Compartmentalized control of skin immunity by resident commensals

Alterations of human skin microbiome and expansion of antimicrobial resistance after systemic antibiotics

[Figure: see text].

Epidermis as a Platform for Bacterial Transmission

The epidermis constitutes a continuous external layer covering the body, offering protection against bacteria, the most abundant living organisms that come into contact with this barrier. The epidermis is heavily colonized by commensal bacterial organisms that help protect against pathogenic bacteria. The highly regulated and dynamic interaction between the epidermis and commensals involves the host’s production of nutritional factors promoting bacterial growth together to chemical and immunological bacterial inhibitors. Signal trafficking ensures the system’s homeostasis; conditions that favor colonization by pathogens frequently foster commensal growth, thereby increasing the bacterial population size and inducing the skin’s antibacterial response, eliminating the pathogens and re-establishing the normal density of commensals. The microecological conditions of the epidermis favors Gram-positive organisms and are unsuitable for long-term Gram-negative colonization. However, the epidermis acts as the most important host-to-host transmission platform for bacteria, including those that colonize human mucous membranes. Bacteria are frequently shared by relatives, partners, and coworkers. The epidermal bacterial transmission platform of healthcare workers and visitors can contaminate hospitalized patients, eventually contributing to cross-infections. Epidermal transmission occurs mostly via the hands and particularly through fingers. The three-dimensional physical structure of the epidermis, particularly the fingertips, which have frictional ridges, multiplies the possibilities for bacterial adhesion and release. Research into the biology of bacterial transmission via the hands is still in its infancy; however, tribology, the science of interacting surfaces in relative motion, including friction, wear and lubrication, will certainly be an important part of it. Experiments on finger-to-finger transmission of microorganisms have shown significant interindividual differences in the ability to transmit microorganisms, presumably due to genetics, age, sex, and the gland density, which determines the physical, chemical, adhesive, nutritional, and immunological status of the epidermal surface. These studies are needed to optimize interventions and strategies for preventing the hand transmission of microorganisms.

Periodontal Disease: The Good, The Bad, and The Unknown

Periodontal disease is classically characterized by progressive destruction of the soft and hard tissues of the periodontal complex, mediated by an interplay between dysbiotic microbial communities and aberrant immune responses within gingival and periodontal tissues. Putative periodontal pathogens are enriched as the resident oral microbiota becomes dysbiotic and inflammatory responses evoke tissue destruction, thus inducing an unremitting positive feedback loop of proteolysis, inflammation, and enrichment for periodontal pathogens. Keystone microbial pathogens and sustained gingival inflammation are critical to periodontal disease progression. However, recent studies have revealed the importance of previously unidentified microbes involved in disease progression, including various viruses, phages and bacterial species. Moreover, newly identified immunological and genetic mechanisms, as well as environmental host factors, including diet and lifestyle, have been discerned in recent years as further contributory factors in periodontitis. These factors have collectively expanded the established narrative of periodontal disease progression. In line with this, new ideologies related to maintaining periodontal health and treating existing disease have been explored, such as the application of oral probiotics, to limit and attenuate disease progression. The role of systemic host pathologies, such as autoimmune disorders and diabetes, in periodontal disease pathogenesis has been well noted. Recent studies have additionally identified the reciprocated importance of periodontal disease in potentiating systemic disease states at distal sites, such as in Alzheimer's disease, inflammatory bowel diseases, and oral cancer, further highlighting the importance of the oral cavity in systemic health. Here we review long-standing knowledge of periodontal disease progression while integrating novel research concepts that have broadened our understanding of periodontal health and disease. Further, we delve into innovative hypotheses that may evolve to address significant gaps in the foundational knowledge of periodontal disease.

Skin pH varies among bat species and seasons and between wild and captive bats

Skin is a key aspect of the immune system in the defence against pathogens. Skin pH regulates the activity of enzymes produced both by hosts and by microbes on host skin, thus implicating pH in disease susceptibility. Skin pH varies inter- and intra-specifically and is influenced by a variety of intrinsic and extrinsic variables. Increased skin alkalinity is associated with a predisposition to cutaneous infections in humans and dogs, and inter-specific and inter-individual variation in skin pH is implicated in differential susceptibility to some skin diseases. The cutaneous pH of bats has not been characterized but is postulated to play a role in susceptibility to white-nose syndrome (WNS), a fungal infection that has decimated several Nearctic bat species. We used non-invasive probes to measure the pH of bat flight membranes in five species with differing susceptibility to WNS. Skin pH ranged from 4.67 to 8.59 and varied among bat species, geographic locations, body parts, age classes, sexes and seasons. Wild Eptesicus fuscus were consistently more acidic than wild Myotis lucifugus, Myotis leibii and Perimyotis subflavus. Juvenile bats had more acidic skin than adults during maternity season but did not differ during swarming. Male M. lucifugus were more acidic than females during maternity season, yet this trend reversed during swarming. Bat skin was more acidic in summer compared to winter, a pattern also reported in humans. Skin pH was more acidic in captive than wild E. fuscus, suggesting environmental impacts on skin pH. The pH of roosting substrates affects skin pH in captive bats and may partially explain seasonal patterns in wild bats that use different roost types across seasons. Future research on the influence of pH on microbial pathogenic factors and skin barrier function may provide valuable insights on new therapeutic targets for treating bat skin conditions.

Of mice and men and women: Sexual dimorphism of the gut microbiome

The gut microbiome plays a critical role in developing and educating our immune system. Therefore, its now well-established role in autoimmunity and immune disorders is in some ways not surprising. However, it is well-documented in the literature that there is a female predisposition to autoimmune disorders, while sexual dimorphisms in the human microbiome have been confined largely to areas outside of the gut. Herein, we will review the evidence of sexual dimorphism in the gut microbiome in both mice and humans, how this differs in animal models versus humans, and how such dimorphisms may be established and influenced by both host and environmental factors. We will conclude with a discussion on how these aspects of the gut microbiome may contribute to both the study and pathogenesis of gender-specific autoimmunity and immune disorders.

Rapidly Growing Mycobacterium Species: The Long and Winding Road from Tuberculosis Vaccines to Potent Stress-Resilience Agents

Inflammatory diseases and stressor-related psychiatric disorders, for which inflammation is a risk factor, are increasing in modern Western societies. Recent studies suggest that immunoregulatory approaches are a promising tool in reducing the risk of suffering from such disorders. Specifically, the environmental saprophyte Mycobacterium vaccae National Collection of Type Cultures (NCTC) 11659 has recently gained attention for the prevention and treatment of stress-related psychiatric disorders. However, effective use requires a sophisticated understanding of the effects of M. vaccae NCTC 11659 and related rapidly growing mycobacteria (RGMs) on microbiome–gut–immune–brain interactions. This historical narrative review is intended as a first step in exploring these mechanisms and provides an overview of preclinical and clinical studies on M. vaccae NCTC 11659 and related RGMs. The overall objective of this review article is to increase the comprehension of, and interest in, the mechanisms through which M. vaccae NCTC 11659 and related RGMs promote stress resilience, with the intention of fostering novel clinical strategies for the prevention and treatment of stressor-related disorders.

