S. aureus drives itch and scratch-induced skin damage through a V8 protease-PAR1 axis

Microbiological insights and dermatological applications of live biotherapeutic products

As our understanding of dermatological conditions advances, it becomes increasingly evident that traditional pharmaceutical interventions are not universally effective. The intricate balance of the skin microbiota plays a pivotal role in the development of various skin conditions, prompting a growing interest in probiotics, or live biotherapeutic products (LBPs), as potential remedies. Specifically, the topical application of LBPs to modulate bacterial populations on the skin has emerged as a promising approach to alleviate symptoms associated with common skin conditions. This review considers LBPs and their application in addressing a wide spectrum of dermatological conditions with particular emphasis on three key areas: acne, atopic dermatitis, and wound healing. Within this context, the critical role of strain selection is presented as a pivotal factor in effectively managing these dermatological concerns. Additionally, the review considers formulation challenges associated with probiotic viability and proposes a personalised approach to facilitate compatibility with the skin's unique microenvironment. This analysis offers valuable insights into the potential of LBPs in dermatological applications, underlining their promise in reshaping the landscape of dermatological treatments while acknowledging the hurdles that must be overcome to unlock their full potential.

Adjunctive treatment of atopic dermatitis with novel at-home handheld narrow-band UVB phototherapy

While conventional in-office phototherapy has long been utilized as a successful treatment for atopic dermatitis (AD), it is associated with potential barriers including inconvenience, poor adherence, time and financial expense. In this retrospective study, we examine the efficacy, adherence, and patient-satisfaction of using adjunctive at-home, self-administered phototherapy utilizing a novel handheld narrow-band ultraviolet B (NB-UVB) device for the treatment of refractory mild to severe AD. Included AD patients were initially trained on proper use of the device. These patients treated involved areas three times per week for a period of 12 weeks. Phototherapy dosing protocol was based on skin type. The cohort included 52 patients, who were aged 20-69 and represented all skin types. They were initially categorized by disease involvement as mild, moderate, and severe. Patients were also queried to self-score their disease severity and level of satisfaction. Compared to baseline, at 12 weeks, 48% percent of patients indicated that at least one site was Clear/Almost Clear, 38% stated that more than 50% of body locations were Clear/Almost Clear, and 28% reported that 100% (all) treated sites were Clear/Almost Clear. After using at-home hand-held NB-UVB for the study duration, 67% (35/52) of patients experienced disease improvement. Mean overall satisfaction was extremely high at 4.43 on a 5-point scale. Skin type, age, gender, and disease severity at inception did not significantly affect patient satisfaction scores. Overall adherence rate among participants across all groups was 73%. In this small retrospective study, at-home handheld NB-UVB phototherapy was found to be an effective, well-tolerated, adjunctive treatment method for patients with refractory AD, which was associated with a high level of patient satisfaction and adherence.

Navigating the evolving landscape of atopic dermatitis: Challenges and future opportunities: The 4th Davos declaration

The 4th Davos Declaration was developed during the Global Allergy Forum in Davos which aimed to elevate the care of patients with atopic dermatitis (AD) by uniting experts and stakeholders. The forum addressed the high prevalence of AD, with a strategic focus on advancing research, treatment, and management to meet the evolving challenges in the field. This multidisciplinary forum brought together top leaders from research, clinical practice, policy, and patient advocacy to discuss the critical aspects of AD, including neuroimmunology, environmental factors, comorbidities, and breakthroughs in prevention, diagnosis, and treatment. The discussions were geared towards fostering a collaborative approach to integrate these advancements into practical, patient-centric care. The forum underlined the mounting burden of AD, attributing it to significant environmental and lifestyle changes. It acknowledged the progress in understanding AD and in developing targeted therapies but recognized a gap in translating these innovations into clinical practice. Emphasis was placed on the need for enhanced awareness, education, and stakeholder engagement to address this gap effectively and to consider environmental and lifestyle factors in a comprehensive disease management strategy. The 4th Davos Declaration marks a significant milestone in the journey to improve care for people with AD. By promoting a holistic approach that combines research, education, and clinical application, the Forum sets a roadmap for stakeholders to collaborate to improve patient outcomes in AD, reflecting a commitment to adapt and respond to the dynamic challenges of AD in a changing world.

