Exacerbation of allergen-induced eczema in TLR4- and TRIF-deficient mice

Toll-like receptors in atopic dermatitis: pathogenesis and therapeutic implications

Toll-like receptors (TLR), the key players of the innate immune system, contribute to the pathogenesis of atopic dermatitis (AD) through multiple pathways. TLRs play a crucial role in delaying barrier repair, promoting Th2-mediated dermatitis, shifting the response toward Th1 in the chronic phase, and contributing to the establishment of the itch-scratch cycle, as well as mediating the effects of UV radiation. The dysregulation of proinflammatory and immunomodulatory effects of TLRs can be attributed to their ligand structures, receptor heterodimerization, the relative frequency of each TLR, interactions with other receptors/signalling pathways, cytokine milieu, and genetic polymorphisms. Current AD treatments like vitamin-D analogs, tacrolimus, and cyclosporine partially work through TLR modulation. Direct TLR stimulation using different compounds has shown therapeutic benefits in preclinical studies. However, significant challenges exist, including off-target effects due to ubiquitous TLR expression and complex roles in immune responses. Future directions include CRISPR-based gene editing to understand TLR functions, development of specific TLR modulators for targeted therapy, and machine learning applications to predict drug responses and identify novel ligands. Patient heterogeneity, including the presence or absence of polymorphisms, variations in TLR expression levels, and differences in immune responses, underscores the need for personalized therapeutic approaches.

Arctiin Alleviates Atopic Dermatitis Against Inflammation and Pyroptosis Through Suppressing TLR4/MyD88/NF-κB and NLRP3/Caspase-1/GSDMD Signaling Pathways

Purpose

Atopic dermatitis (AD) is a prevalent skin condition worldwide. The immune response plays a crucial role in the pathogenesis of AD. Arctiin (ARC), a natural lignan, has been extensively investigated because of its anti-inflammatory, antioxidant, and anticancer properties. However, the impact of ARC on AD remains uncertain. Therefore, this study investigated the therapeutic effects of ARC in AD.

Methods

AD-like lesions were induced in mice by applying 2,4-dinitrochlorobenzene (DNCB). The efficacy of ARC in AD was assessed by measuring skin lesion scores and thickness, pathological observation, and serum IgE concentrations. The expression of relevant proteins and genes in the back skin of the mice was assessed. Moreover, the TLR4/MyD88/NF-κB and NLRP3/Caspase-1/GSDMD signaling pathways were assessed in HaCaT cells stimulated with TNF-α and IFN-γ.

Results

ARC effectively alleviated AD-like dermatitis induced by DNCB in mice, reducing the skin thickness, mast cell infiltration in skin tissue, and serum total IgE levels. In addition, the expression of IL-1β and the mRNA transcription of TSLP and IFN-γ were downregulated. ARC also suppressed the TLR4/MyD88/NF-κB pathway, and molecular docking confirmed that ARC had exceptional binding properties with TLR4. Moreover, ARC ameliorated pyroptosis by inhibiting the activation of the nod-like receptor protein-3/Caspase-1/GSDMD cascade.

Conclusion

ARC has remarkable anti-AD effects by inhibiting inflammation and pyroptosis through the TLR4/MyD88/NF-κB and NLRP3/Caspase-1/GSDMD signaling pathways. This suggests that ARC has potential as a new drug candidate for treating AD, which provides a novel approach to the clinical management of AD.

Application of lipopolysaccharide in establishing inflammatory models

Lipopolysaccharide (LPS), a unique component of the outer membrane of Gram-negative bacteria, possesses immune-activating properties. It induces an immune response by stimulating host cells to produce a lot of inflammatory cytokines with a thermogenic effect, which may cause an inflammatory response. In the past few decades, the structure and function of LPS and its mechanism leading to inflammation have been extensively analyzed. Since LPS can cause inflammation, it is often used to establish inflammation models. These models are crucial in the study of inflammatory diseases that pose a serious threat to human health. In addition, the non-pro-inflammatory effects of LPS under certain circumstances are also being studied widely. This review summarizes the methods by which LPS has been used to establish inflammatory models at the cellular and animal levels to study related diseases. It also introduces in detail the evaluation indicators necessary for the successful establishment of these models, providing a reference for future research.

