IgE and anaphylaxis specific to the carbohydrate alpha-gal depend on IL-4.

BACKGROUND: Alpha-gal (Galα1-3Galß1-4GlcNAc) is a carbohydrate with the potential to elicit fatal allergic reactions to mammalian meat and drugs of mammalian origin. This type of allergy is induced by tick bites, and therapeutic options for this skin-driven food allergy are limited to the avoidance of the allergen and treatment of symptoms. Thus, a better understanding of the immune mechanisms resulting in sensitization through the skin is crucial, especially in the case of a carbohydrate allergen for which underlying immune responses are poorly understood. OBJECTIVE: We aimed to establish a mouse model of alpha-gal allergy for in-depth immunologic analyses. METHODS: Alpha-galactosyltransferase 1-deficient mice devoid of alpha-gal glycosylations were sensitized with the alpha-gal-carrying self-protein mouse serum albumin by repetitive intracutaneous injections in combination with the adjuvant aluminum hydroxide. The role of basophils and IL-4 in sensitization was investigated by antibody-mediated depletion. RESULTS: Alpha-gal-sensitized mice displayed increased levels of alpha-gal-specific IgE and IgG1 and developed systemic anaphylaxis on challenge with both alpha-gal-containing glycoproteins and glycolipids. In accordance with alpha-gal-allergic patients, we detected elevated numbers of basophils at the site of sensitization as well as increased numbers of alpha-gal-specific B cells, germinal center B cells, and B cells of IgE and IgG1 isotypes in skin-draining lymph nodes. By depleting IL-4 during sensitization, we demonstrated for the first time that sensitization and elicitation of allergy to alpha-gal and correspondingly to a carbohydrate allergen is dependent on IL-4. CONCLUSION: These findings establish IL-4 as a potential target to interfere with alpha-gal allergy elicited by tick bites.

Basophil activation in insect venom allergy: comparison of an established test using liquid reagents with a test using 5-color tubes with dried antibody reagents.

BACKGROUND: Flow cytometry-based basophil activation tests (BAT) have been performed with various modifications, differing in the use of distinct identification and activation markers. Established tests use liquid reagents while a new development involves the use of tubes with dried antibody reagents. The aim of this pilot study was to compare these two techniques in patients with insect venom allergy. METHODS: Seventeen patients with an insect venom allergy were included in the study. The established "BAT 1" utilizes conventional antibody solutions of anti-CCR3 for basophil identification and anti-CD63 to assess basophil activation, whereas "BAT 2" uses dried anti-CD45, anti-CD3, anti-CRTH2, anti-203c and anti-CD63 for identification and activation measurement of basophils. Negative and positive controls as well as incubations with honey bee venom and yellow jacket venom at three concentrations were performed. RESULTS: Seven patients had to be excluded due to low basophil counts, high values in negative controls or negative positive controls. For the remaining 10 patients the overall mean (± SD) difference in activated basophils between the two tests was 0.2 (± 12.2) %P. In a Bland-Altman plot, the limit of agreement (LoA) ranged from 24.0 to -23.7. In the qualitative evaluation (value below/above cut-off) Cohen's kappa was 0.77 indicating substantial agreement. BAT 2 took longer to perform than BAT 1 and was more expensive. CONCLUSION: The BAT 2 technique represents an interesting innovation, however, it was found to be less suitable compared to an established BAT for the routine diagnosis of insect venom allergies.

Next generation mycological diagnosis: Artificial intelligence-based classifier of the presence of Malassezia yeasts in tape strip samples.