Controllers of cutaneous regulatory T cells: ultraviolet radiation and the skin microbiome

For the maintenance of homeostasis termination of immune reactions is as equally important as their induction. In this scenario regulatory T cells (Treg) play an important role. Accordingly a variety of inflammatory diseases are caused by an impairment of Treg. Hence, it is important to identify triggers by which Treg can be induced and activated, respectively. For quite a long time it is known that ultraviolet radiation can induce Treg which inhibit cutaneous immune reactions including contact hypersensitivity. Since these Treg inhibit in an antigen-specific fashion they may harbor therapeutic potential. However similar Treg can be induced also by other triggers which include vitamin D and antimicrobial peptides. Recently it was discovered that the gut microbiome controls the development of Treg in the intestine. The same may apply for the skin. Short chain fatty acids, microbiota-derived bacterial fermentation products, appear to induce and to activate Treg in the skin. Topical application of short chain fatty acids was shown to inhibit contact hypersensitivity and to reduce inflammation in the murine imiquimod-induced psoriasis-like skin inflammation model. Together, these data indicate that induction and activation of Treg may be a potential therapeutic strategy to treat inflammatory diseases in the future.

Impact of low-dose calcipotriol ointment on wound healing, pruritus and pain in patients with dystrophic epidermolysis bullosa: A randomized, double-blind, placebo-controlled trial

Background

Wound management is a critical factor when treating patients with the inherited skin fragility disease dystrophic epidermolysis bullosa (DEB). Due to genetic defects in structural proteins, skin and mucous epithelia are prone to blistering and chronic wounding upon minor trauma. Furthermore, these wounds are commonly associated with excessive pruritus and predispose to the development of life-threatening squamous cell carcinomas, underscoring the unmet need for new therapeutic options to improve wound healing in this patient cohort. Vitamin D3 is acknowledged to play an important role in wound healing by modulating different cellular processes that impact epidermal homeostasis and immune responses. In this study, we evaluate the safety and efficacy of low-dose calcipotriol, a vitamin D3 analogue, in promoting wound healing and reducing itch and pain in patients with DEB.

Methods

Eligible DEB patients, aged ≥ 6 years and with a known mutation in the COL7A1 gene, were recruited to a placebo-controlled, randomized, double blind, cross-over phase II monocentric clinical trial. Patients were required to have at least two wounds with a minimum size of 6 cm² per wound. The primary objective was to evaluate efficacy of daily topical application of a 0.05 µg/g calcipotriol ointment in reducing wound size within a 4-week treatment regimen. Secondary objectives were to assess safety, as well as the impact of treatment on pruritus, pain, and bacterial wound colonization in these patients.

Results

Six patients completed the clinical trial and were included into the final analysis. Topical low-dose calcipotriol treatment led to a significant reduction in wound area at day 14 compared to placebo (88.4% vs. 65.5%, P < 0.05). Patients also reported a significant reduction of pruritus with calcipotriol ointment compared to placebo over the entire course of the treatment as shown by itch scores of 3.16 vs 4.83 (P < 0.05) and 1.83 vs 5.52 (P < 0.0001) at days 14 and 28, respectively. Treatment with low-dose calcipotriol did not affect serum calcium levels and improved the species richness of the wound microbiome, albeit with no statistical significance.

Conclusions

Our results show that topical treatment with low-dose calcipotriol can accelerate wound closure and significantly reduces itch, and can be considered a safe and readily-available option to improve local wound care in DEB patients.

TrialRegistration EudraCT: 2016–001,967-35. Registered 28 June 2016, https://www.clinicaltrialsregister.eu/ctr-search/trial/2016-001967-35/AT

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02062-2.

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.

Resistance Against Leishmania major Infection Depends on Microbiota-Guided Macrophage Activation

Innate immune cells present a dual role during leishmaniasis: they constitute the first line of host defense but are also the main host cells for the parasite. Response against the infection that results in the control of parasite growth and lesion healing depends on activation of macrophages into a classical activated phenotype. We report an essential role for the microbiota in driving macrophage and monocyte-derived macrophage activation towards a resistance phenotype against Leishmania major infection in mice. Both germ-free and dysbiotic mice showed a higher number of myeloid innate cells in lesions and increased number of infected cells, mainly dermal resident and inflammatory macrophages. Despite developing a Th1 immune response characterized by the same levels of IFN-γ production as the conventional mice, germ-free mice presented reduced numbers of iNOS+ macrophages at the peak of infection. Absence or disturbance of host microbiota impaired the capacity of bone marrow-derived macrophage to be activated for Leishmania killing in vitro, even when stimulated by Th1 cytokines. These cells presented reduced expression of inos mRNA, and diminished production of microbicidal molecules, such as ROS, while presenting a permissive activation status, characterized by increased expression of arginase I and il-10 mRNA and higher arginase activity. Colonization of germ-free mice with complete microbiota from conventional mice rescued their ability to control the infection. This study demonstrates the essential role of host microbiota on innate immune response against L. major infection, driving host macrophages to a resistance phenotype.

Newborn infant skin gene expression: Remarkable differences versus adults

At birth, human infants are poised to survive in harsh, hostile conditions. An understanding of the state of newborn skin development and maturation is key to the maintenance of health, optimum response to injury, healing and disease. The observational study collected full-thickness newborn skin samples from 27 infants at surgery and compared them to skin samples from 43 adult sites protected from ultraviolet radiation exposure, as the standard for stable, mature skin. Transcriptomics profiling and gene set enrichment analysis were performed. Statistical analysis established over 25,000 differentially regulated probe sets, representing 10,647 distinct genes, in infant skin compared to adult skin. Gene set enrichment analysis showed a significant increase in 143 biological processes (adjusted p < 0.01) in infant skin, versus adult skin samples, including extracellular matrix (ECM) organization, cell adhesion, collagen fibril organization and fatty acid metabolic process. ECM organization and ECM structure organization were the biological processes in infant skin with the lowest adjusted P-value. Genes involving epidermal development, immune function, cell differentiation, and hair cycle were overexpressed in adults, representing 101 significantly enriched biological processes (adjusted p < 0.01). The processes with the highest significant difference were skin and epidermal development, e.g., keratinocyte differentiation, keratinization and cornification intermediate filament cytoskeleton organization and hair cycle. Enriched Gene Ontology (GO) biological processes also involved immune function, including antigen processing and presentation. When compared to ultraviolet radiation-protected adult skin, our results provide essential insight into infant skin and its ability to support the newborn's preparedness to survive and flourish, despite the infant's new environment laden with microbes, high oxygen tension and potential irritants. This fundamental knowledge is expected to guide strategies to protect and preserve the features of unperturbed, young skin.

Patients with senile pruritus have a distinct skin microbiota and epidermal barrier in comparison with healthy controls

Senile pruritus (SP) is a common skin disease in the elderly. The role of skin dysbacteriosis in the development of various skin diseases has been studied in recent years. However, the research about the skin microbiota of senile pruritus patients is lacking at present. The purpose of this cross-sectional study was to investigate the differences of skin microbiota in senile pruritus patients and their relationship with the epidermal barrier. Thirty patients with senile pruritus and 30 age- and sex-matched healthy controls were enrolled in this study. The skin barrier indexes were recorded by multi-functional skin tester. The skin bacterial diversity was analyzed by using hyper-variable tag sequencing of the V3-V4 region of the 16S rDNA. Compared with the healthy control group, the patients had significantly lower skin hydration (p = 0.014) and higher pH value (p = 0.021). Skin microbial diversity was significantly increased in patients according to the alpha diversity. At the genus level, Acinetobacter (p = 0.002) and Lactobacillus (p = 0.002) increased and Cutibacterium (p = 0.043) decreased. The pH value was positively associated with observed_species diversity (p = 0.026). The transdermal water loss was negatively related to the genus of Lactobacillus (p = 0.036), while the skin hydration was positively associated with the genus of Lactobacillus (p = 0.038). As a result, the damaged skin barrier function and skin dysbacteriosis complemented each other and may be associated with the occurrence of senile pruritus, but their role still needs further study.

