IL-21R is essential for epicutaneous sensitization and allergic skin inflammation in humans and mice

Atopic dermatitis (AD) is a common allergic inflammatory skin disease caused by a combination of intense pruritus, scratching, and epicutaneous (e.c.) sensitization with allergens. To explore the roles of IL-21 and IL-21 receptor (IL-21R) in AD, we examined skin lesions from patients with AD and used a mouse model of allergic skin inflammation. IL-21 and IL-21R expression was upregulated in acute skin lesions of AD patients and in mouse skin subjected to tape stripping, a surrogate for scratching. The importance of this finding was highlighted by the fact that both Il21r^–/– mice and WT mice treated with soluble IL-21R–IgG2aFc fusion protein failed to develop skin inflammation after e.c. sensitization of tape-stripped skin. Adoptively transferred OVA-specific WT CD4⁺ T cells accumulated poorly in draining LNs (DLNs) of e.c. sensitized Il21r^–/– mice. This was likely caused by both DC-intrinsic and nonintrinsic effects, because trafficking of skin DCs to DLNs was defective in Il21r^–/– mice and, to a lesser extent, in WT mice reconstituted with Il21r^–/– BM. More insight into this defect was provided by the observation that skin DCs from tape-stripped WT mice, but not Il21r^–/– mice, upregulated CCR7 and migrated toward CCR7 ligands. Treatment of epidermal and dermal cells with IL-21 activated MMP2, which has been implicated in trafficking of skin DCs. These results suggest an important role for IL-21R in the mobilization of skin DCs to DLNs and the subsequent allergic response to e.c. introduced antigen.     

Role of IL‐17 in atopy—A systematic review

Purpose of ReviewAtopy is defined as the genetic predisposition to react with type I allergic diseases such as food‐, skin‐, and respiratory allergies. Distinct molecular mechanisms have been described, including the known Th2 driven immune response. IL‐17A (IL‐17) is mainly produced by Th17 cells and belongs to the IL‐17 family of cytokines, IL‐17A to F. While IL‐17 plays a major role in inflammatory and autoimmune disorders, more data was published in recent years elucidating the role of IL‐17 in allergic diseases. The present study aimed to elaborate specifically the role of IL‐17 in atopy.MethodsA systematic literature search was conducted in MEDLINE, Embase, and Cochrane Central Register of Controlled Trials, regarding IL‐17 and atopy/allergic diseases.ResultsIn total, 31 novel publications could be identified (food allergy n = 3, allergic asthma n = 7, allergic rhinitis [AR] n = 10, atopic dermatitis [AD] n = 11). In all allergic diseases, the IL‐17 pathway has been investigated. Serum IL‐17 was elevated in all allergic diseases. In AR, serum and nasal IL‐17 levels correlated with the severity of the disease. In food allergies, serum IL‐17E was also elevated in children. In AD, there is a trend for higher IL‐17 values in the serum and skin specimen, while it is more expressed in acute lesions. In allergic asthma, serum IL‐17 levels were increased. In two studies, higher serum IL‐17 levels were found in severe persistent asthmatic patients than in intermittent asthmatics or healthy controls. Only one therapeutic clinical study exists on allergic diseases (asthma patients) using a monoclonal antibody against the IL‐17 receptor A. No clinical efficacy was found in the total study population, except for a subgroup of patients with (post‐bronchodilator) high reversibility.SummaryThe role of IL 17 in the pathogenesis of allergic diseases is evident, but the involvement of the Th17 cytokine in the pathophysiological pathway is not conclusively defined. IL‐17 is most likely relevant and will be a clinical target in subgroups of patients. The current data indicates that IL‐17 is elevated more often in acute and severe forms of allergic diseases.     

Epicutaneous sensitization with protein antigen induces localized allergic dermatitis and hyperresponsiveness to methacholine after single exposure to aerosolized antigen in mice.

