T-Cell Subtypes and Immune Signatures in Cutaneous Immune-Related Adverse Events in Melanoma Patients under Immune Checkpoint Inhibitor Therapy.

Immune checkpoint inhibition (ICI) improves outcomes in melanoma patients, but associated T-cell activation frequently leads to immune-related cutaneous adverse events (cutAEs). To dynamically identify T-cell subtypes and immune signatures associated with cutAEs, a pilot study was performed in stage III-IV melanoma patients using blood samples for flow cytometry and cytokine analysis. Blood samples were taken from patients before initiation of ICI (naive), at the onset of a cutAE, and after 6 months of ICI treatment. Overall, 30 patients were treated either with anti-PD1 monotherapy or with anti-PD-1/anti-CTLA-4 combination therapy. Flow cytometry analysis of PBMCs showed that ICI induced an overall shift from a Th2 towards a Th1 profile. Twelve patients (40%) developed cutAEs, which were associated with increased Th22 cells and Th17 cells, supported by a tendency to have elevated Th17/Th22-associated cytokines such as IL-17A, IL-22 and IL-23 levels in the plasma. Cytokine signatures specific for urticaria and T-cell-mediated cutAEs were identified in the plasma of patients by a bead-based assay. IL-10 was elevated in non-responders and, interestingly, during cutAEs. In conclusion, we identified distinct immune signatures based on the Th17/Th22 pathway in cutAEs, both in PBMCs and plasma. In addition, our finding of upregulated IL-10 during cutAEs supports the notion of treating these patients early and adequately to avoid implications for the overall outcome.

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.

Inflammatory Cues Direct Skin-Resident Type 1 Innate Lymphoid Cells to Adopt a Psoriasis-Promoting Identity.

Innate lymphoid cells (ILCs) are gatekeepers in barrier organs, where they maintain tissue integrity and contribute to host defense as well as tissue repair. Inappropriate activation of ILCs, however, can lead to immunopathology with detrimental results. In this study, we focused on type 1 ILCs (ILC1s), which under inflammatory conditions constitute a poorly defined population with ambiguous functions. To delineate the properties of ILC1s in skin pathology, we used the well-established mouse model of imiquimod-induced psoriasis. Although ILC1s represented a minority among cutaneous lymphocytes in vehicle-treated controls, they rapidly expanded during early psoriasis and ultimately increased by >20-fold. This rapid increase was verified using two additional psoriasis models. Inflammatory ILC1s from imiquimod-treated skin were defined as CD44+, CXCR6+, and CD11b+ and substantially contributed to TNF-α and GM-CSF production, rendering them a potential candidate to shape the inflammatory infiltrate. In accordance with the psoriasis-specific microenvironment, skin ILC1s upregulated the IL-23 receptor whereas expression of the IL-12Rß2 subunit was diminished. As a consequence, neutralization of IL-12 only had a minor impact, whereas blocking IL-23 reduced both ILC1 abundance and disease severity. Together, our findings identify skin ILC1s as a likely player in early psoriasis and a prospective target for therapeutic approaches.

Fetal Tissue-Derived Mast Cells (MC) as Experimental Surrogate for In Vivo Connective Tissue MC.

Bone-marrow-derived mast cells are matured from bone marrow cells in medium containing 20% fetal calf serum (FCS), interleukin (IL)-3 and stem-cell factor (SCF) and are used as in vitro models to study mast cells (MC) and their role in health and disease. In vivo, however, BM-derived hematopoietic stem cells account for only a fraction of MC; the majority of MC in vivo are and remain tissue resident. In this study we established a side-by-side culture with BMMC, fetal skin MC (FSMC) or fetal liver MC (FLMC) for comparative studies to identify the best surrogates for mature connective tissue MC (CTMC). All three MC types showed comparable morphology by histology and MC phenotype by flow cytometry. Heterogeneity was detected in the transcriptome with the most differentially expressed genes in FSMC compared to BMMC being Hdc and Tpsb2. Expression of ST2 was highly expressed in BMMC and FSMC and reduced in FLMC, diminishing their secretion of type 2 cytokines. Higher granule content, stronger response to FcεRI activation and significantly higher release of histamine from FSMC compared to FLMC and BMMC indicated differences in MC development in vitro dependent on the tissue of origin. Thus, tissues of origin imprint MC precursor cells to acquire distinct phenotypes and signatures despite identical culture conditions. Fetal-derived MC resemble mature CTMC, with FSMC being the most developed.

