Nerve fibres are required to evoke a contact sensitivity response in mice

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.

Skin Inflammation with a Focus on Wound Healing

Significance: The skin is the crucial first-line barrier against foreign pathogens. Compromise of this barrier presents in the context of inflammatory skin conditions and in chronic wounds. Skin conditions arising from dysfunctional inflammatory pathways severely compromise the quality of life of patients and have a high economic impact on the U.S. health care system. The development of a thorough understanding of the mechanisms that can disrupt skin inflammation is imperative to successfully modulate this inflammation with therapies. Recent Advances: Many advances in the understanding of skin inflammation have occurred during the past decade, including the development of multiple new pharmaceuticals. Mechanical force application has been greatly advanced clinically. Bioscaffolds also promote healing, while reducing scarring. Critical Issues: Various skin inflammatory conditions provide a framework for analysis of our understanding of the phases of successful wound healing. The large burden of chronic wounds on our society continues to focus attention on the chronic inflammatory state induced in many of these skin conditions. Future Directions: Better preclinical models of disease states such as chronic wounds, coupled with enhanced diagnostic abilities of human skin, will allow a better understanding of the mechanism of action. This will lead to improved treatments with biologics and other modalities such as the strategic application of mechanical forces and scaffolds, which ultimately results in better outcomes for our patients.

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.

Capsaicin attenuates imiquimod-induced epidermal hyperplasia and cutaneous inflammation in a murine model of psoriasis

Psoriasis is one of the most common chronic inflammatory diseases that is characterized by well-defined erythematous plaques, with typical histopathological findings of lymphocytic infiltration and epidermal hyperplasia. Topical treatments of psoriasis are either associated with limited response or with side effects. Up to date, topicals targeting neuroimmune axis in psoriasis or psoriasiform dermatitis have not been explored. Here, we investigated whether percutaneous delivery of capsaicin could attenuate the pathological change of psoriasiform inflammation. Imiquimod-induced psoriasis-like murine model was used to evaluate therapeutic effects from topical application of capsaicin. An additional model of psoriasiform dermatitis induced by direct IL-23 injection was used to identify the level of action from capsaicin in this neuroimmune axis. Cutaneous inflammation was assessed by erythema level and ear thickness change. Key cytokines, infiltrating cells in the skin, and draining lymph node cells were investigated. The results showed that capsaicin administration obstructed the activation of IL-23/IL-17 pathway induced by imiquimod, presenting with significantly reduced psoriasiform dermatitis both in gross appearance and microscopic features. Tissue gene expression of psoriatic core cytokines induced by imiquimod (including IL-23, IL-17A, IL-22, TNF-α, and IL-6) were greatly decreased by capsaicin application. This protective effect from capsaicin could be hampered by direct intradermal injection of IL-23. CONCLUSION: Epicutaneous delivery of capsaicin on imiquimod-treated murine skin could significantly decrease expression of multiple inflammatory cytokines and the severity of prototypic change of psoriasiform inflammation. The beneficial effect imposed by capsaicin reinforces the neuroimmune contribution towards psoriasiform inflammation and provides a potential non-steroidal therapeutic alternative for topical treatment of psoriasiform dermatitis.

Regional differences in cell-mediated immunity in people with diabetic peripheral neuropathy

AIM

To study cell-mediated immunity in the feet of people with type 2 diabetes with polyneuropathy.

METHODS

In a cohort comprising people with type 2 diabetes with polyneuropathy (n = 17) and without polyneuropathy (n = 12) and a healthy control group (n = 12) indurations due to delayed-type hypersensitivity responses to intracutaneous Candida albicans antigen were determined in the foot and compared with those in the arm (an area relatively spared in diabetic polyneuropathy). The sizes of indurations on the foot were correlated with electromyographic measurements in the participants with diabetes.

RESULTS

No differences were observed in the median size of indurations between the foot and arm in healthy controls and participants without polyneuropathy; in participants with polyneuropathy, induration sizes on the foot were smaller than on the arm: 0 (95% CI 0 to 1) vs 5 (95% CI 2 to 6) mm (P < 0.01). In participants with diabetes, larger indurations correlated with better nerve function (Spearman's rho 0.35 to 0.39).

CONCLUSION

Our findings suggest that diabetic peripheral polyneuropathy negatively affects cell-mediated immunity in the foot. (Clinical Trials registry no.: NCT01370837).