BACKGROUND: Malassezia yeasts are almost universally present on human skin worldwide. While they can cause diseases such as pityriasis versicolor, their implication in skin homeostasis and pathophysiology of other dermatoses is still unclear. Their analysis using native microscopy of skin tape strips is operator dependent and requires skill, training and significant amounts of hands-on time. OBJECTIVES AND METHODS: To standardise and improve the speed and quality of diagnosis of Malassezia in skin tape strip samples, we sought to create an artificial intelligence-based algorithm for this image classification task. Three algorithms, each using different internal architectures, were trained and validated on a manually annotated dataset of 1113 images from 22 samples. RESULTS: The Vision Transformer-based algorithm performed the best with a validation accuracy of 94%, sensitivity of 94.0% and specificity of 93.5%. Visualisations providing insight into the reasoning of the algorithm were presented and discussed. CONCLUSION: Our image classifier achieved very good performance in the diagnosis of the presence of Malassezia yeasts in tape strip samples of human skin and can therefore improve the speed and quality of, and access to this diagnostic test. By expanding data sources and explainability, the algorithm could also provide teaching points for more novice operators in future.

[Medical clinical diagnostics for indoor mould exposure - Update 2023 (AWMF Register No. 161/001)]. / Medizinisch klinische Diagnostik bei Schimmelpilzexposition in Innenräumen ­ Update 2023 (AWMF-Register-Nr. 161/001).

This article is an abridged version of the updated AWMF mould guideline "Medical clinical diagnostics in case of indoor mould exposure - Update 2023", presented in July 2023 by the German Society of Hygiene, Environmental Medicine and Preventive Medicine (Gesellschaft für Hygiene, Umweltmedizin und Präventivmedizin, GHUP), in collaboration with German and Austrian scientific medical societies, and experts. Indoor mould growth is a potential health risk, even if a quantitative and/or causal relationship between the occurrence of individual mould species and health problems has yet to be established. There is no evidence for a causal relationship between moisture/mould damage and human diseases, mainly because of the ubiquitous presence of fungi and hitherto inadequate diagnostic methods. Sufficient evidence for an association between moisture/mould damage and the following health effects has been established for: allergic respiratory diseases, allergic rhinitis, allergic rhino-conjunctivitis, allergic bronchopulmonary aspergillosis (ABPA), other allergic bronchopulmonary mycosis (ABPM), aspergilloma, Aspergillus bronchitis, asthma (manifestation, progression, exacerbation), bronchitis (acute, chronic), community-acquired Aspergillus pneumonia, hypersensitivity pneumonitis (HP; extrinsic allergic alveolitis (EEA)), invasive Aspergillosis, mycoses, organic dust toxic syndrome (ODTS) [workplace exposure], promotion of respiratory infections, pulmonary aspergillosis (subacute, chronic), and rhinosinusitis (acute, chronically invasive, or granulomatous, allergic). In this context the sensitizing potential of moulds is obviously low compared to other environmental allergens. Recent studies show a comparatively low sensitization prevalence of 3-22,5 % in the general population across Europe. Limited or suspected evidence for an association exist with respect to atopic eczema (atopic dermatitis, neurodermatitis; manifestation), chronic obstructive pulmonary disease (COPD), mood disorders, mucous membrane irritation (MMI), odor effects, and sarcoidosis. (iv) Inadequate or insufficient evidence for an association exist for acute idiopathic pulmonary hemorrhage in infants, airborne transmitted mycotoxicosis, arthritis, autoimmune diseases, cancer, chronic fatigue syndrome (CFS), endocrinopathies, gastrointestinal effects, multiple chemical sensitivity (MCS), multiple sclerosis, neuropsychological effects, neurotoxic effects, renal effects, reproductive disorders, rheumatism, sick building syndrome (SBS), sudden infant death syndrome, teratogenicity, thyroid diseases, and urticaria.The risk of infection posed by moulds regularly occurring indoors is low for healthy persons; most species are in risk group 1 and a few in risk group 2 (Aspergillus fumigatus, A. flavus) of the German Biological Agents Act (Biostoffverordnung). Only moulds that are potentially able to form toxins can be triggers of toxic reactions. Whether or not toxin formation occurs in individual cases is determined by environmental and growth conditions, water activity, temperature and above all the growth substrates.In case of indoor moisture/mould damage, everyone can be affected by odor effects and/or mood disorders.However, this is not an acute health hazard. Predisposing factors for odor effects can include genetic and hormonal influences, imprinting, context and adaptation effects. Predisposing factors for mood disorders may include environmental concerns, anxiety, condition, and attribution, as well as various diseases. Risk groups to be protected particularly regarding infection risk are immunocompromised persons according to the classification of the German Commission for Hospital Hygiene and Infection Prevention (Kommission für Krankenhaushygiene und Infektionsprävention, KRINKO) at the Robert Koch-Institute (RKI), persons suffering from severe influenza, persons suffering from severe COVID-19, and persons with cystic fibrosis (mucoviscidosis); with regard to allergic risk, persons with cystic fibrosis (mucoviscidosis) and patients with bronchial asthma must be protected. The rational diagnostics include the medical history, physical examination, and conventional allergy diagnostics including provocation tests if necessary; sometimes cellular test systems are indicated. In the case of mould infections, the reader is referred to the specific guidelines. Regarding mycotoxins, there are currently no useful and validated test procedures for clinical diagnostics. From a preventive medical point of view, it is important that indoor mould infestation in relevant magnitudes cannot be tolerated for precautionary reasons.For evaluation of mould damage in the indoor environment and appropriate remedial procedures, the reader is referred to the mould guideline issued by the German Federal Environment Agency (Umweltbundesamt, UBA).