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.

Munich atopy prediction study (MAPS): protocol for a prospective birth cohort addressing clinical and molecular risk factors for atopic dermatitis in early childhood.

INTRODUCTION: The pathogenesis of atopic diseases is highly complex, and the exact mechanisms leading to atopic dermatitis (AD) onset in infants remain mostly enigmatic. In addition to an interdependent network of components of skin development in young age and skin barrier dysfunction underlying AD development that is only partially understood, a complex interplay between environmental factors and lifestyle habits with skin barrier and immune dysregulation is suspected to contribute to AD onset. This study aims to comprehensively evaluate individual microbiome and immune responses in the context of environmental determinants related the risk of developing AD in the first 4 years of a child's life. METHODS AND ANALYSES: The 'Munich Atopic Prediction Study' is a comprehensive clinical and biological investigation of a prospective birth cohort from Munich, Germany. Information on pregnancy, child development, environmental factors, parental exposures to potential allergens and acute or chronic diseases of children and parents are collected by questionnaires together with a meticulous clinical examination by trained dermatologists focusing on allergies, skin health, and in particular signs of AD at 2 months after birth and then every 6 months. In addition, skin barrier functions are assessed through cutometry, corneometry and transepidermal water loss at every visit. These measurements are completed with allergy diagnostics and extensive microbiome analyses from stool and skin swabs as well as transcriptome analyses using skin microbiopsies.The aim is to assess the relevance of different known and yet unknown risk factors of AD onset and exacerbations in infants and to identify possible accessible and robust biomarkers. ETHICS AND DISSEMINATION: The study is approved by the Ethical Committee of the Medical Faculty of the Technical University of Munich (reference 334/16S). All relevant study results will be presented at national and international conferences and in peer-reviewed journals.

Magnetic nanoparticles in theranostics of malignant melanoma.

Malignant melanoma is an aggressive tumor with a tendency to metastasize early and with an increasing incidence worldwide. Although in early stage, melanoma is well treatable by excision, the chances of cure and thus the survival rate decrease dramatically after metastatic spread. Conventional treatment options for advanced disease include surgical resection of metastases, chemotherapy, radiation, targeted therapy and immunotherapy. Today, targeted kinase inhibitors and immune checkpoint blockers have for the most part replaced less effective chemotherapies. Magnetic nanoparticles as novel agents for theranostic purposes have great potential in the treatment of metastatic melanoma. In the present review, we provide a brief overview of treatment options for malignant melanoma with different magnetic nanocarriers for theranostics. We also discuss current efforts of designing magnetic particles for combined, multimodal therapies (e.g., chemotherapy, immunotherapy) for malignant melanoma.

Targeting tumor-resident mast cells for effective anti-melanoma immune responses.

Immune checkpoint blockade has revolutionized cancer treatment. Patients developing immune mediated adverse events, such as colitis, appear to particularly benefit from immune checkpoint inhibition. Yet, the contributing mechanisms are largely unknown. We identified a systemic LPS signature in melanoma patients with colitis following anti-cytotoxic T lymphocyte-associated antigen 4 (anti-CTLA-4) checkpoint inhibitor treatment and hypothesized that intestinal microbiota-derived LPS contributes to therapeutic efficacy. Because activation of immune cells within the tumor microenvironment is considered most promising to effectively control cancer, we analyzed human and murine melanoma for known sentinels of LPS. We identified mast cells (MCs) accumulating in and around melanomas and showed that effective melanoma immune control was dependent on LPS-activated MCs recruiting tumor-infiltrating effector T cells by secretion of CXCL10. Importantly, CXCL10 was also upregulated in human melanomas with immune regression and in patients with colitis induced by anti-CTLA-4 antibody. Furthermore, we demonstrate that CXCL10 upregulation and an MC signature at the site of melanomas are biomarkers for better patient survival. These findings provide conclusive evidence for a "Trojan horse treatment strategy" in which the plasticity of cancer-resident immune cells, such as MCs, is used as a target to boost tumor immune defense.