Toward the Existence of a Sympathetic Neuroplasticity Adaptive Mechanism Influencing the Immune Response. A Hypothetical View-Part II

In the preceding work, a hypothesis on the existence of a specific neural plasticity program from sympathetic fibers innervating secondary lymphoid organs was introduced. This proposed adaptive mechanism would involve segmental retraction and degeneration of noradrenergic terminals during the immune system (IS) activation followed by regeneration once the IS returns to the steady-state. Starting from such view, this second part presents clinical and experimental evidence allowing to envision that this sympathetic neural plasticity mechanism is also operative on inflamed non-lymphoid peripheral tissues. Importantly, the sympathetic nervous system regulates most of the physiological bodily functions, ranging from cardiovascular, respiratory and gastro-intestinal functions to endocrine and metabolic ones, among others. Thus, it seems sensible to think that compensatory programs should be put into place during inflammation in non-lymphoid tissues as well, to avoid the possible detrimental consequences of a sympathetic blockade. Nevertheless, in many pathological scenarios like severe sepsis, chronic inflammatory diseases, or maladaptive immune responses, such compensatory programs against noradrenergic transmission impairment would fail to develop. This would lead to a manifest sympathetic dysfunction in the above-mentioned settings, partly accounting for their underlying pathophysiological basis; which is also discussed. The physiological/teleological significance for the whole neural plasticity process is postulated, as well.

Disruption of the Sensory System Affects Sterile Cutaneous Inflammation In Vivo

Increasing evidence suggests that nerve fibers responding to noxious stimuli (nociceptors) modulate immunity in a variety of tissues, including the skin. Yet, the role of nociceptors in regulating sterile cutaneous inflammation remains unexplored. To address this question, we have developed a detailed description of the sterile inflammation caused by overexposure to UVB irradiation (i.e., sunburn) in the mouse plantar skin. Using this model, we observed that chemical depletion of nociceptor terminals did not alter the early phase of the inflammatory response to UVB, but it caused a significant increase in the number of dendritic cells and αβ⁺ T cells as well as enhanced extravasation during the later stages of inflammation. Finally, we showed that such regulation was driven by the nociceptive neuropeptide calcitonin gene-related peptide. In conclusion, we propose that nociceptors not only play a crucial role in inflammation through avoidance reflexes and behaviors, but can also regulate sterile cutaneous immunity in vivo.

Skin neurogenic inflammation

The epidermis closely interacts with nerve endings, and both epidermis and nerves produce substances for mutual sustenance. Neuropeptides, like substance P (SP) and calcitonin gene-related protein (CGRP), are produced by sensory nerves in the dermis; they induce mast cells to release vasoactive amines that facilitate infiltration of neutrophils and T cells. Some receptors are more important than others in the generation of itch. The Mas-related G protein-coupled receptors (Mrgpr) family as well as transient receptor potential ankyrin 1 (TRPA1) and protease activated receptor 2(Par2) have important roles in itch and inflammation. The activation of MrgprX1 degranulates mast cells to communicate with sensory nerve and cutaneous cells for developing neurogenic inflammation. Mrgprs and transient receptor potential vanilloid 4 (TRPV4) are crucial for the generation of skin diseases like rosacea, while SP, CGRP, somatostatin, β-endorphin, vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase-activating polypeptide (PACAP) can modulate the immune system during psoriasis development. The increased level of SP, in atopic dermatitis, induces the release of interferon (IFN)-γ, interleukin (IL)-4, tumor necrosis factor (TNF)-α, and IL-10 from the peripheral blood mononuclear leukocytes. We are finally starting to understand the intricate connections between the skin neurons and resident skin cells and how their interaction can be key to controlling inflammation and from there the pathogenesis of diseases like atopic dermatitis, psoriasis, and rosacea.

Sense and Immunity: Context-Dependent Neuro-Immune Interplay

The sensory nervous and immune systems, historically considered autonomous, actually work in concert to promote host defense and tissue homeostasis. These systems interact with each other through a common language of cell surface G protein-coupled receptors and receptor tyrosine kinases as well as cytokines, growth factors, and neuropeptides. While this bidirectional communication is adaptive in many settings, helping protect from danger, it can also become maladaptive and contribute to disease pathophysiology. The fundamental logic of how, where, and when sensory neurons and immune cells contribute to either health or disease remains, however, unclear. Our lab and others’ have begun to explore how this neuro-immune reciprocal dialog contributes to physiological and pathological immune responses and sensory disorders. The cumulative results collected so far indicate that there is an important role for nociceptors (noxious stimulus detecting sensory neurons) in driving immune responses, but that this is highly context dependent. To illustrate this concept, we present our findings in a model of airway inflammation, in which nociceptors seem to have major involvement in type 2 but not type 1 adaptive immunity.

