Epidermal keratinocytes sense dsRNA via the NLRP3 inflammasome,mediating interleukin (IL)‐1β and IL‐18 release

Skin epidermis, in addition to its barrier function, is able to actively sense harmful pathogens using pattern recognition receptors. In immune cells, the nucleotide‐binding oligomerization domain, leucine‐rich repeat and pyrin domain containing 3 (NLRP3) inflammasome can mediate innate immunity against viral infection via a mechanism involving viral dsRNA recognition. Epidermal keratinocytes express NLRP3 inflammasome, which can sense contact sensitizers and mite allergens, leading to pro‐interleukin (IL)‐1β and pro‐IL‐18 cleavage into their active forms. Skin often faces viral infection. However, it is unknown whether viral dsRNA can be detected by the keratinocyte NLRP3 inflammasome. We transfected polyinosinic:polycytidylic acid (poly I:C), a synthetic viral dsRNA analogue, into cultured primary human keratinocytes at the aid of Lipofectamine 2000, and found that transfected poly I:C activated caspase‐1 and induced caspase‐1‐dependent release of IL‐1β and IL‐18, which were suppressed on transfection with NLRP3 siRNA. The activation of keratinocyte NLRP3 inflammasome by transfected poly I:C was dependent on dsRNA‐induced protein kinase (PKR) activation, and priming with type I interferons upregulated NLRP3 inflammasome activation through promoting PKR activation in poly I:C‐transfected keratinocytes. In conclusion, the NLRP3 inflammasome can act as a sensor of dsRNA in epidermal keratinocytes, which may be important in both skin innate immune defense against viral infection and skin inflammation.     

Heparinoid suppresses Der p‐induced IL‐1β production by inhibiting ERK and p38 MAPK pathways in keratinocytes

Epidermal keratinocytes initiate skin inflammation by activating immune cells. The skin barrier is disrupted in atopic dermatitis (AD) and epidermal keratinocytes can be exposed to environmental stimuli, such as house dust mite (HDM) allergens. We showed previously that HDM allergens activate the NLRP3 inflammasome of keratinocytes, thereby releasing pro‐inflammatory cytokines. Heparinoid is an effective moisturizer for atopic dry skin. However, a recent report showed that heparinoid treatment can improve inflammation of lichen planus. Therefore, we hypothesized that it acts on epidermal keratinocytes not only as a moisturizer, but also as a suppressant of the triggers of skin inflammation. We found that HDM allergen‐induced interleukin (IL)‐1β release from keratinocytes was inhibited significantly by heparinoid pretreatment without affecting cell viability. However, heparinoid did not affect caspase‐1 release, suggesting that heparinoid did not affect HDM allergen‐induced inflammasome activation. Heparinoid treatment not only decreased intracellular levels of pro‐IL‐1β, but also suppressed IL‐1β messenger RNA (mRNA) expression in keratinocytes. Among the intracellular signalling pathways, the activation of extracellular signal‐regulated kinase and p38 pathways, which are required for IL‐1β expression in keratinocytes, was inhibited by heparinoid treatment. The inhibitory effect of heparinoid on IL‐1β mRNA expression was also confirmed with living skin equivalents. Our results demonstrated that heparinoid suppresses the initiation of keratinocyte‐mediated skin inflammation.     

Utilization of matrix‐assisted laser desorption and ionization time‐of‐flight mass spectrometry for identification of infantile seborrheic dermatitis‐causing Malassezia and incidence of culture‐based cutaneous Malassezia microbiota of 1‐month‐old infants