Induction of IL-10-balanced immune profiles following exposure to LTA from Staphylococcus epidermidis.

Staphylococcus epidermidis colonises human skin without apparent inflammation, but a dominance of S. epidermidis and S. aureus is characteristic of cutaneous microbial dysbiosis in atopic dermatitis (AD). While S. aureus can trigger AD, the role of S. epidermidis is less understood. We characterised consequences of innate immune sensing of lipoteichoic acid (LTA) preparations derived from S. epidermidis (epi-LTA) or S. aureus (aureus-LTA). Therefore, dendritic cell (DC) activation and consecutive priming of antigen-specific T cells following exposure of DC to epi-LTA or aureus-LTA were investigated. Mimicking acute AD, exposure of DC to IL-4 and LTAs was analysed. Exposure to epi-LTA or aureus-LTA activated human immune cells and murine dendritic cells (DCs) via TLR2/MyD88, however, resulting in divergent immune profiles. Differences between LTAs were significant for IL-6, IL-12p40 and IL-12p70 but not for IL-10, which was best reflected by the IL-12p70-to-IL-10 ratio being IL-10-balanced for epi-LTA but pro-inflammatory for aureus-LTA. LTA-exposed DCs activated CD4+ T cells; however, while T-cell-derived IL-10 was equivalent between LTAs, IFN-γ and IL-17 were significantly higher for aureus-LTA. Mimicking acute AD by exposing DCs to IL-4 and LTAs revealed that IL-4 significantly and uniformly suppressed epi-LTA-induced cytokine production, keeping the IL-12p70-to-IL-10 ratio balanced. In contrast, exposure of DCs to aureus-LTA and IL-4 enhanced IL-12p70 but suppressed IL-10 levels, further unbalancing the IL-12p70-to-IL-10 ratio. These data demonstrate opposing immune consequences following exposure to staphylococcal LTAs. Epi-LTA induced IL-10-balanced, aureus-LTA pro-inflammatory immune profiles.

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.

Sildenafil Potentiates a cGMP-Dependent Pathway to Promote Melanoma Growth.

Sildenafil, an inhibitor of the cGMP-degrading phosphodiesterase 5 that is used to treat erectile dysfunction, has been linked to an increased risk of melanoma. Here, we have examined the potential connection between cGMP-dependent signaling cascades and melanoma growth. Using a combination of biochemical assays and real-time monitoring of melanoma cells, we report a cGMP-dependent growth-promoting pathway in murine and human melanoma cells. We document that C-type natriuretic peptide (CNP), a ligand of the membrane-bound guanylate cyclase B, enhances the activity of cGMP-dependent protein kinase I (cGKI) in melanoma cells by increasing the intracellular levels of cGMP. Activation of this cGMP pathway promotes melanoma cell growth and migration in a p44/42 MAPK-dependent manner. Sildenafil treatment further increases intracellular cGMP concentrations, potentiating activation of this pathway. Collectively, our data identify this cGMP-cGKI pathway as the link between sildenafil usage and increased melanoma risk.

How the innate immune system trains immunity: lessons from studying atopic dermatitis and cutaneous bacteria.

