Mast cells in psoriasis

Mast Cells in Autism Spectrum Disorder-The Enigma to Be Solved?

Autism Spectrum Disorder (ASD) is a disturbance of neurodevelopment with a complicated pathogenesis and unidentified etiology. Many children with ASD have a history of "allergic symptoms", often in the absence of mast cell (MC)-positive tests. Activation of MCs by various stimuli may release molecules related to inflammation and neurotoxicity, contributing to the development of ASD. The aim of the present paper is to enrich the current knowledge on the relationship between MCs and ASD by discussing key molecules and immune pathways associated with MCs in the pathogenesis of autism. Cytokines, essential marker molecules for MC degranulation and therapeutic targets, are also highlighted. Understanding the relationship between ASD and the activation of MCs, as well as the involved molecules and interactions, are the main points contributing to solving the enigma. Key molecules, associated with MCs, may provide new insights to the discovery of drug targets for modeling inflammation in ASD.

TNF stimulates IL-6, CXCL8 and VEGF secretion from human keratinocytes via activation of mTOR, inhibited by tetramethoxyluteolin

Psoriasis is an autoimmune skin disease characterized by keratinocyte hyperproliferation and chronic inflammation. The pathogenesis of psoriasis involves proinflammatory cytokines, such as tumor necrosis factor (TNF), but the mechanism of keratinocyte activation is not well understood. Here, we show that TNF (10 or 50 ng/mL) stimulates a significant (P < .0001) gene expression and secretion of proinflammatory IL-6, CXCL8 and VEGF from both cultured human HaCaT and normal epidermal human keratinocytes (NHEKs). This effect occurs via activation of the mammalian target of rapamycin (mTOR) signalling complex as shown by Western blot analysis and phospho-ELISAs. Pretreatment with the novel natural flavonoid tetramethoxyluteolin (10-100 μmol L^-1 ) significantly (P < .0001) inhibits gene expression and secretion (P < .0001) of all 3 mediators in a concentration-dependent manner. Moreover, tetramethoxyluteolin (50 μmol L^-1 ) appears to be a potent inhibitor of the phosphorylated mTOR substrates (pmTOR^Ser2448 , pp70S6K^Thr389 and p4EBP1^Thr37/46 ) as compared to known mTOR inhibitors in keratinocytes. The present findings indicate that TNF stimulates skin inflammation via mTOR signalling. Inhibition by tetramethoxyluteolin may be used in the treatment for psoriasis.

Lymphangiogenesis: fuel, smoke, or extinguisher of inflammation's fire?

Lymphangiogenesis is a recognized hallmark of inflammatory processes in tissues and organs as diverse as the skin, heart, bowel, and airways. In clinical and animal models wherein the signaling processes of lymphangiogenesis are manipulated, most studies demonstrate that an expanded lymphatic vasculature is necessary for the resolution of inflammation. The fundamental roles that lymphatics play in fluid clearance and immune cell trafficking from the periphery make these results seemingly obvious as a mechanism of alleviating locally inflamed environments: the lymphatics are simply providing a drain. Depending on the tissue site, lymphangiogenic mechanism, or induction timeframe, however, evidence shows that inflammation-associated lymphangiogenesis (IAL) may worsen the pathology. Recent studies have identified lymphatic endothelial cells themselves to be local regulators of immune cell activity and its consequential phenotypes - a more active role in inflammation regulation than previously thought. Indeed, results focusing on the immunocentric roles of peripheral lymphatic function have revealed that the basic drainage task of lymphatic vessels is a complex balance of locally processed and transported antigens as well as interstitial cytokine and immune cell signaling: an interplay that likely defines the function of IAL. This review will summarize the latest findings on how IAL impacts a series of disease states in various tissues in both preclinical models and clinical studies. This discussion will serve to highlight some emerging areas of lymphatic research in an attempt to answer the question relevant to an array of scientists and clinicians of whether IAL helps to fuel or extinguish inflammation. Impact statement Inflammatory progression is present in acute and chronic tissue pathologies throughout the body. Lymphatic vessels play physiological roles relevant to all medical fields as important regulators of fluid balance, immune cell trafficking, and immune identity. Lymphangiogenesis is often concurrent with inflammation and can potentially aide or worsen disease progression. How new lymphatic vessels impact inflammation and by which mechanism is an important consideration in current and future clinical therapies targeting inflammation and/or vasculogenesis. This review identifies, across a range of tissue-specific pathologies, the current understanding of inflammation-associated lymphangiogenesis in the progression or resolution of inflammation.