Cutaneous innate immune sensing of Toll-like receptor 2-6 ligands suppresses T cell immunity by inducing myeloid-derived suppressor cells.

Skin is constantly exposed to bacteria and antigens, and cutaneous innate immune sensing orchestrates adaptive immune responses. In its absence, skin pathogens can expand, entering deeper tissues and leading to life-threatening infectious diseases. To characterize skin-driven immunity better, we applied living bacteria, defined lipopeptides, and antigens cutaneously. We found suppression of immune responses due to cutaneous infection with Gram-positive S. aureus, which was based on bacterial lipopeptides. Skin exposure to Toll-like receptor (TLR)2-6-binding lipopeptides, but not TLR2-1-binding lipopeptides, potently suppressed immune responses through induction of Gr1(+)CD11b(+) myeloid-derived suppressor cells (MDSCs). Investigating human atopic dermatitis, in which Gram-positive bacteria accumulate, we detected high MDSC amounts in blood and skin. TLR2 activation in skin resident cells triggered interleukin-6 (IL-6), which induced suppressive MDSCs, which are then recruited to the skin suppressing T cell-mediated recall responses such as dermatitis. Thus, cutaneous bacteria can negatively regulate skin-driven immune responses by inducing MDSCs via TLR2-6 activation.

Increasing incidence of Trichophyton tonsurans in Munich-A single-centre observation.

BACKGROUND: Tinea capitis and tinea corporis are highly prevalent fungal skin infections, which globally are mainly caused by Microsporum canis and Trichophyton rubrum, respectively. While in the United States and Great Britain Trichophyton tonsurans is widely prevalent as a causative pathogen, it so far only plays a minor role in Germany. OBJECTIVES: Since the frequency of pathogenic species varies regionally and temporally, this study assesses the proportion of Trichophyton tonsurans infections in the dermatology department of a large university hospital in Germany from 2019 to 2022 and thoroughly characterises the affected patient population. PATIENTS/METHODS: This retrospective study at the Technical University of Munich analyses mycological culture results regarding the identified dermatophyte and infection site. Detailed patient and disease-related information on Trichophyton tonsurans positive patients was obtained. RESULTS: In 2022, 23 patients of 111 dermatophyte culture-positive patients tested positive for Trichophyton tonsurans. This accounted for 20.7% and represented a tenfold increase from 2.1% in 2019. Contact sports were only practiced by 21.7% of patients, and no common hotspot or other linkage could be identified between the cases. Additionally, 47.8% of the patients received a systemic treatment, with 30.4% visiting the clinic more than three times. In 2022, 21.7% were diagnosed with a simultaneous infection of the capillitium and body, whereas this was only observed in 7.1% of cases in 2019 to 2021. CONCLUSIONS: This study suggests an increase of Trichophyton tonsurans infections via several routes of transmission.

