Functioning as the exterior interface of the human body with the environment, skin acts as a physical barrier to prevent the invasion of foreign pathogens while providing a home to the commensal microbiota. The harsh physical landscape of skin, particularly the desiccated, nutrient-poor, acidic environment, also contributes to the adversity that pathogens face when colonizing human skin. Despite this, the skin is colonized by a diverse microbiota. In this Review, we describe amplicon and shotgun metagenomic DNA sequencing studies that have been used to assess the taxonomic diversity of microorganisms that are associated with skin from the kingdom to the strain level. We discuss recent insights into skin microbial communities, including their composition in health and disease, the dynamics between species and interactions with the immune system, with a focus on Propionibacterium acnes, Staphylococcus epidermidis and Staphylococcus aureus.

/pdf/the-human-skin-microbiome-znvh6yxg29.pdf

The human skin microbiome

Background Current phenotyping of chronic rhinosinusitis (CRS) into chronic rhinosinusitis with nasal polyps (CRSwNP) and chronic rhinosinusitis without nasal polyps (CRSsNP) might not adequately reflect the pathophysiologic diversity within patients with CRS. Objective We sought to identify inflammatory endotypes of CRS. Therefore we aimed to cluster patients with CRS based solely on immune markers in a phenotype-free approach. Secondarily, we aimed to match clusters to phenotypes. Methods In this multicenter case-control study patients with CRS and control subjects underwent surgery, and tissue was analyzed for IL-5, IFN-γ, IL-17A, TNF-α, IL-22, IL-1β, IL-6, IL-8, eosinophilic cationic protein, myeloperoxidase, TGF-β1, IgE, Staphylococcus aureus enterotoxin–specific IgE, and albumin. We used partition-based clustering. Results Clustering of 173 cases resulted in 10 clusters, of which 4 clusters with low or undetectable IL-5, eosinophilic cationic protein, IgE, and albumin concentrations, and 6 clusters with high concentrations of those markers. The group of IL-5–negative clusters, 3 clusters clinically resembled a predominant chronic rhinosinusitis without nasal polyps (CRSsNP) phenotype without increased asthma prevalence, and 1 cluster had a T H 17 profile and had mixed CRSsNP/CRSwNP. The IL-5–positive clusters were divided into a group with moderate IL-5 concentrations, a mixed CRSsNP/CRSwNP and increased asthma phenotype, and a group with high IL-5 levels, an almost exclusive nasal polyp phenotype with strongly increased asthma prevalence. In the latter group, 2 clusters demonstrated the highest concentrations of IgE and asthma prevalence, with all samples expressing Staphylococcus aureus enterotoxin–specific IgE. Conclusion Distinct CRS clusters with diverse inflammatory mechanisms largely correlated with phenotypes and further differentiated them and provided a more accurate description of the inflammatory mechanisms involved than phenotype information only.

https://www.jacionline.org/article/S0091-6749(16)00184-6/pdf

Inflammatory endotypes of chronic rhinosinusitis based on cluster analysis of biomarkers.

This guideline was developed as a joint interdisciplinary European project, including physicians from all relevant disciplines as well as patients. It is a consensus-based guideline, taking available evidence from other guidelines, systematic reviews and published studies into account. This second part of the guideline covers antimicrobial therapy, systemic treatment, allergen-specific immunotherapy, complementary medicine, psychosomatic counselling and educational interventions, whereas the first part covers methods, patient perspective, general measures and avoidance strategies, basic emollient treatment and bathing, dietary intervention, topical anti-inflammatory therapy, phototherapy and antipruritic therapy. Management of AE must consider the individual clinical variability of the disease. Systemic immunosuppressive treatment with cyclosporine, methotrexate, azathioprine and mycophenolic acid is established option for severe refractory cases, and widely available. Biologicals targeting the T helper 2 pathway such as dupilumab may be a safe and effective, disease-modifying alternative when available. Oral drugs such as JAK inhibitors and histamine 4 receptor antagonists are in development. Microbial colonization and superinfection may cause disease exacerbation and can require additional antimicrobial treatment. Allergen-specific immunotherapy with aeroallergens may be considered in selected cases. Psychosomatic counselling is recommended especially in stress-induced exacerbations. Therapeutic patient education ('Eczema school') is recommended for children and adult patients. General measures, basic emollient treatment, bathing, dietary intervention, topical anti-inflammatory therapy, phototherapy and antipruritic therapy have been addressed in the first part of the guideline.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/jdv.14891

Consensus-based European guidelines for treatment of atopic eczema (atopic dermatitis) in adults and children: part I.

