required the expression of IL-1ß in MCs. Surprisingly, neutralization of TNF-α abrogated IL-1ß production and skin disease in neonatal Nlrp3 mutant mice, but not in affected adult mice. Thus, the microbiota and MCs initiate cellular events leading to dysregulated IL-1ß production and skin inflammation in neonatal mice with the CAPS-associated Nlrp3 mutation.

The receptor LMIR3 negatively regulates mast cell activation and allergic responses by binding to extracellular ceramide.

Mast cells (MCs) are key effector cells in allergic reactions. However, the inhibitory mechanism that prevents excessive activation of MCs remains elusive. Here we show that leukocyte mono-immunoglobulin-like receptor 3 (LMIR3; also called CD300f) is a negative regulator of MC activation in vivo. LMIR3 deficiency exacerbated MC-dependent allergic responses in mice, including anaphylaxis, airway inflammation, and dermatitis. Both physical binding and functional reporter assays via an extracellular domain of LMIR3 showed that several extracellular lipids (including ceramide) and lipoproteins were possible ligands for LMIR3. Importantly, MCs were frequently surrounded by extracellular ceramide in vivo. Upon engagement of high-affinity immunoglobulin E receptor, extracellular ceramide-LMIR3 binding inhibited MC activation via immunoreceptor tyrosine-based inhibitory and switch motifs of LMIR3. Moreover, pretreatment with LMIR3-Fc fusion protein or antibody against either ceramide or LMIR3 interfered with this binding in vivo, thereby exacerbating passive cutaneous anaphylaxis. Thus, the interaction between extracellular ceramide and LMIR3 suppressed MC-dependent allergic responses.

NLRP1 inflammasome activation induces pyroptosis of hematopoietic progenitor cells.

Cytopenias are key prognostic indicators of life-threatening infection, contributing to immunosuppression and mortality. Here we define a role for Caspase-1-dependent death, known as pyroptosis, in infection-induced cytopenias by studying inflammasome activation in hematopoietic progenitor cells. The NLRP1a inflammasome is expressed in hematopoietic progenitor cells and its activation triggers their pyroptotic death. Active NLRP1a induced a lethal systemic inflammatory disease that was driven by Caspase-1 and IL-1ß but was independent of apoptosis-associated speck-like protein containing a CARD (ASC) and ameliorated by IL-18. Surprisingly, in the absence of IL-1ß-driven inflammation, active NLRP1a triggered pyroptosis of hematopoietic progenitor cells resulting in leukopenia at steady state. During periods of hematopoietic stress induced by chemotherapy or lymphocytic choriomeningitis virus (LCMV) infection, active NLRP1a caused prolonged cytopenia, bone marrow hypoplasia, and immunosuppression. Conversely, NLRP1-deficient mice showed enhanced recovery from chemotherapy and LCMV infection, demonstrating that NLRP1 acts as a cellular sentinel to alert Caspase-1 to hematopoietic and infectious stress.

Association of herpes zoster and chronic inflammatory skin disease in US inpatients.

BACKGROUND: Patients with chronic inflammatory skin disease (CISD) have potential risk factors for herpes zoster (HZ). However, little is known about HZ risk in CISD. OBJECTIVE: To determine whether CISD is associated with HZ. METHODS: Data were analyzed from the 2002 to 2012 Nationwide Inpatient Sample, a representative cohort of US hospitalizations (N = 68,088,221 children and adults). RESULTS: In multivariable logistic regression models including age, sex, race/ethnicity, insurance, household income, and long-term systemic corticosteroid use, hospitalization for HZ was associated with atopic dermatitis (adjusted odds ratio [95% confidence interval], 1.38 [1.14-1.68]), psoriasis (4.78 [2.83-8.08]), pemphigus (1.77 [1.01-3.12]), bullous pemphigoid (1.77 [1.01-3.12]), mycosis fungoides (3.79 [2.55-5.65]), dermatomyositis (7.31 [5.27-10.12]), systemic sclerosis (1.92 [1.47-2.53]), cutaneous lupus erythematosus (1.94 [1.10-3.44]), vitiligo (2.00 [1.04-3.85]), and sarcoidosis (1.52 [1.22-1.90]). Only lichen planus (crude odds ratio [95% confidence interval], 3.01 [1.36-6.67]), Sézary syndrome (12.14 [5.20-28.31]), morphea (2.74 [1.36-5.51]), and pyoderma gangrenosum (2.44 [1.16-5.13]) showed increased odds in bivariable models. Sensitivity analyses among those younger than 60 and younger than 50 years showed similar results. Predictors of HZ in CISD included female sex, fewer chronic conditions, and long-term systemic corticosteroid use. LIMITATIONS: Cross-sectional study. CONCLUSIONS: Many CISDs are associated with increased hospitalization for HZ, even below the ages recommended for HZ vaccination. Additional studies are needed to establish CISD-specific vaccination guidelines.

