Epidermal mast cells in atopic dermatitis

Mast Cells Initiate Type 2 Inflammation through Tryptase Released by MRGPRX2/MRGPRB2 Activation in Atopic Dermatitis

Atopic dermatitis (AD) is a common chronic inflammatory skin disease characterized by T helper 2 inflammation as the core pathogenic mechanism. MRGPRX2 plays a key role in nonhistamine allergies and neuroimmune mechanisms in chronic inflammatory dermatitis. However, the role of MRGPRX2 in AD and the development of type 2 inflammation is not yet clear. This study aimed to define the role of MRGPRX2 in type 2 inflammation development and cytokine release in AD by determining its levels in patients with AD and healthy controls. Furthermore, MrgprB2-conditional knockout (MrgprB2-/-) and wild-type mice were used to construct an MC903-induced AD mouse model to observe skin inflammation and cytokine release. Tryptase and its antagonist were applied separately to MrgprB2-/- mice with AD and wild-type mice with AD to confirm the role of the MRGPRB2-tryptase axis in the development of type 2 inflammation in AD. We found that AD severity and type 2 cytokine levels were not associated with IgE levels but were associated with MRGPRX2/MRGPRB2 expression. MrgprB2-/- mice with AD showed milder phenotypes and inflammatory infiltration in the skin than wild-type mice with AD. Tryptase released by MRGPRX2/MRGPRB2 activation is involved in the release of type 2 cytokines, which contributes to inflammatory development in AD.

Atopic dermatitis: Role of the skin barrier, environment, microbiome, and therapeutic agents

Atopic dermatitis (AD) is a chronic, inflammatory skin disorder characterized by eczematous and pruritic skin lesions. In recent decades, the prevalence of AD has increased worldwide, most notably in developing countries. The enormous progress in our understanding of the complex composition and functions of the epidermal barrier allows for a deeper appreciation of the active role that the skin barrier plays in the initiation and maintenance of skin inflammation. The epidermis forms a physical, chemical, immunological, neuro-sensory, and microbial barrier between the internal and external environment. Not only lesional, but also non-lesional areas of AD skin display many morphological, biochemical and functional differences compared with healthy skin. Supporting this notion, genetic defects affecting structural proteins of the skin barrier, including filaggrin, contribute to an increased risk of AD. There is evidence to suggest that natural environmental allergens and man-made pollutants are associated with an increased likelihood of developing AD. A compromised epidermal barrier predisposes the skin to increased permeability of these compounds. Numerous topical and systemic therapies for AD are currently available or in development; while anti-inflammatory therapy is central to the treatment of AD, some existing and novel therapies also appear to exert beneficial effects on skin barrier function. Further research on the skin barrier, particularly addressing epidermal differentiation and inflammation, lipid metabolism, and the role of bacterial communities for skin barrier function, will likely expand our understanding of the complex etiology of AD and lead to identification of novel targets and the development of new therapies.

Mast Cells in the Skin: Defenders of Integrity or Offenders in Inflammation?

Mast cells (MCs) are best-known as key effector cells of immediate-type allergic reactions that may even culminate in life-threatening anaphylactic shock syndromes. However, strategically positioned at the host–environment interfaces and equipped with a plethora of receptors, MCs also play an important role in the first-line defense against pathogens. Their main characteristic, the huge amount of preformed proinflammatory mediators embedded in secretory granules, allows for a rapid response and initiation of further immune effector cell recruitment. The same mechanism, however, may account for detrimental overshooting responses. MCs are not only detrimental in MC-driven diseases but also responsible for disease exacerbation in other inflammatory disorders. Focusing on the skin as the largest immune organ, we herein review both beneficial and detrimental functions of skin MCs, from skin barrier integrity via host defense mechanisms to MC-driven inflammatory skin disorders. Moreover, we emphasize the importance of IgE-independent pathways of MC activation and their role in sustained chronic skin inflammation and disease exacerbation.