The existing evidence for treatment of atopic eczema (atopic dermatitis, AE) is evaluated using the national standard Appraisal of Guidelines Research and Evaluation. The consensus process consisted of a nominal group process and a DELPHI procedure. Management of AE must consider the individual symptomatic variability of the disease. Basic therapy is focused on hydrating topical treatment, and avoidance of specific and unspecific provocation factors. Anti-inflammatory treatment based on topical glucocorticosteroids and topical calcineurin inhibitors (TCI) is used for exacerbation management and more recently for proactive therapy in selected cases. Topical corticosteroids remain the mainstay of therapy, but the TCI tacrolimus and pimecrolimus are preferred in certain locations. Systemic immune-suppressive treatment is an option for severe refractory cases. Microbial colonization and superinfection may induce disease exacerbation and can justify additional antimicrobial treatment. Adjuvant therapy includes UV irradiation preferably with UVA1 wavelength or UVB 311 nm. Dietary recommendations should be specific and given only in diagnosed individual food allergy. Allergen-specific immunotherapy to aeroallergens may be useful in selected cases. Stress-induced exacerbations may make psychosomatic counselling recommendable. 'Eczema school' educational programs have been proven to be helpful. Pruritus is targeted with the majority of the recommended therapies, but some patients need additional antipruritic therapies.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1468-3083.2012.04635.x

Guidelines for treatment of atopic eczema (atopic dermatitis) part I.

The availability of allergen molecules ('components') from several protein families has advanced our understanding of immunoglobulin E (IgE)-mediated responses and enabled 'component-resolved diagnosis' (CRD). The European Academy of Allergy and Clinical Immunology (EAACI) Molecular Allergology User's Guide (MAUG) provides comprehensive information on important allergens and describes the diagnostic options using CRD. Part A of the EAACI MAUG introduces allergen molecules, families, composition of extracts, databases, and diagnostic IgE, skin, and basophil tests. Singleplex and multiplex IgE assays with components improve both sensitivity for low-abundance allergens and analytical specificity; IgE to individual allergens can yield information on clinical risks and distinguish cross-reactivity from true primary sensitization. Part B discusses the clinical and molecular aspects of IgE-mediated allergies to foods (including nuts, seeds, legumes, fruits, vegetables, cereal grains, milk, egg, meat, fish, and shellfish), inhalants (pollen, mold spores, mites, and animal dander), and Hymenoptera venom. Diagnostic algorithms and short case histories provide useful information for the clinical workup of allergic individuals targeted for CRD. Part C covers protein families containing ubiquitous, highly cross-reactive panallergens from plant (lipid transfer proteins, polcalcins, PR-10, profilins) and animal sources (lipocalins, parvalbumins, serum albumins, tropomyosins) and explains their diagnostic and clinical utility. Part D lists 100 important allergen molecules. In conclusion, IgE-mediated reactions and allergic diseases, including allergic rhinoconjunctivitis, asthma, food reactions, and insect sting reactions, are discussed from a novel molecular perspective. The EAACI MAUG documents the rapid progression of molecular allergology from basic research to its integration into clinical practice, a quantum leap in the management of allergic patients.

EAACI Molecular Allergology User's Guide.

Background It has frequently been speculated that pruritus and skin lesions develop after topical exposure to aeroallergens in sensitized patients with atopic dermatitis (AD). Objective We sought to study cutaneous reactions to grass pollen in adult patients with AD with accompanying clear IgE sensitization to grass allergen in an environmental challenge chamber using a monocenter, double-blind, placebo-controlled study design. Methods Subjects were challenged on 2 consecutive days with either 4000 pollen grains/m 3 of Dactylis glomerata pollen or clean air. The severity of AD was assessed at each study visit up to 5 days after challenge by (objective) scoring of AD (SCORAD). Additionally, air-exposed and non–air-exposed skin areas were each scored using local SCORAD scoring and investigator global assessments. Levels of a series of serum cytokines and chemokines were determined by using a Luminex-based immunoassay. The primary end point of the study was the change in objective SCORAD scores between prechallenge and postchallenge values. Results Exposure to grass pollen induced a significant worsening of AD. A pronounced eczema flare-up of air-exposed rather than covered skin areas occurred. In grass pollen–exposed subjects a significantly higher increase in CCL17, CCL22, and IL-4 serum levels was observed. Conclusions This study demonstrates that controlled exposure to airborne allergens of patients with a so-called extrinsic IgE-mediated form of AD induced a worsening of cutaneous symptoms.

