Peptidergic neurons and vasoactive intestinal peptide modulate experimental delayed-type hypersensitivity reactions

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

Previous work has indicated that the dermis and epidermis of skin contains abundant nerve fibres closely associated with Langerhans' cells. We have investigated whether these nerve endings are necessary for inducing and evoking a contact sensitivity (CS) response. Topical application of a general or a peptide (calcitonin gene-related peptide and substance P)-specific neurotoxin was employed to destroy the nerve fibres at skin sites subsequently used to induce or evoke the CS response. Elimination of nerve fibres abolished both induction and effector stages of the specific CS response. Denervation did not destroy the local Langerhans' cells, which were observed in increased numbers, or prevent them from migrating to lymph nodes. The local CS response was also abolished by systemic deletion of capsaicin-sensitive nerve fibres, suggesting that the loss of response was not non-specific but associated with the loss of specific nerve fibres. The results indicate that peptidergic nerve fibres are required to elicit a CS response and may be vital to the normal function of the immune system.

Neuropeptídeos na pele

Há evidências crescentes de que a inervação cutânea é capaz de modular uma variedade de fenômenos cutâneos agudos e crônicos, interagindo com as células da pele e seus componentes imunes. Essa forma de sinalização local entre tecido nervoso e tecido cutâneo ocorre especialmente por meio dos neuropeptídeos, uma numerosa família de neurotransmissores de natureza química comum e nomenclatura heterogênea presentes em todo o sistema nervoso e secretados pelas fibras nervosas cutâneas. São alvo desta revisão os neuropeptídeos substância P (SP), o peptídeo relacionado ao gene da calcitonina (CGRP), o peptídeo vasoativo intestinal (VIP), o peptídeo ativador da adenilato-ciclase pituitária (PACAP), o neuropeptídeo Y (NPY) e a somatostatina (SOM). Serão discutidas suas ações sobre as células da pele e sistema imune, bem como estudos recentes que sugerem a participação dos neuropeptídeos nas respostas inflamatórias cutâneas, nas reações de hipersensibilidade e em dermatoses humanas, notadamente na psoríase, dermatite atópica, hanseníase e alopecia.

Modification of LC phenotype and suppression of contact hypersensitivity response by stress

BACKGROUND

Stress is thought to exacerbate a number of diseases, some of which are skin disorders. Epidermal Langerhans' cells play a major role in cutaneous immune reactions.

OBJECTIVE

The effects of two types of stress on the cutaneous immune system were to be assessed in mice.

METHODS

Mice received stress by immobilization or housing at various population densities. Epidermal sheets were stained for I-A molecules (a member of class II major histocompatibility complex) and analyzed with a confocal-laser- scanning microscope. Contact hypersensitivity reaction to 2,4,6-trinitrochlorobenzene was elicited in mouse ears.

RESULTS

The cell density, intensity of I-A expression, and number of dendrites were decreased as the population density increased. Elicitation of contact hypersensitivity was suppressed in mice that received either population or immobilization stress. Increased I-A expression and number of dendrites were observed in adrenalectomized compared to sham-operated mice. The population-dependent suppression of contact hypersensitivity reaction was not observed in adrenalectomized mice. After incubation with serum from mice that received either immobilization stress or population stress, the expression of I-A molecules on a XS52 Langerhans' cell-like cell line was reduced.

CONCLUSION

Stress affected the cutaneous immune system. There were indications that adrenergic hormones played a role in the regulation of the system.

Neuropeptides and Langerhans cells

The immune system and nervous system are intimately related. In addition to neuroendocrine mechanisms, neuropeptides have a variety of effects on immune cells and are responsible at least in part for neurogenic inflammation. The presence of neuropeptides in the skin has been well documented. The influence of neuropeptides on Langerhans cells is the focus of this paper. The physical presence and effects of calcitonin gene-related peptide on Langerhans cells is emphasized. Discussion also includes the putative inflammatory and immunologic roles of vasoactive intestinal peptide, substance P, neurotensin, neuropeptide Y, and somatostatin in the skin.