Utility of In Vitro Cellular Models of Low-Dose Lipopolysaccharide in Elucidating the Mechanisms of Anti-Inflammatory and Wound-Healing-Promoting Effects of Lipopolysaccharide Administration In Vivo

Lipopolysaccharide (LPS) is a bacterial component that activates intracellular signaling pathways upon binding to the Toll-like receptor (TLR)-4/MD-2 complex. It is well known that LPS injected into animals and high-dose (100 ng/mL to 1 μg/mL) LPS treatment to innate immune cells induce an inflammatory response. In contrast, LPS is naturally present in the gastrointestinal tract, respiratory tract, and skin of humans and animals, and it has been shown that TLR-4-deficient animals cannot maintain their immune balance and gut homeostasis. LPS from commensal bacteria can help maintain homeostasis against mucosal stimulation in healthy individuals. Oral LPS administration has been shown to be effective in preventing allergic and lifestyle-related diseases. However, this effect was not observed after treatment with LPS at high doses. In mice, oral LPS administration resulted in the detection of LPS at a low concentration in the peritoneal fluid. Therefore, LPS administered at low and high doses have different effects. Moreover, the results of in vitro experiments using low-dose LPS may reflect the effects of oral LPS administration. This review summarizes the utility of in vitro models using cells stimulated with LPS at low concentrations (50 pg/mL to 50 ng/mL) in elucidating the mechanisms of oral LPS administration. Low-dose LPS administration has been demonstrated to suppress the upregulation of proinflammatory cytokines and promote wound healing, suggesting that LPS is a potential agent that can be used for the treatment and prevention of lifestyle-related diseases.

Thymic stromal lymphopoietin rather than IL-33 drives food allergy after epicutaneous sensitization to food allergen

BACKGROUND

A major route of sensitization to food allergen is through an impaired skin barrier. IL-33 and thymic stromal lymphopoietin (TSLP) have both been implicated in epicutaneous sensitization and food allergy, albeit in different murine models.

OBJECTIVE

We assessed the respective contributions of TSLP and IL-33 to the development of atopic dermatitis (AD) and subsequent food allergy in TSLP and IL-33 receptor (ST2)-deficient mice using an AD model that does not require tape stripping.

METHOD

TSLP receptor (TSLPR)-/-, ST2-/-, and BALB/cJ control mice were exposed to 3 weekly epicutaneous skin patches of one of saline, ovalbumin (OVA), or a combination of OVA and Aspergillus fumigatus (ASP), followed by repeated intragastric OVA challenges and development of food allergy.

RESULTS

ASP and/or OVA patched, but not OVA-alone patched, BALB/cJ mice developed an AD-like skin phenotype. However, epicutaneous OVA sensitization occurred in OVA patched mice and was decreased in ST2-/- mice, resulting in lower intestinal mast cell degranulation and accumulation, as well as OVA-induced diarrhea occurrences on intragastric OVA challenges. In TSLPR-/- mice, intestinal mast cell accumulation was abrogated, and no diarrhea was observed. AD was significantly milder in OVA + ASP patched TSLPR-/- mice compared to wild type and ST2-/- mice. Accordingly, intestinal mast cell accumulation and degranulation were impaired in OVA + ASP patched TSLPR-/- mice compared to wild type and ST2-/- mice, protecting TSLPR-/- mice from developing allergic diarrhea.

CONCLUSION

Epicutaneous sensitization to food allergen and development of food allergy can occur without skin inflammation and is partly mediated by TSLP, suggesting that prophylactic targeting of TSLP may be useful in mitigating the development of AD and food allergy early in life in at-risk infants.