Mast Cells: Key Players in the Shadow in Oral Inflammation and in Squamous Cell Carcinoma of the Oral Cavity

Although mast cells (MCs) have been discovered over 130 years ago, their function was almost exclusively linked to allergic affections. At the time being, it is well known that MCs possess a great variety of roles, in both physiologic and pathologic conditions. In the oral tissues, MCs release different proinflammatory cytokines, tumor necrosis factor alpha (TNF-α), that promote leukocyte infiltration in various inflammatory states of the oral cavity. These cells play a key role in the inflammatory process and, as a consequence, their number changes in different pathologic conditions of the oral cavity, like gingivitis, periodontitis, and so on. MCs also represent a rich source of proteases, especially of mast cell tryptase and chymase, which directly degrade the extracellular matrix through their proteolytic activity and thus indirectly stimulate angiogenesis and facilitate invasion and metastasis. It may be stated that mast cells could have an impact on primary tumor development, progression, and metastases in oral squamous cell carcinoma. By understanding the role of mast cells in the pathogenesis of different inflammatory and tumor diseases of the oral cavity, these cells may become therapeutic targets that could possibly improve the prognosis and survival of these patients.

Regulation of Th2 Cell Immunity by Dendritic Cells

Th2 cell immunity is required for host defense against helminths, but it is detrimental in allergic diseases in humans. Unlike Th1 cell and Th17 cell subsets, the mechanism by which dendritic cells modulate Th2 cell responses has been obscure, in part because of the inability of dendritic cells to provide IL-4, which is indispensable for Th2 cell lineage commitment. In this regard, immune cells other than dendritic cells, such as basophils and innate lymphoid cells, have been suggested as Th2 cell inducers. More recently, multiple independent researchers have shown that specialized subsets of dendritic cells mediate Th2 cell responses. This review will discuss the current understanding related to the regulation of Th2 cell responses by dendritic cells and other immune cells.

Angiogenesis and lymphangiogenesis in inflammatory skin disorders

Angiogenesis, the growth of new blood vessels from pre-existing vessels, occurs physiologically in wound healing, during inflammatory diseases, and in tumor growth. Lymphangiogenesis can be activated in inflammation and tumor metastasis. The family of vascular endothelial growth factors (VEGFs) and angiopoietins are essential for angiogenesis and lymphangiogenesis. The angiogenic process is tightly regulated by VEGFs, angiopoietins, and endogenous inhibitors. VEGFs and angiopoietins exert their effects by activating specific receptors present on blood and lymphatic endothelial cells. There is now compelling evidence that cells of innate and adaptive immunity (macrophages, mast cells, neutrophils, eosinophils, lymphocytes) are a major source of angiogenic and lymphangiogenic factors. Chronic inflammatory skin diseases such as psoriasis and atopic dermatitis are characterized by altered angiogenesis, lymphangiogenesis, or both. Also such acute inflammatory skin disorders as urticaria, ultraviolet B-induced damage, and angioedema are associated with changes in angiogenic factors. In systemic sclerosis there is a switch from proangiogenic to antiangiogenic factors that play a role in the defective vascular process of this disorder. As yet, there are no clinical trials showing that canonical VEGF/VEGF receptor-targeted strategies can modulate inflammatory skin diseases. Novel strategies targeting other angiogenic/lymphangiogenic pathways should also be investigated.