Matrix‐assisted laser desorption and ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) has been utilized for identification of various microorganisms. Malassezia species, including Malassezia restricta, which is associated with seborrheic dermatitis, has been difficult to identify by traditional means. This study was performed to develop a system for identification of Malassezia species with MALDI‐TOF‐MS and to investigate the incidence and variety of cutaneous Malassezia microbiota of 1‐month‐old infants using this technique. A Malassezia species‐specific MALDI‐TOF‐MS database was developed from eight standard strains, and the availability of this system was assessed using 54 clinical strains isolated from the skin of 1‐month‐old infants. Clinical isolates were cultured initially on CHROMagar Malassezia growth medium, and the 28S ribosomal DNA (D1/D2) sequence was analyzed for confirmatory identification. Using this database, we detected and analyzed Malassezia species in 68% and 44% of infants with and without infantile seborrheic dermatitis, respectively. The results of MALDI‐TOF‐MS analysis were consistent with those of rDNA sequencing identification (100% accuracy rate). To our knowledge, this is the first report of a MALDI‐TOF‐MS database for major skin pathogenic Malassezia species. This system is an easy, rapid and reliable method for identification of Malassezia.     

Malassezia‐derived aryl hydrocarbon receptor ligands enhance the CCL20/Th17/soluble CD163 pathogenic axis in extra‐mammary Paget's disease

Malassezia yeast play a role in the pathogenesis of chronic dermatitis, especially in apocrine areas, by polarizing the local immunologic background to a Th2/Th17 state through aryl hydrocarbon receptor (AhR)‐dependent pathways. Extra‐mammary Paget's disease (EMPD) is an adenocarcinoma of apocrine origin, and except for cases associated with Malassezia yeast and their metabolites, the lesions typically develop in areas not exposed to environmental material. The purpose of this study was to investigate (a) the immunomodulatory effects of Malassezia metabolites on normal human keratinocytes (NHKCs), focusing on interleukin (IL)‐17 and related cytokines/chemokines (IL‐23, IL‐36γ, CCL20), (b) the expression of these factors in lesion‐affected skin in EMPD and (c) the activation of tumor‐associated macrophages (TAMs) by these factors. Malassezia metabolites augmented the expression of cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1), CCL20 and IL‐36γ mRNA in NHKCs in vitro. In lesion‐affected skin of patients with EMPD, epidermal keratinocytes expressed CYP1A1 and CCL20. In addition, Paget cells expressed CCL20 and IL‐23. IL‐17–producing cells were distributed adjacent to Paget cells. Compared to healthy donors, patients with EMPD exhibited significantly increased serum levels of soluble (s)CD163, CXCL5, CXCL10 and CCL20. In addition, serum levels of sCD163 decreased significantly following tumor resection. Our study demonstrates a possible mechanism for the development of EMPD involving AhR‐mediated signalling by epidermal keratinocytes and RANKL‐induced recruitment of Th17 cells and TAMs.     

DAMP molecules S100A9 and S100A8 activated by IL‐17A and house‐dust mites are increased in atopic dermatitis

S100A9 and S100A8 are called damage‐associated molecular pattern (DAMP) molecules because of their pro‐inflammatory properties. Few studies have evaluated S100A9 and S100A8 function as DAMP molecules in atopic dermatitis (AD). We investigated how house‐dust mites affect S100A9 and S100A8 expression in Th2 cytokine‐ and Th17 cytokine‐treated keratinocytes, and how secretion of these molecules affects keratinocyte‐derived cytokines. Finally, we evaluated expression of these DAMP molecules in AD patients. S100A9 expression and S100A8 expression were strongly induced in IL‐17A‐ and Dermatophagoides (D.) farinae‐treated keratinocytes, respectively. Furthermore, co‐treatment with D. farinae and IL‐17A strongly increased expression of S100A9 and S100A8 compared with D. farinae‐Th2 cytokine co‐treatment. The IL‐33 mRNA level increased in a dose‐dependent manner in S100A9‐treated keratinocytes, but TSLP expression did not change. S100A8/A9 levels were also higher in the lesional skin and serum of AD patients, and correlated with disease severity. Taken together, S100A9 and S100A8 may be involved in inducing DAMP‐mediated inflammation in AD triggered by IL‐17A and house‐dust mites.     