Secretory Proteases of the Human Skin Microbiome

The human skin is our outermost layer and serves as a protective barrier against external insults. Advances in next generation sequencing have enabled the discoveries of a rich and diverse community of microbes - bacteria, fungi and viruses that are residents of this surface. The genomes of these microbes also revealed the presence of many secretory enzymes. In particular, proteases which are hydrolytic enzymes capable of protein cleavage and degradation are of special interest in the skin environment which is enriched in proteins and lipids. In this minireview, we will focus on the roles of these skin-relevant microbial secreted proteases, both in terms of their widely studied roles as pathogenic agents in tissue invasion and host immune inactivation, and their recently discovered roles in inter-microbial interactions and modulation of virulence factors. From these studies, it has become apparent that while microbial proteases are capable of a wide range of functions, their expression is tightly regulated and highly responsive to the environments the microbes are in. With the introduction of new biochemical and bioinformatics tools to study protease functions, it will be important to understand the roles played by skin microbial secretory proteases in cutaneous health, especially the less studied commensal microbes with an emphasis on contextual relevance.

Effect of the skincare product on facial skin microbial structure and biophysical parameters: A pilot study

Daily use of cosmetics is known to affect the skin microbiome. This study aimed to determine the bacterial community structure and skin biophysical parameters following the daily application of a skincare product on the face. Twenty-five Korean women, who used the same skincare product for four weeks participated in the study. During this period, skin hydration, texture, sebum content, and pH were measured, and skin swab samples were collected on the cheeks. The microbiota was analyzed using the MiSeq system. Through these experiments, bacterial diversity in facial skin increased and the microbial community changed after four weeks of skincare product application. The relative abundance of Cutibacterium and Staphylococcus increased, significant changes in specific bacterial modules of the skin microbial network were observed, and skin hydration and texture improved. It was suggested that daily use of skincare products could affect the microbial structure of facial skin as well as the biophysical properties of the facial skin. These findings expand our understanding of the role of skincare products on the skin environment.

Early development of the skin microbiome: therapeutic opportunities

As human skin hosts a diverse microbiota in health and disease, there is an emerging consensus that dysregulated interactions between host and microbiome may contribute to chronic inflammatory disease of the skin. Neonatal skin is a unique habitat, structurally similar to the adult but with a different profile of metabolic substrates, environmental stressors, and immune activity. The surface is colonized within moments of birth with a bias toward maternal strains. Initial colonists are outcompeted as environmental exposures increase and host skin matures. Nonetheless, early life microbial acquisitions may have long-lasting effects on health through modulation of host immunity and competitive interactions between bacteria. Microbial ecology and its influence on health have been of interest to dermatologists for >50 years, and an explosion of recent interest in the microbiome has prompted ongoing investigations of several microbial therapeutics for dermatological disease. In this review, we consider how recent insight into the host and microbial factors driving development of the skin microbiome in early life offers new opportunities for therapeutic intervention. IMPACT: Advancement in understanding molecular mechanisms of bacterial competition opens new avenues of investigation into dermatological disease. Primary development of the skin microbiome is determined by immunological features of the cutaneous habitat. Understanding coordinated microbial and immunological development in the pediatric patient requires a multidisciplinary synthesis of primary literature.

Effects of Heat-Killed Lactococcus lactis Strain Plasma on Skin Homeostasis-Related Genes and the Skin Microbiome among Healthy Adults: A Randomized Controlled Double-Blind Study

Lactococcus lactis subsp. lactis strain plasma (LC-plasma) is a bacterial strain that activates plasmacytoid dendritic cells and induces viral resistance genes via the TLR9/MyD88 pathway. We recently showed that oral administration of LC-plasma prevents skin infection by Staphylococcus aureus, possibly by activating skin immunity. In this study, we conducted a double-blind clinical trial to investigate the effect of oral administration of heat-killed LC-plasma on the skin microbiome, gene expression in the skin, and the skin condition of healthy volunteers. Seventy healthy volunteers were randomly assigned to receive either heat-killed LC-plasma or a placebo for eight weeks. Analysis of the skin microbiome by next-generation sequencing suggested that the alpha-diversity of the skin microbiome did not change during the test period in either group. However, the proportion of species that changed significantly during the test period was 10-fold smaller in the LC-plasma group than in the placebo group, suggesting that LC-plasma may maintain the skin microbiome. Quantitative PCR analysis indicated that tight-junction genes, such as CLDN1 and CLDN12, and the antimicrobial peptide gene BD3 were significantly up-regulated in the LC-plasma group but not in the placebo group. Our results suggest that administration of LC-plasma helps to maintain the skin microbiome and that it affects homeostasis-related genes.

The Clinical Relevance of the Microbiome in Hidradenitis Suppurativa: A Systematic Review

Hidradenitis suppurativa is a chronic disease of the pilosebaceous unit. The name of the condition is a testament to the presumed relationship between the disease and the microbiome. The pathophysiology of hidradenitis suppurativa is, however, complex and believed to be the product of a multifactorial interplay between the interfollicular epithelium, pilosebaceous unit, microbiome, as well as genetic and environmental factors. In this review we assimilate the existing literature regarding the role played by the human microbiome in HS in various contexts of the disease, including the pathophysiologic, therapeutic, and potentially, diagnostic as well prognostic. In conclusion, the role played by the microbiome in HS is extensive and relevant and can have bench-to-bedside applications.

Regulation of IL-17A-Producing Cells in Skin Inflammatory Disorders

This review focuses on the IL-17A family of cytokines produced by T lymphocytes and other immune cells and how they are involved in cutaneous pathogenic responses. It will also discuss cutaneous dysbiosis and FOXP3⁺ regulatory T cells in the context of inflammatory conditions linked to IL-17 responses in the skin. Specifically, it will review key literature on chronic mucocutaneous candidiasis and psoriasis.

Mechanisms for control of skin immune function by the microbiome

The skin represents the largest area for direct contact between microbes and host immunocytes and is a site for constant communication between the host and this diverse and essential microbial community. Coagulase-negative staphylococci are an abundant bacterial genus on the human skin and are regulated through various mechanisms that include the epidermal barrier environment and innate and adaptive immune systems within the epidermis and dermis. In turn, some species and strains of these bacteria produce beneficial products that augment host immunity by exerting specifically targeted antimicrobial, anti-inflammatory, or anti-neoplastic activity while also promoting broad innate and adaptive immune responses. The use of selected skin commensals as a therapeutic has shown promise in recent human clinical trials. This emerging concept of bacteriotherapy is defining mechanisms of action and validating the dependence on the microbiome for maintenance of immune homeostasis.

Features of the Skin Microbiota in Common Inflammatory Skin Diseases

Many relatively common chronic inflammatory skin diseases manifest on the face (seborrheic dermatitis, rosacea, acne, perioral/periorificial dermatitis, periocular dermatitis, etc.), thereby significantly impairing patient appearance and quality of life. Given the yet unexplained pathogenesis and numerous factors involved, these diseases often present therapeutic challenges. The term “microbiome” comprises the totality of microorganisms (microbiota), their genomes, and environmental factors in a particular environment. Changes in human skin microbiota composition and/or functionality are believed to trigger immune dysregulation, and consequently an inflammatory response, thereby playing a potentially significant role in the clinical manifestations and treatment of these diseases. Although cultivation methods have traditionally been used in studies of bacterial microbiome species, a large number of bacterial strains cannot be grown in the laboratory. Since standard culture-dependent methods detect fewer than 1% of all bacterial species, a metagenomic approach could be used to detect bacteria that cannot be cultivated. The skin microbiome exhibits spatial distribution associated with the microenvironment (sebaceous, moist, and dry areas). However, although disturbance of the skin microbiome can lead to a number of pathological conditions and diseases, it is still not clear whether skin diseases result from change in the microbiome or cause such a change. Thus far, the skin microbiome has been studied in atopic dermatitis, seborrheic dermatitis, psoriasis, acne, and rosacea. Studies on the possible association between changes in the microbiome and their association with skin diseases have improved the understanding of disease development, diagnostics, and therapeutics. The identification of the bacterial markers associated with particular inflammatory skin diseases would significantly accelerate the diagnostics and reduce treatment costs. Microbiota research and determination could facilitate the identification of potential causes of skin diseases that cannot be detected by simpler methods, thereby contributing to the design and development of more effective therapies.