Sensory TRP channels contribute differentially to skin inflammation and persistent itch

Although both persistent itch and inflammation are commonly associated with allergic contact dermatitis (ACD), it is not known if they are mediated by shared or distinct signaling pathways. Here we show that both TRPA1 and TRPV1 channels are required for generating spontaneous scratching in a mouse model of ACD induced by squaric acid dibutylester (SADBE), a small molecule hapten, through directly promoting the excitability of pruriceptors. TRPV1 but not TRPA1 channels protect the skin inflammation, as genetic ablation of TRPV1 function or pharmacological ablation of TRPV1-positive sensory nerves promotes cutaneous inflammation in the SADBE-induced ACD. Our results demonstrate that persistent itch and inflammation are mediated by distinct cellular and molecular mechanisms in a mouse model of ACD. Identification of distinct roles of TRPA1 and TRPV1 in regulating itch and inflammation may provide new insights into the pathophysiology and treatment of chronic itch and inflammation in ACD patients.

Allergic contact dermatitis is associated both with persistent itch and inflammation, but it is not known if these are mediated by shared signaling pathways. The authors show that persistent itch requires both TRPA1 and TRPV1, while TRPV1 has a protective role against skin inflammation in mice.

TRPA1 mediated aggravation of allergic contact dermatitis induced by DINP and regulated by NF-κB activation

The possible pathogenic role and mechanism of Di-iso-nonyl phthalate (DINP) in allergic dermatitis is still controversial. This work has shown that oral exposure to DINP exacerbated allergic dermatitis tissue lesions in FITC-sensitized mice. The lesions was accompanied by an enhancement of TRPA1 expression and an increase in IgG1, IL-6 and IL-13 levels. This work also found that blocking TRPA1 by HC030031 effectively prevented the development of allergic dermatitis resulting from oral exposure to DINP and/or FITC-sensitized mice. This result is marked by the down regulation of IgG1 levels, a reduction in mast cell degranulation and a decrease in IL-6 and IL-13 levels. We also showed that blocking NF-κB inhibited TRPA1 expression, and that blocking TRPA1 had no significant effect on the activation of NF-κB or TSLP expression. This study helps in understanding the role DINP exposure plays in the development of allergic dermatitis and provides new insight into the mechanisms behind the DINP-induced adjuvant effect.

High-concentration topical capsaicin may abolish the clinical manifestations of allergic contact dermatitis by effects on induction and elicitation

Allergic contact dermatitis (ACD) is a common skin condition caused by a type-IV hypersensitivity reaction. Even though ACD is considered as a T-cell mediated disease, indications exists that peptidergic nerve fibers at the site of allergen exposure and associated with the draining lymph node play a prominent role in both induction and elicitation of ACD. This neuro-immune cross talk seems rely on neuropeptides such as Substance P secreted by nerve fiber terminals. It is hypothesized that local complete or partial cutaneous denervation/defunctionalization of peptidergic fibers in humans could be a feasible approach towards treating allergic contact dermatitis. Recently, human experimental protocols for prominent, temporary defunctionalization of peptidergic fibers have been published relying on prolonged application of 8% topical capsaicin patches. Combined with human experimental ACD models the importance of peptidergic nerve fibers in the induction and elicitation phases of ACD could be accurately established. Understanding the role of cutaneous peptidergic fibers in the pathogenesis and potentially of ACD and how contact sensitization can be modulated by topical defunctionalization of these fibers could lead to new approaches to treatment for ACD. In patients with localized ACD occurring to an allergen that is difficult or unfeasible to evade this would have particular relevance.

The Regulation of Immunological Processes by Peripheral Neurons in Homeostasis and Disease

The nervous system and the immune system are the principal sensory interfaces between the internal and external environment. They are responsible for recognizing, integrating, and responding to varied stimuli, and have the capacity to form memories of these encounters leading to learned or 'adaptive' future responses. We review current understanding of the cross-regulation between these systems. The autonomic and somatosensory nervous systems regulate both the development and deployment of immune cells, with broad functions that impact on hematopoiesis as well as on priming, migration, and cytokine production. In turn, specific immune cell subsets contribute to homeostatic neural circuits such as those controlling metabolism, hypertension, and the inflammatory reflex. We examine the contribution of the somatosensory system to autoimmune, autoinflammatory, allergic, and infectious processes in barrier tissues and, in this context, discuss opportunities for therapeutic manipulation of neuro-immune interactions.