Jageum-Jung improves 2,4-dinitrochlorobenzene-induced atopic dermatitis-like skin lesions in mice and suppresses pro-inflammatory chemokine production by inhibiting TNF-α/IFN-γ-induced STAT-1 and NFκB signaling in HaCaT cells

ETHNOPHARMACOLOGICAL RELEVANCE

Jageum-Jung (JGJ) is an oriental herbal formula comprising five herbs (Melaphis chinensis Bell, Cremastra variabilis Nakai, Knoxia valerianoides Thorel, Euphorbia lathyris L., and Moschus moschiferus L.). It has been used for detoxification and treating cancer and inflammatory diseases in China, Japan, and Korea. However, the mechanism of action of JGJ on keratinocyte inflammatory response is poorly understood.

AIM OF THE STUDY

In the present study, we investigated the anti-inflammatory mechanism of JGJ and studied the effects of JGJ on atopic dermatitis-like skin lesions in mice.

MATERIALS AND METHODS

We elucidated the anti-inflammatory and anti-inflammatory effects of JGJ on tumor necrosis factor-α/interferon-γ (TNF-α/IFN-γ)-treated human keratinocyte cells, IgE-sensitized RBL-2H3 cells, and 2,4-dinitrochlorobenzene (DNCB)-induced atopic dermatitis (AD)-like mice, respectively.

RESULTS

The results showed that JGJ suppressed the production and mRNA revels of IL-8, IL-6 and, conspicuously, both TARC and RANTES. JGJ inhibited nuclear translocation of the inflammatory transcription factors NFκB and STAT-1. Moreover, JGJ improved AD-like skin lesions in DNCB-treated mice and inhibited degranulation of mast cell.

CONCLUSIONS

The results of this study suggest that JGJ can be considered as a candidate agent for AD treatment.

Signal transduction around thymic stromal lymphopoietin (TSLP) in atopic asthma

Thymic stromal lymphopoietin (TSLP), a novel interleukin-7-like cytokine, triggers dendritic cell-mediated inflammatory responses ultimately executed by T helper cells of the Th2 subtype. TSLP emerged as a central player in the development of allergic symptoms, especially in the airways, and is a prime regulatory cytokine at the interface of virus- or antigen-exposed epithelial cells and dendritic cells (DCs). DCs activated by epithelium-derived TSLP can promote naïve CD4+ T cells to adopt a Th2 phenotype, which in turn recruite eosinophilic and basophilic granulocytes as well as mast cells into the airway mucosa. These different cells secrete inflammatory cytokines and chemokines operative in inducing an allergic inflammation and atopic asthma. TSLP is, thus, involved in the control of both an innate and an adaptive immune response. Since TSLP links contact of allergen with the airway epithelium to the onset and maintainance of the asthmatic syndrome, defining the signal transduction underlying TSLP expression and function is of profound interest for a better understandimg of the disease and for the development of new therapeutics.

Histamine prevents apoptosis in human monocytes

BACKGROUND

As chronic atopic dermatitis (AD) is associated with activation of circulating and infiltrating monocytes, monocytes are considered to play a pivotal role in the establishment of chronic lesions in AD. Histamine is an important mediator of inflammatory and allergic responses. Although new immunomodulatory functions of histamine have recently become apparent, the effect of histamine on the life span of monocytes remains unclear.

OBJECTIVE

In the present study, we investigated the effect of histamine on the life span of human monocytes from normal healthy donors and patients with AD.

METHODS

Monocyte apoptosis was induced by serum deprivation, CD95/Fas ligation, or dexamethasone in the presence of histamine, and measured using annexin V-and propidium iodide-staining. Bcl-2 protein and activated caspase-3 were determined by flow cytometry. We also examined the effect of soluble, histamine-induced factors produced by monocytes on apoptosis. Furthermore, we examined whether monocytic apoptosis is dependent on the cAMP pathway.

RESULTS

Histamine prevented monocytic apoptosis induced by serum deprivation, CD95/Fas ligation, or dexamethasone in a dose- and time-dependent fashion. The inhibitory effects of histamine on monocytic apoptosis were blocked by an H2R antagonist, and mimicked by an H2R agonist. Histamine also up-regulated the expression of Bcl-2 and Mcl-1, and inhibited the activation of caspase-3. The culture supernatants from histamine-treated monocytes inhibited monocytic apoptosis, which was partly reversed by the removal of IL-10. Monocytes cultured with anti-IL-10 mAb and histamine did not exhibit an inhibitory effect on apoptosis. The histamine-induced anti-apoptotic effect was attenuated when monocytes were cultured in the presence of a cAMP inhibitor.

