Regulation of Langerhans cell function by nerves containing calcitonin gene-related peptide

Langerhans cells: Central players in the pathophysiology of atopic dermatitis

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease worldwide. AD is a highly complex disease with different subtypes. Many elements of AD pathophysiology have been described, but if/how they interact with each other or which mechanisms are important in which patients is still unclear. Langerhans cells (LCs) are antigen-presenting cells (APCs) in the epidermis. Depending on the context, they can act either pro- or anti-inflammatory. Many different studies have investigated LCs in the context of AD and found them to be connected to all major mechanisms of AD pathophysiology. As APCs, LCs recruit other immune cells and shape the immune response, especially adaptive immunity via polarization of T cells. As sentinel cells, LCs are primary sensors of the skin microbiome and are important for the decision of immunity versus tolerance. LCs are also involved with the integrity of the skin barrier by influencing tight junctions. Finally, LCs are important cells in the neuro-immune crosstalk in the skin. In this review, we provide an overview about the many different roles of LCs in AD. Understanding LCs might bring us closer to a more complete understanding of this highly complex disease. Potentially, modulating LCs might offer new options for targeted therapies for AD patients.

Neural and Inflammatory Interactions in Wound Healing

ABSTRACT

The skin is an intricate network of both neurons and immunocytes, where emerging evidence has indicated that the regulation of neural-inflammatory processes may play a crucial role in mediating wound healing. Disease associated abnormal immunological dysfunction and peripheral neuropathy are implicated in the pathogenesis of wound healing impairment. However, the mechanisms through which neural-inflammatory interactions modulate wound healing remain ambiguous. Understanding the underlying mechanisms may provide novel insights to develop therapeutic devices, which could manipulate neural-inflammatory crosstalk to aid wound healing. This review aims to comprehensively illustrate the neural-inflammatory interactions during different stages of the repair process. Numerous mediators including neuropeptides secreted by the sensory and autonomic nerve fibers and cytokines produced by immunocytes play an essential part during the distinct phases of wound healing.

The neurotransmitter calcitonin gene-related peptide shapes an immunosuppressive microenvironment in medullary thyroid cancer

Neurotransmitters are key modulators in neuro-immune circuits and have been linked to tumor progression. Medullary thyroid cancer (MTC), an aggressive neuroendocrine tumor, expresses neurotransmitter calcitonin gene-related peptide (CGRP), is insensitive to chemo- and radiotherapies, and the effectiveness of immunotherapies remains unknown. Thus, a comprehensive analysis of the tumor microenvironment would facilitate effective therapies and provide evidence on CGRP's function outside the nervous system. Here, we compare the single-cell landscape of MTC and papillary thyroid cancer (PTC) and find that expression of CGRP in MTC is associated with dendritic cell (DC) abnormal development characterized by activation of cAMP related pathways and high levels of Kruppel Like Factor 2 (KLF2), correlated with an impaired activity of tumor infiltrating T cells. A CGRP receptor antagonist could offset CGRP detrimental impact on DC development in vitro. Our study provides insights of the MTC immunosuppressive microenvironment, and proposes CGRP receptor as a potential therapeutic target.

Interactions between skin-resident dendritic and Langerhans cells and pain-sensing neurons

Various immune cells in the skin contribute to its function as a first line of defense against infection and disease, and the skin's dense innervation by pain-sensing sensory neurons protects the host against injury or damage signals. Dendritic cells (DCs) are a heterogeneous population of cells that link the innate immune response to the adaptive response by capturing, processing, and presenting antigens to promote T-cell differentiation and activation. DCs are abundant across peripheral tissues, including the skin, where they are found in the dermis and epidermis. Langerhans cells (LCs) are a DC subset located only in the epidermis; both populations of cells can migrate to lymph nodes to contribute to broad immune responses. Dermal DCs and LCs are found in close apposition with sensory nerve fibers in the skin and express neurotransmitter receptors, allowing them to communicate directly with the peripheral nervous system. Thus, neuroimmune signaling between DCs and/or LCs and sensory neurons can modulate physiologic and pathophysiologic pathways, including immune cell regulation, host defense, allergic response, homeostasis, and wound repair. Here, we summarize the latest discoveries on DC- and LC-neuron interaction with neurons while providing an overview of gaps and areas not previously explored. Understanding the interactions between these 2 defence systems may provide key insight into developing therapeutic targets for treating diseases such as psoriasis, neuropathic pain, and lupus.

Altered immunity in migraine: a comprehensive scoping review

BACKGROUND

The pathogenesis of migraine remains unclear; however, a large body of evidence supports the hypothesis that immunological mechanisms play a key role. Therefore, we aimed to review current studies on altered immunity in individuals with migraine during and outside attacks.

METHODS

We searched the PubMed database to investigate immunological changes in patients with migraine. We then added other relevant articles on altered immunity in migraine to our search.

RESULTS

Database screening identified 1,102 articles, of which 41 were selected. We added another 104 relevant articles. We found studies reporting elevated interictal levels of some proinflammatory cytokines, including IL-6 and TNF-α. Anti-inflammatory cytokines showed various findings, such as increased TGF-β and decreased IL-10. Other changes in humoral immunity included increased levels of chemokines, adhesion molecules, and matrix metalloproteinases; activation of the complement system; and increased IgM and IgA. Changes in cellular immunity included an increase in T helper cells, decreased cytotoxic T cells, decreased regulatory T cells, and an increase in a subset of natural killer cells. A significant comorbidity of autoimmune and allergic diseases with migraine was observed.

CONCLUSIONS

Our review summarizes the findings regarding altered humoral and cellular immunological findings in human migraine. We highlight the possible involvement of immunological mechanisms in the pathogenesis of migraine. However, further studies are needed to expand our knowledge of the exact role of immunological mechanisms in migraine pathogenesis.

Rho-associated kinase regulates Langerhans cell morphology and responsiveness to tissue damage

Skin damage requires efficient immune cell responses to restore organ function. Epidermal-resident immune cells known as Langerhans cells use dendritic protrusions to surveil the skin microenvironment, which contains keratinocytes and peripheral axons. The mechanisms governing Langerhans cell dendrite dynamics and responses to tissue damage are poorly understood. Using skin explants from adult zebrafish, we show that Langerhans cells maintain normal surveillance following axonal degeneration and use their dendrites to engulf small axonal debris. By contrast, a ramified-to-rounded shape transition accommodates the engulfment of larger keratinocyte debris. We find that Langerhans cell dendrites are populated with actin and sensitive to a broad-spectrum actin inhibitor. We show that Rho-associated kinase (ROCK) inhibition leads to elongated dendrites, perturbed clearance of large debris, and reduced Langerhans cell migration to epidermal wounds. Our work describes the dynamics of Langerhans cells and involvement of the ROCK pathway in immune cell responses.