Our understanding of the pathogenesis of atopic dermatitis (AD) and its relationship to asthma remains incomplete. Herein, we describe a murine model of epicutaneous (EC) sensitization to the protein allergen, chicken egg albumin, ovalbumin (OVA), which results in a rise in total and OVA-specific serum IgE and leads to the development of a dermatitis characterized by infiltration of CD3(+) T cells, eosinophils, and neutrophils and by local expression of mRNA for the cytokines IL-4, IL-5, and interferon-gamma. A single exposure of the EC sensitized mice to aerosolized OVA induced eosinophilia in the bronchoalveolar lavage fluid and airway hyperresponsiveness to intravenous methacholine as assessed by measurement of pulmonary dynamic compliance (Cdyn). These results suggest a possible role for EC exposure to antigen in atopic dermatitis and in the development of allergic asthma.     

Enhancement of allergic skin wheal responses in patients with atopic eczema/dermatitis syndrome by playing video games or by a frequently ringing mobile phone

BACKGROUND: Playing video games causes physical and psychological stress, including increased heart rate and blood pressure and aggression-related feelings. Use of mobile phones is very popular in Japan, and frequent ringing is a common and intrusive part of Japanese life. Atopic eczema/dermatitis syndrome is often exacerbated by stress. Stress increases serum IgE levels, skews cytokine pattern towards Th2 type, enhances allergen-induced skin wheal responses, and triggers mast cell degranulation via substance P, vasoactive intestinal peptide and nerve growth factor. MATERIALS AND METHODS: (1). In the video game study, normal subjects (n = 25), patients with allergic rhinitis (n = 25) or atopic eczema/dermatitis syndrome (n = 25) played a video game (STREET FIGHTER II) for 2 h. Before and after the study, allergen-induced wheal responses, plasma levels of substance P, vasoactive intestinal peptide and nerve growth factor, and in vitro production of total IgE, antihouse dust mite IgE and cytokines were measured. (2). In the mobile phone study, normal subjects (n = 27), patients with allergic rhinitis (n = 27) or atopic eczema/dermatitis syndrome (n = 27) were exposed to 30 incidences of ringing mobile phones during 30 min. Before and after the study, allergen-induced wheal responses, plasma levels of substance P, vasoactive intestinal peptide and nerve growth factor were measured. RESULTS: Playing video games had no effect on the normal subjects or the patients with allergic rhinitis. In contrast, playing video games significantly enhanced allergen-induced skin wheal responses and increased plasma levels of substance P, vasoactive intestinal peptide and nerve growth factors in the patients with atopic eczema/dermatitis syndrome. Moreover, playing video games enhanced in vitro production of total IgE and anti-house dust mite IgE with concomitant increased production of IL-4, IL-10 and IL-13 and decreased production of IFN-gamma and IL-12 in the patients with atopic eczema/dermatitis syndrome. However, exposure to frequently ringing mobile phones significantly enhanced allergen-induced skin wheal responses, plasma levels of substance P, vasoactive intestinal peptide and nerve growth factors in the patients with atopic eczema/dermatitis syndrome, but not in the normal subjects or the patients with allergic rhinitis. CONCLUSION: Playing video games enhanced allergic responses with a concomitant increased release of substance P, vasoactive intestinal peptide and nerve growth factor, and skewing of the cytokine pattern toward Th2 type in the patients with atopic eczema/dermatitis syndrome. In addition, exposure to frequently ringing mobile phones also enhanced allergic responses with a concomitant increased release of substance P, vasoactive intestinal peptide and nerve growth factor Collectively, high technology causes stress, which in turn may aggravate symptoms of atopic eczema/dermatitis syndrome.     

Spontaneous atopic dermatitis in mice expressing an inducible thymic stromal lymphopoietin transgene specifically in the skin

The cytokine thymic stromal lymphopoietin (TSLP) has recently been implicated in the pathogenesis of atopic dermatitis (AD) and other allergic diseases in humans. To further characterize its role in this disease process, transgenic mice were generated that express a keratinocyte-specific, tetracycline-inducible TSLP transgene. Skin-specific overexpression of TSLP resulted in an AD-like phenotype, with the development of eczematous lesions containing inflammatory dermal cellular infiltrates, a dramatic increase in Th2 CD4+ T cells expressing cutaneous homing receptors, and elevated serum levels of IgE. These transgenic mice demonstrate that TSLP can initiate a cascade of allergic inflammation in the skin and provide a valuable animal model for future study of this common disease.     