The skin is the largest organ at the interface between environment and host. It plays a major protective role against pathogens as physical barrier, as site of first recognition, and as orchestrator of consecutive immune responses. In this process, immunological crosstalk between skin-resident and immune cells is required, and fixed innate immune responses were previously believed to orchestrate adaptive immunity of B and T lymphocytes. Today, we understand that diverse qualities of immune responses to different microbes need to be regulated by also varying responses at the level of first microbe recognition through receptors of the innate immune system. Only fine-tuning of the innate immune system allows for the orchestration of immune responses to the microbiota in the absence of inflammation as well as to pathogens in the context of protective responses including inflammation. Understanding how innate immunity precisely adapts is also important for diseases such as atopic dermatitis (AD) with chronic inflammation. In this review, we present data on how the innate immune system actually fine-tunes its responses with special focus on the immunological consequences of cutaneous innate immune sensing through TLR2. These new insights are highly relevant for understanding microbiota-associated state of health, immune defense, and the pathogenesis underlying chronic cutaneous inflammation as seen in AD.

The role of innate immune signaling in the pathogenesis of atopic dermatitis and consequences for treatments.

The skin is the largest organ at the interface between the environment and the host. Consequently, the skin plays a central role in mounting effective host defense. In addition to pathogens, the microbiota and the host immune system are in permanent contact and communication via the skin. Consequences of this permanent interaction are a unique and partly symbiotic relationship, a tight interdependence between these partners, and also a functional "setting the clock," in which, in the healthy steady state, an induction of protective responses to pathogens is guaranteed. At the same time, commensal microbes contribute to the alertness of the immune system and to the maintenance of immune tolerance. Atopic dermatitis (AD) is a chronic inflammatory skin disease based on a complex genetic trait with defects in cutaneous barrier, in stabilizing skin integrity. Most of AD patients develop deviated innate and adaptive immune responses. As a result, increased susceptibility to cutaneous infection is found in AD patients, and the interactions between these microbes and the skin participate in the development of chronic cutaneous inflammation. The role of the adaptive immune system was characterized in much detail, less though the contribution of innate immunity to AD pathogenesis. It is rather recent evidence that demonstrates a dominant role of components of the innate immune system not only for protecting from microbial invasion but also by orchestrating chronic skin inflammation. In this review we discuss the role of innate immune signaling and consecutive immune networks important for the pathogenesis and management of AD.

Regulation of T Cell Immunity in Atopic Dermatitis by Microbes: The Yin and Yang of Cutaneous Inflammation.

Atopic dermatitis (AD) is a chronic inflammatory skin disease predominantly mediated by T helper cells. While numerous adaptive immune mechanisms in AD pathophysiology have been elucidated in detail, deciphering the impact of innate immunity in AD pathogenesis has made substantial progress in recent years and is currently a fast evolving field. As innate and adaptive immunity are intimately linked, cross-talks between these two branches of the immune system are critically influencing the resulting immune response and disease. Innate immune recognition of the cutaneous microbiota was identified to substantially contribute to immune homeostasis and shaping of protective adaptive immunity in the absence of inflammation. Disturbances in the composition of the skin microbiome with reduced microbial diversity and overabundance of Staphylococcus spp. have been shown to be associated with AD inflammation. Distinct Staphylococcus aureus associated microbial associated molecular patterns (MAMPs) binding to TLR2 heterodimers could be identified to initiate long-lasting cutaneous inflammation driven by T helper cells and consecutively local immune suppression by induction of myeloid-derived suppressor cells further favoring secondary skin infections as often seen in AD patients. Moreover dissecting cellular and molecular mechanisms in cutaneous innate immune sensing in AD pathogenesis paved the way for exploiting regulatory and anti-inflammatory pathways to attenuate skin inflammation. Activation of the innate immune system by MAMPs of non-pathogenic bacteria on AD skin alleviated cutaneous inflammation. The induction of tolerogenic dendritic cells, interleukin-10 expression and regulatory Tr1 cells were shown to mediate this beneficial effect. Thus, activation of innate immunity by MAMPs of non-pathogenic bacteria for induction of regulatory T cell phenotypes seems to be a promising strategy for treatment of inflammatory skin disorders such as AD. These new findings demonstrate how detailed analyses identify partly opposing consequences of microbe sensing by the innate immune system and how these mechanisms translate into AD pathogenesis as well as new therapeutic strategies.