Insights into the Pathogenesis of HS and Therapeutical Approaches

Hidradenitis suppurativa (HS) is a debilitating, chronic, (auto)inflammatory disease primarily affecting apocrine gland-rich areas of the body. Although pathogenic mechanisms responsible for HS have not yet been fully elucidated, it is a multifactorial process whose main target is the terminal follicle. The role of the inflammatory process (and consequently of cytokine milieu) and of several other factors (genetics, lifestyle, hormonal status, microbiome, innate and adaptive immune systems) involved in HS pathogenesis has been investigated (and often defined) over the years with a view to transferring research results from bench to bedside and describing a unique and universally accepted pathogenetic model. This review will update readers on recent advances in our understanding of HS pathogenesis and novel (potential) medical therapies for patients with moderate-to-severe HS.

Crosstalk between γδ T cells and the microbiota

The role of the microbiota in the development and function of γδ T cells-a T cell subset characterized by a T cell receptor composed of one γ-chain and one δ-chain-has been investigated in multiple organs in mice and humans. Interactions between the microbiota and γδ T cells affect both tissue homeostasis and disease pathologies. Notably, microbiota-induced interleukin-17 (IL-17)-producing-γδ T cells can mediate a range of immunological processes, from metabolic disorders to neuroinflammation via the gut-brain axis. However, the bidirectional interactions between γδ T cells and the microbiota have not been fully determined. In this Perspective, we dissect the roles of microbiota in modulating γδ T cell development and function, and evaluate the evidence for γδ T cell selection of commensal communities. We also discuss the potential implications of these cells in health and disease and the major open questions and research avenues in the field.

Epithelial-immune crosstalk with the skin microbiota in homeostasis and atopic dermatitis - a mini review

The skin is a complex and dynamic ecosystem, wherein epithelial cells, immune cells and the skin microbiota actively interact and maintain barrier integrity and functional immunity. Skin microbes actively tune the functions of the resident immune cells. Dysbiosis - alterations in the resident microbiota - leads to the dysregulation of host immunity. Microbiome analyses in humans and dogs with atopic dermatitis (AD) have shown shifts in microbial diversity, and in particular, an increased proportion of staphylococci. Monogenic diseases that manifest AD-like symptoms provide insights into the pathogenesis of AD and the mechanisms of dysbiosis, from both the epithelial and immunological perspectives. The symbiotic relationships between the host and microbiota must be maintained constitutively. Detailed mechanisms of how host immunity regulates commensal bacteria in the steady state have been reported. The skin harbours multiple tissue-resident immune cells, including both innate and adaptive immune cells. Recent studies have highlighted the fundamental role of innate lymphoid cells (ILCs) in the maintenance of barrier functions and tissue homeostasis. ILCs directly respond to tissue-derived signals and are instrumental in barrier immunity. Epithelial cells produce alarmins such as thymic stromal lymphopoietin (TSLP) and interleukins (IL)-33 and IL-25, all of which activate group 2 ILCs (ILC2s), which produce type 2 cytokines, such as IL-5 and IL-13, boosting type 2 immune reactions. Dysregulation of the epithelial-ILC crosstalk results in allergic inflammation. This review highlights our understanding of the active interactions between the host epithelial and immune cells, and microbiota, providing a foundation for novel therapeutic strategies for inflammatory skin diseases.

The Bigger Picture: Why Oral Mucosa Heals Better Than Skin

Wound healing is an essential process to restore tissue integrity after trauma. Large skin wounds such as burns often heal with hypertrophic scarring and contractures, resulting in disfigurements and reduced joint mobility. Such adverse healing outcomes are less common in the oral mucosa, which generally heals faster compared to skin. Several studies have identified differences between oral and skin wound healing. Most of these studies however focus only on a single stage of wound healing or a single cell type. The aim of this review is to provide an extensive overview of wound healing in skin versus oral mucosa during all stages of wound healing and including all cell types and molecules involved in the process and also taking into account environmental specific factors such as exposure to saliva and the microbiome. Next to intrinsic properties of resident cells and differential expression of cytokines and growth factors, multiple external factors have been identified that contribute to oral wound healing. It can be concluded that faster wound closure, the presence of saliva, a more rapid immune response, and increased extracellular matrix remodeling all contribute to the superior wound healing and reduced scar formation in oral mucosa, compared to skin.

Microbiome analysis, the immune response and transplantation in the era of next generation sequencing

The human gastrointestinal tract, skin and mucosal surfaces are inhabited by a complex system of bacteria, viruses, fungi, archaea, protists, and eukaryotic parasites with predominance of bacteria and bacterial viruses (bacteriophages). Collectively these microbes form the microbiota of the microecosystem of humans. Recent advancement in technologies for nucleic acid isolation from various environmental samples, feces and body secretions and advancements in shotgun throughput massive parallel DNA and RNA sequencing along with 16S ribosomal gene sequencing have unraveled the identity of otherwise unknown microbial entities constituting the human microecosystem. The improved transcriptome analysis, technological developments in biochemical analytical methods and availability of complex bioinformatics tools have allowed us to begin to understand the metabolome of the microbiome and the biochemical pathways and potential signal transduction pathways in human cells in response to microbial infections and their products. Also, developments in human whole genome sequencing, targeted gene sequencing of histocompatibility genes and other immune response associated genes by Next Generation Sequencing (NGS) have allowed us to have a better conceptualization of immune responses, and alloimmune responses. These modern technologies have enabled us to dive into the intricate relationship between commensal symbiotic and pathogenic microbiome and immune system. For the most part, the commensal symbiotic microbiota helps to maintain normal immune homeostasis besides providing healthy nutrients, facilitating digestion, and protecting the skin, mucosal and intestinal barriers. However, changes in diets, administration of therapeutic agents like antibiotics, chemotherapeutic agents, immunosuppressants etc. along with certain host factors including human histocompatibility antigens may alter the microbial ecosystem balance by causing changes in microbial constituents, hierarchy of microbial species and even dysbiosis. Such alterations may cause immune dysregulation, breach of barrier protection and lead to immunopathogenesis rather than immune homeostasis. The effects of human microbiome on immunity, health and disease are currently under intense research with cutting edge technologies in molecular biology, biochemistry, and bioinformatics along with tremendous ability to characterize immune response at single cell level. This review will discuss the contemporary status on human microbiome immune system interactions and their potential effects on health, immune homeostasis and allograft transplantation.

Towards Optimal pH of the Skin and Topical Formulations: From the Current State of the Art to Tailored Products

Acidic pH of the skin surface has been recognized as a regulating factor for the maintenance of the stratum corneum homeostasis and barrier permeability. The most important functions of acidic pH seem to be related to the keratinocyte differentiation process, the formation and function of epidermal lipids and the corneocyte lipid envelope, the maintenance of the skin microbiome and, consequently, skin disturbances and diseases. As acknowledged extrinsic factors that affect skin pH, topically applied products could contribute to skin health maintenance via skin pH value control. The obtained knowledge on skins’ pH could be used in the formulation of more effective topical products, which would add to the development of the so-called products ‘for skin health maintenance’. There is a high level of agreement that topical products should be acidified and possess pH in the range of 4 to 6. However, formulators, dermatologists and consumers would benefit from some more precise guidance concerning favorable products pH values and the selection of cosmetic ingredients which could be responsible for acidification, together with a more extensive understanding of the mechanisms underlaying the process of skin acidification by topical products.