In vivo blockade of OX40 ligand inhibits thymic stromal lymphopoietin driven atopic inflammation

Thymic stromal lymphopoietin (TSLP) potently induces deregulation of Th2 responses, a hallmark feature of allergic inflammatory diseases such as asthma, atopic dermatitis, and allergic rhinitis. However, direct downstream in vivo mediators in the TSLP-induced atopic immune cascade have not been identified. In our current study, we have shown that OX40 ligand (OX40L) is a critical in vivo mediator of TSLP-mediated Th2 responses. Treating mice with OX40L-blocking antibodies substantially inhibited immune responses induced by TSLP in the lung and skin, including Th2 inflammatory cell infiltration, cytokine secretion, and IgE production. OX40L-blocking antibodies also inhibited antigen-driven Th2 inflammation in mouse and nonhuman primate models of asthma. This treatment resulted in both blockade of the OX40-OX40L receptor-ligand interaction and depletion of OX40L-positive cells. The use of a blocking, OX40L-specific mAb thus presents a promising strategy for the treatment of allergic diseases associated with pathologic Th2 immune responses.     

Periostin promotes chronic allergic inflammation in response to Th2 cytokines

Allergic inflammation triggered by exposure of an allergen frequently leads to the onset of chronic inflammatory diseases such as atopic dermatitis (AD) and bronchial asthma. The mechanisms underlying chronicity in allergic inflammation remain unresolved. Periostin, a recently characterized matricellular protein, interacts with several cell surface integrin molecules, providing signals for tissue development and remodeling. Here we show that periostin is a critical mediator for the amplification and persistence of allergic inflammation using a mouse model of skin inflammation. Th2 cytokines IL-4 and IL-13 stimulated fibroblasts to produce periostin, which interacted with αv integrin, a functional periostin receptor on keratinocytes, inducing production of proinflammatory cytokines, which consequently accelerated Th2-type immune responses. Accordingly, inhibition of periostin or αv integrin prevented the development or progression of allergen-induced skin inflammation. Thus, periostin sets up a vicious circle that links Th2-type immune responses to keratinocyte activation and plays a critical role in the amplification and chronicity of allergic skin inflammation.     

IgE-activated basophils regulate eosinophil tissue entry by modulating endothelial function