Pathogenic Mechanism of Der p 38 as a Novel Allergen Homologous to RipA and RipB Proteins in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic relapsing pruritic disease encompassing skin inflammation and barrier dysfunction. House dust mites are key allergens that augment the development of atopic dermatitis. We aimed to investigate the pathogenic mechanism of AD due to Der p 38, recently identified by us. The frequency of IgE reactivity to Der p 38 in AD subjects was 52.6% (10/19) in the skin prick test and 57.9% (11/19) in the dot blot assay. In human keratinocyte HaCaT cells, Der p 38 triggered the impairment of filaggrin expression and induced pro-inflammatory cytokines such as IL-6, IL-8 and MCP-1 through TLR4, PI3K, AKT, c-Jun N-terminal kinase (JNK) and NF-κB pathway. Supernatants from Der p 38-treated cells blocked filaggrin expression and neutrophil apoptosis. The anti-apoptotic effect of the Der p 38-released molecules on neutrophils was accomplished by inhibition of the caspase 9/3 pathway, and by increased MCL-1 expression and BCL-2/BAX expression ratio. In C57BL/6 wild type (WT) mice, Der p 38 induced a dose-dependent increase of AD-like skin lesions, with enhanced expressions of total and Der p 38-specific IgE. Der p 38 also diminished the expressions of skin barrier proteins and induced JNK activation. However, the AD-like features following cutaneous Der p 38 exposure were observed to be reduced in the TLR4 knockout (KO) group, as compared to the WT group. Skin infiltration of neutrophils, eosinophils and mast cells was increased in the WT mice, but was not portrayed in the TLR4 KO mice. These findings indicate that Der p 38 is a novel mite allergen that triggers AD by lowering skin barrier proteins and increasing inflammatory cells. Results of this study have thereby paved the way to unveil the pathogenic mechanisms of AD.

Disease-associated KIF3A variants alter gene methylation and expression impacting skin barrier and atopic dermatitis risk

Single nucleotide polymorphisms (SNPs) in the gene encoding kinesin family member 3A, KIF3A, have been associated with atopic dermatitis (AD), a chronic inflammatory skin disorder. We find that KIF3A SNP rs11740584 and rs2299007 risk alleles create cytosine-phosphate-guanine sites, which are highly methylated and result in lower KIF3A expression, and this methylation is associated with increased transepidermal water loss (TEWL) in risk allele carriers. Kif3a^K14∆/∆ mice have increased TEWL, disrupted junctional proteins, and increased susceptibility to develop AD. Thus, KIF3A is required for skin barrier homeostasis whereby decreased KIF3A skin expression causes disrupted skin barrier function and promotes development of AD.

Genetic variants in KIF3A are associated with atopic dermatitis (AD). Here, the authors identify two AD-risk alleles that show high methylation resulting in lower KIF3A expression. Mice with epidermis-specific loss of Kif3a show disrupted skin barrier homeostasis and increased AD susceptibility.

TLR4-directed Molecular Strategies Targeting Skin Photodamage and Carcinogenesis

Background:

Exposure to solar ultraviolet (UV) radiation is a causative factor in skin photodamage and carcinogenesis, and inflammatory dysregulation is a key mechanism underlying detrimental effects of acute and chronic UV exposure. The health and economic burden of skin cancer treatment is substantial, creating an increasingly urgent need for the development of improved molecular strategies for photoprotection and photochemoprevention.

Methods:

A structured search of bibliographic databases for peer-reviewed research literature revealed 139 articles including our own that are presented and critically evaluated in this TLR4-directed review.

Objective:

To understand the molecular role of Toll-like receptor 4 (TLR4) as a key regulator of skin anti-microbial defense, wound healing, and cutaneous tumorigenic inflammation. The specific focus of this review is on recent published evidence suggesting that TLR4 represents a novel molecular target for skin photoprotection and cancer photochemoprevention.