https://www.jacionline.org/article/S0091-6749(15)00575-8/pdf

Exacerbation of atopic dermatitis on grass pollen exposure in an environmental challenge chamber.

To cite this article: Kasraie S, Niebuhr M, Werfel T. Interleukin (IL)-31 induces pro-inflammatory cytokines in human monocytes and macrophages following stimulation with staphylococcal exotoxins. Allergy 2010; 65: 712–721.



Abstract

Background:  IL-31 is a cytokine expressed by T cells following activation with cytokines or staphylococcal exotoxins. A major function of IL-31 in atopic dermatitis (AD) is the induction of pruritus in the skin via the IL-31 receptor on sensory nerve cells. However, the regulation of the IL-31 receptor and pro-inflammatory functions of IL-31 in human monocytes and monocyte-derived cells are yet to be studied in detail.



Objective:  To investigate the regulation and function of IL-31 receptors in resting and activated human monocytes, macrophages and dendritic cells.



Methods:  Human monocytes, macrophages and dendritic cells were stimulated with staphylococcal exotoxins (SEB, α-toxin) or cytokines (IFN-γ, IL-13). IL-31RA expression and regulation were then investigated at both the mRNA and the protein level. Subsequently, functional effects of IL-31 stimulation on cytokine secretion were measured at the protein level.



Results:  Staphylococcal exotoxins significantly up-regulated IL-31RA expression on monocytes and macrophages but not on dendritic cells at both the mRNA and the protein level. IL-31 enhanced the secretion of IL-1β, IL-6 and IL-18 and up-regulated CD86 expression. In patients with AD, functional IL-31RA was also detected following stimulation of PBMC with IFN-γ. However, this was not observed in healthy individuals.



Conclusion:  IL-31 induces pro-inflammatory effects in activated human monocytes and macrophages. This may have implications for cutaneous inflammation in eczema where an over-expression of IL-31 has been described previously. Moreover, our findings provide a new link between staphylococcal colonization and the worsening of inflammation via IL-31. Further therapeutic considerations may include IL-31 as a target in AD.

Interleukin (IL)-31 induces pro-inflammatory cytokines in human monocytes and macrophages following stimulation with staphylococcal exotoxins.

Background Patients with atopic dermatitis (AD) and psoriasis are frequently colonized with Staphylococcus aureus that produces staphylococcal enterotoxin B (SEB) and α-toxin. In patients with AD, S aureus colonization is positively correlated with the severity of their eczema. Moreover, IL-22–producing cells have been shown to accumulate in AD skin and to correlate with disease severity. Objective To assess IL-22 production in response to SEB and sublytic α-toxin stimulation in patients with AD and psoriasis compared with healthy controls. Methods IL-22 induction was investigated in PBMCs, T cells, and autologous cocultures of keratinocytes and T cells on SEB and α-toxin stimulation in a time-dependent and dose-dependent manner at the mRNA and protein (ELISA and flow cytometry) level. Anti–IL-1 receptor or anti–IL-6 antibodies were used in blocking experiments. Results Staphylococcal enterotoxin B and sublytic α-toxin concentrations induced IL-22 production in PBMCs and isolated CD4 + T cells. IL-22 secretion was enhanced by α-toxin stimulation in autologous cocultures of keratinocytes and T cells. In T cells and PBMCs from patients with AD, IL-22 secretion was significantly enhanced on α-toxin stimulation compared with patients with psoriasis and healthy controls. Conclusion Increased IL-22 secretion induced by staphylococcal exotoxins in the skin partially explains how skin colonization and infection with S aureus can contribute to chronic skin inflammation in AD.

https://www.jacionline.org/article/S0091-6749(10)01264-9/pdf

Staphylococcal exotoxins are strong inducers of IL-22: A potential role in atopic dermatitis

To cite this article: Kasraie S, Niebuhr M, Baumert K, Werfel T. Functional effects of Interleukin 31 in human primary keratinocytes. Allergy 2011; 66: 845–852.