Cutaneous Barriers and Skin Immunity.

The skin barrier provides us with several lines of protection from outside hazards. Its most outward layers, the stratum corneum and the epidermis seal our body with an acidic, dry, and rather cool surface, hostile to microbes. Yet, there are also fine-tuned interactions between the mostly commensal microbiota on top of the skin surface, with underlying epidermal cells as well as the immune system, to preserve a healthy steady state and to initiate repair processes when necessary. We take a concise look at the recent insights on the inner workings of this complex barrier.

The specific PKC-α inhibitor chelerythrine blunts costunolide-induced eryptosis.

Costunolide, a natural sesquiterpene lactone, has multiple pharmacological activities such as neuroprotection or induction of apoptosis and eryptosis. However, the effects of costunolide on pro-survival factors and enzymes in human erythrocytes, e.g. glutathione and glucose-6-phosphate dehydrogenase (G6PDH) respectively, have not been studied yet. Our aim was to determine the mechanisms underlying costunolide-induced eryptosis and to reverse this process. Phosphatidylserine exposure was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry, and intracellular glutathione [GSH]i from high performance liquid chromatography. The oxidized status of intracellular glutathione and enzyme activities were measured by spectrophotometry. Treatment of erythrocytes with costunolide dose-dependently enhanced the percentage of annexin-V-binding cells, decreased the cell volume, depleted [GSH]i and completely inhibited G6PDH activity. The effects of costunolide on annexin-V-binding and cell volume were significantly reversed by pre-treatment of erythrocytes with the specific PKC-α inhibitor chelerythrine. The latter, however, had no effect on costunolide-induced GSH depletion. Costunolide induces eryptosis, depletes [GSH]i and inactivates G6PDH activity. Furthermore, our study reveals an inhibitory effect of chelerythrine on costunolide-induced eryptosis, indicating a relationship between costunolide and PKC-α. In addition, chelerythrine acts independently of the GSH depletion. Understanding the mechanisms of G6PDH inhibition accompanied by GSH depletion should be useful for development of anti-malarial therapeutic strategies or for synthetic lethality-based approaches to escalate oxidative stress in cancer cells for their sensitization to chemotherapy and radiotherapy.

Googling for Ticks and Borreliosis in Germany: Nationwide Google Search Analysis From 2015 to 2018.

BACKGROUND: Borreliosis is the most frequently transmitted tick-borne disease in Europe. It is difficult to estimate the incidence of tick bites and associated diseases in the German population due to the lack of an obligation to register across all 16 federal states of Germany. OBJECTIVE: The aim of this study is to show that Google data can be used to generate general trends of infectious diseases on the basis of borreliosis and tick bites. In addition, the possibility of using Google AdWord data to estimate incidences of infectious diseases, where there is inconsistency in the obligation to notify authorities, is investigated with the perspective to facilitate public health studies. METHODS: Google AdWords Keyword Planner was used to identify search terms related to ticks and borreliosis in Germany from January 2015 to December 2018. The search volume data from the identified search terms was assessed using Excel version 15.23. In addition, SPSS version 24.0 was used to calculate the correlation between search volumes, registered cases, and temperature. RESULTS: A total of 1999 tick-related and 542 borreliosis-related search terms were identified, with a total of 209,679,640 Google searches in all 16 German federal states in the period under review. The analysis showed a high correlation between temperature and borreliosis (r=0.88), and temperature and tick bite (r=0.83), and a very high correlation between borreliosis and tick bite (r=0.94). Furthermore, a high to very high correlation between Google searches and registered cases in each federal state was observed (Brandenburg r=0.80, Mecklenburg-West Pomerania r= 0.77, Saxony r= 0.74, and Saxony-Anhalt r=0.90; all P<.001). CONCLUSIONS: Our study provides insight into annual trends concerning interest in ticks and borreliosis that are relevant to the German population exemplary in the data of a large internet search engine. Public health studies collecting incidence data may benefit from the results indicating a significant correlation between internet search data and incidences of infectious diseases.