Sensory sentinels: Neuroimmune detection and food allergy

Food allergy is classically characterized by an inappropriate type-2 immune response to allergenic food antigens. However, how allergens are detected and how that detection leads to the initiation of allergic immunity is poorly understood. In addition to the gastrointestinal tract, the barrier epithelium of the skin may also act as a site of food allergen sensitization. These barrier epithelia are densely innervated by sensory neurons, which respond to diverse physical environmental stimuli. Recent findings suggest that sensory neurons can directly detect a broad array of immunogens, including allergens, triggering sensory responses and the release of neuropeptides that influence immune cell function. Reciprocally, immune mediators modulate the activation or responsiveness of sensory neurons, forming neuroimmune feedback loops that may impact allergic immune responses. By utilizing cutaneous allergen exposure as a model, this review explores the pivotal role of sensory neurons in allergen detection and their dynamic bidirectional communication with the immune system, which ultimately orchestrates the type-2 immune response. Furthermore, it sheds light on how peripheral signals are integrated within the central nervous system to coordinate hallmark features of allergic reactions. Drawing from this emerging evidence, we propose that atopy arises from a dysregulated neuroimmune circuit.

Eosinophil extracellular vesicles and DNA traps in allergic inflammation

Eosinophil granulocytes, a specialized subset of white blood cells, have traditionally been associated with allergic responses and parasitic infections. However, recent research has unveiled their versatile roles in immune regulation beyond these classical functions. This review highlights the emerging field of eosinophil biology, with a particular focus on their release of extracellular vesicles (EVs) and extracellular DNA traps (EETs). It further explores potential implications of eosinophil-derived EVs and EETs for immune responses during inflammatory diseases. The release of EVs/EETs from eosinophils, which also affects the eosinophils themselves, may influence both local and systemic immune reactions, affecting the pathophysiology of conditions such as airway inflammation, chronic rhinosinusitis and atopic dermatitis.

Structural basis of tethered agonism and G protein coupling of protease-activated receptors

Protease-activated receptors (PARs) are a unique group within the G protein-coupled receptor superfamily, orchestrating cellular responses to extracellular proteases via enzymatic cleavage, which triggers intracellular signaling pathways. Protease-activated receptor 1 (PAR1) is a key member of this family and is recognized as a critical pharmacological target for managing thrombotic disorders. In this study, we present cryo-electron microscopy structures of PAR1 in its activated state, induced by its natural tethered agonist (TA), in complex with two distinct downstream proteins, the Gq and Gi heterotrimers, respectively. The TA peptide is positioned within a surface pocket, prompting PAR1 activation through notable conformational shifts. Contrary to the typical receptor activation that involves the outward movement of transmembrane helix 6 (TM6), PAR1 activation is characterized by the simultaneous downward shift of TM6 and TM7, coupled with the rotation of a group of aromatic residues. This results in the displacement of an intracellular anion, creating space for downstream G protein binding. Our findings delineate the TA recognition pattern and highlight a distinct role of the second extracellular loop in forming β-sheets with TA within the PAR family, a feature not observed in other TA-activated receptors. Moreover, the nuanced differences in the interactions between intracellular loops 2/3 and the Gα subunit of different G proteins are crucial for determining the specificity of G protein coupling. These insights contribute to our understanding of the ligand binding and activation mechanisms of PARs, illuminating the basis for PAR1's versatility in G protein coupling.

Staphylococcus aureus Proteases: Orchestrators of Skin Inflammation

Skin homeostasis relies on a delicate balance between host proteases and protease inhibitors along with those secreted from microbial communities, as disruption to this harmony contributes to the pathogenesis of inflammatory skin disorders, including atopic dermatitis and Netherton's syndrome. In addition to being a prominent cause of skin and soft tissue infections, the gram-positive bacterium Staphylococcus aureus is a key player in inflammatory skin conditions due to its array of 10 secreted proteases. Herein we review how S. aureus proteases augment the development of inflammation in skin disorders. These mechanisms include degradation of skin barrier integrity, immune dysregulation and pruritis, and impairment of host defenses. Delineating the diverse roles of S. aureus proteases has the potential to reveal novel therapeutic strategies, such as inhibitors of proteases or their cognate target, as well as neutralizing vaccines to alleviate the burden of inflammatory skin disorders in patients.