Quantitative determination of 12-hydroxyeicosatetraenoic acids by chiral liquid chromatography tandem mass spectrometry in a murine atopic dermatitis model

Atopic dermatitis, one of the most important skin diseases, is characterized by both skin barrier impairment and immunological abnormalities. Although several studies have demonstrated the significant relationship between atopic dermatitis and immunological abnormalities, the role of hydroxyeicosatetraenoic acids (HETE) in atopic dermatitis remains unknown. To develop chiral methods for characterization of 12-HETE enantiomers in a 1-chloro-2,4-dinitrochlorobenzene (DNCB)-induced atopic dermatitis mouse model and evaluate the effects of 12-HETE on atopic dermatitis, BALB/c mice were treated with either DNCB or acetone/olive oil (AOO) to induce atopic dermatitis, after which 12(R)- and 12(S)-HETEs in the plasma, skin, spleen, and lymph nodes were quantified by chiral liquid chromatography-tandem mass spectrometry. 12(R)- and 12(S)-HETEs in biological samples of DNCB-induced atopic dermatitis mice increased significantly compared with the AOO group, reflecting the involvement of 12(R)- and 12(S)-HETEs in atopic dermatitis. These findings indicate that 12(R)- and 12(S)-HETEs could be a useful guide for understanding the pathogenesis of atopic dermatitis.

Luteolin inhibits human keratinocyte activation and decreases NF-κB induction that is increased in psoriatic skin

Psoriasis (Ps) is an autoimmune disease characterized by keratinocyte hyperproliferation and chronic inflammation, with increased expression of tumor necrosis factor (TNF) and vascular endothelial growth factor (VEGF). Anti-TNF biologic agents are effective in treating Ps, but are associated with increased risk of infections and blood malignancies. Moreover, keratinocyte hyperproliferation and activation have yet to be addressed. Flavonoids, such as luteolin, are natural compounds with potent anti-inflammatory properties, but their actions on keratinocytes remain unknown. We show that TNF (50 ng/mL) triggers significant production of inflammatory mediators interleukin-6, interleukin-8 and VEGF from both human HaCaT and primary keratinocytes. Pretreatment with the flavonoid luteolin (10–100 µM) significantly inhibits mRNA expression and release of all three mediators in a concentration-dependent manner. More importantly, luteolin decreases TNF-induced phosphorylation, nuclear translocation and DNA binding of the nuclear factor-kappa B (NF-κB) typically involved in inflammatory mediator transcription. We also report that luteolin reduces TNF-induced mRNA expression of two genes (NFKB1 and RELA) encoding two NF-κB subunits (NF-κB p50 and NF-κB p65, respectively). Interestingly, we show that gene expression of RELA is increased in human psoriatic skin. Keratinocyte proliferation, which is a characteristic feature of psoriatic skin, is effectively reduced by luteolin in HaCaT cells, but not in primary keratinocytes. Finally, luteolin does not affect intracellular ATP production or viability. Appropriate formulations of luteolin and related flavones may be promising candidates to be developed into local and systemic treatments for Ps and other inflammatory skin diseases.

Genetic Epidemiology of Psoriasis

Psoriasis is a chronic, inflammatory, immune-mediated skin condition with a prevalence of 0-11.8% across the world. It is associated with a number of cardiovascular, metabolic, and autoimmune disease co-morbidities. Psoriasis is a multifactorial disorder, influenced by both genetic and environmental factors. Its genetic basis has long been established through twin studies and familial clustering. The association of psoriasis with the HLA-Cw6 allele has been shown in many studies. Recent genome-wide association studies have identified a large number of other genes associated with psoriasis. Many of these genes regulate the innate and adaptive immune system. These findings indicate that a dysregulated immune system may play a major role in the pathogenesis of psoriasis. In this article, we review the clinical and genetic epidemiology of psoriasis with a brief description of the pathogenesis of disease.