Neuroimmunity: Physiology and Pathology

Evolution has yielded multiple complex and complementary mechanisms to detect environmental danger and protect tissues from damage. The nervous system rapidly processes information and coordinates complex defense behaviors, and the immune system eliminates diverse threats by virtue of mobile, specialized cell populations. The two systems are tightly integrated, cooperating in local and systemic reflexes that restore homeostasis in response to tissue injury and infection. They further share a broad common language of cytokines, growth factors, and neuropeptides that enables bidirectional communication. However, this reciprocal cross talk permits amplification of maladaptive feedforward inflammatory loops that contribute to the development of allergy, autoimmunity, itch, and pain. Appreciating the immune and nervous systems as a holistic, coordinated defense system provides both new insights into inflammation and exciting opportunities for managing acute and chronic inflammatory diseases.

Central neural activation following contact sensitivity peripheral immune challenge: evidence of brain-immune regulation through C fibres

This study tested the hypothesis that peripheral immune challenges will produce predictable activation patterns in the rat brain consistent with sympathetic excitation. As part of examining this hypothesis, this study asked whether central activation is dependent on capsaicin-sensitive C-fibres. We induced skin contact sensitivity immune responses with 2,4-dinitrochlorobenzene (DNCB), in the presence or absence of the acute C-fibre toxin capsaicin (8-methyl-N-vanillyl-6-nonenamide) to trigger immune responses with and without diminished activity of C-fibres. Innovative blood-oxygen-level-dependent functional magnetic resonance imaging data revealed that the skin contact sensitivity immune responses induced with DNCB were associated with localized increases in brain neuronal activity in treated rats. This response was diminished by pre-treatment with capsaicin 1 week before scans. In the same animals, we found expression of the immediate early gene c-Fos in sub-regions of the amygdala and hypothalamic sympathetic brain nuclei. Significant increases in c-Fos expression were found in the supraoptic nucleus, central amygdala and medial habenula following immune challenges. Our results support the idea that selective brain regions, some of which are associated with sympathetic function, process or modulate immune function through pathways that are partially dependent on C-fibres. Together with previous studies demonstrating the motor control pathways from brain to immune targets, these findings indicate a central neuroimmune system to monitor host status and coordinate appropriate host responses.

Contact sensitizer 2,4-dinitrochlorobenzene is a highly potent human TRPA1 agonist

2,4-Dinitrochlorobenzene (DNCB) is widely used in human clinical studies and in experimental animal studies to evoke allergic contact dermatitis. 2,4-Dinitrochlorobenzene is a potent immunogen capable of inducing contact sensitization in all humans exposed. However, the mechanism by which DNCB evokes such symptoms is presently unknown. TRPA1 is a nonselective cation channel that is expressed in peptidergic sensory neurons and fibroblasts. TRPA1 activation was recently implicated in the pathophysiology of atopic dermatitis especially in transducing cutaneous itch signals. Here, we test the hypothesis that DNCB acts as a TRPA1 agonist and thereby evokes allergic symptoms. We found that DNCB activates human TRPA1 dose dependently in FLIPR experiments with an EC50 of 167 nM, an effect that was fully blocked by selective TRPA1 antagonists Chembridge-5861528 and A-967079. Similarly, DNCB activated nonselective TRPA1 current in patch clamp studies. Neutralization of 3 critical cysteines in TRPA1 resulted in a loss of DNCB agonism.

Calcitonin gene-related peptide is a key neurotransmitter in the neuro-immune axis

The question of how the neural and immune systems interact in host defense is important, integrating a system that senses the whole body with one that protects. Understanding the mechanisms and routes of control could produce novel and powerful ways of promoting and enhancing normal functions as well as preventing or treating abnormal functions. Fragmentation of biological research into specialities has resulted in some failures in recognizing and understanding interactions across different systems and this is most striking across immunology, hematology, and neuroscience. This reductionist approach does not allow understanding of the in vivo orchestrated response generated through integration of all systems. However, many factors make the understanding of multisystem cross-talk in response to a threat difficult, for instance the nervous and immune systems share communication molecules and receptors for a wide range of physiological signals. But, it is clear that physical, hard-wired connections exist between the two systems, with the key link involving sensory, unmyelinated nerve fibers (c fibers) containing the neuropeptide calcitonin gene-related peptide (CGRP), and modified macrophages, mast cells and other immune and host defense cells in various locations throughout the body. In this review we will therefore focus on the induction of CGRP and its key role in the neuroimmune axis.