Dietary supplementation of Bacillus velezensis B8 enhances immune response and resistance against Aeromonas veronii in grass carp

The heavy use of prophylactic antibiotics in aquaculture leads to elevated antibiotic residues, posing a huge hidden danger in aquaculture products and other natural aquatic environments. Therefore, this study aims to isolate probiotics that can replace antibiotics from the gut of grass carp for disease control. Bacillus velezensis B8 was isolated from the gut of grass carp and showed broad-spectrum antimicrobial activity against several fish pathogenic bacteria, including Aeromonas hydrophilis, Aeromonas veronii, Vibrio parahaemolyticus, Escherichia coli, Edwardsiella tarda and Vibrio mimicus. The safety evaluation showed that the strain B8 was non-toxic to grass carp, had no hemolytic activity, and was sensitive to most antibiotics. In vitro study indicated that strain B8 was viable at pH 2-7, had weak tolerance to 0.1% (w/v) bile salt, and could grow at 10°C-40 °C. The grass carps were fed with diets containing 0 (control), 10⁷, and 10⁹ cfu/g of strain B8 for 4 weeks. Various immune parameters were measured at 1, 2, 3, and 4 weeks of post-feeding. The results of non-specific immunoassay showed that diets supplemented with B8 significantly increased alkaline phosphatase (AKP) and superoxide dismutase (SOD) activity in serum samples (p < 0.05). The expression levels of immune-related genes in the kidney and spleen of grass carp were measured. Among them, the expression levels of IgM and TNF-α both in spleen and kidney were significantly increased after 3 and 4 weeks of post-feeding (p < 0.05). The expression of IgD and MHCI in kidney was significantly upregulated in high-dose groups after 2 and 3 weeks of feeding, respectively (p < 0.05). In addition, after 7 days of challenging with A. veronii, the high-dose group and low-dose group had 48% and 53% survival compared to 25% survival for the control group. These results suggest that B. velezensis B8 has the potential to be developed into a microecological preparation for the alternatives of antibiotics in aquaculture.

Dysbiotic stress increases the sensitivity of the tumor vasculature to radiotherapy and c-Met inhibitors

Antibiotic-induced microbial imbalance, or dysbiosis, has systemic and long-lasting effects on the host and response to cancer therapies. However, the effects on tumor endothelial cells are largely unknown. Therefore, the goal of the current study was to generate matched B16-F10 melanoma associated endothelial cell lines isolated from mice with and without antibiotic-induced dysbiosis. After validating endothelial cell markers on a genomic and proteomic level, functional angiogenesis assays (i.e., migration and tube formation) also confirmed their vasculature origin. Subsequently, we found that tumor endothelial cells derived from dysbiotic mice (TEC-Dys) were more sensitive to ionizing radiotherapy in the range of clinically-relevant hypofractionated doses, as compared to tumor endothelial cells derived from orthobiotic mice (TEC-Ortho). In order to identify tumor vasculature-associated drug targets during dysbiosis, we used tandem mass tag mass spectroscopy and focused on the statistically significant cellular membrane proteins overexpressed in TEC-Dys. By these criteria c-Met was the most differentially expressed protein, which was validated histologically by comparing tumors with or without dysbiosis. Moreover, in vitro, c-Met inhibitors Foretinib, Crizotinib and Cabozantinib were significantly more effective against TEC-Dys than TEC-Ortho. In vivo, Foretinib inhibited tumor growth to a greater extent during dysbiosis as compared to orthobiotic conditions. Thus, we surmise that tumor response in dysbiotic patients may be greatly improved by targeting dysbiosis-induced pathways, such as c-Met, distinct from the many targets suppressed due to dysbiosis.

Deciphering the role of skin surface microbiome in skin health: an integrative multi-omics approach reveals three distinct metabolite-microbe clusters

The advent of 16S RNA profiling and shotgun metagenomics has enabled a holistic approach to the study of the skin microbiome composition. Despite the interesting findings in this rapidly developing scientific area, the big question remains: What role does the microbiome play in skin physiology? To begin answering this question, we employed an integrative methodology for microbiome and metabolome analysis of skin surface samples collected from the volar forearm of healthy 3 to 6-month-old infants. While the infant skin metabolome was dominated by amino acids, lipids, and xenobiotics, the primary phyla of the microbiome were Firmicutes, Actinobacteria, and Proteobacteria. Zooming in on the species level revealed a large contribution of commensals belonging to the Cutibacterium and Staphylococcus genera, including Cutibacterium acnes, Staphylococcus epidermidis, and Staphylococcus aureus. This heterogeneity was further highlighted when combining the microbiome with metabolome data. Integrative analyses delineated the co-existence of three distinct metabolite-microbe clusters: one dominated by Cutibacterium linked to hydrophobic elements of the skin barrier, one associating Staphylococcus genus with amino acids relevant to the water holding capacity and pH regulation of the skin surface and one characterized by Streptococcus and independent of any particular metabolomic profile.

The role of interleukin-1β in the immune response to contact allergens

Interleukin-1β (IL-1β) is an important pro-inflammatory cytokine that has an effect on almost every cell lineage in the body. By blocking IL-1β and investigating the IL-1β signaling pathway, several studies have demonstrated a central role of IL-1β in the response to contact allergens. This review summarizes the current literature regarding the basic immunological mechanisms mediated by IL-1β in the different phases of allergic contact dermatitis (ACD) and highlights potential IL-1β-targeted treatment options, which in the future may be relevant in the treatment of patients with ACD. This review is based primarily on studies using various mouse models and human in vitro studies, since clinical studies on the effect of IL-1β in ACD are lacking.

Increased interleukin-17A-producing γδT cells predict favorable survival in elderly patients with LUAD and LUSC

PURPOSE

Aging is closely related to the occurrence of many diseases, including cancer, and involves changes in the immune microenvironment. γδT cells are important components of resident lymphocytes in mucosal tissues. However, little is known about the effects that the aged lung has on γδT cells and their prognostic significance in non-small cell lung cancer.

METHODS

In the current study, the expression of γδTCR and IL-17A was measured by immunohistochemistry in paraffin-embedded lung tissues from 168 patients with adenocarcinoma (LUAD) and 144 patients with squamous cell carcinoma (LUSC). Furthermore, gene transcription patterns in LUAD and LUSC tumors and normal controls were extracted from TCGA and GTEx databases and were analyzed.

RESULTS

High frequency of γδT cells was observed in patients with LUAD and LUSC, whereas the levels of CD4 + T cells, CD8 + T cells and CD56 + cells were decreased. Elevated γδT cells in tumors were mainly IL-17A-releasing γδT17 cells, which were found to be enriched in aged patients. High γδT cell levels positively corelated with the overall survival (OS) of patients, especially the 5-year OS in the elderly. Further analysis of gene transcription patterns indicated that increased expression of LTBR, HES1, RORC, CCR6, IL1, and IL23A may contribute to the transformation of the tumor microenvironment in a manner conducive to γδT17 cell development and differentiation. Finally, gene analysis between different age groups revealed that the expression of CCR6 and IL7 in LUAD, as well as Hes1, IL7, and IL23A in LUSC, were remarkably higher in elderly (age ≥ 60 years) than in younger individuals (age < 60 years).