CONCLUSIONS

These results indicate that the H2R signals induced by histamine allow monocytes to prolong their life span and infiltrate to the site of inflammation. This process may contribute to the establishment of chronic allergic disorders, such as AD.

Thymic stromal lymphopoietin is released by human epithelial cells in response to microbes, trauma, or inflammation and potently activates mast cells

Compelling evidence suggests that the epithelial cell-derived cytokine thymic stromal lymphopoietin (TSLP) may initiate asthma or atopic dermatitis through a dendritic cell-mediated T helper (Th)2 response. Here, we describe how TSLP might initiate and aggravate allergic inflammation in the absence of T lymphocytes and immunoglobulin E antibodies via the innate immune system. We show that TSLP, synergistically with interleukin 1 and tumor necrosis factor, stimulates the production of high levels of Th2 cytokines by human mast cells (MCs). We next report that TSLP is released by primary epithelial cells in response to certain microbial products, physical injury, or inflammatory cytokines. Direct epithelial cell-mediated, TSLP-dependent activation of MCs may play a central role in "intrinsic" forms of atopic diseases and explain the aggravating role of infection and scratching in these diseases.

The receptor for erythropoietin is present on cutaneous mast cells

Skin samples from patients with extra-mammary Paget disease, Bowen's disease, atopic dermatitis, psoriasis and non-lesional skin of nevus pigmentosus were immunohistochemically examined with an anti-soluble erythropoietin receptor antibody (anti-sEPOR antibody), and only the dermal mast cells positively stained in all skin samples were examined. These positively stained dermal cells were proved to be mast cells by double staining with anti-sEPOR antibody and either with anti-bikunin antibody or anti-tryptase antibody. Immunoelectron microscopically these EPOR were found in the secretory granules of the dermal mast cells. Further, EPOR in the mast cells may be consisting of only the extracellular domain of erythropoietin receptor molecule as the mast cells were immunohistochemically not reacted with an antibody to the C-terminal peptide of EPOR. Human mast cell line, HMC-1 cells has immunohistochemically the erythropoietin receptor, which was consisting of a 43 kDa major protein and a 20 kDa minor protein in the immunoelectrophoresis. These data may indicate that EPOR in the mast cells may not be the whole molecule, but probably the soluble one of EPOR.

Histamine Induces the Generation of Monocyte-Derived Dendritic Cells that Express CD14 but not CD1a

The local cytokine environment and the presence of stimulatory signals determine whether monocytes acquire dendritic cell or macrophage characteristics and functions. In this study, we examined the effect of histamine, a prototypic mediator of allergic inflammation, on the granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4-driven differentiation of monocytes into monocyte-derived dendritic cells (MoDC), which typically showed CD1a+CD14- phenotype. Monocytes from healthy adult donors were cultured with GM-CSF and IL-4 in the presence or absence of histamine, and the phenotypes and function of these cells were analyzed. Histamine induced the generation of CD1a-CD14+ cells, which exhibited cytological and phenotypical characteristics of dendritic cells (DC), showed enhanced phagocytic activity and cytokine-producing capacity, but demonstrated weak allo-stimulatory capacity compared with CD1a+CD14- MoDC. The inhibitory effects of histamine on CD1a+CD14- MoDC differentiation were antagonized by cimetidine, an H2 receptor antagonist, but not by H1 and H3 receptor blockers, and were mimicked by an H2 receptor agonist. Culture supernatant of histamine-treated monocytes also inhibited CD1a+CD14- MoDC differentiation, which was restored by the removal of IL-10. These results suggest that histamine-driven CD1a-CD14+ DC amplify their antigen-independent inflammatory reaction and may contribute to the exacerbation of allergic diseases.