LPS exacerbates TRPV4-mediated itch through the intracellular TLR4-PI3K signalling

Pruritus is often accompanied with bacterial infections, but the underlying mechanism is not fully understood. Although previous studies revealed that lipopolysaccharides (LPS) could directly activate TRPV4 channel and TRPV4 is involved in the generation of both acute itch and chronic itch, whether and how LPS affects TRPV4-mediated itch sensation remains unclear. Here, we showed that LPS-mediated TRPV4 sensitization exacerbated GSK101-induced scratching behaviour in mice. Moreover, this effect was compromised in TLR4-knockout mice, suggesting LPS acted through a TLR4-dependent mechanism. Mechanistically, LPS enhanced GSK101-evoked calcium influx in mouse ear skin cells and HEK293T cells transfected with TRPV4. Further, LPS sensitized TRPV4 channel through the intracellular TLR4-PI3K-AKT signalling. In summary, our study found a modulatory role of LPS in TRPV4 function and highlighted the TLR4-TRPV4 interaction in itch signal amplification.

Atopic dermatitis and IgE-mediated food allergy: Common biologic targets for therapy and prevention

OBJECTIVE

To highlight common mechanistic targets for the treatment of atopic dermatitis (AD) and IgE-mediated food allergy (IgE-FA) with potential to be effective for both diseases and prevent atopic progression.

DATA SOURCES

Data sources were PubMed searches or National Clinical Trials (NCT)-registered clinical trials related to AD, IgE-FA, and other atopic conditions, especially focused on the pediatric population.

STUDY SELECTIONS

Human seminal studies and/or articles published in the past decade were emphasized with reference to preclinical models when relevant. NCT-registered clinical trials were filtered by inclusion of pediatric subjects younger than 18 years with special focus on children younger than 12 years as a critical period when AD and IgE-FA diseases may often be concurrent.

RESULTS

AD and IgE-FA share several pathophysiologic features, including epithelial barrier dysfunction, innate and adaptive immune abnormalities, and microbial dysbiosis, which may be critical for the clinical progression between these diseases. Revolutionary advances in targeted biologic therapies have shown the benefit of inhibiting type 2 immune responses, using dupilumab (anti-interleukin-4Rα) or omalizumab (anti-IgE), to potentially reduce symptom burden for both diseases in pediatric populations. Although the potential for biologics to promote disease remission (AD) or sustained unresponsiveness (IgE-FA) remains unclear, the refinement of biomarkers to predict infants at risk for atopic disorders provides promise for prevention through timely intervention.

CONCLUSION

AD and IgE-FA exhibit common features that may be leveraged to develop biologic therapeutic strategies to treat both conditions and even prevent atopic progression. Future studies should be designed with consistent age stratification in the pediatric population and standardized regimens of adjuvant oral immunotherapy or dose escalation (IgE-FA) to improve cross-study interpretation.

The extracellular serine protease from Staphylococcus epidermidis elicits a type 2-biased immune response in atopic dermatitis patients

Background

Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin disease with skin barrier defects and a misdirected type 2 immune response against harmless antigens. The skin microbiome in AD is characterized by a reduction in microbial diversity with a dominance of staphylococci, including Staphylococcus epidermidis (S. epidermidis).

Objective

To assess whether S. epidermidis antigens play a role in AD, we screened for candidate allergens and studied the T cell and humoral immune response against the extracellular serine protease (Esp).

Methods

To identify candidate allergens, we analyzed the binding of human serum IgG4, as a surrogate of IgE, to S. epidermidis extracellular proteins using 2-dimensional immunoblotting and mass spectrometry. We then measured serum IgE and IgG1 binding to recombinant Esp by ELISA in healthy and AD individuals. We also stimulated T cells from AD patients and control subjects with Esp and measured the secreted cytokines. Finally, we analyzed the proteolytic activity of Esp against IL-33 and determined the cleavage sites by mass spectrometry.

Results

We identified Esp as the dominant candidate allergen of S. epidermidis. Esp-specific IgE was present in human serum; AD patients had higher concentrations than controls. T cells reacting to Esp were detectable in both AD patients and healthy controls. The T cell response in healthy adults was characterized by IL-17, IL-22, IFN-γ, and IL-10, whereas the AD patients' T cells lacked IL-17 production and released only low amounts of IL-22, IFN-γ, and IL-10. In contrast, Th2 cytokine release was higher in T cells from AD patients than from healthy controls. Mature Esp cleaved and activated the alarmin IL-33.

Conclusion

The extracellular serine protease Esp of S. epidermidis can activate IL-33. As an antigen, Esp elicits a type 2-biased antibody and T cell response in AD patients. This suggests that S. epidermidis can aggravate AD through the allergenic properties of Esp.