Vertebrate immunity has evolved a modular architecture in response to perturbations. Allergic inflammation represents such a module, with signature features of antigen-specific IgE and tissue eosinophilia, although the cellular and molecular circuitry coupling these responses remains unclear. Here, we use genetic and imaging approaches in models of IgE-dependent eosinophilic dermatitis to demonstrate a requisite role for basophils. After antigenic inflammation, basophils initiate transmigration like other granulocytes but, upon activation via their high-affinity IgE receptor, alter their migratory kinetics to persist at the endothelium. Prolonged basophil–endothelial interactions, in part dependent on activation of focal adhesion kinases, promote delivery of basophil-derived IL-4 to the endothelium and subsequent induction of endothelial vascular cell adhesion molecule-1 (VCAM-1), which is required for eosinophil accumulation. Thus, basophils are gatekeepers that link adaptive immunity with innate effector programs by altering access to tissue sites by activation-induced interactions with the endothelium.Inflammation comprises the immune response to infection or injury and is characterized by activation of a multistep cascade leading to the accumulation of leukocytes in involved tissues (Medzhitov, 2008). In response to a range of insults, vertebrates have evolved a “modular” immune system whereby distinct inflammatory programs are engaged depending on the nature of the perturbation. Although the cellular constituents of these inflammatory modules are largely defined, a detailed understanding of how specific modules are engaged and reinforced is lacking. Clarifying these checkpoints will enhance our understanding of immune responses in host defense and injury and across the spectrum of chronic inflammatory diseases.Allergic inflammation is an immune module that is associated with parasitic infections and prevalent human diseases, such as asthma and atopic dermatitis. In each of these, the hallmark features of allergic inflammation include the accumulation of eosinophils in target tissues and a rise in serum antigen-specific IgE (Simon et al., 2004; Woodruff et al., 2009). Both parameters serve as biomarkers for allergic disease with the activity of IgE related to its ability to interact with high-affinity IgE receptor–bearing myeloid cells, principally mast cells and basophils. In mice and humans, Fcε receptor I (FcεRI) is constitutively expressed on mast cells and basophils, although additional cell types in humans, such as certain dendritic cells and monocytes, also express this receptor (Gould and Sutton, 2008). Mast cells and basophils derive from a common developmental precursor (Qi et al., 2013), but mature cells are anatomically separated. Basophils are rare, short-lived, blood-borne cells, whereas mast cells are long-lived, tissue-resident cells found in abundance at barrier surfaces like the skin and mucosa. Mast cells are in close proximity to blood vessels, where they can acquire serum IgE by probing the vascular space and can alter vascular function by elaboration of vasoactive mediators, such as histamine (Galli and Tsai, 2010; Cheng et al., 2013). This perivascular positioning led to the suggestion that IgE-loaded tissue mast cells released eosinophil-attracting eicosanoids and cytokines and/or promoted sensitization of effector T cells in response to allergens that promoted eosinophil ingress into tissues (Liu et al., 2011). However, recent studies in a variety of models suggest an unexpected contribution of circulating basophils to allergic inflammatory responses, including the accumulation of eosinophils in target tissues (Mukai et al., 2005; Ohnmacht et al., 2010; Jin et al., 2012; Matsuoka et al., 2013). How circulating basophils influence localized eosinophil recruitment is unclear, but elucidation of this pathway could uncover new strategies for regulating allergic inflammation.We used models of IgE-dependent eosinophilic skin inflammation that allowed us to establish the hierarchical relationships between IgE and tissue eosinophilia. Through a combination of genetic and imaging approaches, we define a role for IgE-activated basophils in regulating eosinophil accumulation. Basophils exert this effect through a three-step process. First, injury attracts rare, circulating basophils through up-regulation and activation of local vascular adhesion molecules by a process similar to that for other granulocytes. Second, activation of basophil FcεRI by antigen leads to secretion of IL-4, a necessary component of the allergic phenotype. Finally, activated basophils arrest their migration into tissues and engage in prolonged endothelial interactions, thus enabling the development of IL-4–induced endothelial vascular cell adhesion molecule-1 (VCAM-1), which is required for the arrest and recruitment of circulating eosinophils. The establishment of enhanced endothelial interactions induced by FcεRI engagement during basophil transendothelial migration into tissues explains how a rare circulating cell can establish portals of entry for eosinophils, thus uniting these canonical adaptive and innate components of allergic immunity.     

CCR6 is required for IL-23–induced psoriasis-like inflammation in mice

Psoriasis is a common immune-mediated chronic inflammatory skin disorder, but the mechanisms of pathogenesis are still poorly understood. IL-23 is expressed in psoriatic skin, and IL-23 injection produces IL-22–dependent psoriasiform changes in mouse skin. Th17 cells produce IL-22 and display CCR6, the CCL20 receptor; CCR6⁺ T cells and CCL20 are abundant in psoriatic skin. We investigated a possible role for CCR6 in recruiting Th17 cells and producing psoriasiform pathology by injecting IL-23 into the skin of WT and Ccr6^–/– mice. Unlike for WT mice, IL-23–injected ears of Ccr6^–/– mice showed neither substantial epidermal/dermal changes nor increased Il22 mRNA expression. However, injection of IL-22 yielded equivalent psoriasiform changes in WT and Ccr6^–/– mice. Surprisingly, IL-23–injected ears of WT and Ccr6^–/– mice contained similar numbers of Th cells able to make IL-17A and/or IL-22. Furthermore, in ears of Rag1^–/– mice, IL-23 initially induced skin changes and levels of Il22 mRNA that were indistinguishable from WT mice, revealing at least one non–T cell source for IL-22. We conclude that CCR6 is essential in a model of IL-23–induced, IL-22–mediated dermatitis, which develops in sequential T cell–independent and T cell–dependent phases. These findings reveal an expanded role for CCR6 in IL-23–related responses and identify CCR6 as a potential therapeutic target in psoriasis.     