Prostaglandin E2 enhances neurotrophin-4 production via EP3 receptor in human keratinocytes

Atopic dermatitis is characterized by increased skin innervation. The expression of neurotrophin-4 is enhanced in the epidermal keratinocytes of lesions with atopic dermatitis and may be related to hyperinnervation in these lesions. Prostaglandin E(2) (PGE(2)) levels are increased in lesions with atopic dermatitis; thus, PGE(2) may be involved in the development of this disease. We examined the in vitro effects of PGE(2) on neurotrophin-4 production in human keratinocytes. PGE(2) and EP1/EP3 agonist sulprostone increased neurotrophin-4 secretion and mRNA levels without altering its mRNA stability. Antisense Sp1 oligodeoxynucleotide and Sp1 inhibitor mithramycin A suppressed PGE(2) and sulprostone-induced neurotrophin-4 expression, indicating the requirement for Sp1 for expression. PGE(2) or sulprostone markedly enhanced the phosphorylation, DNA binding, and transcriptional activity of Sp1 and modestly increased Sp1 mRNA and protein levels. PGE(2) or sulprostone induced the membrane translocation of protein kinase Calpha and the phosphorylation of extracellular signal-regulated kinase (ERK). PGE(2)-induced increases in neurotrophin-4 expression, Sp1 transcriptional and DNA-binding activity, Sp1 mRNA and protein levels, and ERK phosphorylation were suppressed by antisense EP3 oligodeoxynucleotide, inhibitors of phosphatidylinositol-specific phospholipase C, conventional protein kinase C, and mitogen-activated protein kinase/ERK kinase 1 (MEK1). These results suggest that PGE(2) enhances neurotrophin-4 production by activating Sp1 via the EP3/phosphatidylinositol-specific phospholipase C/protein kinase Calpha/MEK1/ERK pathway. PGE(2) may promote innervation in skin lesions with atopic dermatitis via the induction of neurotrophin-4.

Prostaglandin E(2) suppresses CCL27 production through EP2 and EP3 receptors in human keratinocytes

BACKGROUND

The chemokine CCL27 attracts skin-homing T cells. CCL27 production by keratinocytes is enhanced in skin lesions from patients with atopic dermatitis or psoriasis vulgaris. It is suggested that prostaglandin E(2) (PGE(2)) regulates skin inflammation.

OBJECTIVE

We examined the in vitro effects of PGE(2) on CCL27 production in human keratinocytes.

METHODS

Keratinocytes were incubated with TNF-alpha in the presence or absence of PGE(2) . CCL27 secretion and mRNA level were analyzed by means of ELISA and RT-PCR, respectively. Nuclear factor kappaB (NF-kappaB)-dependent transcriptional activity was analyzed by using luciferase assays.

RESULTS

TNF-alpha increased CCL27 secretion and mRNA levels in parallel to NF-kappaB activity in keratinocytes. NF-kappaB p50 or p65 antisense oligonucleotides suppressed TNF-alpha-induced CCL27 production, indicating the requirement of NF-kappaB for CCL27 production. PGE(2) , EP2, or EP3 agonists reduced TNF-alpha-induced CCL27 secretion and mRNA levels in parallel to NF-kappaB activity and CCL2, CCL5, CXCL8, and CXCL10 mRNA levels. Either EP3-specific or dual EP1-EP2 antagonist partially blocked the inhibitory effects of PGE(2) on CCL27 production and NF-kappaB activity, and the addition of both completely abrogated the inhibition, whereas EP1 or EP4 antagonists were ineffective. Intracellular Ca(2+) chelator BAPTA/AM or cyclic adenosine monophosphate (cAMP)-dependent protein kinase inhibitor H-89 partially blocked the inhibitory effects of PGE(2) on CCL27 production and NF-kappaB activity, and the addition of both completely abrogated the inhibition. PGE(2) or EP3 agonist increased intracellular Ca(2+) concentrations. PGE(2) or EP2 agonist increased intracellular cAMP concentrations.

CONCLUSION

PGE(2) might suppress CCL27 production by inhibiting NF-kappaB activity through EP2-mediated cAMP and EP3-mediated Ca(2+) signals. PGE 2 might terminate T cell-mediated skin inflammation by inhibiting CCL27 production.