CONCLUSION

Our findings suggest that intrinsic alterations in the aging lung lead to γδT17 cell enrichment, which subsequently may exert anti-tumor effects in the elderly.

Identification of Metagenomics Structure and Function Associated With Temporal Changes in Rat (Rattus norvegicus) Skin Microbiome During Health and Cutaneous Burn

The cutaneous skin microbiome is host to a vast ensemble of resident microbes that provide essential capabilities including protection of skin barrier integrity and modulation of the host immune response. Cutaneous burn-injury promotes alteration of cutaneous and systemic immune response that can affect both commensal and pathogenic microbes. A cross-sectional study of a limited number of burn patients revealed a difference in the bacteriome of burned versus control participants. Temporal changes of the skin microbiome during health and cutaneous burn-injury remains largely unknown. Furthermore, how this microbial shift relates to community function in the collective metagenome remain elusive. Due to cost considerations and reduced healing time, rodents are frequently used in burn research, despite inherent physiological differences between rodents and human skin. Using a rat burn model, a longitudinal study was conducted to characterize the rat skin bacterial residents and associated community functions in states of health (n = 30) (sham-burned) and when compromised by burn-injury (n = 24). To address the knowledge gap, traumatic thermal injury and disruption of cutaneous surface is associated with genus-level changes in the microbiota, reduced bacterial richness, and altered representation of bacterial genes and associated predicted functions across different skin microbial communities. These findings demonstrate that, upon burn-injury, there is a shift in diversity of the skin's organismal assemblages, yielding a core microbiome that is distinct at the genome and functional level. Moreover, deviations from the core community correlate with temporal changes post-injury and community transition from the state of cutaneous health to disease (burn-injury).

Metatranscriptomics for the Human Microbiome and Microbial Community Functional Profiling

Shotgun metatranscriptomics (MTX) is an increasingly practical way to survey microbial community gene function and regulation at scale. This review begins by summarizing the motivations for community transcriptomics and the history of the field. We then explore the principles, best practices, and challenges of contemporary MTX workflows: beginning with laboratory methods for isolation and sequencing of community RNA, followed by informatics methods for quantifying RNA features, and finally statistical methods for detecting differential expression in a community context. In thesecond half of the review, we survey important biological findings from the MTX literature, drawing examples from the human microbiome, other (nonhuman) host-associated microbiomes, and the environment. Across these examples, MTX methods prove invaluable for probing microbe-microbe and host-microbe interactions, the dynamics of energy harvest and chemical cycling, and responses to environmental stresses. We conclude with a review of open challenges in the MTX field, including making assays and analyses more robust, accessible, and adaptable to new technologies; deciphering roles for millions of uncharacterized microbial transcripts; and solving applied problems such as biomarker discovery and development of microbial therapeutics.

Topical emollient therapy with sunflower seed oil alters the skin microbiota of young children with severe acute malnutrition in Bangladesh: A randomised, controlled study

Background

Topical emollient therapy with sunflower seed oil (SSO) reduces risk of sepsis and mortality in very preterm infants in low- or middle-income countries (LMICs). Proposed mechanisms include modulation of skin and possibly gut barrier function. The skin and gut microbiota play important roles in regulating barrier function, but the effects of emollient therapy on these microbiotas are poorly understood.

Methods

We characterised microbiota structure and diversity with 16S rRNA gene amplicon sequence data and ecological statistics in 20 children with severe acute malnutrition (SAM) aged 2-24 months, at four skin sites and in stool, during a randomised, controlled trial of emollient therapy with SSO in Bangladesh. Microbes associated with therapy were identified with tree-based sparse discriminant analysis.

Results

The skin microbiota of Bangladeshi children with SAM was highly diverse and displayed significant variation in structure as a function of physical distance between sites. Microbiota structure differed between the study groups (P = 0.005), was more diverse in emollient-treated subjects–including on the forehead which did not receive direct treatment–and changed with each day (P = 0.005) at all skin sites. Overall, Prevotellaceae were the most differentially affected by emollient treatment; several genera within this family became more abundant in the emollient group than in the controls across several skin sites. Gut microbiota structure was associated with sample day (P = 0.045) and subject age (P = 0.045), but was not significantly affected by emollient treatment (P = 0.060).

Conclusions

Emollient therapy altered the skin microbiota in a consistent and temporally coherent manner. We speculate that therapy with SSO enhances skin barrier function in part through alterations in the microbiota, and through systemic mechanisms. Strategies to strengthen skin and gut barrier function in populations at risk, such as children in LMICs like Bangladesh, might include deliberate manipulation of their skin microbiota.

Trial registration

ClinicalTrials.gov: NCT02616289.

SPNS2 enables T cell egress from lymph nodes during an immune response

T cell expression of sphingosine 1-phosphate (S1P) receptor 1 (S1PR1) enables T cell exit from lymph nodes (LNs) into lymph, while endothelial S1PR1 expression regulates vascular permeability. Drugs targeting S1PR1 treat autoimmune disease by trapping pathogenic T cells within LNs, but they have adverse cardiovascular side effects. In homeostasis, the transporter SPNS2 supplies lymph S1P and enables T cell exit, while the transporter MFSD2B supplies most blood S1P and supports vascular function. It is unknown whether SPNS2 remains necessary to supply lymph S1P during an immune response, or whether in inflammation other compensatory transporters are upregulated. Here, using a model of dermal inflammation, we demonstrate that SPNS2 supplies the S1P that guides T cells out of LNs with an ongoing immune response. Furthermore, deletion of Spns2 is protective in a mouse model of multiple sclerosis. These results support the therapeutic potential of SPNS2 inhibitors to achieve spatially specific modulation of S1P signaling.

Glycan-Dependent Corneocyte Adherence of Staphylococcus epidermidis Mediated by the Lectin Subdomain of Aap

Staphylococcus epidermidis and other coagulase-negative staphylococci (CoNS) that colonize skin are known to promote skin immunity and inhibit colonization of pathogens that cause skin and soft tissue infections, including Staphylococcus aureus. However, S. epidermidis adherence to corneocytes, the cells that constitute the uppermost layer of the skin epidermis, remains poorly understood. Our study documents that S. epidermidis corneocyte adherence is dependent upon the accumulation-associated protein (Aap). Aap is composed of two distinct A and B domains. The A domain is comprised of a repeat region and a conserved L-type lectin domain, whereas the fibrillar B domain, which is comprised of G5 and E repeats, is linked to the cell wall in a sortase-dependent manner. Our studies revealed that adherence to corneocytes is dependent upon the lectin subdomain within the A domain. However, significant adherence was only observed when the lectin domain was expressed with both the A repeat and the B domain, suggesting further interactions between these three domains. Our data also suggest that the A repeat domain is important for stability or expression of Aap. Deglycosylation treatment suggested that glycans expressed in the host stratum corneum serve as potential binding partners for Aap-mediated corneocyte adherence. Last, bioinformatic analyses of the predominant commensal species of CoNS identified open reading frames (ORFs) homologous to aap, thus suggesting that Aap orthologues containing lectin-like domains may provide the basis for staphylococcal colonization of skin. Corroborating these observations, adherence to corneocytes in an S. aureus mgrA mutant was dependent upon SasG, the Aap orthologue in S. aureus. IMPORTANCE Staphylococcus aureus is the most significant cause of skin and soft tissue infections yet it rarely colonizes the skin of healthy individuals. This is believed to be due, in part, to inhibition of colonization via toxic substances produced by normal skin flora, including by S. epidermidis. Furthermore, we surmise that S. aureus colonization inhibition may also be due to competition for binding sites on host corneocytes. To understand these potential interactions between S. aureus and S. epidermidis and, potentially, other coagulase-negative staphylococci, we must first understand how staphylococci adhere to corneocytes. This work documents that S. epidermidis adherence to corneocytes is dependent upon the fibrillar cell wall-associated protein Aap. Our work further documents that Aap binds to glycans exposed on the corneocyte surface, which are commonly exploited by bacteria to facilitate adherence to host cells. Furthermore, we find that Aap orthologues may be responsible for corneocyte adherence in other staphylococci, including in S. aureus.