Time‐dependent progression from the acute to chronic phases in atopic dermatitis induced by epicutaneous allergen stimulation in NC/Nga mice

Atopic dermatitis (AD) is a complicated skin condition influenced by genetic background and environmental factors. In this study, we applied Dermatophagoides farinae body extract (DfE) to the barrier‐disrupted skin of NC/Nga mice twice a week for 8 weeks to identify the clinical and immunological factors in AD progression. Repeated application of the DfE to the skin of NC/Nga mice showed the similar consequences for the natural course of progression in human AD, histologically and immunologically. We confirmed that the AD‐like skin lesions in NC/Nga mice did not last for the whole period of our experiment in spite of repeated topical applications of DfE twice a week. Topical DfE stimulation increased the skin mRNA expressions of Th1‐, Th2‐ and Th17‐related cytokines in the acute phase. The expression patterns of IL‐4 and IL‐13 in splenic T cells and skin lesions were consistent with the time course alterations of clinical features of AD‐like skin symptoms. We also showed that there was a remission phase either just before or right after the chronic phase in this experimental model. Interestingly, splenic T‐cell‐derived IL‐5 expression began to increase in the chronic phase, while skin‐derived IL‐5 mRNA expression increased in the acute phase. In conclusion, our results suggest that we should pay attention to the characteristics of each stage of AD progression and choose a suitable corresponding stage of animal model not only to elucidate the pathogenesis of AD but also to develop and evaluate therapeutic drugs for AD.     

Oral administration of poly‐γ‐glutamic acid prevents the development of atopic dermatitis in NC/Nga mice

Bacillus subtilis‐derived poly‐γ‐glutamic acid (γPGA) has demonstrated adjuvant activity in promoting Th1/Th17 cell differentiation. Here, the NC/Nga (NC) mouse model was used to determine whether γPGA modulates the outcome of atopic dermatitis (AD), which is known to be a Th2‐biased immune disease. We found that oral administration of γPGA dramatically reduced the development of AD in NC mice. Antigen‐presenting cells activated with γPGA produced pro‐inflammatory cytokines, such as IL12/23 and IFNγ, which, in turn, induced the differentiation of Th1 and Th17 cells. Concomitantly, Th2 responses, such as high levels of serum IgE, were dramatically decreased. Furthermore, in vivo γPGA treatment altered several cellular components of allergic reactions, such as mast cells and eosinophils. Taken together, our results strongly demonstrate that in vivo treatment with γPGA at early time points can prevent the development of AD in NC mice and suggest that γPGA may have therapeutic applications for human AD.     

Study of pro‐ and anti‐inflammatory cytokine profile in the patients with parthenium dermatitis

Background: Parthenium dermatitis is a common airborne allergic contact dermatitis induced by exposures to the weed Parthenium hysterophorus. The disease manifests as itchy erythematous papules, papulovesicular and plaque lesions on exposed areas of the body. Objectives: The aim of this study was to show the alterations in pro/anti‐inflammatory cytokines in parthenium dermatitis. Methods: The study included 50 patients with parthenium dermatitis confirmed by patch testing using aqueous extracts of P. hysterophorus and 50 age‐matched healthy controls. The levels of pro‐inflammatory [tumour necrosis factor‐α (TNF‐α), interleukin (IL)‐6, IL‐8, and IL‐17] and anti‐inflammatory (IL‐4 and IL‐10) cytokines were estimated by commercially available high sensitivity enzyme‐linked immunosorbent assay (ELISA) kits. Results: All the dermatitis patients showed significantly (P < 0.001) elevated levels of TNF‐α, IL‐6, IL‐8, and IL‐17 levels as compared to healthy controls. In contrast, the anti‐inflammatory cytokine IL‐4 showed an insignificant decrease (P < 0.217) and a decrease in level of IL‐10 was statistically significant (0.001) compared with controls. Conclusions: The present study suggests the involvement of pro‐inflammatory cytokines in the pathogenesis of parthenium dermatitis. A decrease in levels of anti‐inflammatory cytokines was demonstrated, which could not downregulate pro‐inflammatory cytokines in parthenium dermatitis.     

Microorganisms inhabiting follicular contents of facial acne are not only Propionibacterium but also Malassezia spp.