Results:

Cumulative experimental evidence indicates that pharmacological and genetic antagonism of TLR4 suppresses UV-induced inflammatory signaling involving the attenuation of cutaneous NF-κB and AP-1 stress signaling observable in vitro and in vivo. TLR4-directed small molecule pharmacological antagonists [including eritoran, (+)-naloxone, ST2825, and resatorvid] have now been identified as a novel class of molecular therapeutics. TLR4 antagonists are in various stages of preclinical and clinical development for the modulation of dysregulated TLR4-dependent inflammatory signaling that may also contribute to skin photodamage and photocarcinogenesis in human populations.

Conclusion:

Future research should explore the skin photoprotective and photochemopreventive efficacy of topical TLR4 antagonism if employed in conjunction with other molecular strategies including sunscreens.

[Endosomal control of intracellular signaling]

Membrane receptors control essential processes such as cell growth, adhesion, differentiation and metabolism through the activation of specific signaling pathways. Nowadays, these receptors are not only known to signal from the plasma membrane but also from intracellular compartments. Indeed, after being internalized with their ligands via different endocytic pathways, some membrane receptors can initiate signal only after reaching the sorting endosome where they associate with specific protein partners. This review illustrates how this spatio-temporal regulation of signal transduction can occur, with several examples, including interferon receptors which activate JAK/STAT signaling pathways. The literature presented here explains why this control of signaling pathways occuring at the endosomal level creates a higher degree of tuning for the affected cellular processes.

Clinical efficacy of sublingual immunotherapy is associated with restoration of steady-state serum lipocalin 2 after SLIT: a pilot study

Background

So far, only a few biomarkers in allergen immunotherapy exist that are associated with a clinical benefit. We thus investigated in a pilot study whether innate molecules such as the molecule lipocalin-2 (LCN2), with implications in immune tolerance demonstrated in other fields, may discriminate A) between allergic and non-allergic individuals, and B) between patients clinically responding or non-responding to sublingual allergen immunotherapy (SLIT) with house dust mite (HDM) extract. Moreover, we assessed haematological changes potentially correlating with allergic symptoms.

Methods

LCN2-concentrations were assessed in sera of healthy and allergic subjects (n = 126) as well as of house dust mite (HDM) allergics before and during HDM- sublingual immunotherapy (SLIT) in a randomized, double-blind, placebo-controlled trial for 24 weeks. Sera pre-SLIT (week 0), post-SLIT (week 24) and 9 months after SLIT were assessed for LCN2 levels and correlated with total nasal symptom scores (TNSS) obtained during chamber challenge at week 24 in patients receiving HDM- (n = 31) or placebo-SLIT (n = 10).

Results

Allergic individuals had significantly (p < 0.0001) lower LCN2-levels than healthy controls. HDM-allergic patients who received HDM-SLIT showed a significant increase in LCN2 9 months after termination of HDM-SLIT (p < 0.001), whereas in subjects receiving placebo no increase in LCN2 was observed. Among blood parameters a lower absolute rise in the lymphocyte population (p < 0.05) negatively correlated with symptom improvement (Pearson r 0.3395), and a lower relative increase in the neutrophils were associated with improvement in TNSS (p < 0.05). LCN2 levels 9 months after immunotherapy showed a low positive correlation with the relative improvement of symptoms (Pearson r 0.3293). LCN2-levels 9 months off-SLIT were significantly higher in patients whose symptoms improved during chamber challenge than in those whose symptoms aggravated (p < 0.01).

Conclusion

Serum LCN2 concentrations 9 months off-SLIT correlated with clinical reactivity in allergic patients. An increase in the LCN2 levels 9 months after HDM-SLIT was associated with a clinical benefit. Serum LCN2 may thus contribute to assess clinical reactivity in allergic patients.

Trial registration

Part of the data were generated from clinicaltrials.gov Identifier NCT01644617.