Role of neurogenic inflammation in the pathogenesis of alopecia areata

Alopecia areata refers to an autoimmune illness indicated by persistent inflammation. The key requirement for alopecia areata occurrence is the disruption of immune-privileged regions within the hair follicles. Recent research has indicated that neuropeptides play a role in the damage to hair follicles by triggering neurogenic inflammation, stimulating mast cells ambient the follicles, and promoting apoptotic processes in keratinocytes. However, the exact pathogenesis of alopecia areata requires further investigation. Recently, there has been an increasing focus on understanding the mechanisms of immune diseases resulting from the interplay between the nervous and the immune system. Neurogenic inflammation due to neuroimmune disorders of the skin system may disrupt the inflammatory microenvironment of the hair follicle, which plays a crucial part in the progression of alopecia areata.

Analysis of the ocular surface functional unit in episodic migraine

AIM

Migraine is a chronic neurovascular disease that affects the trigeminovascular system. The purpose of this study was to evaluate corneal subbasal nerve fibers, dendritic cells and to measure tear film parameters in migraine.

PATIENTS AND METHODS

87 eyes of 44 patients suffering from migraine with a mean age of 33.23 ± 11.41 years were included in our study. 25 age-matched controls (mean age of 30.16 ± 12.59 years; P = 0.162) were recruited. The corneal subbasal plexus and the dendritic cells (DC) were analyzed using in vivo confocal microscopy (Heidelberg Retina Tomograph II Rostock Cornea Module; Heidelberg Engineering GmbH), and the tear film was imaged using LacryDiag (Quantel Medical, France).

RESULTS

Regarding the subbasal nerve fibers of the cornea, none of the examined parameters differed significantly in migraine patients from controls. We found a significant increase in the corneal DC density (P < 0.0001) and DC area (P < 0.0001) in migraine patients compared to healthy volunteers. DC density showed a positive correlation with the monthly attack frequency (r = 0.32, P = 0.041) and the DC area a negative correlation with corneal nerve branch density (r = -0.233, P = 0.039), nerve fiber length (r = -0.232, P = 0.04) and total branch density (r = -0.233, P = 0.039). Using LacryDiag a significant loss of Meibomian gland area could be detected on the superior eyelid (P = 0.005) in migraine.

CONCLUSIONS

Our results suggest the presence of neuroinflammation in the cornea of migraine patients affecting the peripheral trigeminal system. Dendritic cells surrounding the subbasal plexus may be involved in the activation and modulation of pain in migraine.

Epithelial dendritic cells vs. Langerhans cells: Implications for mucosal vaccines

Next-generation vaccines may be delivered via the skin and mucosa. The stratified squamous epithelium (SSE) represents the outermost layer of the skin (epidermis) and type II mucosa (epithelium). Langerhans cells (LCs) have been considered the sole antigen-presenting cells (APCs) to inhabit the SSE; however, it is now clear that dendritic cells (DCs) are also present. Importantly, there are functional differences in how LCs and DCs take up and process pathogens as well as their ability to activate and polarize T cells, though whether DCs participate in neuroimmune interactions like LCs is yet to be elucidated. A correct definition and functional characterization of APCs in the skin and anogenital tissues are of utmost importance for the design of better vaccines and blocking pathogen transmission. Here, we provide a historical perspective on the evolution of our understanding of the APCs that inhabit the SSE, including a detailed review of the most recent literature.

Nerve-myeloid cell interactions in persistent human pain: a reappraisal using updated cell subset classifications

ABSTRACT

The past 20 years have seen a dramatic shift in our understanding of the role of the immune system in initiating and maintaining pain. Myeloid cells, including macrophages, dendritic cells, Langerhans cells, and mast cells, are increasingly implicated in bidirectional interactions with nerve fibres in rodent pain models. However, our understanding of the human setting is still poor. High-dimensional functional analyses have substantially changed myeloid cell classifications, with recently described subsets such as epidermal dendritic cells and DC3s unveiling new insight into how myeloid cells interact with nerve fibres. However, it is unclear whether this new understanding has informed the study of human chronic pain. In this article, we perform a scoping review investigating neuroimmune interactions between myeloid cells and peripheral nerve fibres in human chronic pain conditions. We found 37 papers from multiple pain states addressing this aim in skin, cornea, peripheral nerve, endometrium, and tumour, with macrophages, Langerhans cells, and mast cells the most investigated. The directionality of results between studies was inconsistent, although the clearest pattern was an increase in macrophage frequency across conditions, phases, and tissues. Myeloid cell definitions were often outdated and lacked correspondence with the stated cell types of interest; overreliance on morphology and traditional structural markers gave limited insight into the functional characteristics of investigated cells. We therefore critically reappraise the existing literature considering contemporary myeloid cell biology and advocate for the application of established and emerging high-dimensional proteomic and transcriptomic single-cell technologies to clarify the role of specific neuroimmune interactions in chronic pain.

Skin neuropathy and immunomodulation in diseases

Skin is a vital barrier tissue of the body. Immune responses in the skin must be precisely controlled, which would otherwise cause severe disease conditions such as psoriasis, atopic dermatitis, or pathogenic infection. Research evidence has increasingly demonstrated the essential roles of neural innervations, i.e., sensory and sympathetic signals, in modulating skin immunity. Notably, neuropathic changes of such neural structures have been observed in skin disease conditions, implicating their direct involvement in various pathological processes. An in-depth understanding of the mechanism underlying skin neuropathy and its immunomodulatory effects could help reveal novel entry points for therapeutic interventions. Here, we summarize the neuroimmune interactions between neuropathic events and skin immunity, highlighting the current knowledge and future perspectives of this emerging research frontier.

From pain to tumor immunity: influence of peripheral sensory neurons in cancer

The nervous and immune systems are the primary sensory interfaces of the body, allowing it to recognize, process, and respond to various stimuli from both the external and internal environment. These systems work in concert through various mechanisms of neuro-immune crosstalk to detect threats, provide defense against pathogens, and maintain or restore homeostasis, but can also contribute to the development of diseases. Among peripheral sensory neurons (PSNs), nociceptive PSNs are of particular interest. They possess a remarkable capability to detect noxious stimuli in the periphery and transmit this information to the brain, resulting in the perception of pain and the activation of adaptive responses. Pain is an early symptom of cancer, often leading to its diagnosis, but it is also a major source of distress for patients as the disease progresses. In this review, we aim to provide an overview of the mechanisms within tumors that are likely to induce cancer pain, exploring a range of factors from etiological elements to cellular and molecular mediators. In addition to transmitting sensory information to the central nervous system, PSNs are also capable, when activated, to produce and release neuropeptides (e.g., CGRP and SP) from their peripheral terminals. These neuropeptides have been shown to modulate immunity in cases of inflammation, infection, and cancer. PSNs, often found within solid tumors, are likely to play a significant role in the tumor microenvironment, potentially influencing both tumor growth and anti-tumor immune responses. In this review, we discuss the current state of knowledge about the degree of sensory innervation in tumors. We also seek to understand whether and how PSNs may influence the tumor growth and associated anti-tumor immunity in different mouse models of cancer. Finally, we discuss the extent to which the tumor is able to influence the development and functions of the PSNs that innervate it.