Mast cells as protectors of health.

Mast cells (MCs), which are well known for their effector functions in TH2-skewed allergic and also autoimmune inflammation, have become increasingly acknowledged for their role in protection of health. It is now clear that they are also key modulators of immune responses at interface organs, such as the skin or gut. MCs can prime tissues for adequate inflammatory responses and cooperate with dendritic cells in T-cell activation. They also regulate harmful immune responses in trauma and help to successfully orchestrate pregnancy. This review focuses on the beneficial effects of MCs on tissue homeostasis and elimination of toxins or venoms. MCs can enhance pathogen clearance in many bacterial, viral, and parasitic infections, such as through Toll-like receptor 2-triggered degranulation, secretion of antimicrobial cathelicidins, neutrophil recruitment, or provision of extracellular DNA traps. The role of MCs in tumors is more ambiguous; however, encouraging new findings show they can change the tumor microenvironment toward antitumor immunity when adequately triggered. Uterine tissue remodeling by α-chymase (mast cell protease [MCP] 5) is crucial for successful embryo implantation. MCP-4 and the tryptase MCP-6 emerge to be protective in central nervous system trauma by reducing inflammatory damage and excessive scar formation, thereby protecting axon growth. Last but not least, proteases, such as carboxypeptidase A, released by FcεRI-activated MCs detoxify an increasing number of venoms and endogenous toxins. A better understanding of the plasticity of MCs will help improve these advantageous effects and hint at ways to cut down detrimental MC actions.

IL-4 abrogates T(H)17 cell-mediated inflammation by selective silencing of IL-23 in antigen-presenting cells.

Interleukin 4 (IL-4) can suppress delayed-type hypersensitivity reactions (DTHRs), including organ-specific autoimmune diseases in mice and humans. Despite the broadly documented antiinflammatory effect of IL-4, the underlying mode of action remains incompletely understood, as IL-4 also promotes IL-12 production by dendritic cells (DCs) and IFN-γ-producing T(H)1 cells in vivo. Studying the impact of IL-4 on the polarization of human and mouse DCs, we found that IL-4 exerts opposing effects on the production of either IL-12 or IL-23. While promoting IL-12-producing capacity of DCs, IL-4 completely abrogates IL-23. Bone marrow chimeras proved that IL-4-mediated suppression of DTHRs relies on the signal transducer and activator of transcription 6 (STAT6)-dependent abrogation of IL-23 in antigen-presenting cells. Moreover, IL-4 therapy attenuated DTHRs by STAT6- and activating transcription factor 3 (ATF3)-dependent suppression of the IL-23/T(H)17 responses despite simultaneous enhancement of IL-12/TH1 responses. As IL-4 therapy also improves psoriasis in humans and suppresses IL-23/T(H)17 responses without blocking IL-12/T(H)1, selective IL-4-mediated IL-23/T(H)17 silencing is promising as treatment against harmful inflammation, while sparing the IL-12-dependent T(H)1 responses.

Trifluoperazine-Induced Suicidal Erythrocyte Death and S-Nitrosylation Inhibition, Reversed by the Nitric Oxide Donor Sodium Nitroprusside.