To clarify the relationship between major cutaneous microorganisms (Propionibacterium, Staphylococcus and Malassezia spp.) and acne vulgaris (acne), we examined the microbiota quantitatively in the follicular contents of inflammatory acne and on the facial skin of patients with acne. Fifteen Japanese untreated acne outpatients were studied. The follicular contents from inflammatory acne lesions of the face were collected using a comedo extractor. The skin surface samples were obtained by the swab method from 10 cm² of facial skin. The microbiota was analyzed using polymerase chain reaction. The microbiota in follicular contents was similar to that on the skin surface, namely, there were large populations of Propionibacterium spp., Staphylococcus spp. and Malassezia spp. Moreover, the number of Malassezia spp. on the skin surface was correlated with that of inflammatory acne and that in follicular contents. This study clarified that there are large populations of Propionibacterium spp., Staphylococcus spp. and Malassezia spp. in follicular contents. These results suggest the possibility that not only Propionibacterium acnes but also other cutaneous resident microorganisms are related to acne. Particularly, we considered that Malassezia spp. is closely related.     

Tinea versicolor in dark‐skinned individuals

In this article, we review the salient features of tinea versicolor and describe the epidemiology, clinical presentation, and histopathology of this mycosis in dark‐skinned individuals. Tinea versicolor is caused by an overgrowth of the Malassezia genus. It manifests clinically as asymptomatic hypopigmented macules, hyperpigmented macules, or a combination of the two. Under light microscopy, Malassezia presents as a dimorphic fungus – in both the hyphal and yeast form. Most clinicians have found that the majority of dark‐skinned patients present solely with hypopigmented lesions. Under light microscopy, lesions on dark skin involved with tinea versicolor tend to have a thicker stratum corneum, more tonofilaments in the granulosum, and more sequestered melanosomes. Differential diagnosis includes confluent and reticulated papillomatosis, seborrheic dermatitis, pityriasis rosea, pityriasis alba, and vitiligo. Tinea versicolor can be successfully managed in most cases with topical antifungal treatments. Cases of recurrence, such as those seen in immunocompromised patients, may necessitate scheduled oral or topical therapy.     

Allergic contact dermatitis beyond IL‐1β role of additional family members

Contact dermatitis is one of the most frequent pathological manifestations of the skin and plays a central role in clinical dermatology. The IL‐1 family consists a large group of cytokines, which currently contains 11 members with different pro‐ and anti‐inflammatory properties. Among the more pro‐inflammatory‐acting cytokines from the IL‐1 family, IL‐1β, IL‐18, IL‐33 and IL‐36 have been shown to be upregulated in different inflammatory mouse experimental models or skin diseases. The article by Mattii et al. represents a thorough analysis of the expression of IL‐1 family members including IL‐33 in skin samples from patients with allergic contact dermatitis. Although a lot of research is performed in this area, data from human samples are rather scarce. Therefore, Mattii et al. support the development of novel therapeutic concepts, which might include the use of antagonistic molecules targeting the IL‐1 family network.     

Staphylococcal α‐toxin induces a functional upregulation of TLR‐2 on human peripheral blood monocytes