TRPA1 controls inflammation and pruritogen responses in allergic contact dermatitis

Allergic contact dermatitis is a common skin disease associated with inflammation and persistent pruritus. Transient receptor potential (TRP) ion channels in skin-innervating sensory neurons mediate acute inflammatory and pruritic responses following exogenous stimulation and may contribute to allergic responses. Genetic ablation or pharmacological inhibition of TRPA1, but not TRPV1, inhibited skin edema, keratinocyte hyperplasia, nerve growth, leukocyte infiltration, and antihistamine-resistant scratching behavior in mice exposed to the haptens, oxazolone and urushiol, the contact allergen of poison ivy. Hapten-challenged skin of TRPA1-deficient mice contained diminished levels of inflammatory cytokines, nerve growth factor, and endogenous pruritogens, such as substance P (SP) and serotonin. TRPA1-deficient sensory neurons were defective in SP signaling, and SP-induced scratching behavior was abolished in Trpa1(-/-) mice. SP receptor antagonists, such as aprepitant inhibited both hapten-induced cutaneous inflammation and scratching behavior. These findings support a central role for TRPA1 and SP in the integration of immune and neuronal mechanisms leading to chronic inflammatory responses and pruritus associated with contact dermatitis.

High dose dietary pyridoxine induces T-helper type 1 polarization and decreases contact hypersensitivity response to fluorescein isothiocyanate in mice

Pyridoxine (vitamin B(6)) is commonly used as a dietary supplement and beneficial effects of it are expected. However, excess ingestion of pyridoxine has been shown to cause a severe sensory neuropathy in humans and experimental animals. We have been studying the linkage between the nervous and immune systems using a fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS) mouse model. We have found that activation of transient receptor potential ankyrin 1 (TRPA1), which is expressed on sensory neurons, enhances skin sensitization to FITC. Another feature of FITC-induced CHS is its dependence on T helper 2 (Th2) type responses. We hypothesized that the excess intake of pyridoxine may affect sensitization to FITC and influence helper T-cell polarization. We examined FITC-induced CHS in BALB/c mice fed a diet containing excess pyridoxine (120 mg/kg diet) for 3 weeks. We found that mice fed on the excess-pyridoxine diet exhibited a lower response as to FITC-induced CHS compared with ones fed on a diet with a standard pyridoxine content (6.0 mg/kg diet). Moreover, the interferon (IFN)-γ/interleukin (IL)-4 ratio produced by draining lymph node cells was significantly higher with the excess-pyridoxine diet. This suggested that the cytokine balance was shifted toward Th1 with the excess-pyridoxine diet. Consistently, Th1-dependent oxazolone-induced CHS was enhanced with the excess-pyridoxine diet. These results suggested that an excess pyridoxine intake actively influences the immune system by altering helper T cell polarization.

Antimicrobial anxiety: the impact of stress on antimicrobial immunity

Leukocytes and epithelial cells are fundamental to antimicrobial immunity. Their antimicrobial responses are an evolutionarily conserved component of the innate immune system and are influenced by the host's response to external stimuli. The efficacy of host defense via antimicrobial responses derives from the ability of AMPs to rapidly identify and eradicate foreign microbes and activate proinflammatory pathways, and from the capacity of later innate and adaptive immune responses to amplify protection through distinct biochemical mechanisms. Recent advances in neuroimmunology have identified a direct link between the neuroendocrine and immune systems, where environmental stimuli are generally believed to promote a transient effect on the immune system in response to environmental challenges and are presumably brought back to baseline levels via neuroendocrine pathways. Stress is an environmental stimulus that flares from a variety of circumstances and has become engrained in human society. Small bouts of stress are believed to enhance the host's immune response; however, prolonged periods of stress can be detrimental through excess production of neuroendocrine-derived mediators that dampen immune responses to invasive pathogens. Elucidation of the mechanisms behind stress-induced immune modulation of antimicrobial responses will ultimately lead to the development of more effective therapeutic interventions for pathologic conditions. It is the intent of this review to broaden the existing paradigm of how stress-related molecules dampen immune responses through suppression of antimicrobial mechanisms, and to emphasize that bacteria can use these factors to enhance microbial pathogenesis during stress.

The neurology of the immune system: neural reflexes regulate immunity

Parallel advances in neuroscience and immunology established the anatomical and cellular basis for bidirectional interactions between the nervous and immune systems. Like other physiological systems, the immune system--and the development of immunity--is modulated by neural reflexes. A prototypical example is the inflammatory reflex, comprised of an afferent arm that senses inflammation and an efferent arm, the cholinergic anti-inflammatory pathway, that inhibits innate immune responses. This mechanism is dependent on the alpha7 subunit of the nicotinic acetylcholine receptor, which inhibits NF-kappaB nuclear translocation and suppresses cytokine release by monocytes and macrophages. Here we summarize evidence showing that innate immunity is reflexive. Future advances will come from applying an integrative physiology approach that utilizes methods adapted from neuroscience and immunology.