Hematopoietic reconstitution of neonatal immunocompetent mice to study conditions with a perinatal window of susceptibility

Efficient hematopoietic reconstitution of wild type mice requires preconditioning. Established experimental protocols exist to transplant hematopoietic stem cells into lethally irradiated or chemically myeloablated adult mice or unirradiated immunodeficient mice. We sought to develop a protocol to reconstitute immuno-replete neonatal mice. We describe irradiation and injection procedures for two-day old mice that lead to efficient long-term reconstitution of primary and secondary lymphoid organs. We demonstrate that the frequencies of lymphoid and myeloid cells in primary and secondary lymphoid organs are indistinguishable from unirradiated uninjected sex- and age-matched control animals by 5 weeks post-reconstitution. Thus, this system will facilitate studies aimed at understanding the developmental and environmental mechanisms that contribute to conditions that have a window of susceptibility during the perinatal period.

Toll-like receptor 4 attenuates a murine model of atopic dermatitis through inhibition of langerin-positive DCs migration

Atopic dermatitis (AD) is a common chronic inflammatory skin disease that is often associated with skin barrier dysfunction leading to a higher frequency of bacterial and viral skin infections. Toll-like receptor (TLR) 4 on resident skin cells was involved in sensing pathogens and eliciting pathogen-specific innate and adaptive immune responses. Previous studies have demonstrated that TLR4 was linked to AD severity in context of pathogen infection. However, the immune regulatory role of TLR4 in AD remains to be defined. We here investigated the immune regulatory function of TLR4 in AD induced by repeated epicutaneous application of a hapten, 2,4-dinitrochlorobenzene (DNCB). Our results showed that TLR4-deficient (TLR4^-/- ) mice exhibited more severe AD symptoms than WT mice after DNCB challenge. The DNCB-treated TLR4^-/- mice also displayed higher expression levels of inflammatory cytokines and stronger Th2 response than WT counterparts. Moreover, the skin expression of thymic stromal lymphopoietin (TSLP), an important potential contributor to allergic inflammation, was significantly elevated in TLR4^-/- mice compared with that in WT mice upon DNCB administration. Furthermore, we demonstrated that the migration of langerin-positive dendritic cells (DCs) into draining lymph nodes was enhanced in TLR4^-/- mice following DNCB challenge, which is partially dependent on the production of pro-inflammatory cytokine TNF-α. Together, these results determined that TLR4 affected the hapten-induced skin inflammation in the absence of exogenous pathogen infection, suggesting that TLR4 not only regulates infection but also may serve as a modulator of the immune response during AD development.

A novel mouse model of atopic dermatitis that is T helper 2 (Th2)-polarized by an epicutaneous allergen

The pathogenesis of atopic dermatitis (AD) involves T helper 2 (Th2) cells, and effective therapies remain elusive due to the paucity of animal models. We aimed to develop a mouse model of an immune system aberration caused by allergen. Experiments were conducted in two phases. In experiment 1, BALB/c mice were sensitized with one of four chemical allergens - toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), trimellitic anhydride (TMA), or 2,4-dinitrochlorobenzene (DNCB) - for 3 weeks. Based on results of experiment 1, immunological features were compared between TMA-sensitized BALB/c mice and NC/Nga mice, after exposure to mite extracts, harmful chemicals and detergents in experiment 2. Sensitization by allergen caused a large number of pathological changes in the skin, and an increase in mast cell number. TMA-sensitized BALB/c mice models showed higher sensitivity to an environmental allergen than NC/Nga mice did. Overall, the initial sensitization with TMA leads to disturbances in Th2-mediated immunity.