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.

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.

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.

Nonpathogenic bacteria alleviating atopic dermatitis inflammation induce IL-10-producing dendritic cells and regulatory Tr1 cells.

The beneficial effects of nonpathogenic bacteria are increasingly being recognized. We reported in a placebo-controlled study with atopic dermatitis (AD) patients that cutaneous exposure to lysates of nonpathogenic bacteria alleviates skin inflammation. To now unravel underlying mechanisms, immune consequences of sensing nonpathogenic bacterium Vitreoscilla filiformis lysate (Vf) were characterized analyzing (1) differentiation of dendritic cells (DCs) and, consecutively, (2) effector functions of DCs and T helper (Th) cells in vitro and in a murine model of AD in NC/Nga mice in vivo. Topical treatment with Vf significantly reduced AD-like inflammation in NC/Nga mice. Importantly, cutaneous exposure to Vf in combination with the allergen FITC significantly also reduced subsequent allergen-induced dermatitis indicating active immune modulation. Indeed, innate sensing of Vf predominantly induced IL-10-producing DCs, which was dependent on Toll-like receptor 2 (TLR2) activation. Vf-induced IL-10+ DCs primed naive CD4+ T helper cells to become regulatory IFN-γ(low) IL-10(high) Tr1 (type 1 regulatory T) cells. These IL-10(high) Tr1 cells were also induced by Vf in vivo and strongly suppressed T effector cells and inflammation. In conclusion, we show that innate sensing of nonpathogenic bacteria by TLR2 induces tolerogenic DCs and regulatory Tr1 cells suppressing T effector cells and cutaneous inflammation. These findings indicate a promising therapeutic strategy for inflammatory skin diseases like AD.

Glycosylation of Candida albicans cell wall proteins is critical for induction of innate immune responses and apoptosis of epithelial cells.

C. albicans is one of the most common fungal pathogen of humans, causing local and superficial mucosal infections in immunocompromised individuals. Given that the key structure mediating host-C. albicans interactions is the fungal cell wall, we aimed to identify features of the cell wall inducing epithelial responses and be associated with fungal pathogenesis. We demonstrate here the importance of cell wall protein glycosylation in epithelial immune activation with a predominant role for the highly branched N-glycosylation residues. Moreover, these glycan moieties induce growth arrest and apoptosis of epithelial cells. Using an in vitro model of oral candidosis we demonstrate, that apoptosis induction by C. albicans wild-type occurs in early stage of infection and strongly depends on intact cell wall protein glycosylation. These novel findings demonstrate that glycosylation of the C. albicans cell wall proteins appears essential for modulation of epithelial immunity and apoptosis induction, both of which may promote fungal pathogenesis in vivo.

Tetraspanins in mast cells.

Mast cells (MC) are key mediators of the immune system, most prominently known for their role in eliciting harmful allergic reactions. Mast cell mediator release (e.g. by degranulation) is triggered by FcεRI recognition of antigen - IgE complexes. Until today no therapeutic targeting of this and other mast cell activation pathways is established. Among possible new candidates there are tetraspanins that have been described on MC already several years ago. Tetraspanins are transmembrane proteins acting as scaffolds, mediating local clustering of their interaction partners, and thus amplify their activities. More recently, tetraspanins were also found to exert intrinsic receptor functions. Tetraspanins have been found to be crucial components of fundamental biological processes like cell motility and adhesion. In immune cells, they not only boost the effectiveness of antigen presentation by clustering MHC molecules, they are also key players in all kinds of degranulation events and immune receptor clustering. This review focuses on the contribution of tetraspanins clustered with FcεRI or residing in granule membranes to classical MC functions but also undertakes an outlook on the possible contribution of tetraspanins to newly described mast cell functions and discusses possible targets for drug development.