The skin microbiome in pediatric atopic dermatitis and food allergy

The skin microbiome is an extensive community of bacteria, fungi, mites, viruses and archaea colonizing the skin. Fluctuations in the composition of the skin microbiome have been observed in atopic dermatitis (AD) and food allergy (FA), particularly in early life, established disease, and associated with therapeutics. However, AD is a multifactorial disease characterized by skin barrier aberrations modulated by genetics, immunology, and environmental influences, thus the skin microbiome is not the sole feature of this disease. Future research should focus on mechanistic understanding of how early-life skin microbial shifts may influence AD and FA onset, to guide potential early intervention strategies or as microbial biomarkers to identify high-risk infants who may benefit from possible microbiome-based biotherapeutic strategies. Harnessing skin microbes as AD biotherapeutics is an emerging field, but more work is needed to investigate whether this approach can lead to sustained clinical responses.

Staphylococcus aureus: The Bug Behind the Itch in Atopic Dermatitis

Pruritus or itch is a defining symptom of atopic dermatitis (AD). The origins of itch are complex, and it is considered both a defense mechanism and a cause of disease that leads to inflammation and psychological stress. Considerable progress has been made in understanding the processes that trigger itch, particularly the pruritoceptive origins that are generated in the skin. This perspective review discusses the implications of a recent observation that the V8 protease expressed by Staphylococcus aureus can directly trigger sensory neurons in the skin through activation of protease-activated receptor 1. This may be a key to understanding why itch is so common in AD because S. aureus commonly overgrows in this disease owing to deficient antimicrobial defense from both the epidermis and the cutaneous microbiome. Increased understanding of the role of microbes in AD provides increased opportunities for safely improving the treatment of this disorder.

Adding Fuel to the Fire? The Skin Microbiome in Atopic Dermatitis

Atopic dermatitis (AD) is a multifactorial, heterogeneous disease characterized by epidermal barrier dysfunction, immune system dysregulation, and skin microbiome alterations. Skin microbiome studies in AD have demonstrated that disease flares are associated with microbial shifts, particularly Staphylococcus aureus predominance. AD-associated S. aureus strains differ from those in healthy individuals across various genomic loci, including virulence factors, adhesion proteins, and proinflammatory molecules-which may contribute to complex microbiome barrier-immune system interactions in AD. Different microbially based treatments for AD have been explored, and their future therapeutic successes will depend on a deeper understanding of the potential microbial contributions to the disease.

Sensory neuronal control of skin barrier immunity

Peripheral sensory neurons recognize diverse noxious stimuli, including microbial products and allergens traditionally thought to be targets of the mammalian immune system. Activation of sensory neurons by these stimuli leads to pain and itch responses as well as the release of neuropeptides that interact with their cognate receptors expressed on immune cells, such as dendritic cells (DCs). Neuronal control of immune cell function through neuropeptide release not only affects local inflammatory responses but can impact adaptive immune responses through downstream effects on T cell priming. Numerous neuropeptide receptors are expressed by DCs but only a few have been characterized, presenting opportunities for further investigation of the pathways by which cutaneous neuroimmune interactions modulate host immunity.

Emerging drugs for the treatment of atopic dermatitis: a focus on phase 2 and phase 3 trials

INTRODUCTION

Atopic dermatitis (AD) is an inflammatory skin condition that affects millions of pediatric and adult patients with well-studied impact on morbidity and quality of life. Management occurs in a stepwise fashion beginning with preventative measures before immunomodulators are introduced. However, challenges remain in treatment of moderate-to-severe atopic dermatitis that is refractory to first- and second-line treatments and there are only few topical anti-inflammatory options, especially for pediatric patients.

AREAS COVERED

New medications are required to address these gaps as lesions may persist despite treatment or patients may discontinue treatment due to actual or anticipated adverse effects of mainstay medications. Emerging research into the pathophysiology of AD and the immune system at large has provided opportunities for novel interventions aimed at stopping AD mechanisms at new checkpoints. Clinical trials for 36 agents currently in phase 2 or phase 3 are evaluated with particular focus on the studies for, B244, CBP-201, tapinarof, lebrikizumab, nemolizumab, amlitelimab, and rocatinlimab as they explore novel pathways and have some of the most promising results.

EXPERT OPINION

These clinical trials contribute to the evolution of AD treatment toward greater precision based on salient pathways with a particular focus on moderate-to-severe AD to enhance efficacy and minimize adverse effects.