BACKGROUND AND PURPOSE: The high potency antipsychotic drug trifluoperazine (10-[3-(4-methyl-1-piperazinyl)-propyl]-2-(trifluoromethyl)-(10)H-phenothiazine dihydrochloride; TFP) may either counteract or promote suicidal cell death or apoptosis. Similar to apoptosis, erythrocytes may enter eryptosis, characterized by phosphatidylserine exposure at the cell surface and cell shrinkage. Eryptosis can be stimulated by an increase in cytoplasmic Ca2+ concentration ([Ca2+]i) and inhibited by nitric oxide (NO). We explored whether TFP treatment of erythrocytes induces phosphatidylserine exposure, cell shrinkage, and calcium influx, whether it impairs S-nitrosylation and whether these effects are inhibited by NO. METHODS: Phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca2+]i from Fluo3-fluorescence, and protein nitrosylation from fluorescence switch of the Bodipy-TMR/Sypro Ruby signal. RESULTS: Exposure of human erythrocytes to TFP significantly enhanced the percentage of annexin-V-binding cells, raised [Ca2+]i, and decreased S-nitrosylation. The effect of TFP on annexin-V-binding was not affected by removal of extracellular Ca2+ alone, but was significantly inhibited by pre-treatment with sodium nitroprusside (SNP), an effect significantly augmented by additional removal of extracellular Ca2+. A 3 hours treatment with 0.1 µM Ca2+ ionophore ionomycin triggered annexin-V-binding and cell shrinkage, effects fully reversed by removal of extracellular Ca2+. CONCLUSIONS: TFP induces eryptosis and decreases protein S-nitrosylation, effects blunted by nitroprusside. The effect of nitroprusside is attenuated in the presence of extracellular Ca2+.

Staphylococcus aureus-derived lipoteichoic acid induces temporary T-cell paralysis independent of Toll-like receptor 2.

BACKGROUND: The interplay between microbes and surface organs, such as the skin, shapes a complex immune system with several checks and balances. The first-line defense is mediated by innate immune pathways leading to inflammation. In the second phase specific T cells invade the infected organ, amplifying inflammation and defense. Consecutively, termination of inflammation is crucial to avoid chronic inflammation triggered by microbes, such as in patients with atopic dermatitis. OBJECTIVE: We aimed to elucidate how the Staphylococcus aureus-derived cell-wall component lipoteichoic acid (LTA) governs the second phase of immune responses when high concentrations of LTA access T cells directly through disrupted skin. METHODS: We analyzed the direct exposure of T cells to LTA in vitro. For in vivo analyses, we used fluorescein isothiocyanate contact hypersensitivity and ovalbumin-induced dermatitis as models for TH2-mediated cutaneous inflammation. RESULTS: We observed that LTA potently suppressed T-lymphocyte activation in a Toll-like receptor 2-independent manner. LTA-exposed T cells did not proliferate and did not produce cytokines. Importantly, these T cells remained completely viable and were responsive to consecutive activation signals on subsequent removal of LTA. Thus LTA exposure resulted in temporary functional T-cell paralysis. In vivo experiments revealed that T-cell cytokine production and cutaneous recall responses were significantly suppressed by LTA. CONCLUSION: We identified a new mechanism through which bacterial compounds directly but temporarily modulate adaptive immune responses.

Fungal chitin dampens inflammation through IL-10 induction mediated by NOD2 and TLR9 activation.

Chitin is an essential structural polysaccharide of fungal pathogens and parasites, but its role in human immune responses remains largely unknown. It is the second most abundant polysaccharide in nature after cellulose and its derivatives today are widely used for medical and industrial purposes. We analysed the immunological properties of purified chitin particles derived from the opportunistic human fungal pathogen Candida albicans, which led to the selective secretion of the anti-inflammatory cytokine IL-10. We identified NOD2, TLR9 and the mannose receptor as essential fungal chitin-recognition receptors for the induction of this response. Chitin reduced LPS-induced inflammation in vivo and may therefore contribute to the resolution of the immune response once the pathogen has been defeated. Fungal chitin also induced eosinophilia in vivo, underpinning its ability to induce asthma. Polymorphisms in the identified chitin receptors, NOD2 and TLR9, predispose individuals to inflammatory conditions and dysregulated expression of chitinases and chitinase-like binding proteins, whose activity is essential to generate IL-10-inducing fungal chitin particles in vitro, have also been linked to inflammatory conditions and asthma. Chitin recognition is therefore critical for immune homeostasis and is likely to have a significant role in infectious and allergic disease.