Mast cells and inflammation

Mast cells are well known for their role in allergic and anaphylactic reactions, as well as their involvement in acquired and innate immunity. Increasing evidence now implicates mast cells in inflammatory diseases where they are activated by non-allergic triggers, such as neuropeptides and cytokines, often exerting synergistic effects as in the case of IL-33 and neurotensin. Mast cells can also release pro-inflammatory mediators selectively without degranulation. In particular, IL-1 induces selective release of IL-6, while corticotropin-releasing hormone secreted under stress induces the release of vascular endothelial growth factor. Many inflammatory diseases involve mast cells in cross-talk with T cells, such as atopic dermatitis, psoriasis and multiple sclerosis, which all worsen by stress. How mast cell differential responses are regulated is still unresolved. Preliminary evidence suggests that mitochondrial function and dynamics control mast cell degranulation, but not selective release. Recent findings also indicate that mast cells have immunomodulatory properties. Understanding selective release of mediators could explain how mast cells participate in numerous diverse biologic processes, and how they exert both immunostimulatory and immunosuppressive actions. Unraveling selective mast cell secretion could also help develop unique mast cell inhibitors with novel therapeutic applications. This article is part of a Special Issue entitled: Mast cells in inflammation.

Substance P (SP) induces expression of functional corticotropin-releasing hormone receptor-1 (CRHR-1) in human mast cells

Corticotropin-releasing hormone (CRH) is secreted under stress and regulates the hypothalamic-pituitary-adrenal axis. However, CRH is also secreted outside the brain where it exerts proinflammatory effects through activation of mast cells, which are increasingly implicated in immunity and inflammation. Substance P (SP) is also involved in inflammatory diseases. Human LAD2 leukemic mast cells express only CRHR-1 mRNA weakly. Treatment of LAD2 cells with SP (0.5-2 μM) for 6 hours significantly increases corticotropin-releasing hormone receptor-1 (CRHR-1) mRNA and protein expression. Addition of CRH (1 μM) to LAD2 cells, which are "primed" with SP for 48 hours and then washed, induces synthesis and release of IL-8, tumor necrosis factor (TNF), and vascular endothelial growth factor (VEGF) 24 hours later. These effects are blocked by pretreatment with an NK-1 receptor antagonist. Treatment of LAD2 cells with CRH (1 μM) for 6 hours induces gene expression of NK-1 as compared with controls. However, repeated stimulation of mast cells with CRH (1 μM) leads to downregulation of CRHR-1 and upregulation in NK-1 gene expression. These results indicate that SP can stimulate mast cells and also increase expression of functional CRHR-1, whereas CRH induces NK-1 gene expression. These results may explain CRHR-1 and NK-1 expression in lesional skin of psoriatic patients.

IL-33 augments substance P-induced VEGF secretion from human mast cells and is increased in psoriatic skin

The peptide substance P (SP) has been implicated in inflammatory conditions, such as psoriasis, where mast cells and VEGF are increased. A relationship between SP and VEGF has not been well studied, nor has any interaction with the proinflammatory cytokines, especially IL-33. Here we report that SP (0.1-10 microM) induces gene expression and secretion of VEGF from human LAD2 mast cells and human umbilical core blood-derived cultured mast cells (hCBMCs). This effect is significantly increased by coadministration of IL-33 (5-100 ng/mL) in both cell types. The effect of SP on VEGF release is inhibited by treatment with the NK-1 receptor antagonist 733,060. SP rapidly increases cytosolic calcium, and so does IL-33 to a smaller extent; the addition of IL-33 augments the calcium increase. SP-induced VEGF production involves calcium-dependent PKC isoforms, as well as the ERK and JNK MAPKs. Gene expression of IL-33 and histidine decarboxylase (HDC), an indicator of mast cell presence/activation, is significantly increased in affected and unaffected (at least 15 cm away from the lesion) psoriatic skin, as compared with normal control skin. Immunohistochemistry indicates that IL-33 is associated with endothelial cells in both the unaffected and affected sites, but is stronger and also associated with immune cells in the affected site. These results imply that functional interactions among SP, IL-33, and mast cells leading to VEGF release contribute to inflammatory conditions, such as the psoriasis, a nonallergic hyperproliferative skin inflammatory disorder with a neurogenic component.