COVID-19 vaccine safety and efficacy in patients with immune-mediated inflammatory disease: Review of available evidence.

Dermatologists diagnose and treat many immune-mediated inflammatory diseases (IMID). Understanding the inherent immune dysregulation of these diseases as well as the additional disruption that comes as a result of IMID treatments has been important during the COVID-19 pandemic. With vaccines becoming widely available, dermatologists need to be familiar with the risks and benefits of vaccination in these patients, particularly those taking biologics, in order to have informed discussions with their patients. In this review, we present the current evidence related to COVID-19 vaccine safety and efficacy in patients with IMID and review existing recommendations for vaccination against SARS-CoV-2. Given the current evidence, there is minimal concern that these patients are at any greater risk of harm from COVID-19 vaccination compared to healthy controls. For most, the benefit of avoiding severe COVID-19 through vaccination will outweigh the theoretical risk of these vaccines. A question that is still outstanding is whether patients on biologics will generate a sufficient immune response to the vaccine, which may be dependent on the specific biologic therapy and indication being treated. This underscores the importance of following patients with IMID after vaccination to determine the safety, efficacy, and duration of the vaccine in this population.

Perivascular Adventitial Fibroblast Specialization Accompanies T Cell Retention in the Inflamed Human Dermis.

Perivascular accumulation of lymphocytes can be a prominent histopathologic feature of various human inflammatory skin diseases. Select examples include systemic sclerosis, spongiotic dermatitis, and cutaneous lupus. Although a large body of work has described various aspects of the endothelial and vascular smooth muscle layers in these diseases, the outer adventitial compartment is poorly explored. The goal of the current study was to characterize perivascular adventitial fibroblast states in inflammatory human skin diseases and relate these states to perivascular lymphocyte accumulation. In normal skin, adventitial fibroblasts are distinguished by CD90 expression, and dense perivascular lymphocytic infiltrates are uncommon. In systemic sclerosis, this compartment expands, but lymphocyte infiltrates remain sparse. In contrast, perivascular adventitial fibroblast expression of VCAM1 is upregulated in spongiotic dermatitis and lupus and is associated with a dense perivascular T cell infiltrate. VCAM1 expression marks transitioned fibroblasts that show some resemblance to the reticular stromal cells in secondary lymphoid organs. Expanded adventitial compartments with perivascular infiltrates similar to the human settings were not seen in the inflamed murine dermis. This species difference may hinder the dissection of aspects of perivascular adventitial pathology. The altered perivascular adventitial compartment and its associated reticular network form a niche for lymphocytes and appear to be fundamental in the development of an inflammatory pattern.

Exposure to additives or multigrain flour is associated with high risk of work-related allergic symptoms among bakers.