Sensory neurons: An integrated component of innate immunity

The sensory nervous system possesses the ability to integrate exogenous threats and endogenous signals to mediate downstream effector functions. Sensory neurons have been shown to activate or suppress host defense and immunity against pathogens, depending on the tissue and disease state. Through this lens, pro- and anti-inflammatory neuroimmune effector functions can be interpreted as evolutionary adaptations by host or pathogen. Here, we discuss recent and impactful examples of neuroimmune circuitry that regulate tissue homeostasis, autoinflammation, and host defense. Apparently paradoxical or conflicting reports in the literature also highlight the complexity of neuroimmune interactions that may depend on tissue- and microbe-specific cues. These findings expand our understanding of the nuanced mechanisms and the greater context of sensory neurons in innate immunity.

Neuroimmune recognition and regulation in the respiratory system

Neuroimmune recognition and regulation in the respiratory system is a complex and highly coordinated process involving interactions between the nervous and immune systems to detect and respond to pathogens, pollutants and other potential hazards in the respiratory tract. This interaction helps maintain the health and integrity of the respiratory system. Therefore, understanding the complex interactions between the respiratory nervous system and immune system is critical to maintaining lung health and developing treatments for respiratory diseases. In this review, we summarise the projection distribution of different types of neurons (trigeminal nerve, glossopharyngeal nerve, vagus nerve, spinal dorsal root nerve, sympathetic nerve) in the respiratory tract. We also introduce several types of cells in the respiratory epithelium that closely interact with nerves (pulmonary neuroendocrine cells, brush cells, solitary chemosensory cells and tastebuds). These cells are primarily located at key positions in the respiratory tract, where nerves project to them, forming neuroepithelial recognition units, thus enhancing the ability of neural recognition. Furthermore, we summarise the roles played by these different neurons in sensing or responding to specific pathogens (influenza, severe acute respiratory syndrome coronavirus 2, respiratory syncytial virus, human metapneumovirus, herpes viruses, Sendai parainfluenza virus, Mycobacterium tuberculosis, Pseudomonas aeruginosa, Staphylococcus aureus, amoebae), allergens, atmospheric pollutants (smoking, exhaust pollution), and their potential roles in regulating interactions among different pathogens. We also summarise the prospects of bioelectronic medicine as a third therapeutic approach following drugs and surgery, as well as the potential mechanisms of meditation breathing as an adjunct therapy.

Skin Deep: The Potential of Microbiome Cosmetics

The interplay between the skin microbiome and its host is a complex facet of dermatological health and has become a critical focus in the development of microbiome cosmetics. The skin microbiome, comprising various microorganisms, is essential from birth, develops over the lifespan, and performs vital roles in protecting our body against pathogens, training the immune system, and facilitating the breakdown of organic matter. Dysbiosis, an imbalance of these microorganisms, has been implicated in a number of skin conditions such as acne, atopic dermatitis, and skin cancer. Recent scientific findings have spurred cosmetic companies to develop products that preserve and enhance the skin's microbial diversity balance. These products may incorporate elements like prebiotics, probiotics, and postbiotics, which are beneficial for the skin microbiome. Beyond topical products, there's increasing interest in ingestible beauty supplements (i.e. oral probiotics), highlighting the connection between the gut and skin. This review examines the influence of the microbiome on skin health and the emerging trends of microbiome skincare products.

Neutrophils are itching to specialize

Neutrophils are heterogeneous, but the mechanisms underlying their ability to polarize remain unclear. In this issue of Immunity, Gour et al. demonstrate that the GPCR Mrgpra1 and the neuropeptide NPFF, molecules involved in pain and itch, direct neutrophil polarization that impacts host defense and pneumonia susceptibility.

Better than being aPARt: S. aureus itches to get close to sensory neurons

In a recent issue of Cell, Deng et al. show that S. aureus serine protease V8 triggers itch, independent of inflammation, by activating sensory neurons through PAR1. This study presents mechanistic insights into pruritogenic bacteria and their interactions with sensory neurons while providing a possible approach for treating itch-related diseases.

Staphylococcus scratches its itch

Itch exacerbates infection and inflammation-associated skin pathology. In this issue of Cell, Deng et al. identify a V8 protease released by Staphylococcus aureus triggering itch via neuronal protease-activated receptor 1. In so doing, they uncover profound consequences of microbial neurosensory modulation and the ensuing scratch-induced tissue damage that potentiates infection.