Atopic eczema treatment now and in the future: Targeting the skin barrier and key immune mechanisms in human skin

The skin facilitates a number of key roles but its functioning can be impaired by disease. Atopic eczema is a chronic inflammatory disease where the skin barrier has become leaky, and inflammation occurs. It affects up to 20% of children and 3% of adults worldwide, manifesting as red itchy patches of skin with varying severity. This review aims to investigate the leaky skin barrier and immune mechanisms from the perspective of potential novel treatments. The complexity of atopic eczema as a disease is what makes it difficult to treat. Genome-wide association studies have highlighted possible genetic variations associated with atopic eczema, however in some cases, individuals develop the disease without these genetic risk factors. Loss of function mutations in the filaggrin gene are one of these associations and this is plausible due to its key role in barrier function. The Th2 immune response is the link with regards to the immune mechanisms as atopic inflammation often occurs through increased levels of interleukin (IL)-4 and IL-13. Eczematous inflammation also creates susceptibility to colonisation and damage by bacteria such as Staphylococcus aureus. Potential novel treatments are becoming ever more specific, offering the hope of fewer side effects and better disease control. The best new treatments highlighted in this review target the immune response with human beta defensin 2, phosphodiesterase-4 inhibitors and monoclonal antibodies all showing promise.

Trim32 Deficiency Enhances Th2 Immunity and Predisposes to Features of Atopic Dermatitis

Altered innate immunity is a feature of certain skin inflammatory diseases such as psoriasis and atopic dermatitis (AD). In this study, we provide evidence that deficiency in Trim32 (a tripartite motif [TRIM] protein with innate antiviral activity) contributes to a T helper type 2 biased response and predisposes to features of AD in mice. On treatment with the toll-like receptor 7 agonist imquimod (IMQ), Trim32 knockout mice displayed compromised psoriasiform phenotypes and defective T helper type 17 response. Instead, IMQ treatment of Trim32 knockout mice induced AD-like phenotypes with enhanced skin infiltration of eosinophils and mast cells, elevation of T helper type 2 cytokines/chemokines expression, and reduced expression of filaggrin protein expression. Furthermore, although the induction of phosphorylated Stat3 and RelA was compromised after IMQ treatment in the knockout mice, phosphorylated Stat6 was elevated. CC chemokine ligand 20 induction by tumor necrosis factor-α and IL-17A was reduced in Trim32-deficient keratinocytes, whereas CC chemokine ligand 5 induction by tumor necrosis factor-α and IL-4 was enhanced. In addition, Trim32 protein levels were elevated in mice treated with IMQ. Unlike Trim32 overexpression in psoriasis, TRIM32 levels were low in patients with AD. Based on Trim32 induction by IMQ, the lower levels of TRIM32 in AD skin compared with healthy control and psoriatic skin suggest a defective TRIM32 pathway in AD pathogenesis.

Immunohistochemical study of toll-like receptors 2, 4, and 9 expressions in pemphigus and bullous pemphigoid lesions

Pemphigus and bullous pemphigoid (BP) are severe autoimmune skin diseases. Whether innate immunity could be a trigger or a part of the pathogeneses is unknown. Toll-like receptors (TLRs) are important components of the innate immune system, with no previous evaluation of TLRs in autoimmune bullous diseases. This work aims to investigate TLRs 2, 4, and 9 expressions in pemphigus and bullous pemphigoid. Thirty-six patients with pemphigus vulgaris (PV), pemphigus foliaceus (PF), bullous pemphigoid (BP), and six healthy controls were studied. Skin biopsies from the patients and the controls were examined immunohistochemically for TLR2, 4, and 9 expressions. The TLR4 expressed mainly at the basal layer of epidermis in controls, but in the cases with autoimmune bullous diseases, TLR4 staining located at basal layer and suprabasal layer, even superficial layer of epidermis. The immunostaining-intensity-distribution (IID) index of TLR4 in patients with PF (13.83, P = 0.001), PV (13.08, P = 0.003), and BP (11.42, P = 0.042) were significantly higher than that of the controls (6.17). TLR2 and TLR9 showed no significantly changes at epidermal expression (P > 0.05) compared with controls. There was no correlation found between the expressions of these TLRs. This work, thus, shows a re-localization of TLR4 expression sites with increased expression in pemphigus and bullous pemphigoid lesions. Targeting TLR4 signaling is expected to be a novel treatment strategy for autoimmune bullous diseases.