Resistance to bacterial skin infections, for example with Staphylococcus aureus (S. aureus), is based on the function of intact innate immune mechanisms. Toll‐like receptor (TLR)‐2 recognizes components of S. aureus and is known to be expressed on monocytes. Staphylococcal exotoxins such as staphylococcal enterotoxin B (SEB) or α‐toxin are produced by many S. aureus strains. To investigate TLR‐2 regulation and function on human monocytes upon stimulation with staphylococcal exotoxins to elucidate a putative feedback loop between different staphylococcal components. Monocytes were stimulated with α‐toxin or SEB, respectively. TLR‐2 expression and regulation as well as functional effects of TLR‐2 stimulation with Pam3Cys (TLR‐2/TLR‐1), lipoteichoic acid (LTA) (TLR‐2/TLR‐6) and peptidoglycan (PGN) (TLR‐2 and Nod) were then investigated both at the mRNA and protein level and compared to monocytes from patients with psoriasis. α‐toxin significantly upregulated TLR‐2 expression. TLR‐2 mediated IL‐1β, IL‐6 and IL‐8 secretion was significantly augmented after upregulation with staphylococcal exotoxins. CD36 expression was significantly more downregulated after TLR‐2 upregulation with SEB and consecutive LTA stimulation and TLR‐2 upregulation with α‐toxin following LTA and PGN stimulation, respectively. PGN enhanced CD54 expression after upregulation of the receptor with α‐toxin. Expression of HLA‐DR was unaffected. However, no differences were observed in monocytes from psoriasis patients compared to healthy controls. Together, our findings provide a new link between staphylococcal α‐toxin and TLR‐2 signalling in monocytes which may have implications for skin diseases where skin colonization with S. aureus and dysregulation of TLR‐2 have been described.     

CD4+ T cells producing interleukin (IL)‐17, IL‐22 and interferon‐γ are major effector T cells in nickel allergy

Background It has been suggested that interleukin (IL)‐17 and IL‐22 play important roles in the elicitation of human allergic contact dermatitis; however, the frequencies of T cell subtypes producing IL‐17 and IL‐22 in human allergic contact dermatitis are unknown. Objectives To determine the frequencies of CD4⁺, CD8⁺ and γδ T cells producing IL‐17, IL‐22 and interferon (IFN)‐γ in the blood and skin from nickel‐allergic patients. Patients/materials/methods Blood samples were collected from 14 patients and 17 controls, and analysed by flow cytometry. Biopsies were taken from 5 patients and 6 controls, and analysed by immunohistochemistry and flow cytometry of skin lymphocytes. Results We found an increased frequency of γδ T cells in the blood, but no differences in the distribution of cytokine‐producing CLA⁺ T cell subtypes in nickel‐allergic patients as compared with controls. In nickel‐allergic patients, there was massive cellular infiltration dominated by CD4⁺ T cells producing IL‐17, IL‐22 and IFN‐γ in nickel‐challenged skin but not in vehicle‐challenged skin. Conclusion CD4⁺ T cells producing IL‐17, IL‐22 and IFN‐γ are important effector cells in the eczematous reactions of nickel‐induced allergic contact dermatitis in humans.     

NADPH oxidase‐2 is a key regulator of human dermal fibroblasts: a potential therapeutic strategy for the treatment of skin fibrosis

The proliferation of human skin dermal fibroblasts (HDFs) is a critical step in skin fibrosis, and transforming growth factor‐beta1 (TGF‐β1) exerts pro‐oxidant and fibrogenic effects on HDFs. In addition, the oxidative stress system has been implicated in the pathogenesis of skin disease. However, the role of NADPH oxidase as a mediator of TGF‐β1‐induced effects in HDFs remains unknown. Thus, our aim was to investigate the role of NADPH in human skin dermal fibroblasts. Primary fibroblasts were cultured and pretreated with various stimulants. Real‐time Q‐PCR and Western blotting analyses were used for mRNA and protein detection. In addition, siRNA technology was applied for gene knock‐down analysis. Hydrogen peroxide production and 2′,7′‐dichlorofluorescein diacetate (DCFDA) measurement assay were performed. Here, our findings demonstrated that HDFs express key components of non‐phagocytic NADPH oxidase mRNA. TGF‐β1 induced NOX2 and reactive oxygen species formation via NADPH oxidase activity. In contrast, NOX3 was barely detectable, and other NOXs did not display significant changes. In addition, TGF‐β1 phosphorylated MAPKs and increased activator protein‐1 (AP‐1) in a redox‐sensitive manner, and NOX2 suppression inhibited baseline and TGF‐β1‐mediated stimulation of Smad2 phosphorylation. Moreover, TGF‐β1 stimulated cell proliferation, migration, collagen I and fibronectin expression, and bFGF and PAI‐1 secretion: these effects were attenuated by diphenylene iodonium (DPI), an NADPH oxidase inhibitor, and NOX2 siRNA. Importantly, NOX2 siRNA suppresses collagen production in primary keloid dermal fibroblasts. These findings provide the proof of concept for NADPH oxidase as a potential target for the treatment of skin fibrosis.     