OBJECTIVES: Wheat flour exposure in bakers can elicit respiratory and skin symptoms. Scarce data are available on the prevalence of such conditions in bakers. We investigated the prevalence of work-related rhinitis, asthma-like symptoms and dermatitis in bakers according to job task and type of allergens involved. METHODS: Of the 229 traditional bakeries in Verona area who were invited to participate in a cross-sectional survey, 211 (92%) accepted; 727 employees in these bakeries answered a modified version of a questionnaire on job tasks; allergen exposure within the bakery; and work-related nasal, asthma-like and skin symptoms during 2010-2014. Determinants of work-related nasal, asthma-like or skin disorders were separately evaluated using different logistic models. RESULTS: The prevalence of work-related nasal and asthma-like symptoms was, respectively, 15.1% and 4.2% in bakery shop assistants, increasing to 25.7% and 9.5% in bakers using only wheat flour, and further to 31.8% and 13.6% in bakers using flour and additives, and then to 34.1% and 18.2% in bakers using flour with additives and multigrain (p<0.001). The risk of work-related asthma-like symptoms was more than doubled in bakers using additives without or with multigrain than in shop assistants (OR 2.3, 95% CI 1.0 to 5.5 and OR 3.4, 95% CI 1.1 to 10.8, respectively). Making bread with additives alone or with multigrain significantly increased the risk of work-related nasal symptoms in shop assistants, while the risk of skin symptoms was not significantly affected. CONCLUSIONS: Bakers using additives alone or with multigrain are at a high risk of experiencing nasal and asthma-like symptoms.

Serum IgE Predicts Difference of Population and Allergens in Allergic Diseases: Data from Weifang City, China.

BACKGROUND: Immunoglobulin E (IgE) is the most important promoter of allergic inflammation. However, there are few systematic studies on IgE in age range, genders, disease spectrum, and time regularity. AIM: To screen the common allergens, allergen spectrum, and IgE difference between type 2 inflammatory allergic diseases and other allergic diseases in Weifang, China. METHODS: A retrospective study was performed by estimating patients' clinical data suffering from allergic diseases (urticaria, pollinosis, allergic rhinitis, atopic dermatitis, and bronchial asthma) between May 2019 and April 2020 using an allergen detection kit of Macro-Union Pharmaceutical. RESULTS: 732 of the 1367 patients showed different antigen positive, and the positive rate was 53.5%. The most common allergens were dust mites, mixed fungi, Artemisia pollen, cat/dog dander, and cockroaches. There were 27.0% (369/1367) of the patients with single positive allergen-specific IgE (sIgE), 26.5% (363/1367) with multiple-positive IgE. The total immunoglobulin E (tIgE) levels varied with gender, age, and type of disease. There was a difference in the distribution of allergens between children and adults. A positive correlation between the serum-specific IgE and the corresponding local inhaled allergen density was observed. CONCLUSIONS: In this study, we found that type 2 inflammatory allergic diseases have higher serum IgE and a higher probability of inhaled sIgE positive. According to age, gender, and condition, serological IgE detection of allergens provides new insight into the early diagnosis and prevention of allergic diseases.

CD8+ Lymphogranulomatous Dermatitis as a Manifestation of Malignancy-Associated Immunodeficiency: Rethinking Paraneoplastic Granulomas.

ABSTRACT: Paraneoplastic granulomatous disease occurs in approximately 7.3% of patients with non-Hodgkin lymphoma, most commonly among patients with chronic lymphocytic leukemia (CLL). These lesions are often reported to appear similar to sarcoidosis in clinical presentation and under light microscopy. However, comprehensive descriptions of the cytomorphologic characteristics of these paraneoplastic granulomas are lacking, and the mechanisms involved in their formation remain ill-defined. Noninfectious dermal granulomatous reactions have also been reported in many primary immunodeficiencies, including common variable immune deficiency and ataxia-telangiectasia. We present a case of noninfectious CD8+ predominant granulomatous dermatitis with ocular involvement occurring in the setting of CLL and marked hypogammaglobulinemia. Based on the analysis of shared factors in patients with primary immunodeficiencies and CLL, we conclude that the presence of pan-humoral immunodeficiency could itself be a risk factor for developing a CD8+ lymphogranulomatous reaction. This report and associated discussion evince that CD8+ predominant granulomatous reactions, distinct from sarcoidosis, may represent a previously unappreciated segment of the paraneoplastic granulomas observed in hematologic malignancies.