Mast cells and vasculature in atopic dermatitis--potential stimulus of neoangiogenesis

BACKGROUND

Atopic dermatitis skin lesions are characterized by inflammatory changes and epithelial hyperplasia requiring angiogenesis. As mast cells may participate in this process via bidirectional secretion of tissue-damaging enzymes and pro-angiogenic factors, the present study aimed to assess the occurrence and possible function of mast cells in the papillary dermis and in epidermal layers of atopic dermatitis lesions.

METHODS

Semi-thin and serial sections in combination with immunohistochemistry, histochemistry and proliferating cell nuclear antigen (PCNA)-activity assays were used and related to epidermal thickness and targeted gene expression studies.

RESULTS

Mast cells were located in the papillary dermis and migrated through the basal lamina into the epidermis of atopic dermatitis lesions. An increased PCNA-activity in cells of superficial epidermal layers indicated an activation of keratinocytes and stimulation of endothelial growth. Only approximately 30% of the papillary mast cells stained with the tryptase were toluidin-blue-positive, and approximately 80% were chymase positive. A high number of mast cells expressed c-kit. Most papillary and epidermal mast cells were localized close to endothelial cells. Vascular expression of endoglin (CD105) demonstrated neoangiogenic processes. Mast cells stimulation led to the expression of proangiogenic factors. Also, gene expression of tissue-damaging factors such as matrix metalloproteinases was increased.

CONCLUSIONS

These data suggest that in atopic dermatitis, mast cells are abundantly localized close to and within the epidermis where they may stimulate neoangiogenesis. Via the new vessels, inflammatory cells, together with complement components and antibodies, can be transported to the epidermis to aid in the defense against environmental antigens and to maintain chronic inflammation.

Activation of bacterial ceramidase by anionic glycerophospholipids: possible involvement in ceramide hydrolysis on atopic skin by Pseudomonas ceramidase

We have reported previously that the ceramidase from Pseudomonas aeruginosa AN17 isolated from a patient with atopic dermatitis requires detergents for hydrolysis of ceramide (Cer) [Okino, Tani, Imayama and Ito (1998) J. Biol. Chem. 273, 14368--14373]. In the present study, we report that some glycerophospholipids strongly activated the hydrolysis of Cer by Pseudomonas ceramidase in the absence of detergents. Among the glycerophospholipids tested, cardiolipin was most effective in stimulating hydrolysis of Cer followed by phosphatidic acid, phosphatidylethanolamine and phosphatidylglycerol, whereas phosphatidylcholine, lysophosphatidic acid and diacylglycerol were less effective. Interestingly, Staphylococcus aureus-derived lipids, which contain cardiolipin and phosphatidylglycerol as major lipid components, also strongly enhanced the hydrolysis of normal Cer, as well as the human skin-specific omega-hydroxyacyl Cer, by the enzyme in the absence of detergents. It was confirmed that several strains of P. aeruginosa, including AN17, secrete a significant amount of staphylolytic proteases to lyse S. aureus cells, resulting in the release of cardiolipin and phosphatidylglycerol. Since both P. aeruginosa and S. aureus are suspected of being present in microflora of atopic skin, we speculate that S. aureus-derived glycerophospholipids stimulate the hydrolysis of Cer in atopic skin by bacterial ceramidase.

Proteinase-activated receptor-2 in human skin: tissue distribution and activation of keratinocytes by mast cell tryptase