TRPA1 and TRPV1 activation is a novel adjuvant effect mechanism in contact hypersensitivity

We have revealed that local stimulation of sensory neurons is involved in the adjuvant effect of dibutyl phthalate (DBP) in a fluorescein isothiocyanate-induced mouse contact hypersensitivity model. Transient receptor potential (TRP) A1 and TRPV1 seemed to be candidate DBP targets. Here we directly demonstrated that DBP activates a subset of neurons in mouse dorsal root ganglia responsive to TRPA1 and TRPV1 agonists. TRPA1 and TRPV1 activation was further demonstrated using cultured cells expressing TRP channels. Among structurally different phthalate esters, there is a positive relationship between the activation of TRPA1- or TRPV1-expressing cells and the adjuvant effect.

Upregulation of the Axonal Growth and the Expression of Substance P and its NK1 Receptor in Human Allergic Contact Dermatitis

Nerve fibers and sensory neuropeptides substance P and calcitonin gene-related peptide (CGRP) have been reported to be involved in allergic contact dermatitis (ACD). In the present study, we investigated the general innervation (using antibody against protein gene product 9.5, PGP 9.5), axonal growth (using antibody against growth associated protein, GAP-43), CGRP, and substance P with its receptor neurokinin 1 (NK1), in positive epicutaneous reactions to nickel sulphate from nickel-allergic patients, at the peak of inflammation, 72 hr after challenge with the antigen. There was an increased (p < 0.01) number of GAP-43 positive fibers in the eczematous compared with control skin, indicating an increased axonal growth already at 72 hr postchallenge. Double staining revealed a coexpression of CGRP and GAP-43 on dermal nerve fibers. There was no difference in the number of substance P and CGRP positive nerve fibers between eczematous and control skin. However, semiquantification analyses showed an increased expression of substance P positive inflammatory cells, being CD3, CD4, or CD8 positive, and NK1R positive inflammatory cells, being tryptase or CD3 positive. These results indicate a contribution of regenerating nerve fibers and substance P to the contact allergic reaction.

Neurovascular control and neurogenic inflammation in diabetes

Loss of pain perception is currently seen as a key factor in the development of diabetic foot ulcers. However, recent studies suggest that nerves play a central role in tissue homeostasis and can orchestrate complex reparative as well as destructive processes in the feet. Evidence is presented that suggests that denervation can result in altered capillary blood flow (in patients with type 2 diabetes), oxygen delivery, fluid filtration, and inflammatory responses. These processes could render the feet of diabetic patients with neuropathy more susceptible to tissue damage, infection and perhaps, in a subset of patients, to the development of acute Charcot neuro-osteoarthropathy (CN).

Skin biopsy as a diagnostic tool in peripheral neuropathy

Skin biopsy is a safe, minimally invasive, painless and cheap tool for providing diagnostic information on small nerve fibers, which are invisible to routine neurophysiological tests. Biopsy can be performed in hairy skin to investigate unmyelinated and thinly myelinated fibers and in glabrous skin to examine large myelinated fibers. Morphometric analysis of skin nerves is readily accomplished through the use of immunohistochemical techniques, and has proved to be reliable, reproducible and unaffected by the severity of neuropathy. One further advantage of skin biopsy over conventional nerve biopsy is that it allows somatic nerve fibers to be distinguished from autonomic nerve fibers. Morphological changes, axonal degeneration and abnormal regeneration occur in cutaneous nerves very early in the course of peripheral neuropathies, making skin biopsy a promising tool for investigating the progression of neuropathy and the effect of neuroprotective treatments in clinical practice and trials. This article reviews the techniques that are used to investigate the innervation of human skin, the possible uses of skin biopsy in diagnosing and monitoring peripheral neuropathies, and correlations between skin biopsy findings and those of other diagnostic methods.

Influence of local treatments with capsaicin or allyl isothiocyanate in the sensitization phase of a fluorescein-isothiocyanate-induced contact sensitivity model

BACKGROUND

In fluorescein isothiocyanate (FITC)-induced contact hypersensitivity models, dibutyl phthalate has been empirically used as a solvent ingredient. We have demonstrated that dibutyl phthalate has an adjuvant effect through the facilitation of trafficking FITC-presenting dendritic cells (DC) from the skin to draining lymph nodes. Here we investigated the effects of local pretreatment with substances that are capable of desensitizing sensory neurons in the sensitization phase.

METHODS

Local pretreatment of BALB/c mice with capsaicin (epicutaneous), allyl isothiocyanate (epicutaneous) or a truncated form of calcitonin gene-related peptide (CGRP(8-37); intradermal) was performed before contact sensitization to FITC. The ear swelling test was employed to monitor sensitization. The appearance of FITC-presenting CD11c-positive cells in the draining lymph nodes was detected by flow cytometry. Cytokine production in local lymph node cell cultures was determined by ELISA.