Neurotrophic keratitis: inflammatory pathogenesis and novel therapies

PURPOSE OF REVIEW

Neurotrophic keratitis is a rare degenerative disease characterized by decrease or absence of corneal sensation. Neurotrophic keratitis varies from mild forms with mild epitheliopathy to severe manifestations such as corneal ulceration, melting and perforation that can lead to irreversible visual loss. The cause of neurotrophic keratitis comprises a long list of diseases, medications, congenital or genetic conditions as well as trauma. The mechanism of neurotrophic keratitis is complex and multifactorial and its understanding is crucial to better address the treatment strategies. We aimed to review neurotrophic keratitis pathology, mechanisms and management.

RECENT FINDINGS

Corneal nerves are critical for the homeostasis of a healthy ocular surface. The lack of nerve-derived neuromediators and corneal-released neuropeptides, neuro-trophins and neurotrophic factors in neurotrophic keratitis leads to a decrease in trophic supply to corneal cells in addition to a decrease in afferent signaling to the brain. This results in pathological tear secretion, decreased blinking rate, corneal healing along with ocular surface and corneal inflammation. Lately, nerve growth factor in special gained emphasis as a treatment strategy targeting the disease mechanism rather than its manifestations. Other therapies, including surgical interventions, are in the pipeline of neurotrophic keratitis management. However, there are still no proper therapeutic guidelines and neurotrophic keratitis treatment remains challenging.

SUMMARY

Neurotrophic keratitis may have a devastating outcome and treatment is still challenging. Understanding the disease pathology may assist in the development of new treatment strategies. Prompt disease recognition and immediate intervention are key factors to promote corneal healing and avoid further deterioration.

Neural Mechanisms Underlying the Coughing Reflex

Breathing is an intrinsic natural behavior and physiological process that maintains life. The rhythmic exchange of gases regulates the delicate balance of chemical constituents within an organism throughout its lifespan. However, chronic airway diseases, including asthma and chronic obstructive pulmonary disease, affect millions of people worldwide. Pathological airway conditions can disrupt respiration, causing asphyxia, cardiac arrest, and potential death. The innervation of the respiratory tract and the action of the immune system confer robust airway surveillance and protection against environmental irritants and pathogens. However, aberrant activation of the immune system or sensitization of the nervous system can contribute to the development of autoimmune airway disorders. Transient receptor potential ion channels and voltage-gated Na+ channels play critical roles in sensing noxious stimuli within the respiratory tract and interacting with the immune system to generate neurogenic inflammation and airway hypersensitivity. Although recent studies have revealed the involvement of nociceptor neurons in airway diseases, the further neural circuitry underlying airway protection remains elusive. Unraveling the mechanism underpinning neural circuit regulation in the airway may provide precise therapeutic strategies and valuable insights into the management of airway diseases.

Rho-associated kinase regulates Langerhans cell morphology and responsiveness to tissue damage

Skin is often the first physical barrier to encounter invading pathogens and physical damage. Damage to the skin must be resolved quickly and efficiently to maintain organ homeostasis. Epidermal-resident immune cells known as Langerhans cells use dendritic protrusions to dynamically surveil the skin microenvironment, which contains epithelial keratinocytes and somatosensory peripheral axons. The mechanisms governing Langerhans cell dendrite dynamics and responses to tissue damage are not well understood. Using skin explants from adult zebrafish, we show that Langerhans cells maintain normal surveillance activity following axonal degeneration and use their dynamic dendrites to engulf small axonal debris. By contrast, a ramified-to-rounded shape transition accommodates the engulfment of larger keratinocyte debris. We find that Langerhans cell dendrites are richly populated with actin and sensitive to a broad spectrum actin inhibitor. We further show that Rho-associated kinase (ROCK) inhibition leads to elongated dendrites, perturbed clearance of large debris, and reduced Langerhans cell migration to tissue-scale wounds. Altogether, our work describes the unique dynamics of Langerhans cells and involvement of the ROCK pathway in immune cell responses to damage of varying magnitude.

Mastocytosis and Skin Cancer: The Current State of Knowledge

Mastocytosis is a heterogeneous group of diseases associated with excessive proliferation and accumulation of mast cells in different organs. Recent studies have demonstrated that patients suffering from mastocytosis face an increased risk of melanoma and non-melanoma skin cancer. The cause of this has not yet been clearly identified. In the literature, the potential influence of several factors has been suggested, including genetic background, the role of cytokines produced by mast cells, iatrogenic and hormonal factors. The article summarizes the current state of knowledge regarding the epidemiology, pathogenesis, diagnosis, and management of skin neoplasia in mastocytosis patients.

Differential regulation of cutaneous immunity by sensory neuron subsets

The nervous and immune systems have classically been studied as separate entities, but there is now mounting evidence for bidirectional communication between them in various organs, including the skin. The skin is an epithelial tissue with important sensory and immune functions. The skin is highly innervated with specialized subclasses of primary sensory neurons (PSNs) that can be in contact with skin-resident innate and adaptive immune cells. Neuroimmune crosstalk in the skin, through interactions of PSNs with the immune system, has been shown to regulate host cutaneous defense, inflammation, and tissue repair. Here, we review current knowledge about the cellular and molecular mechanisms involved in this crosstalk, as depicted via mouse model studies. We highlight the ways in which different immune challenges engage specialized subsets of PSNs to produce mediators acting on immune cell subsets and modulating their function.

Research Progress in Calcitonin Gene-Related Peptide and Bone Repair

Calcitonin gene-related peptide (CGRP) has 37 amino acids. Initially, CGRP had vasodilatory and nociceptive effects. As research progressed, evidence revealed that the peripheral nervous system is closely associated with bone metabolism, osteogenesis, and bone remodeling. Thus, CGRP is the bridge between the nervous system and the skeletal muscle system. CGRP can promote osteogenesis, inhibit bone resorption, promote vascular growth, and regulate the immune microenvironment. The G protein-coupled pathway is vital for its effects, while MAPK, Hippo, NF-κB, and other pathways have signal crosstalk, affecting cell proliferation and differentiation. The current review provides a detailed description of the bone repair effects of CGRP, subjected to several therapeutic studies, such as drug injection, gene editing, and novel bone repair materials.

Decoding nociceptor-DC dialogues

Neuro-immune interactions link physiological and immune responses in host defense. Hanč et al.¹ report that nociceptors attract dendritic cells (DCs) via the chemokine (C-C motif) ligand 2 (CCL2), initiate a "sentinel" DC program via the neuropeptide calcitonin gene-related peptide (CGRP), and enhance DC inflammatory responses through direct connections. These neuroimmune units integrate nociceptors' rapid responsiveness with DCs' immune coordination, functioning as an advanced warning system.