Interleukin‐1 from epithelial cells fosters T cell‐dependent skin inflammation

Background Chronic inflammatory skin diseases such as atopic dermatitis and psoriasis are characterized by the infiltration of lymphocytes into the epidermal compartment. Several studies point to an active role of skin epithelial cells in the pathophysiology of such diseases. Objectives In this study we addressed the regulatory function of primary human keratinocytes in the interaction with autologous T cells and monocytes. Methods We used a human coculture model with keratinocytes grown from epidermal stem cells of the outer root sheath of human hair follicles and autologous T cells. Results In our coculture system we observed a high production of interferon (IFN)‐γ, but not Th2 cytokines, in the presence of superantigen or antigen‐pulsed autologous monocytes. Critical parameters for this effect were: (i) T‐cell receptor activation, (ii) an intercellular adhesion molecule‐1/lymphocyte function‐associated antigen (LFA)‐1‐dependent interaction between keratinocytes and T cells, and (iii) secretion of interleukin (IL)‐1β. Remarkably, in the presence of activated T cells, epithelial cells seemed to be a more significant source of IL‐1β than monocytes. Application of the LFA‐1 blocker efalizumab or IL‐1 receptor antagonist anakinra enabled us to suppress completely the production of IFN‐γ by T cells in the coculture. Conclusions IL‐1 secretion and the physical contact between keratinocytes and activated, infiltrating T cells may be central for the development of chronic inflammatory skin conditions.     

Phospholipase activity after β‐endorphin exposure discriminates Malassezia strains isolated from healthy and seborrhoeic dermatitis skin

Background Phospholipase activity and its induction by β‐endorphin have been associated with pathogenic Malassezia pachydermatis animal isolates. Objective To evaluate Malassezia phosholipase activity in human isolates from seborrhoeic dermatitis (SD) and healthy controls before and after β‐endorphin exposure. Methods Eighty‐four volunteers with or without SD (N = 41) were sampled. Isolated Malassezia strains were incubated in Dixon’s medium with and without 100 nmol/L β‐endorphin. Subsequently, phospholipase activity was assessed in egg‐yolk agar and the results were compared employing Wilcoxon sign test for paired data, chi‐squared test and multinomial logistic regression analysis. Results A total of 64 Malassezia strains were isolated. SD strains tended to have decreased phospholipase activity before (P = 0.057) and increased after exposure to β‐endorphin (P = 0.061) compared to isolates from healthy skin. Phospholipase activity after β‐endorphin exposure related to basal enzyme activity as a measure of per strain phospholipase inducibility by β‐endorphin did not depend on Malassezia species (P = 0.652). However, this latter biochemical trait discriminates strains isolated from SD lesional and healthy skin (P = 0.036). Conclusion β‐endorphin exposure modifies the in vitro phosholipase activity in Malassezia species isolated from SD lesional skin. This is in accordance with emerging evidence that enhanced local lipase activity is involved in the pathogenesis of SD.     

Modulation of HMGB1 translocation and RAGE/NFκB cascade by quercetin treatment mitigates atopic dermatitis in NC/Nga transgenic mice