Proteinase-activated receptor-2 (PAR-2) is a G-protein coupled receptor. Tryptic proteases cleave PAR-2 exposing a tethered ligand (SLIGKV), which binds and activates the receptor. Although PAR-2 is highly expressed by cultured keratinocytes and is an inflammatory mediator, its precise localization in the normal and inflamed human skin is unknown, and the proteases that activate PAR-2 in the skin have not been identified. We localized PAR-2 in human skin by immunohistochemistry, examined PAR-2 expression by RT-PCR and RNA blotting, and investigated PAR-2 activation by mast cell tryptase. PAR-2 was localized to keratinocytes, especially in the granular layer, to endothelial cells, hair follicles, myoepithelial cells of sweat glands, and dermal dendritic-like cells. PAR-2 was also highly expressed in keratinocytes and endothelial cells of inflamed skin. PAR-2 mRNA was detected in normal human skin by RT-PCR, and in cultured human keratinocytes and dermal microvascular endothelial cells by Northern hybridization. Trypsin, tryptase and a peptide corresponding to the tethered ligand (SLIGKVNH2) increased [Ca2+]i in keratinocytes, measured using Fura-2/AM. Although tryptase-containing mast cells were sparsely scattered in the normal dermis, they were numerous in the dermis in atopic dermatitis, and in the dermis, dermal-epidermal border, and occasionally within the lower epidermis in psoriasis. Tryptase may activate PAR-2 on keratinocytes and endothelial cells during inflammation.

Ceramidase activity in bacterial skin flora as a possible cause of ceramide deficiency in atopic dermatitis

A marked decrease in the content of ceramide has been reported in the horny layer of the epidermis in atopic dermatitis (AD). This decrease impairs the permeability barrier of the epidermis, resulting in the characteristic dry and easily antigen-permeable skin of AD, since ceramide serves as the major water-holding molecule in the extracellular space of the horny layer. On the other hand, the skin of such patients is frequently colonized by bacteria, most typically by Staphylococcus aureus, possessing genes such as those for sphingomyelinase, which are related to sphingolipid metabolism. We therefore tried to identify a possible correlation between the ceramide content and the bacterial flora obtained from the skin of 25 patients with AD versus that of 24 healthy subjects, using a thin-layer chromatographic assay of the sphingomyelin-associated enzyme activities secreted from the bacteria. The findings of the assay demonstrated that ceramidase, which breaks ceramide down into sphingosine and fatty acid, was secreted significantly more from the bacterial flora obtained from both the lesional and the nonlesional skin of patients with AD than from the skin of healthy subjects; sphingomyelinase, which breaks sphingomyelin down into ceramide and phosphorylcholine, was secreted from the bacterial flora obtained from all types of skin at similar levels for the patients with AD and the healthy controls. The finding that the skin of patients with AD is colonized by ceramidase-secreting bacteria thus suggests that microorganisms are related to the deficiency of ceramide in the horny layer of the epidermis, which increases the hypersensitivity of skin in AD patients by impairing the permeability barrier.

Presence of elevated carcinoembryonic antigen on absorbent disks applied to nipple area of breast carcinoma patients

BACKGROUND

Carcinoembryonic antigen (CEA) is used as a serum marker to detect and monitor the status of various kinds of malignant tumors. To determine whether CEA might be detected in secretions collected topically from around the nipple area, and whether its secretion might differ in a cancerous versus a noncancerous breast, we developed a simple method for collecting and measuring CEA, using a small cellulose membrane disk and an enzyme immunoassay.

METHODS

We measured the amount of CEA excreted from the nipple area of 22 healthy control women and 32 women with unilateral breast carcinoma confirmed histologically. Secretions were collected from the nipple area by affixing a small (20 mm diameter) absorbent disk made of nitrocellulose membrane backed with filter paper to that area for 24 hours. Substances absorbed by the membrane were then subjected to an immunoassay for CEA using anti-CEA antibodies.

RESULTS

In the 22 healthy subjects, a small amount of CEA (0.6 +/- 0.9 units) was secreted from each nipple, which was equally low regardless of the phase of the menstrual cycle. In contrast, 30 of the 32 women with breast carcinoma secreted significantly greater amounts of CEA from the cancerous (16.1 +/- 8.2) than the noncancerous (2.0 +/- 2.2) breast. Such a difference (14.1 +/- 8.0) in CEA excretion was not observed in the healthy controls (0 +/- 0).

CONCLUSIONS

These findings suggest that such disks may provide a simple and noninvasive method of collecting trace molecules, including CEA, in skin secretions around the nipple to evaluate functional disorders of the mammary glands, particularly breast carcinoma. Additional studies are indicated in larger groups of women with various stages of breast carcinoma as well as with benign breast diseases.