Control of myeloid cell functions by nociceptors

The immune system has evolved to protect the host from infectious agents, parasites, and tumor growth, and to ensure the maintenance of homeostasis. Similarly, the primary function of the somatosensory branch of the peripheral nervous system is to collect and interpret sensory information about the environment, allowing the organism to react to or avoid situations that could otherwise have deleterious effects. Consequently, a teleological argument can be made that it is of advantage for the two systems to cooperate and form an “integrated defense system” that benefits from the unique strengths of both subsystems. Indeed, nociceptors, sensory neurons that detect noxious stimuli and elicit the sensation of pain or itch, exhibit potent immunomodulatory capabilities. Depending on the context and the cellular identity of their communication partners, nociceptors can play both pro- or anti-inflammatory roles, promote tissue repair or aggravate inflammatory damage, improve resistance to pathogens or impair their clearance. In light of such variability, it is not surprising that the full extent of interactions between nociceptors and the immune system remains to be established. Nonetheless, the field of peripheral neuroimmunology is advancing at a rapid pace, and general rules that appear to govern the outcomes of such neuroimmune interactions are beginning to emerge. Thus, in this review, we summarize our current understanding of the interaction between nociceptors and, specifically, the myeloid cells of the innate immune system, while pointing out some of the outstanding questions and unresolved controversies in the field. We focus on such interactions within the densely innervated barrier tissues, which can serve as points of entry for infectious agents and, where known, highlight the molecular mechanisms underlying these interactions.

Anatomical contacts between sensory neurons and epidermal cells: an unrecognized anatomical network for neuro-immuno-cutaneous crosstalk

Sensory neurons innervating the skin are conventionally thought to be the sole transducers of touch, temperature, pain and itch. However, recent studies have shown that keratinocytes - like Merkel cells - act as sensory transducers, whether for innocuous or noxious mechanical, thermal or chemical stimuli, and communicate with intraepidermal free nerve endings via chemical synaptic contacts. This paradigm shift leads to consideration of the whole epidermis as a sensory epithelium. Sensory neurons additionally function as an efferent system. Through the release of neuropeptides in intimate neuroepidermal contact areas, they contribute to epidermal homeostasis and to the pathogenesis of inflammatory skin diseases. To counteract the dogma regarding neurocutaneous interactions, seen exclusively from the perspective of soluble and spreading mediators, this review highlights the essential contribution of the unrecognized anatomical contacts between sensory neurons and epidermal cells (keratinocytes, melanocytes, Langerhans cells and Merkel cells), which take part in the reciprocal dialogue between the skin, nervous system and immune system.

Sensory Phenotype of the Oesophageal Mucosa in Gastro-Oesophageal Reflux Disease

Gastroesophageal reflux disease (GORD) affects up to 20% of Western populations, yet sensory mechanisms underlying heartburn pathogenesis remain incompletely understood. While central mechanisms of heartburn perception have been established in earlier studies, recent studies have highlighted an important role of neurochemical, inflammatory, and cellular changes occurring in the oesophageal mucosa itself. The localization and neurochemical characterisation of sensory afferent nerve endings differ among GORD phenotypes, and could explain symptom heterogeneity among patients who are exposed to similar levels of reflux. Acid-induced stimulation of nociceptors on pain-sensing nerve endings can regulate afferent signal transmission. This review considers the role of peripheral mechanisms of sensitization in the amplification of oesophageal sensitivity in patients with GORD.

Effects of Neuropeptides on Dendritic Cells in the Pathogenesis of Psoriasis

Psoriasis is an autoimmune disease that is characterized by discolored, scaled patches of skin. Clinically, it is found that psychological factors often induce or aggravate the disease. Current research suggests that the pathogenesis of psoriasis involves the nervous and immune systems. This article reviews how neuropeptides secreted by nerve fibers affect dendritic cells in psoriasis. In this review, we describe that the neuropeptides calcitonin gene-related peptide, substance P, and vasoactive intestinal peptide can act on dendritic cells and participate in the pathogenesis of psoriasis. These neuropeptides can affect the secretion of interleukin (IL)-12 and IL-23 by dendritic cells, which stimulate T helper (Th)1, Th17, and Th22 cells to produce immune responses and cause the manifestation of psoriasis. The application of neuropeptide inhibitors can improve the skin lesions of psoriasis, which has been confirmed in clinical trials. Therefore, neuroimmune response may be a new direction to develop new drug treatments and perspectives in the development of psoriasis.

Corneal dendritic cells in diabetes mellitus: A narrative review

Diabetes mellitus is a global public health problem with both macrovascular and microvascular complications, such as diabetic corneal neuropathy (DCN). Using in-vivo confocal microscopy, corneal nerve changes in DCN patients can be examined. Additionally, changes in the morphology and quantity of corneal dendritic cells (DCs) in diabetic corneas have also been observed. DCs are bone marrow-derived antigen-presenting cells that serve both immunological and non-immunological roles in human corneas. However, the role and pathogenesis of corneal DC in diabetic corneas have not been well understood. In this article, we provide a comprehensive review of both animal and clinical studies that report changes in DCs, including the DC density, maturation stages, as well as relationships between the corneal DCs, corneal nerves, and corneal epithelium, in diabetic corneas. We have also discussed the associations between the changes in corneal DCs and various clinical or imaging parameters, including age, corneal nerve status, and blood metabolic parameters. Such information would provide valuable insight into the development of diagnostic, preventive, and therapeutic strategies for DM-associated ocular surface complications.

Lidocaine alleviates inflammation and pruritus in atopic dermatitis by blocking different population of sensory neurons

BACKGROUND AND PURPOSE

Atopic dermatitis is a common chronic pruritic inflammatory disease of the skin involving neuro-immune communication. Neuronal mechanism-based therapeutic treatments remain lacking. We investigated the efficacy of intravenous lidocaine therapy on atopic dermatitis and the underlying neuro-immune mechanism.

EXPERIMENTAL APPROACH

Pharmacological intervention, immunofluorescence, RNA-sequencing, genetic modification and immunoassay were performed to dissect the neuro-immune basis of itch and inflammation in atopic dermatitis-like mouse model and in patients.

KEY RESULTS

Lidocaine alleviated skin lesions and itch in both atopic dermatitis patients and calcipotriol (MC903)-induced atopic dermatitis model by blocking subpopulation of sensory neurons. QX-314, a charged Na_V blocker that enters through pathologically activated large-pore ion channels and selectivity inhibits a subpopulation of sensory neurons, has the same effects as lidocaine in atopic dermatitis model. Genetic silencing Na_V 1.8-expressing sensory neurons was sufficient to restrict cutaneous inflammation and itch in the atopic dermatitis model. However, pharmacological blockade of TRPV1-positive nociceptors only abolished persistent itch but did not affect skin inflammation in the atopic dermatitis model, indicating a difference between sensory neuronal modulation of skin inflammation and itch. Inhibition of activity-dependent release of calcitonin gene-related peptide (CGRP) from sensory neurons by lidocaine largely accounts for the therapeutic effect of lidocaine in the atopic dermatitis model.

CONCLUSION AND IMPLICATIONS

Na_V 1.8⁺ sensory neurons play a critical role in pathogenesis of atopic dermatitis and lidocaine is a potential anti-inflammatory and anti-pruritic agent for atopic dermatitis. A dissociable difference for sensory neuronal modulation of skin inflammation and itch contributes to further understanding of pathogenesis in atopic dermatitis.