Abstract

Background:  Interleukin (IL)-31 is a T-cell cytokine acting through a heterodimeric receptor composed of IL-31RA and OSMR which is expressed on epithelial cells including keratinocytes. A major function of IL-31 in atopic dermatitis (AD) is the induction of pruritus in the skin. Inflammatory effects of IL-31 in human primary keratinocytes (HPKs) still remain unclear. We investigated expression, regulation of the IL-31 receptor as well as functions of IL-31 in HPKs.



Methods:  Human primary keratinocytes were stimulated with TLR-2 ligands (Pam3Cys, lipoteichoic acid and peptidoglycan), or Th1 and Th2 associated cytokines (IFN-γ and IL-4), respectively. IL-31R expression and regulation as well as functional effects of IL-31 stimulation were then investigated at both the mRNA and protein level and compared with HPKs from patients with AD. The STAT signalling pathway and TLR-2 expression were investigated using Western blot and Immunohistochemical stainings, respectively.



Results:  Pam3Cys or IFN-γ significantly up-regulated IL-31RA and OSMR expression. IL-31 activated STAT-3 phosphorylation in HPKs which was augmented after preactivation with Pam3Cys or IFN-γ. IL-31 enhanced the secretion of CCL2 after up-regulation of the receptor with Pam3Cys or IFN-γ. However, this was not observed in keratinocytes from AD patients where an impaired TLR-2 expression was found.



Conclusions:  Together, our findings show a functional role of IL-31 in HPKs and provide a new link between TLR-2 ligands and IL-31 which might be dysregulated in AD. Altered function of IL-31 may have implications for cutaneous inflammation in eczema where skin colonization with Staphylococcus aureus and dysregulation of TLR-2 have been described.

Functional effects of interleukin 31 in human primary keratinocytes

Background IgE-mediated cross-reactivity between fungal antigens and human proteins has been described in patients with atopic dermatitis (AD), but it remains to be elucidated whether there is also cross-reactivity at the T-cell level. Objective We sought to explore cross-reactivity at the T-cell level between the fungal thioredoxin (Mala s 13) of the skin-colonizing yeast Malassezia sympodialis and its homologous human thioredoxin (hTrx). Methods T-cell lines (TCLs) were generated in the presence of rMala s 13 from the peripheral blood and from skin biopsy specimens of positive patch test reactions of patients with AD sensitized to Mala s 13 and hTrx. Patients with AD not sensitized to Malassezia species, healthy subjects, and patients with psoriasis served as control subjects. Mala s 13–specific T-cell clones (TCCs) were generated from TCLs. TCCs were characterized by antigen specificity, phenotype, and cytokine secretion pattern. Human keratinocytes were stimulated with IFN-γ, TNF-α, and IL-4, and the release of hTrx was determined by means of ELISA. Results Mala s 13–specific TCLs and TCCs from the blood and skin of patients with AD sensitized to Mala s 13 and hTrx were fully cross-reactive with hTrx. Mala s 13– and hTrx–specific TCCs could not be generated from control subjects. The majority of cross-reactive TCCs were CD4 + and coexpressed cutaneous lymphocyte antigen. In addition to T H 1 and T H 2 TCCs, we could also identify TCCs secreting IL-17 and IL-22. After stimulation with IFN-γ and TNF-α, keratinocytes released substantial amounts of thioredoxin. Conclusion In patients with AD sensitized to Malassezia species, cross-reactivity at the T-cell level to Mala s 13 and the homologous hTrx is detectable. hTrx autoreactive skin-homing T cells might be relevant for cutaneous inflammation in patients with AD.

Margarete Niebuhr

Papers

Exacerbation of atopic dermatitis on grass pollen exposure in an environmental challenge chamber.

Interleukin (IL)-31 induces pro-inflammatory cytokines in human monocytes and macrophages following stimulation with staphylococcal exotoxins.

Staphylococcal exotoxins are strong inducers of IL-22: A potential role in atopic dermatitis

Functional effects of interleukin 31 in human primary keratinocytes

Malassezia sympodialis thioredoxin–specific T cells are highly cross-reactive to human thioredoxin in atopic dermatitis