Role of ß1 integrins and bacterial adhesins for Yop injection into leukocytes in Yersinia enterocolitica systemic mouse infection.

Injection of Yersinia outer proteins (Yops) into host cells by a type III secretion system is an important immune evasion mechanism of Yersinia enterocolitica (Ye). In this process Ye invasin (Inv) binds directly while Yersinia adhesin A (YadA) binds indirectly via extracellular matrix (ECM) proteins to ß1 integrins on host cells. Although leukocytes turned out to be an important target of Yop injection by Ye, it was unclear which Ye adhesins and which leukocyte receptors are required for Yop injection. To explain this, we investigated the role of YadA, Inv and ß1 integrins for Yop injection into leukocytes and their impact on the course of systemic Ye infection in mice. Ex vivo infection experiments revealed that adhesion of Ye via Inv or YadA is sufficient to promote Yop injection into leukocytes as revealed by a ß-lactamase reporter assay. Serum factors inhibit YadA- but not Inv-mediated Yop injection into B and T cells, shifting YadA-mediated Yop injection in the direction of neutrophils and other myeloid cells. Systemic Ye mouse infection experiments demonstrated that YadA is essential for Ye virulence and Yop injection into leukocytes, while Inv is dispensable for virulence and plays only a transient and minor role for Yop injection in the early phase of infection. Ye infection of mice with ß1 integrin-depleted leukocytes demonstrated that ß1 integrins are dispensable for YadA-mediated Yop injection into leukocytes, but contribute to Inv-mediated Yop injection. Despite reduced Yop injection into leukocytes, ß1 integrin-deficient mice exhibited an increased susceptibility for Ye infection, suggesting an important role of ß1 integrins in immune defense against Ye. This study demonstrates that Yop injection into leukocytes by Ye is largely mediated by YadA exploiting, as yet unknown, leukocyte receptors.

Toll-like receptor 2 ligands promote chronic atopic dermatitis through IL-4-mediated suppression of IL-10.

BACKGROUND: Atopic dermatitis (AD) is a T cell-mediated inflammatory skin disease, with TH2 cells initiating acute flares. This inflamed skin is immediately colonized with Staphylococcus aureus, which provides potent Toll-like receptor (TLR) 2 ligands. However, the effect of TLR2 ligands on the development of TH2-mediated AD inflammation remains unclear. OBJECTIVE: We investigated the progression of TH2 cell-mediated dermatitis after TLR2 activation. METHODS: Using models for acute AD with TH2 cells initiating cutaneous inflammation, we investigated the consequences of TLR2 activation. Dermatitis, as assessed by changes in ear skin thickness and histology, was analyzed in different BALB/c and C57BL/6 wild-type and knockout mouse strains, and immune profiling was carried out by using in vitro and ex vivo cytokine analyses. RESULTS: We show that TH2 cell-mediated dermatitis is self-limiting and depends on IL-4. Activation of TLR2 converted the limited TH2 dermatitis to chronic cutaneous inflammation. We demonstrate that the concerted activation of TLR2 and IL-4 receptor on dendritic cells is sufficient for this conversion. As an underlying mechanism, we found that the combinatorial sensing of the innate TLR2 ligands and the adaptive TH2 cytokine IL-4 suppressed anti-inflammatory IL-10 and consequently led to the exacerbation and persistence of dermatitis. CONCLUSION: Our data demonstrate that innate TLR2 signals convert transient TH2 cell-mediated dermatitis into persistent inflammation, as seen in chronic human AD, through IL-4-mediated suppression of IL-10. For the first time, these data show how initial AD lesions convert to chronic inflammation and provide another rationale for targeting IL-4 in patients with AD, a therapeutic approach that is currently under development.