Soluble mediators in the function of the epidermal-immune-neuro unit in the skin

Skin is the largest, environmentally exposed (barrier) organ, capable of integrating various signals into effective defensive responses. The functional significance of interactions among the epidermis and the immune and nervous systems in regulating and maintaining skin barrier function is only now becoming recognized in relation to skin pathophysiology. This review focuses on newly described pathways that involve soluble mediator-mediated crosstalk between these compartments. Dysregulation of these connections can lead to chronic inflammatory diseases and/or pathologic conditions associated with chronic pain or itch.

Aberrant Corneal Homeostasis in Neurosurgery-Induced Neurotrophic Keratopathy

The characteristic features of neurotrophic keratopathy have been well documented by in vivo and in vitro studies using animal models. However, case reports of neurotrophic keratopathy induced by neurosurgery are limited. We describe the clinical characteristics, anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscopy (IVCM) findings of neurotrophic keratopathy induced by surgery for intracranial lesions. This is a case series including 6 eyes of 3 patients (mean age, 69.67 ± 12.50 years) with unilateral neurotrophic keratopathy. The clinical findings of three patients were described and IVCM findings of three patients were analyzed. The duration of neuropathy ranged from 2 to 30 years (median, 22 years). Thickening of the epithelial layer and higher reflection density of the anterior stroma were observed during the healing process using AS-OCT. The mean nerve fiber density of the subepithelial plexus, as determined by IVCM, was 1943 ± 1000 μm/mm2 for neurotrophic eyes and 2242 ± 600.3 μm/mm2 for contralateral eyes (p = 0.0347). The mean respective dendritic cell densities were 30.8 ± 21.8 and 6.25 ± 5.59 cells/mm2 (p < 0.0001), while the mean basal cell sizes were 259 ± 86.5 and 185 ± 45.9 μm2 (p < 0.0001), respectively. These findings suggest that neurosurgery-induced neurotrophic keratopathy may be associated with alterations in the healing process and immune cell distribution in the cornea.

Calcitonin gene-related peptide upregulates IL-17A and IL-22 in γδ-T cells through the paracrine effect of langerhans cells on LC/γδ-T co-culture model

Intense mental stimulation and stress often directly induce or exacerbate psoriasis. On the contrary, patients with nerve injury and nervous system dysfunction have psoriasis remission. The nervous system plays an important role in the inflammatory process of psoriasis, and neuropeptides are considered as local mediators of disease maintenance. To examine the molecular mechanism involved in this, first we analyzed calcitonin gene-related peptide (CGRP)-treated langerhans Cells and γδ-T cells separately. CGRP induced IL-23 mRNA and protein expression via PDK1-Rsk signaling pathway. However, CGRP had no effect on secretion of IL-17A and IL-22 in γδ-T cells. Then we treated LCs/γδ-T cells Co-culture Model with CGRP. CGRP upregulated IL-17A and IL-22 expression in co-culture model through the paracrine effect of LCs. IL-17A and IL-22 are key cytokines of psoriasis. These findings provide a potential mechanism by which nerve factors affect the development of psoriasis.

Analysis of Globular Cells in Corneal Nerve Vortex

Purpose

Less was known about globular cells which were a type of dendritic cells (DCs) in cornea. We aimed to investigate the morphological and distribution characteristics of globular cells in corneal vortex and their clinical correlations with ocular surface.

Methods

Case records of patients who underwent in vivo confocal microscopy (IVCM) were evaluated retrospectively. The morphology and distribution features of globular cells in cornea nerve vortex and their co-existence status with Langerhans cells (LCs) were analyzed. Data of ocular surface symptoms and signs were collected and their correlations with globular cells distribution patterns and dendritic forms were performed. Dry eye patients without LCs were treated with preservative-free artificial tears, while patients with LCs were treated with artificial tears and fluoromethalone until the activated LCs disappeared.

Results

A total of 836 eyes from 451 individuals were included. Three distribution patterns of globular cells in vortex were investigated, type 1 scattered globular cells (57.66%), type 2 large amounts of globular cells (≥50 cells) gathering in vortex and along some fixed vortex direction horizontally (13.52%) and type 3 no globular cells (28.83%). Their location and cell count altered slightly in the follow-ups but would not disappear. LCs could co-exist with globular cells and could fade after treatment. The type 2 distribution pattern was associated with older age (p = 0.000) and higher upper eyelid Meiboscore (p = 0.006). Dendritic globular cells had higher Meiboscore than Non-dendritic forms.

Conclusions

Globular cells had characteristic distribution patterns and biological features different from LCs. They were associated with long-term irritation of the meibomian gland dysfunction.

Pruritus: A Sensory Symptom Generated in Cutaneous Immuno-Neuronal Crosstalk

Pruritus or itch generated in the skin is one of the most widespread symptoms associated with various dermatological and systemic (immunological) conditions. Although many details about the molecular mechanisms of the development of both acute and chronic itch were uncovered in the last 2 decades, our understanding is still incomplete and the clinical management of pruritic conditions is one of the biggest challenges in daily dermatological practice. Recent research revealed molecular interactions between pruriceptive sensory neurons and surrounding cutaneous cell types including keratinocytes, as well as resident and transient cells of innate and adaptive immunity. Especially in inflammatory conditions, these cutaneous cells can produce various mediators, which can contribute to the excitation of pruriceptive sensory fibers resulting in itch sensation. There also exists significant communication in the opposite direction: sensory neurons can release mediators that maintain an inflamed, pruritic tissue-environment. In this review, we summarize the current knowledge about the sensory transduction of pruritus detailing the local intercellular interactions that generate itch. We especially emphasize the role of various pruritic mediators in the bidirectional crosstalk between cutaneous non-neuronal cells and sensory fibers. We also list various dermatoses and immunological conditions associated with itch, and discuss the potential immune-neuronal interactions promoting the development of pruritus in the particular diseases. These data may unveil putative new targets for antipruritic pharmacological interventions.

The Influence of Modern Neurophysiology on the Previous Definitions of "Segment" and "Interference Field" in Neural Therapy

BACKGROUND

In neural therapy, local anesthetics are injected for diagnostic and therapeutic purposes. Up until now, a distinction has been made between "local/segmental neural therapy" and "interference field therapy". This division dating back to the middle of the last century was based on the assumption that anatomical and clinical segments were identical. However, this is only true for the projection symptoms, which are limited to metamerism. All pathophysiological processes beyond this segment were called "interference field events" ("outside of any segmental order" and "not explainable by neuroanatomical circuitry").

SUMMARY

However, modern neurophysiology no longer recognizes segmental boundaries, taking into account the occurrence of cross-segmental sensitization processes, neuroplastic changes, immune processes, and neurogenic inflammation. In addition, new insights into neuroanatomical circuitry have also contributed to segmental expansion. Thus, the former definition of the interference field effect (considered to be outside any segmental order) is considered obsolete. Nowadays, interference fields are called "neuromodulatory triggers". They can act anywhere, both locally and fairly distant, and even systemically. Key Message: Thus, it is no longer tenable to classify interference field therapy as "unscientific" and "not recognized" while local and segmental neural therapy is being scientifically recognized.