Quercetin, glycosylated form of flavonoid compound, has potent antioxidant and anti‐inflammatory properties. In this study, we have investigated the effects of quercetin on skin lesion, high‐mobility group box (HMGB)1 cascade signalling and inflammation in atopic dermatitis (AD) mouse model. AD‐like lesion was induced by the application of house dust mite extract to the dorsal skin of NC/Nga transgenic mouse. After AD induction, quercetin (50 mg/kg, p.o) was administered daily for 2 weeks. We evaluated dermatitis severity, histopathological changes and changes in protein expression by Western blotting for HMGB1, receptor for advanced glycation end products (RAGE), toll‐like receptor (TLR)4, nuclear factor (NF)κB, nuclear factor erythroid‐2‐related factor (Nrf)2, kelch‐like ECH‐associated protein (Keap)1, extracellular signal‐regulated kinase (ERK)1/2, cyclooxygenase (COX)2, tumor necrosis factor (TNF)α, interleukin (IL)‐1β, IL‐2Rα and other inflammatory markers in the skin of AD mice. In addition, serum levels of T helper (Th) cytokines (interferon (IFN)γ, IL‐4) were measured by enzyme‐linked immunosorbent assay. Quercetin treatment attenuated the development of AD‐like skin lesions. Histological analysis showed that quercetin inhibited hyperkeratosis, parakeratosis, acanthosis, mast cells and infiltration of inflammatory cells. Furthermore, quercetin treatment downregulated cytoplasmic HMGB1, RAGE, nuclear p‐NFκB, p‐ERK1/2, COX2, TNFα, IL‐1β, IL‐2Rα, IFNγ and IL‐4 and upregulated nuclear Nrf2. Our data demonstrated that the HMGB1/RAGE/NFκB signalling might play an important role in skin inflammation, and quercetin treatment could be a promising agent for AD by modulating the HMGB1/RAGE/NFκB signalling and induction of Nrf2 protein.     

Impaired T‐cell‐dependent protection against Leishmania major infection in HIV‐positive patients is associated with worsened disease outcome

Cutaneous leishmaniasis (CL) patients coinfected with HIV are known to show a more severe, prolonged course of disease; the immunological basis is not known. We now assessed clinical features, sera and skin biopsies of HIV⁺ and HIV^? patients with CL to identify drivers of increased susceptibility to Leishmania. CL lesion numbers, surface, and healing duration were significantly increased in HIV⁺ as compared to HIV^? patients (2.5, 14 and >4‐fold, respectively). Patients with HIV infection exhibited lower serum Leishmania‐specific IgG levels and decreased IL‐6 and IL‐8. Most importantly, dramatically decreased numbers of CD4⁺ T cells (approximately eightfold), but not CD8⁺ cells, together with fewer CXCR3⁺ Th1 cells, fewer Foxp3⁺ effector/regulatory T cells, and reduced levels of IFN‐γ expression were found in lesional skin. Our findings suggest that compromised CD4⁺ T‐cell responses may be responsible for worsened disease outcome leading to defects in parasite elimination in the absence of sufficient numbers of IFN‐γ‐producing Th1 cells.     

Histamine suppresses regulatory T cells mediated by TGF‐β in murine chronic allergic contact dermatitis

Regulatory T cells (Tregs) suppress effector T cells and ameliorate contact hypersensitivity (CH); however, the role of Tregs in chronic allergic contact dermatitis (CACD) has not been assessed. Repeated elicitation of CH has been used to produce CACD models in mice. We previously showed that the presence of histamine facilitates the creation of eczematous lesions in this model using histidine decarboxylase (HDC) (?/?) mice. Therefore, the effects of histamine on Tregs in the CACD model were investigated in this study. CACD was developed by repeated epicutaneous application of 2, 4, 6‐trinitro‐1‐chlorobenzene (TNCB) on HDC (+/+) and HDC (?/?) murine skin to assess the effects of histamine in CACD. Histamine aggravated CACD in the murine model and suppressed the number of Tregs in the skin. Histamine also suppressed the level of TGF‐β1 in this model. Recombinant TGF‐β1 or anti‐TGF‐β1 antibody was injected into the dorsal dermis of HDC (+/+) mice daily just before TNCB challenge to determine the effects of histamine‐regulated TGF‐β on the Treg population in CACD. Recombinant TGF‐β1 injection promoted the infiltration of Tregs in the skin and the production of IL‐10; however, anti‐TGF‐β1 antibody injection suppressed the number of Tregs in the skin and the production of IL‐10. Histamine suppresses the number of Tregs in CACD, and this effect is mediated by TGF‐β.