RESULTS

The ear swelling response was reduced in mice pretreated with capsaicin or allyl isothiocyanate. DC trafficking and maturation (based on the levels of co-stimulators CD80 and CD86) were inhibited. Interleukin-4 production by local lymph nodes was suppressed with allyl isothiocyanate but not with capsaicin. Pretreatment with CGRP(8-37) suppressed sensitization to FITC.

CONCLUSIONS

Local pretreatment with substances that are capable of desensitizing sensory neurons through the respective transient receptor potential channels suppressed skin sensitization to FITC in a mouse model. This was associated with reduced trafficking and maturation of FITC-presenting DC. A CGRP antagonist also suppressed the sensitization to FITC, suggesting the possible involvement of sensory neurons in sensitization.

Mast cell-derived tumor necrosis factor can promote nerve fiber elongation in the skin during contact hypersensitivity in mice

In humans, lesions of contact eczema or atopic dermatitis can exhibit increases in epidermal nerves, but the mechanism resulting in such nerve elongation are not fully understood. We found that contact hypersensitivity reactions to oxazolone in mice were associated with significant increases in the length of nerves in the epidermis and dermis. Using genetically mast cell-deficient c-kit mutant mice selectively repaired of their dermal mast cell deficiency with either wild-type or tumor necrosis factor (TNF)-deficient mast cells, we found that mast cells, and mast cell-derived TNF, significantly contributed to the elongation of epidermal and dermal PGP 9.5+ nerves and dermal CGRP+ nerves, as well as to the inflammation observed at sites of contact hypersensitivity in response to oxazolone. Moreover, the percentage of mast cells in close proximity to dermal PGP 9.5+ nerve fibers was significantly higher in wild-type mice and in c-kit mutant mice repaired of their dermal mast cell deficiency by the adoptive transfer of wild-type mast cells than in TNF-deficient mice or in TNF-/- mast cell-engrafted c-kit mutant mice. These observations show that mast cells, and mast cell-derived TNF, can promote the elongation of cutaneous nerve fibers during contact hypersensitivity in the mouse.

Neurokinin 1 receptor signaling mediates sex differences in μ and κ opioid-induced enhancement of contact hypersensitivity

Contact hypersensitivity (CHS) is a type of cutaneous inflammation that is exacerbated by neurogenic factors. Both mu- and kappa-opioids enhance CHS to a greater extent in females than males. It was hypothesized that potentiated neurokinin 1 (NK1) receptor signaling following opioid treatment accounts for sex differences in the magnitude of CHS. Following morphine or spiradoline treatment the NK1 receptor antagonist SR140,333 significantly attenuated the magnitude of CHS in females but not males. By contrast, the NK2 antagonist SR48968 had no effect on morphine modulation of CHS. Taken together, these data indicate that NK1 receptor signaling is a key mediator of sex differences in opioid-induced enhancement of CHS.

Influence of the intensity, level and phase of spinal cord injury on the proliferation of T cells and T-cell-dependent antibody reactions in rats

STUDY DESIGN

Three independent experiments in a rat model of contusive spinal cord (SC) injury were performed. Two studied the alterations induced by SC injury on some immunological aspects of the T-cell response. The third one evaluated the motor recovery of rats with low-thoracic injuries.

OBJECTIVE

To examine the effect of level, intensity and phase of SC injury on T-cell proliferation and T-cell-dependent antibody response.

SETTING

Neuroimmunology Department, UIMEN, IMSS-CAMINA Research Center.

METHODS

Lymphocyte proliferation and hemagglutination assays were performed. Animals were injured either moderately or severely at T1 or T12 SC segments. Analysis of peripheral T-cell proliferation in response to mitogens and to myelin basic protein (MBP), as well as of antibody production against a T-dependent antigen, was performed at acute, subacute and chronic phases.

RESULTS

A significant decrease of both response to mitogens and antibody production was found especially during the acute phase and in animals with severe and high (T1)-level injury. Animals with low (T12) and moderate contusions recovered to control levels at the chronic phase. An autoimmune reaction against MBP was observed only in animals with severe contusion at low level.

CONCLUSIONS

The intensity, level and phase of SC injury differentially alter the function of T cells. These results will allow a better interpretation of studies directed to elucidate the role of T lymphocytes in various processes developed after SC injury.