Regulation of acute reflectory hyperinflammation in viral and other diseases by means of stellate ganglion block. A conceptual view with a focus on Covid-19

Whereas the autonomic nervous system (ANS) and the immune system used to be assigned separate functions, it has now become clear that the ANS and the immune system (and thereby inflammatory cascades) work closely together. During an acute immune response (e. g., in viral infection like Covid-19) the ANS and the immune system establish a fast interaction resulting in "physiological" inflammation. Based on our knowledge of the modulation of inflammation by the ANS we propose that a reflectory malfunction of the ANS with hyperactivity of the sympathetic nervous system (SNS) may be involved in the generation of acute hyperinflammation. We believe that sympathetic hyperactivity triggers a hyperresponsiveness of the immune system ("cytokine storm") with consecutive tissue damage. These reflectory neuroimmunological and inflammatory cascades constitute a general reaction principle of the organism under the leadership of the ANS and does not only occur in viral infections, although Covid-19 is a typical current example therefore. Within the overreaction several interdependent pathological positive feedback loops can be detected in which the SNS plays an important part. Consequently, there is a chance to regulate the hyperinflammation by influencing the SNS. This can be achieved by a stellate ganglion block (SGB) with local anesthetics, temporarily disrupting the pathological positive feedback loops. Thereafter, the complex neuroimmune system has the chance to reorganize itself. Previous clinical and experimental data have confirmed a favorable outcome in hyperinflammation (including pneumonia) after SGB (measurable e. g. by a reduction in proinflammatory cytokines).

Chemogenetic modulation of sensory neurons reveals their regulating role in melanoma progression

Sensory neurons have recently emerged as components of the tumor microenvironment. Nevertheless, whether sensory neuronal activity is important for tumor progression remains unknown. Here we used Designer Receptors Exclusively Activated by a Designer Drug (DREADD) technology to inhibit or activate sensory neurons' firing within the melanoma tumor. Melanoma growth and angiogenesis were accelerated following inhibition of sensory neurons' activity and were reduced following overstimulation of these neurons. Sensory neuron-specific overactivation also induced a boost in the immune surveillance by increasing tumor-infiltrating anti-tumor lymphocytes, while reducing immune-suppressor cells. In humans, a retrospective in silico analysis of melanoma biopsies revealed that increased expression of sensory neurons-related genes within melanoma was associated with improved survival. These findings suggest that sensory innervations regulate melanoma progression, indicating that manipulation of sensory neurons' activity may provide a valuable tool to improve melanoma patients' outcomes.

Roles of calcitonin gene-related peptide in the skin, and other physiological and pathophysiological functions

Skin immunity is regulated by many mediator molecules. One is the neuropeptide calcitonin gene-related peptide (CGRP). CGRP has roles in regulating the function of components of the immune system including T cells, B cells, dendritic cells (DCs), endothelial cells (ECs), and mast cells (MCs).

Herein we discuss actions of CGRP in mediating inflammatory and vascular effects in various cutaneous models and disorders.

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CGRP can help to recruit immune cells through endothelium-dependent vasodilation.

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CGRP plays an important role in the pathogenesis of neurogenic inflammation.

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Functions of many components in the immune system are influenced by CGRP.

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CGRP regulates various inflammatory processes in human skin by affecting different cell-types.

Nerve-associated transient receptor potential ion channels can contribute to intrinsic resistance to bacterial adhesion in vivo

The cornea of the eye differs from other mucosal surfaces in that it lacks a viable bacterial microbiome and by its unusually high density of sensory nerve endings. Here, we explored the role of corneal nerves in preventing bacterial adhesion. Pharmacological and genetic methods were used to inhibit the function of corneal sensory nerves or their associated transient receptor potential cation channels TRPA1 and TRPV1. Impacts on bacterial adhesion, resident immune cells, and epithelial integrity were examined using fluorescent labeling and quantitative confocal imaging. TRPA1/TRPV1 double gene-knockout mice were more susceptible to adhesion of environmental bacteria and to that of deliberately-inoculated Pseudomonas aeruginosa. Supporting the involvement of TRPA1/TRPV1-expressing corneal nerves, P. aeruginosa adhesion was also promoted by treatment with bupivacaine, or ablation of TRPA1/TRPV1-expressing nerves using RTX. Moreover, TRPA1/TRPV1-dependent defense was abolished by enucleation which severs corneal nerves. High-resolution imaging showed normal corneal ultrastructure and surface-labeling by wheat-germ agglutinin for TRPA1/TRPV1 knockout murine corneas, and intact barrier function by absence of fluorescein staining. P. aeruginosa adhering to corneas after perturbation of nerve or TRPA1/TRPV1 function failed to penetrate the surface. Single gene-knockout mice showed roles for both TRPA1 and TRPV1, with TRPA1^-/- more susceptible to P. aeruginosa adhesion while TRPV1^-/- corneas instead accumulated environmental bacteria. Corneal CD45+/CD11c+ cell responses to P. aeruginosa challenge, previously shown to counter bacterial adhesion, also depended on TRPA1/TRPV1 and sensory nerves. Together, these results demonstrate roles for corneal nerves and TRPA1/TRPV1 in corneal resistance to bacterial adhesion in vivo and suggest that the mechanisms involve resident immune cell populations.

The Role of Neuropeptides in Pathogenesis of Dry Dye

Neuropeptides are known as important mediators between the nervous and immune systems. Recently, the role of the corneal nerve in the pathogenesis of various ocular surface diseases, including dry eye disease, has been highlighted. Neuropeptides are thought to be important factors in the pathogenesis of dry eye disease, as suggested by the well-known role between the nervous and immune systems, and several recently published studies have elucidated the previously unknown pathogenic mechanisms involved in the role of the neuropeptides secreted from the corneal nerves in dry eye disease. Here, we reviewed the emerging concept of neurogenic inflammation as one of the pathogenic mechanisms of dry eye disease, the recent results of related studies, and the direction of future research.

Investigation of the Sympathetic Regulation in Delayed Onset Muscle Soreness: Results of an RCT

Sports-related pain and injury is directly linked to tissue inflammation, thus involving the autonomic nervous system (ANS). In the present experimental study, we disable the sympathetic part of the ANS by applying a stellate ganglion block (SGB) in an experimental model of delayed onset muscle soreness (DOMS) of the biceps muscle. We included 45 healthy participants (female 11, male 34, age 24.16 ± 6.67 years [range 18-53], BMI 23.22 ± 2.09 kg/m2) who were equally randomized to receive either (i) an SGB prior to exercise-induced DOMS (preventive), (ii) sham intervention in addition to DOMS (control/sham), or (iii) SGB after the induction of DOMS (rehabilitative). The aim of the study was to determine whether and to what extent sympathetically maintained pain (SMP) is involved in DOMS processing. Focusing on the muscular area with the greatest eccentric load (biceps distal fifth), a significant time × group interaction on the pressure pain threshold was observed between preventive SGB and sham (p = 0.034). There was a significant effect on pain at motion (p = 0.048), with post hoc statistical difference at 48 h (preventive SGB Δ1.09 ± 0.82 cm VAS vs. sham Δ2.05 ± 1.51 cm VAS; p = 0.04). DOMS mediated an increase in venous cfDNA -as a potential molecular/inflammatory marker of DOMS- within the first 24 h after eccentric exercise (time effect p = 0.018), with a peak at 20 and 60 min. After 60 min, cfDNA levels were significantly decreased comparing preventive SGB to sham (unpaired t-test p = 0.008). At both times, 20 and 60 min, cfDNA significantly correlated with observed changes in PPT. The 20-min increase was more sensitive, as it tended toward significance at 48 h (r = 0.44; p = 0.1) and predicted the early decrease of PPT following preventive stellate blocks at 24 h (r = 0.53; p = 0.04). Our study reveals the broad impact of the ANS on DOMS and exercise-induced pain. For the first time, we have obtained insights into the sympathetic regulation of pain and inflammation following exercise overload. As this study is of a translational pilot character, further research is encouraged to confirm and specify our observations.