Endogenous retroviruses promote homeostatic and inflammatory responses to the microbiota

The microbiota plays a fundamental role in regulating host immunity. However, the processes involved in the initiation and regulation of immunity to the microbiota remain largely unknown. Here, we show that the skin microbiota promotes the discrete expression of defined endogenous retroviruses (ERVs). Keratinocyte-intrinsic responses to ERVs depended on cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes protein (STING) signaling and promoted the induction of commensal-specific T cells. Inhibition of ERV reverse transcription significantly impacted these responses, resulting in impaired immunity to the microbiota and its associated tissue repair function. Conversely, a lipid-enriched diet primed the skin for heightened ERV- expression in response to commensal colonization, leading to increased immune responses and tissue inflammation. Together, our results support the idea that the host may have co-opted its endogenous virome as a means to communicate with the exogenous microbiota, resulting in a multi-kingdom dialog that controls both tissue homeostasis and inflammation.

Microbiome of Barrier Organs in Allergy: Who Runs the World? Germs!

Over the last few decades, allergic diseases have been steadily increasing worldwide, a phenomenon that is not yet completely understood. Recent evidence, however, suggests that alterations in the microbiome may be a contributing factor. The microbiome refers to all microorganisms in a habitat including bacteria, fungi, and viruses. Using modern sequencing technologies, we are now capable of detecting and analyzing the human microbiome in more detail than ever before. Epidemiological and experimental studies have indicated that a complex intestinal microbiome supports the development of the immune system during childhood, thus providing protection from allergic diseases, including food allergy. The microbiome becomes an important part of human physiology and forms dynamic relationships with our various barrier systems. For example, bacterial dysbiosis is a hallmark of atopic eczema and correlates with disease progression. Similarly, the lung and nasopharyngeal microbiome is altered in patients with asthma and allergic rhinitis. While these results are interesting, the underlying mechanisms are still unclear and need to be investigated with functional studies. This review gives a short overview of the terminology and methods used in microbiome research before highlighting results concerning the lung, skin, and intestinal microbiome in allergic diseases.

Commensal microbiota regulates skin barrier function and repair via signaling through the aryl hydrocarbon receptor

The epidermis forms a barrier that defends the body from desiccation and entry of harmful substances, while also sensing and integrating environmental signals. The tightly orchestrated cellular changes needed for the formation and maintenance of this epidermal barrier occur in the context of the skin microbiome. Using germ-free mice, we demonstrate the microbiota is necessary for proper differentiation and repair of the epidermal barrier. These effects are mediated by microbiota signaling through the aryl hydrocarbon receptor (AHR) in keratinocytes, a xenobiotic receptor also implicated in epidermal differentiation. Mice lacking keratinocyte AHR are more susceptible to barrier damage and infection, during steady-state and epicutaneous sensitization. Colonization with a defined consortium of human skin isolates restored barrier competence in an AHR-dependent manner. We reveal a fundamental mechanism whereby the microbiota regulates skin barrier formation and repair, which has far-reaching implications for the numerous skin disorders characterized by epidermal barrier dysfunction.

The Mammalian Metaorganism: A Holistic View on How Microbes of All Kingdoms and Niches Shape Local and Systemic Immunity

The field of microbiome research has developed rapidly over the past decades and has become a topic of major interest to basic, preclinical, and clinical research, the pharmaceutical industry as well as the general public. The microbiome is a complex and diverse ecosystem and defined as the collection of all host-associated microorganisms and their genes. It is acquired through vertical transmission and environmental exposure and includes microbes of all kingdoms: bacteria, archaea, prokaryotic and eukaryotic viruses, fungi, protozoa, and the meiofauna. These microorganisms co-evolved with their respective hosts over millions of years, thereby establishing a mutually beneficial, symbiotic relationship on all epithelial barriers. Thus, the microbiome plays a pivotal role in virtually every aspect of mammalian physiology, particularly in the development, homeostasis, and function of the immune system. Consequently, the combination of the host genome and the microbial genome, together referred to as the metagenome, largely drives the mammalian phenotype. So far, the majority of studies have unilaterally focused on the gastrointestinal bacterial microbiota. However, recent work illustrating the impact of viruses, fungi, and protozoa on host immunity urges us towards a holistic view of the mammalian microbiome and the appreciation for its non-bacterial kingdoms. In addition, the importance of microbiota on epithelial barriers other than the gut as well as their systemic effects via microbially-derived biologically active compounds is increasingly recognized. Here, we want to provide a brief but comprehensive overview of the most important findings and the current knowledge on how microbes of all kingdoms and microbial niches shape local and systemic immunity in health and disease.

The role of the skin microbiota in the modulation of cutaneous inflammation-Lessons from the gut

Inflammation is a vital defense mechanism used to protect the body from invading pathogens, but dysregulation can lead to chronic inflammatory disorders such as psoriasis and atopic dermatitis. Differences in microbiota composition have been observed in patients with inflammatory skin conditions compared with healthy individuals, particularly within lesions. There is also increasing evidence accumulating to support the notion that the microbiome contributes to the onset or modulates the severity of inflammatory diseases. Despite the known protective effects of orally administered lactic acid bacteria against inflammation, few studies have investigated the potential protective effects of topical application of bacteria on skin health and even fewer have looked at the potential anti-inflammatory effects of skin commensals. If lack of diversity and reduction in the abundance of specific commensal strains is observed in inflammatory skin lesions, and it is known that commensal bacteria can produce anti-inflammatory compounds, we suggest that certain members of the skin microbiota have anti-inflammatory properties that can be harnessed for use as topical therapeutics in inflammatory skin disorders.

Systemic lupus erythematosus patients have a distinct structural and functional skin microbiota compared with controls

OBJECTIVE

The skin is the second most affected organ after articular involvement in systemic lupus erythematosus (SLE) patients. Cutaneous involvement occurs in approximately 80% of patients during the course of SLE. Interaction between the host and skin microorganism is a complex process. There are few studies on the diversity of skin microbes in SLE patients. Therefore, this study aims to explore the relationship between skin microorganisms and SLE.

METHODS

A total of 20 SLE patients, 20 controls with rosacea and 20 healthy controls were selected as study subjects. Both the skin microbiota of rash region and non-rash region for each SLE patient were collected.16S rRNA gene sequencing was used to detected skin microbiota from 80 specimens. α-Diversity and β-diversity of skin microbiota were analyzed based on operational taxonomic units (OTUs) and minimal entropy decomposition (MED). Using Wilcoxon test and Linear Discriminate Analysis Effect Size (LEfSe), skin microbial diversity and composition were analyzed. Functional capabilities of microbiota were estimated through Kyoto Encyclopedia of Genes and Genomes database.

RESULTS

Compared to rash region of SLE, diversity and richness were increased in healthy controls, and decreased in non-rash region of SLE and rash region of controls with rosacea. Additionally, changes of skin microbial composition were found at different taxonomic levels between four groups. For example, genus Halomonas was increased and genera Pelagibacterium, Novosphingobium, and Curvibacter were decreased in rash region compared to non-rash region of SLE based on OTUs and MED. Based on OTUs, metabolic pathways were also found differences in SLE patients, such as Xenobiotics Biodegradation and Metabolism.