The leukotriene d4 receptor antagonist, montelukast, inhibits mast cell degranulation in the dermis induced by water avoidance stress

Cysteinyl leukotrienes play a part in inflammatory reactions such as asthma and inflammatory bowel diseases. The leukotrienes exert their actions by binding to and activating various receptors. Montelukast, a leukotriene receptor antagonist, which is used in the treatment of asthma has been shown to be effective in inhibiting the action or formation of leukotrienes. Many skin disorders, such as atopic dermatitis and psoriasis, worsen during stress and seem to be related to infiltration and activation of mast cells that are releasing vasoactive and pro-inflammatory mediators. The aim of the present study was to investigate the effects of montelukast on the degranulation of mast cells in the dermis that is induced by water avoidance stress (WAS). Wistar albino rats were divided into four groups of 8 animals each. Control rats were injected with (1) the vehicle solution or (2) the montelukast solution in the absence of WAS. (3) the WAS group of rats was administered vehicle solution following WAS exposure for 2h daily for 5 days. (4) The WAS+ML group was administered montelukast 10mg/kg; i.p. following WAS exposure for 2h daily for 5 days. Dermal mast cell numbers were determined with toluidine blue and tryptase immunohistochemistry and observed using a light microscope. Numbers of both granulated and degranulated mast cells were significantly increased in the WAS group when compared to control rats. Montelukast treatment decreased the number of both mature granulated and degranulated mast cells in rats subjected to WAS. In conclusion, chronic montelukast treatment reduced WAS-induced infiltration and activation of mast cells in the dermis and may provide a useful therapeutic option in stress-induced skin disorders.

Expression of serotonergic receptors in psoriatic skin

Psoriasis appears to be influenced by stress, which causes release of adrenal hormones. Serotonin, or hormonal actions on serotonin and serotonin receptors, may have a role in psoriasis. Distribution of serotonin receptors was studied in involved and noninvolved skin in patients with psoriasis and compared to normal skin, by using immunohistochemistry and antibodies to 5-HT1A, 5-HT2A and 5-HT3 receptors (R). There was a decreased (P<0.001) number of 5-HT1AR positive cells, the majority being tryptase positive, in involved and noninvolved psoriatic papillary dermis, compared to normal skin. 5-HTlAR expression was also found in the upper part of the epidermis, on vessel walls and on melanocytes. 5-HT2AR expressing papillary mononuclear cells, CD3 positive, were increased (P<0.001 and P<0.01, respectively) in involved and noninvolved psoriatic skin, compared to normal skin, an increase (P<0.01) also being found in the involved compared to noninvolved skin. Expression of 5-HT3R could be found in the basal epidermal layer of noninvolved but not in the involved skin of psoriasis, where it was only found in the acrosyringium. The present findings are compatible with the 5-HT1A and 5-HT2A receptors having antagonistic functions, and raise the possibility of using receptor specific drugs in the treatment of psoriasis.