Neuropeptides in the skin: interactions between the neuroendocrine and the skin immune systems

The interaction between components of the nervous system and multiple target cells in the cutaneous immune system has been receiving increasing attention. It has been observed that certain skin diseases such as psoriasis and atopic dermatitis have a neurogenic component. Neuropeptides released by sensory nerves that innervate the skin and often contact epidermal and dermal cells can directly modulate functions of keratinocytes, Langerhans cells (LC), mast cells, dermal microvascular endothelial cells and infiltrating immune cells. Among these neuropeptides the tachykinins substance P (SP) and neurokinin A (NKA), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and somatostatin (SOM) have been reported to effectively modulate skin and immune cell functions such as cell proliferation, cytokine production or antigen presentation under physiological or pathophysiological conditions. Expression and regulation of their corresponding receptors that are expressed on a variety of skin cells as well as the presence of neuropeptide-specific peptidases such as neutral endopeptidase (NEP) or angiotensin-converting enzyme (ACE) determine the final biological response mediated by these peptides on the target cell or tissue. Likewise, skin cells like keratinocytes or fibroblasts are a source for neurotrophins such as nerve growth factor that are required not only for survival and regeneration of sensory neurons but also to control responsiveness of these neurons to external stimuli. Therefore, neuropeptides, neuropeptide receptors, neuropeptide-degrading enzymes and neurotrophins participate in a complex, interdependent network of mediators that modulate skin inflammation, wound healing and the skin immune system. This review will focus on recent studies demonstrating the role of tachykinins, CGRP, SOM and VIP and their receptors and neuropeptide-degrading enzymes in mediating neurogenic inflammation in the skin.

Neuropeptides, nerve growth factor and eczema

Considerable evidence indicates that peripheral nerve fibres play an active regulatory role during eczematous reactions. Many basic features of the inflammatory process are potentially subject to neuropeptidergic modulation, such as vascular changes, cellular trafficking activation and trophism in vivo and in vitro investigations suggest that neuropeptides are part of the complex network of mediators that initiate and maintain the eczematous process in the skin. In general, peptidergic fibres seem to exert a global protective role, but with specific and selective effects in the different phases. Evidence that the inflammatory process induces bio-chemical changes at a neuronal level has also been obtained. The possible mediators of the neuronal recruitment in the course of the eczematous reaction are still unknown. Nevertheless, nerve growth factor, which is locally increased during inflammatory processes and may induce peptidergic alterations, should be considered as a potential candidate molecule.

Epidermal cytokine and neuronal peptide modulation of contact hypersensitivity reactions

Cellular and molecular mechanisms underlying contact hypersensitivity reactions have been, and still are, fields under intense investigation, not only for the importance of these reactions in clinical medicine, but also because they are considered prototypic of a vast group of T cell-mediated immune diseases of the skin. Interestingly, potent contributions by non-bone marrow-derived cells have been shown clearly, demonstrating that epidermal cells are far more than mere spectators of these reactions, and undergo a functional activation after contact with the hapten causing the hypersensitivity reaction. In particular, keratinocyte contribution to the onset as well as modulation of contact hypersensitivity reactions through the release of a plethora of cytokines, has been widely documented. Moreover, an important control over these reactions is exerted by local release of neuropeptides by nerve endings. This review paper focuses on epidermal cytokine and neuronal peptide modulation of contact hypersensitivity reactions, trying to document the complexity of the regulatory systems, active during these immune processes of the skin.

Substance P Is Diminished and Vasoactive Intestinal Peptide Is Augmented in Psoriatic Lesions and These Peptides Exert Disparate Effects on the Proliferation of Cultured Human Keratinocytes

An involvement of neurogenic components in the pathogenesis of psoriatic lesions has been suggested and neuropeptides are thought to play a modulatory role in cutaneous inflammation. In this study, we evaluated the immunoreactivity of the neuropeptides vasoactive intestinal polypeptide (VIP) and substance P (SP) in the skin of patients with chronic plaque psoriasis, by immunohistochemistry and radioimmunoassay. No differences were observed, by immunohistochemistry, in the expression and localization of VIP and SP between psoriatic and normal skin. Using the radioimmunologic technique on whole skin homogenates, VIP levels were significantly increased in psoriatic lesions as compared to normal skin. By contrast, SP levels were significantly lower in lesional and non-lesional psoriatic skin than in normal skin. In addition, we examined the effect of VIP and SP on the proliferation of cultured normal human keratinocytes. VIP (1-28) (1 nM-1 microM) as well as VIP fragments (10-28) (1 nM-1 microM) and (22-28) (1 nM-1 microM) stimulated the proliferation of keratinocytes in a dose-dependent manner, whereas the VIP fragment (1-12) (1 nM-1 microM) was ineffective. The VIP antagonist (N-Ac-Tyr1, D-Phe2)-GRF (1-29)-NH2 (0.1 microM) significantly inhibited the VIP effect on keratinocytes. On the other hand, SP (0.1 microM) not only failed to stimulate keratinocyte growth, but also blocked the VIP-induced stimulation of these cells. The imbalance of cutaneous VIP and SP and their disparate effects on the proliferation of normal human keratinocytes in culture would suggest that these peptides are involved in the pathogenesis of psoriasis and may exert different modulatory activities in the mechanisms underlying the psoriatic lesion.