CONCLUSION

Compositions and diversity of skin microbiota in SLE patients are changed. This pilot study provides some suggestive evidence for further exploration of skin microbiota in SLE patients with cutaneous involvement.

IL-23R variant rs11805303 is associated with susceptibility to the development of cutaneous leishmaniasis in Leishmania guyanensis-infected individuals

BACKGROUND

Emerging evidence suggests that the IL-17/IL-23 axis may play a role in the pathogenesis of leishmaniasis. Our aim was to investigate whether the IL-23R variant rs11805303 is a risk factor for the development of cutaneous leishmaniasis (CL) in Leishmania guyanensis-infected individuals.

METHODS

We genotyped by polymerase chain reaction-restriction fragment length polymorphism the rs11805303 C/T in 828 patients with CL and 806 healthy individuals. Plasma TNF-α, IL-6, IFG-γ, IL-1β and IL-17 were measured with the Bioplex assay.

RESULTS

The distribution of the genotypes differed between patients with CL and HC with a common odds ratio (OR) of 1.78 (p = 2.2 x10 -11) for the disease-associated T allele. L. guyanensis-infected individuals homozygous for the T allele show a 200% increased risk of progressing to disease development, with a 95% confidence interval (CI) ranging from 81% to 400% (P = 9.9 x 10 -6) in comparison to individuals homozygous for the C allele. Males homozygous for the T allele have higher plasma levels of IL-17 compared with heterozygous or homozygous CC individuals.

CONCLUSION

The present association of the IL-23R variant rs11805303 with the development of cutaneous leishmaniasis suggests that the IL-17/IL-23 axis may play an important role in the pathogenesis of CL.

Tissue-Specific Contributions to Control of T Cell Immunity

T cells are critical for orchestrating appropriate adaptive immune responses and maintaining homeostasis in the face of persistent nonpathogenic Ags. T cell function is controlled in part by environmental signals received upon activation and derived from the tissue environment in which Ag is encountered. Indeed, tissue-specific environments play important roles in controlling the T cell response to Ag, and recent evidence suggests that tissue draining lymph nodes can mirror those local differences. Thus, tissue-specific immunity may begin at priming in secondary lymph nodes, where local signals have an important role in T cell fate. In this study, we discuss the tissue-specific signals that may impact T cell differentiation and function, including the microbiome, metabolism, and tissue-specific innate cell imprinting. We argue that these individual contributions create tissue-specific niches that likely play important roles in T cell differentiation and function controlling the outcome of the response to Ags.

The Future of Functional Clothing for an Improved Skin and Textile Microbiome Relationship

The skin microbiome has become a hot field of research in the last few years. The emergence of next-generation sequencing has given unprecedented insights into the impact and involvement of microbiota in skin conditions. More and more cosmetics contain probiotics or bacteria as an active ingredient, with or without scientific data. This research is also acknowledged by the textile industry. There has been a more holistic approach on how the skin and textile microbiome interacts and how they influence the pH, moisture content and odour generation. To date, most of the ingredients have a broad-spectrum antibacterial action. This manuscript covers the current research and industry developments in the field of skin and textiles. It explores the nature of antimicrobial finishing in textiles which can disrupt the skin microbiome, and the benefits of more natural and microbiome friendly therapies to combat skin conditions, malodour and skin infection.

Shaped by the epithelium - postnatal immune mechanisms of oral homeostasis

The first encounter of mucosal barriers with the microbiota initiates host-microbiota feedback loops instructing the tailored development of both the immune system and microbiota at each mucosal site. Once established, balanced immunological interactions enable symbiotic relationships with the microbiota in adult life. This process has been extensively investigated in the mammalian monolayer epithelium-covered intestine and lung mucosae; however, the postnatal mechanisms engaged by the oral mucosa to establish homeostasis are currently being discovered. Here, we discuss the early life dialogue between the oral mucosa and the microbiota, with particular emphasis on the central role the multilayer epithelium plays to protect the oral mucosa. These intricate and unique postnatal immunological processes shape oral homeostasis, which can potentially affect buccal and systemic health in adult life.

Visualizing the In Vivo Dynamics of Anti-Leishmania Immunity: Discoveries and Challenges

Intravital microscopy, such as 2-photon microscopy, is now a mainstay in immunological research to visually characterize immune cell dynamics during homeostasis and pathogen infections. This approach has been especially beneficial in describing the complex process of host immune responses to parasitic infections in vivo, such as Leishmania. Human-parasite co-evolution has endowed parasites with multiple strategies to subvert host immunity in order to establish chronic infections and ensure human-to-human transmission. While much focus has been placed on viral and bacterial infections, intravital microscopy studies during parasitic infections have been comparatively sparse. In this review, we will discuss how in vivo microscopy has provided important insights into the generation of innate and adaptive immunity in various organs during parasitic infections, with a primary focus on Leishmania. We highlight how microscopy-based approaches may be key to providing mechanistic insights into Leishmania persistence in vivo and to devise strategies for better parasite control.

Microbial Sharing between Pediatric Patients and Therapy Dogs during Hospital Animal-Assisted Intervention Programs

Microbial sharing between humans and animals has been demonstrated in a variety of settings. However, the extent of microbial sharing that occurs within the healthcare setting during animal-assisted intervention programs is unknown. Understanding microbial transmission between patients and therapy dogs can provide important insights into potential health benefits for patients, in addition to addressing concerns regarding potential pathogen transmission that limits program utilization. This study evaluated for potential microbial sharing between pediatric patients and therapy dogs and tested whether patient-dog contact level and a dog decolonization protocol modified this sharing. Patients, therapy dogs, and the hospital environment were sampled before and after every group therapy session and samples underwent 16S rRNA sequencing to characterize microbial communities. Both patients and dogs experienced changes in the relative abundance and overall diversity of their nasal microbiome, suggesting that the exchange of microorganisms had occurred. Increased contact was associated with greater sharing between patients and therapy dogs, as well as between patients. A topical chlorhexidine-based dog decolonization was associated with decreased microbial sharing between therapy dogs and patients but did not significantly affect sharing between patients. These data suggest that the therapy dog is both a potential source of and a vehicle for the transfer of microorganisms to patients but not necessarily the only source. The relative contribution of other potential sources (e.g., other patients, the hospital environment) should be further explored to determine their relative importance.

The Skin Microbiota: Balancing Risk and Reward

The skin microbiome is an ecosystem comprised of a multitude of microbial species interacting with their surroundings, including other microbes and host epithelial and immune cells. These interactions are the basis of important roles within the skin microbiome that provide benefit to the host, boosting multiple aspects of barrier function, a critical function of this essential organ. However, with reward always comes risk; resident skin microbes function in a context-dependent manner, set on the backdrop of a dynamic host and microbial milieu. Here, we discuss the reward of hosting a microbial ecosystem on the skin, including protection from pathogens and tuning of the skin microenvironment. We also give consideration to how these skin residents, often termed "commensals" can cause disorder, damage, and promote skin disease.

The Impact of the Microbiome on Immunity to Vaccination in Humans

Vaccines are the most effective means available for preventing infectious diseases. However, vaccine-induced immune responses are highly variable between individuals and between populations in different regions of the world. Understanding the basis of this variation is, thus, of fundamental importance to human health. Although the factors that are associated with intra- and inter-population variation in vaccine responses are manifold, emerging evidence points to a key role for the gut microbiome in controlling immune responses to vaccination. Much of this evidence comes from studies in mice, and causal evidence for the impact of the microbiome on human immunity is sparse. However, recent studies on vaccination in subjects treated with broad-spectrum antibiotics have provided causal evidence and mechanistic insights into how the microbiota controls immune responses in humans.