Corticotropin-releasing hormone induces skin vascular permeability through a neurotensin-dependent process

Many skin disorders are associated with increased numbers of activated mast cells and are worsened by stress; however, the mechanism underlying these processes is not understood. Corticotropin-releasing hormone (CRH) is secreted under stress from the hypothalamus, but also in the skin, where it induces mast cell activation and vascular permeability. We investigated the effect of CRH in a number of animal models by using i.v. Evans blue extravasation as a marker of vascular permeability. Intradermal CRH is among the most potent peptides at 100 nM, its effect being nearly comparable to that of neurotensin (NT). Pretreatment of skin injection sites with the NT receptor antagonist SR48692 blocks CRH-induced vascular permeability, which is diminished in NT-/- mice, implying that NT is necessary for the effect of CRH. CRH and NT precursor mRNA are shown to be expressed in both dorsal root ganglia and skin, whereas the latter also expresses mRNA for prohormone convertase 5, an enzyme that cleaves pro-NT into its active form. We also show that the effect of both CRH and NT is absent in W/W(v) mast cell-deficient mice; however, only a fraction of skin mast cells express CRH receptors, as shown by FACS analysis of CRH receptor (CRHR) and c-kit double-positive disaggregated mouse skin mast cells. These findings suggest that CRH induces skin vascular permeability through NT acting on mast cells and that both peptides should be considered in the pathogenesis of skin disorders exacerbated by stress.

NK-1 antagonist CP99994 inhibits stress-induced mast cell degranulation in rats

Mast cells are implicated in stress-induced inflammatory skin diseases such as psoriasis. Mechanisms of stress-induced mast cell degranulation however, are not entirely clear. Here we explore the role of activation of a Substance P (SP) receptor (NK-1) on mast cell degranulation upon exposure to stress in rats. A specific nonpeptide NK-1 antagonist, CP99994 was used to treat the rats either peripherally or intracerebroventricularly. Because increased SP activity in the brain may mediate the stress response, we also examined cutaneous mast cell degranulation after central injection of SP. Stress, as well as SP injected centrally, increased mast cell degranulation. Both central and peripheral injection of CP99994 prevented stress-induced mast cell degranulation. Surprisingly, the combination of stress with SP decreased mast cell degranulation, suggesting that high levels of SP may counteract the stress responses. Results in this animal model suggest that NK-1 antagonists may be used therapeutically to treat stress-induced inflammatory skin diseases; however, drug doses should be chosen carefully.

The protective effects of melatonin against water avoidance stress-induced mast cell degranulation in dermis

Nontraumatic psychological water avoidance stress has been shown to induce mucosal degeneration, inflammatory cell infiltration and mast cell degranulation in stomach, ileum, colon and urinary bladder. Many skin disorders, such as atopic dermatitis and psoriasis, worsen during stress and seem to be related with infiltration and activation of mast cells releasing vasoactive and proinflammatory mediators. Melatonin is a free radical scavenger and has cytoprotective effects in inflammatory conditions. The aim of the present study was to investigate the effects of melatonin on water avoidance stress (WAS)-induced degranulation of mast cells in the dermis. Wistar rats were exposed to acute WAS (aWAS group) or chronic WAS (cWAS group). Before exposing to acute WAS, one group of animals was treated with 10mg/kg melatonin (aWAS+mel group). In the cWAS+mel group, treatment with melatonin lasted for 5 days. Dermal mast cells were stained with toluidine blue and investigated using light microscopy. Numbers of mast cells were increased in both aWAS and cWAS groups, but numbers of degranulated mast cells were increased significantly only in the cWAS group when compared to the control group. Numbers of mature granulated and degranulated mast cells were decreased in the cWAS+mel group when compared to the cWAS group. In conclusion, chronic melatonin treatment reduced WAS-induced infiltration and activation of mast cells in dermis and may provide a useful therapeutic option in stress-induced skin disorders.