Recent developments in atopic dermatitis

PURPOSE OF REVIEW

Research on atopic dermatitis is actively growing and continuously completing our knowledge on the pathophysiology of this complex disease.

RECENT FINDINGS

Genome-wide association studies revealed new susceptibility loci for atopic dermatitis. In addition, different tissue-specific patterns of DNA methylation have been identified as first evidence for the relevance of epigenetic modifications in atopic dermatitis. Moreover, interest is emerging on the role of the skin and gut microbiome in atopic dermatitis. Signals mediated via pattern recognition receptors of the innate immune system have been analyzed in more detail, and the role of cytokines, such as IL-22, IL-25, IL-31 and IL-33 as well as innate lymphoid cells, has been studied.

SUMMARY

Taken together, better knowledge of atopic dermatitis pathways will form the basis for the development of rationale-based therapeutic approaches in the future.

Innate immune programing by endotoxin and its pathological consequences

Monocytes and macrophages play pivotal roles in inflammation and homeostasis. Recent studies suggest that dynamic programing of macrophages and monocytes may give rise to distinct "memory" states. Lipopolysaccharide (LPS), a classical pattern recognition molecule, dynamically programs innate immune responses. Emerging studies have revealed complex dynamics of cellular responses to LPS, with high doses causing acute, resolving inflammation, while lower doses are associated with low-grade and chronic non-resolving inflammation. These phenomena hint at dynamic complexities of intra-cellular signaling circuits downstream of the Toll-like receptor 4 (TLR4). In this review, we examine pathological effects of varying LPS doses with respect to the dynamics of innate immune responses and key molecular regulatory circuits responsible for these effects.

Trif-dependent induction of Th17 immunity by lung dendritic cells

Allergic asthma is thought to stem largely from maladaptive T helper 2 (Th2) responses to inhaled allergens, which in turn lead to airway eosinophilia and airway hyperresponsiveness (AHR). However, many individuals with asthma have airway inflammation that is predominantly neutrophilic and resistant to treatment with inhaled glucocorticoids. An improved understanding of the molecular basis of this form of asthma might lead to improved strategies for its treatment. Here, we identify novel roles of the adaptor protein, TRIF (TIR-domain-containing adapter-inducing interferon-β), in neutrophilic responses to inhaled allergens. In different mouse models of asthma, Trif-deficient animals had marked reductions in interleukin (IL)-17, airway neutrophils, and AHR compared with wild-type (WT) mice, whereas airway eosinophils were generally similar in these two strains. Compared with lung dendritic cells (DCs) from WT mice, lung DCs from Trif-deficient mice displayed impaired lipopolysaccharide (LPS)-induced migration to regional lymph nodes, lower levels of the costimulatory molecule, CD40, and produced smaller amounts of the T helper 17 (Th17)-promoting cytokines, IL-6, and IL-1β. When cultured with allergen-specific, naive T cells, Trif-deficient lung DCs stimulated robust Th2 cell differentiation but very weak Th1 and Th17 cell differentiation. Together, these findings reveal a TRIF-CD40-Th17 axis in the development of IL-17-associated neutrophilic asthma.

Why we scratch an itch: the molecules, cells and circuits of itch

Itch is described as an irritating sensation that triggers a desire to scratch. However, this definition hardly seems fitting for the millions of people who suffer from intractable itch. Indeed, the Buddhist philosopher Nāgārjuna more aptly stated, "There is pleasure when an itch is scratched. But to be without an itch is more pleasurable still." Chronic itch is widespread and very difficult to treat. In this review we focus on the molecules, cells and circuits in the peripheral and central nervous systems that drive acute and chronic itch transmission. Understanding the itch circuitry is critical to developing new therapies for this intractable disease.