Potential of nanoparticulate based delivery systems for effective management of alopecia

In recent times, more than 50 % of the global population is facing hair-related issues (alopecia) which is seen mostly amongst the people in the age group of 30-40 years. The conventional topical dosage forms available in the market falls short in effectively managing alopecia. Despite various advancements in topical dosage forms, it is still disposed to limited clinical application and provides poor penetration of drug molecules into the skin. The exact etiology of alopecia is still unknown and various researchers link lifestyle, hereditary, and auto immune-based events with its existence. Nanoparticulate-based delivery are hence brought in use to enhance the permeability properties of the drug. In comparison to conventional methods nanotechnology-based drug delivery system tames drug molecules to a specific site with much better efficacy. This review is engrossed in the journey and role of nano technological-based drug delivery in the management of alopecia and its clinical application.

Molecular Subtypes of Oral Squamous Cell Carcinoma Based on Immunosuppression Genes Using a Deep Learning Approach

Background: The mechanisms through which immunosuppressed patients bear increased risk and worse survival in oral squamous cell carcinoma (OSCC) are unclear. Here, we used deep learning to investigate the genetic mechanisms underlying immunosuppression in the survival of OSCC patients, especially from the aspect of various survival-related subtypes. Materials and methods: OSCC samples data were obtained from The Cancer Genome Atlas (TCGA), International Cancer Genome Consortium (ICGC), and OSCC-related genetic datasets with survival data in the National Center for Biotechnology Information (NCBI). Immunosuppression genes (ISGs) were obtained from the HisgAtlas and DisGeNET databases. Survival analyses were performed to identify the ISGs with significant prognostic values in OSCC. A deep learning (DL)-based model was established for robustly differentiating the survival subpopulations of OSCC samples. In order to understand the characteristics of the different survival-risk subtypes of OSCC samples, differential expression analysis and functional enrichment analysis were performed. Results: A total of 317 OSCC samples were divided into one inferring cohort (TCGA) and four confirmation cohorts (ICGC set, GSE41613, GSE42743, and GSE75538). Eleven ISGs (i.e., BGLAP, CALCA, CTLA4, CXCL8, FGFR3, HPRT1, IL22, ORMDL3, TLR3, SPHK1, and INHBB) showed prognostic value in OSCC. The DL-based model provided two optimal subgroups of TCGA-OSCC samples with significant differences (p = 4.91E-22) and good model fitness [concordance index (C-index) = 0.77]. The DL model was validated by using four external confirmation cohorts: ICGC cohort (n = 40, C-index = 0.39), GSE41613 dataset (n = 97, C-index = 0.86), GSE42743 dataset (n = 71, C-index = 0.87), and GSE75538 dataset (n = 14, C-index = 0.48). Importantly, subtype Sub1 demonstrated a lower probability of survival and thus a more aggressive nature compared with subtype Sub2. ISGs in subtype Sub1 were enriched in the tumor-infiltrating immune cells-related pathways and cancer progression-related pathways, while those in subtype Sub2 were enriched in the metabolism-related pathways. Conclusion: The two survival subtypes of OSCC identified by deep learning can benefit clinical practitioners to divide immunocompromised patients with oral cancer into two subpopulations and give them target drugs and thus might be helpful for improving the survival of these patients and providing novel therapeutic strategies in the precision medicine area.

Activation of Conjunctiva-Associated Lymphoid Tissue in Patients With Infectious Keratitis Using In Vivo Confocal Microscopy

Purpose

We aimed to evaluate activation of conjunctiva-associated lymphoid tissue (CALT) in patients with keratitis using in vivo confocal microscopy (IVCM) and conjunctival impression cytology (CIC).

Methods

In addition to anterior segment photography and corneal fluorescein staining, IVCM revealed the palpebral conjunctiva in all subjects, and CIC and immunofluorescence staining were performed.

Results

Diffuse lymphoid tissue cell density in the eyes of patients with keratitis was significantly greater compared with healthy volunteers (P < 0.001). Similar trends were found in perifollicular lymphocyte density (P < 0.001), follicular density (P = 0.029), follicular center reflection intensity (P = 0.011), and follicular area (P < 0.001). Immunofluorescence staining showed that the proportions of CD4⁺ (61.7% ± 8.0% vs. 17.3% ± 10.2%, respectively, P < 0.001) and CD8⁺ (46.9% ± 10.0% vs. 19.6% ± 11.5%, respectively, P < 0.001) cells in patients with keratitis was greater compared with healthy volunteers. Interestingly, we also observed changes in the contralateral eye in subjects with keratitis.

Conclusions

Our research suggests that CALT, as an ocular immune structure, is activated and plays an important role in the pathogenesis of keratitis. This has been overlooked previously. CALT is also active in the contralateral eye of subjects with keratitis.

An Integrated View on Neuronal Subsets in the Peripheral Nervous System and Their Role in Immunoregulation

The peripheral nervous system consists of sensory circuits that respond to external and internal stimuli and effector circuits that adapt physiologic functions to environmental challenges. Identifying neurotransmitters and neuropeptides and the corresponding receptors on immune cells implies an essential role for the nervous system in regulating immune reactions. Vice versa, neurons express functional cytokine receptors to respond to inflammatory signals directly. Recent advances in single-cell and single-nuclei sequencing have provided an unprecedented depth in neuronal analysis and allowed to refine the classification of distinct neuronal subsets of the peripheral nervous system. Delineating the sensory and immunoregulatory capacity of different neuronal subsets could inform a better understanding of the response happening in tissues that coordinate physiologic functions, tissue homeostasis and immunity. Here, we summarize current subsets of peripheral neurons and discuss neuronal regulation of immune responses, focusing on neuro-immune interactions in the gastrointestinal tract. The nervous system as a central coordinator of immune reactions and tissue homeostasis may predispose for novel promising therapeutic approaches for a large variety of diseases including but not limited to chronic inflammation.

Distribution of Corneal TRPV1 and Its Association With Immune Cells During Homeostasis and Injury

Purpose

Given the role of corneal sensory nerves during epithelial wound repair, we sought to examine the relationship between immune cells and polymodal nociceptors following corneal injury.

Methods

Young C57BL/6J mice received a 2 mm corneal epithelial injury. One week later, corneal wholemounts were immunostained using β-tubulin-488, TRPV1 (transient receptor potential ion channel subfamily V member-1, a nonselective cation channel) and immune cell (MHC-II, CD45 and CD68) antibodies. The sum length of TRPV1⁺ and TRPV1^– nerve fibers, and their spatial association with immune cells, was quantified in intact and injured corneas.