Possible contribution of stem cell factor in psoriasis vulgaris

It is suggested that mast cell is implicated to play a role in the pathogenesis of psoriasis. In this study, to determine the role of stem cell factor (SCF), which is a growth factor of mast cells, we have examined the immunohistochemical localization and serum level of SCF in patients with psoriasis vulgaris. Immunohistochemical analysis revealed diffuse staining for SCF on keratinocytes in acanthotic epidermis in psoriasis, along with endothelial cells and fibroblasts. Serum SCF level, which was measured by enzyme-linked immunosorbent assay (ELISA), was significantly increased in patients with psoriasis vulgaris (1033+/-334 pg/ml) (n=24) than that of normal subjects (666+/-196 pg/ml) (n=15) (P<0.05). However, serum SCF did not show a correlation with the disease severity assessed by psoriasis activity and severity index (PASI) score. As patients with psoriasis vulgaris occasionally complain itching, next we divided 20 patients into two groups, those with itching (Group I) (n=8) and those without (Group II) (n=12), and compared the mast cell number located in the papillary dermis between thickened psoriatic epidermis, serum SCF and plasma histamine levels. Results showed that mast cell numbers (56.3+/-22.3/mm(2) in Group I vs 31.5+/-10. 3/mm(2) in Group II, P<0.05) and plasma histamine level (1.5+/-0.59 ng/ml vs 0.39+/-0.15 ng/ml, P<0.01) were significantly higher in patients of Group I than those of patients of Group II, however, the difference of serum SCF level (1132+/-368 pg/ml vs 890+/-373 pg/ml) did not reach a statistical significance. Finally, in a separate experiment, we examined whether exogenous SCF is capable of inducing psoriatic architecture on the transplanted uninvolved psoriatic skin onto severe combined immunodeficient (SCID) mice. SCF injection for 2 weeks could not induce a psoriasiform architecture such as acanthosis on the transplanted uninvolved psoriatic skin, although mast cells were increased in number. These results raised a possibility that keratinocyte-derived SCF plays a role, in part, in the increased number of mast cells in the papillary dermis of psoriasis, which may lead pruritus associated with psoriasis. Elevated serum SCF level may also be responsible for increment of mast cells in psoriasis vulgaris. Mast cell-derived factor stimulated by exogenous SCF could not induce psoriatic epidermis, suggesting that other factors such as activated lymphocytes or macrophages are further required for the development of psoriatic lesions.

Acute immobilization stress triggers skin mast cell degranulation via corticotropin releasing hormone, neurotensin, and substance P: A link to neurogenic skin disorders

Many skin disorders, such as atopic dermatitis and psoriasis, worsen during stress and are associated with increased numbers and activation of mast cells which release vasoactive, nociceptive, and proinflammatory mediators. Nontraumatic acute psychological stress by immobilization has been shown to induce mast cell degranulation in the rat dura and colon. Moreover, intradermal injection of corticotropin-releasing hormone (CRH) or its analogue urocortin (10(-5)-10(-7) M) induced skin mast cell degranulation and increased vascular permeability. Here, we investigated the effect of acute immobilization stress on skin mast cell degranulation by light microscopy and electron microscopy. Immobilization for 30 min resulted (P < 0.05) in degranulation of 40.7 +/- 9.1% of skin mast cells compared to 22.2 +/- 7.3% in controls killed by CO(2) or 17.8 +/- 2.4% in controls killed by pentobarbital. Pretreatment intraperitoneally (ip) with antiserum to CRH for 60 min prior to stress reduced (P < 0.05) skin mast cell degranulation to 21.0 +/- 3. 3%. Pretreatment with the neurotensin (NT) receptor antagonist SR48692 reduced (P < 0.05) mast cell degranulation to 12.5 +/- 3.4%, which was significantly (P < 0.05) below control levels. In animals treated neonatally with capsaicin to deplete their sensory neurons of their neuropeptides, such as substance P (SP), mast cell degranulation due to immobilization stress was reduced to about 15%. This is the first time that stress has been shown to trigger skin mast cell degranulation, an action not only dependent on CRH, but apparently also involving NT and SP. These findings may have implications for the pathophysiology and possible therapy of neuroinflammatory skin disorders such as atopic dermatitis, neurogenic pruritus, or psoriasis, which are induced or exacerbated by stress.