Without nerves, immunology remains incomplete -in vivo veritas

Interest in the interactions between nervous and immune systems involved in both pathological and homeostatic mechanisms of host defence has prompted studies of neuroendocrine immune modulation and cytokine involvement in neuropathologies. In this review we concentrate on a distinct area of homeostatic control of both normal and abnormal host defence activity involving the network of peripheral c-fibre nerve fibres. These nerve fibres have long been recognized by dermatologists and gastroenterologists as key players in abnormal inflammatory processes, such as dermatitis and eczema. However, the involvement of nerves can all too easily be regarded as that of isolated elements in a local phenomenon. On the contrary, it is becoming increasingly clear that neural monitoring of host defence activities takes place, and that involvement of central/spinal mechanisms are crucial in the co-ordination of the adaptive response to host challenge. We describe studies demonstrating neural control of host defence and use the specific examples of bone marrow haemopoiesis and contact sensitivity to highlight the role of direct nerve fibre connections in these activities. We propose a host monitoring system that requires interaction between specialized immune cells and nerve fibres distributed throughout the body and that gives rise to both neural and immune memories of prior challenge. While immunological mechanisms alone may be sufficient for local responsiveness to subsequent challenge, data are discussed that implicate the neural memory in co-ordination of host defence across the body, at distinct sites not served by the same nerve fibres, consistent with central nervous mediation.

Evidence for autonomic responses to pungent chemical stimuli applied to the skin vs inhaled via the nasal cavity

AIM OF THE STUDY

Chemical stimuli can produce different sensations from tingling to pain. Responses to chemical stimuli differ in relation to many factors. This study aims at examining two factors, i.e. the localization of their application and the implied sensory modality.

METHODS

Twenty volunteer students participated in the experiment. Skin conductance responses (SCRs) were recorded to compare the autonomic nervous activation to maximal stimulation with the same irritant stimulus (mustard oil (MO) diluted at 25%) applied to the skin or delivered into the nasal cavity.

RESULTS

The SCRs obtained following maximal nasal stimulation with MO were significantly different from those obtained following maximal skin stimulation. Application of MO on skin elicited higher SCR amplitude as well as a longer rising time and latency when compared to nasal stimulation.

CONCLUSIONS

These findings indicate that the autonomic nervous activation following maximal chemical irritation differ in temporal, amplitude and shape response characteristics. These results are discussed in terms of cutaneous and nasal innervation's.

Evidence for a novel protective role of the vanilloid TRPV1 receptor in a cutaneous contact allergic dermatitis model

The purpose of this study was to examine the involvement of the transient receptor potential vanilloid receptor 1 (TRPV1) in inflammatory processes observed in murine allergic contact dermatitis (ACD). Oxazolone-induced ACD evoked a significant ear swelling after 24-72 h. It was augmented in TRPV1 knockout mice at all time points and supported by histological analysis and measure of TNF-alpha. However, tissue swelling and cytokine generation was significantly reduced in both neurokinin 1 receptor and calcitonin gene-related peptide (CGRP) knockout mice. A protective involvement of the TRPV1 receptor was identified of contact dermatitis distinct from mechanisms involving the major pro-inflammatory neuropeptides.

Mobilisation of specific T cells from lymph nodes in contact sensitivity requires substance P

Capsaicin-mediated depletion of neuropeptides in the skin was previously shown to abolish a dinitrocholorobenzene (DNCB)-induced contact sensitivity (CS) response. To understand the basis for this disruption, we explored whether nerve fibres innervating the draining lymph node (LN) could be involved. As expected, removal of the draining LN after DNCB sensitisation abolished the CS response. Furthermore, the CS response could be abolished by destroying the nerve fibres in the draining LN and could be restored by providing the LN with the neuropeptide substance P. The size of the CS response restored by substance P was dose dependent. The response was also inhibited by exposing the lymph node to a neurokinin-1 receptor antagonist which blocks binding of substance P. The results suggest that an afferent signal from the skin via the sympathetic arm of the central nervous system evokes an efferent signal to the LN which combines to regulate the CS response. The efferent signal may serve to control or release from the LN primed effector lymphocytes into the circulation.

Close encounters of the monoamine kind: immune cells betray their nervous disposition

Here we review the evidence for immune cells expressing multiple components of the serotonergic and dopaminergic systems that are more commonly associated with the central nervous system (CNS). We discuss where and how peripheral encounters with these biogenic monoamines occur and posit reasons as to why the immune system would wish to deploy these pathways. A full taxonomy of serotonergic and dopaminergic constituents and their workings in component cells of the immune system should facilitate the formulation of novel therapeutic approaches in diseases characterized by immune dysfunction and potentially provide a range of surrogate peripheral markers for registering and monitoring disturbances within the CNS.