Results

TRPV1⁺ nerves account for ∼40% of the nerve fiber length in the intact corneal epithelium and ∼80% in the stroma. In the superficial epithelial layers, TRPV1⁺ nerve terminal length was similar in injured and intact corneas. In intact corneas, the density (sum length) of basal epithelial TRPV1⁺ and TRPV1⁻ nerve fibers was similar, however, in injured corneas, TRPV1⁺ nerve density was higher compared to TRPV1⁻ nerves. The degree of physical association between TRPV1⁺ nerves and intraepithelial CD45⁺ MHC-II⁺ CD11c⁺ cells was similar in intact and injured corneas. Stromal leukocytes co-expressed TRPV1, which was partially localized to CD68⁺ lysosomes, and this expression pattern was lower in injured corneas.

Conclusions

TRPV1⁺ nerves accounted for a higher proportion of corneal nerves after injury, which may provide insights into the pathophysiology of neuropathic pain following corneal trauma. The close interactions of TRPV1⁺ nerves with intraepithelial immune cells and expression of TRPV1 by stromal macrophages provide evidence of neuroimmune interactions in the cornea.

TRPV1: Role in Skin and Skin Diseases and Potential Target for Improving Wound Healing

Skin is innervated by a multitude of sensory nerves that are important to the function of this barrier tissue in homeostasis and injury. The role of innervation and neuromediators has been previously reviewed so here we focus on the role of the transient receptor potential cation channel, subfamily V member 1 (TRPV1) in wound healing, with the intent of targeting it in treatment of non-healing wounds. TRPV1 structure and function as well as the outcomes of TRPV1-targeted therapies utilized in several diseases and tissues are summarized. In skin, keratinocytes, sebocytes, nociceptors, and several immune cells express TRPV1, making it an attractive focus area for treating wounds. Many intrinsic and extrinsic factors confound the function and targeting of TRPV1 and may lead to adverse or off-target effects. Therefore, a better understanding of what is known about the role of TRPV1 in skin and wound healing will inform future therapies to treat impaired and chronic wounds to improve healing.

Crosstalk Between Epithelial Cells, Neurons and Immune Mediators in HSV-1 Skin Infection

Herpes simplex virus type 1 (HSV-1) infection is highly prevalent in humans, with approximately two-thirds of the world population living with this virus. However, only a fraction of those carrying HSV-1, which elicits lifelong infections, are symptomatic. HSV-1 mainly causes lesions in the skin and mucosae but reaches the termini of sensory neurons innervating these tissues and travels in a retrograde manner to the neuron cell body where it establishes persistent infection and remains in a latent state until reactivated by different stimuli. When productive reactivations occur, the virus travels back along axons to the primary infection site, where new rounds of replication are initiated in the skin, in recurrent or secondary infections. During this process, new neuron infections occur. Noteworthy, the mechanisms underlying viral reactivations and the exit of latency are somewhat poorly understood and may be regulated by a crosstalk between the infected neurons and components of the immune system. Here, we review and discuss the immune responses that occur at the skin during primary and recurrent infections by HSV-1, as well as at the interphase of latently-infected neurons. Moreover, we discuss the implications of neuronal signals over the priming and migration of immune cells in the context of HSV-1 infection.

Neuropeptides and neurohormones in immune, inflammatory and cellular responses to ultraviolet radiation

Humans are exposed to varying amounts of ultraviolet radiation (UVR) through sunlight. UVR penetrates into human skin leading to release of neuropeptides, neurotransmitters and neuroendocrine hormones. These messengers released from local sensory nerves, keratinocytes, Langerhans cells (LCs), mast cells, melanocytes and endothelial cells (ECs) modulate local and systemic immune responses, mediate inflammation and promote differing cell biologic effects. In this review, we will focus on both animal and human studies that elucidate the roles of calcitonin gene-related peptide (CGRP), substance P (SP), nerve growth factor (NGF), nitric oxide and proopiomelanocortin (POMC) derivatives in mediating immune and inflammatory effects of exposure to UVR as well as other cell biologic effects of UVR exposure.

Nonpeptidergic neurons suppress mast cells via glutamate to maintain skin homeostasis

Cutaneous mast cells mediate numerous skin inflammatory processes and have anatomical and functional associations with sensory afferent neurons. We reveal that epidermal nerve endings from a subset of sensory nonpeptidergic neurons expressing MrgprD are reduced by the absence of Langerhans cells. Loss of epidermal innervation or ablation of MrgprD-expressing neurons increased expression of a mast cell gene module, including the activating receptor, Mrgprb2, resulting in increased mast cell degranulation and cutaneous inflammation in multiple disease models. Agonism of MrgprD-expressing neurons reduced expression of module genes and suppressed mast cell responses. MrgprD-expressing neurons released glutamate which was increased by MrgprD agonism. Inhibiting glutamate release or glutamate receptor binding yielded hyperresponsive mast cells with a genomic state similar to that in mice lacking MrgprD-expressing neurons. These data demonstrate that MrgprD-expressing neurons suppress mast cell hyperresponsiveness and skin inflammation via glutamate release, thereby revealing an unexpected neuroimmune mechanism maintaining cutaneous immune homeostasis.

Anti-migraine agents from an immunological point of view

The new wave of anti-migraine agents is nothing less than a milestone in our battle to manage this devastating disease. However, concerns have recently increased regarding the safety of these drugs. CGRP, while known as a potent vasodilator, is also a key neural and immune modulator. The roles of CGRP in immune determination, have been studied in depth, with particular focus on its functional significance with respect to common immune challenges i.e., bacterial, viral, fungal and parasitic infections. This review discusses many potential areas of concern in regard to blocking CGRP function and its potential influence on immune milieus during infection, and the risk of adverse effects. Finally, this review recommends specific measures to be taken into consideration when administering anti-CGRP/CGRPR agents.

Psychobiotics: The Next-Generation Probiotics for the Brain

Psychobiotics are a special class of probiotics, which deliver mental health benefits to individuals. They differ from conventional probiotics in their ability to produce or stimulate the production of neurotransmitters, short-chain fatty acids, enteroendocrine hormones and anti-inflammatory cytokines. Owing to this potential, psychobiotics have a broad spectrum of applications ranging from mood and stress alleviation to being an adjuvant in therapeutic treatment for various neurodevelopment and neurodegenerative disorders. The common psychobiotic bacteria belong to the family Lactobacilli, Streptococci, Bifidobacteria, Escherichia and Enterococci. The two-way crosstalk between the brain and the gastrointestinal system is influenced by these bacteria. The neurons present in the enteric nervous system interact directly with the neurochemicals produced by microbiota of the gut, thereby influencing the signaling to central nervous system. The present review highlights the scope and advancements made in the field, enlisting numerous commercial psychobiotic products that have flooded the market. In the latter part we discuss the potential concerns with respect to psychobiotics, such as the effects due to withdrawal, compatibility with immunocompromised patients, and the relatively unregulated probiotic market.