The association of asthma,atopic dermatitis,and allergic rhinitis with peripartum mental disorders

BackgroundAtopic diseases are characterized by dysregulated inflammatory response, which may incur the onset of peripartum mental disorders, but the impact remains unknown. This study examined whether and to what extent the history of atopic diseases is associated with newly onset peripartum mental disorders.MethodsUsing population‐based registries, we identified all primiparous women who gave birth to live singletons in Denmark during 1978–2016 (n = 937,422). The exposure was hospital contact due to the three major types of atopic diseases—asthma, atopic dermatitis, and allergic rhinitis—before conception. The primary outcome was any hospital contact for mental disorder during pregnancy and 1‐year postpartum, which was further classified into affective disorders, neurotic, stress‐related and somatoform disorders, and substance abuse. The follow‐up started from the date of conception and ended at the date of the first diagnosis of mental disorders, 1‐year postpartum, death, emigration, or December 31, 2016, whichever came first. Cox regression was used, adjusted for calendar year, age at childbirth, education, residence, and Charlson comorbidity index.ResultsA total of 24,016 (2.6%) women received diagnosis of at least one of the three atopic diseases before conception (asthma, 1.7%; atopic dermatitis, 0.6%; and allergic rhinitis, 0.8%). Exposure to asthma, atopic dermatitis, or allergic rhinitis was associated with a 37% increased overall risk of peripartum mental disorders (hazard ratio [HR], 1.37; 95% confidence interval [CI], 1.27–1.49). Higher risks were observed among women with more frequent hospital contacts for atopic disease (HR, 1.80; 95% CI, 1.37–2.35; ≥5 times), and with recent hospital contacts for atopic disease (HR, 1.74; 95% CI, 1.48–2.06; within 2 years before conception). Specific associations were observed between asthma and neurotic, stress‐related and somatoform disorders (HR, 1.40; 95% CI, 1.21–1.62), and between atopic dermatitis and substance abuse (HR, 1.62; 95% CI, 1.12–2.34).ConclusionsHistory of asthma, atopic dermatitis, and allergic rhinitis before conception was associated with increased risks of peripartum mental disorders. Women who have atopic diseases before pregnancy may benefit from systematic mental health monitoring.     

Psoriasiform dermatitis is driven by IL-36–mediated DC-keratinocyte crosstalk

Psoriasis is a chronic inflammatory disorder of the skin affecting approximately 2% of the world’s population. Accumulating evidence has revealed that the IL-23/IL-17/IL-22 pathway is key for development of skin immunopathology. However, the role of keratinocytes and their crosstalk with immune cells at the onset of disease remains poorly understood. Here, we show that IL-36R–deficient (Il36r^–/–) mice were protected from imiquimod-induced expansion of dermal IL-17–producing γδ T cells and psoriasiform dermatitis. Furthermore, IL-36R antagonist-deficient (Il36rn^–/–) mice showed exacerbated pathology. TLR7 ligation on DCs induced IL-36–mediated crosstalk with keratinocytes and dermal mesenchymal cells that was crucial for control of the pathological IL-23/IL-17/IL-22 axis and disease development. Notably, mice lacking IL-23, IL-17, or IL-22 were less well protected from disease compared with Il36r^–/– mice, indicating an additional distinct activity of IL-36 beyond induction of the pathological IL-23 axis. Moreover, while the absence of IL-1R1 prevented neutrophil infiltration, it did not protect from acanthosis and hyperkeratosis, demonstrating that neutrophils are dispensable for disease manifestation. These results highlight a central and unique IL-1–independent role for IL-36 in control of the IL-23/IL-17/IL-22 pathway and development of psoriasiform dermatitis.     

Immunoregulatory effects of Lactococcus lactis‐derived extracellular vesicles in allergic asthma

BackgroundProbiotics have been shown to prevent various allergic diseases by producing extracellular vesicles (EVs). However, the role of EVs in allergic asthma has not yet been completely determined.MethodsGut microbial composition, mainly genera related to probiotics, was investigated in allergic asthmatic mice. Moreover, EVs were isolated from Lactococcus lactis (L. lactis, a selected bacterium) and EV proteins were identified by peptide mass fingerprinting. EV functions in immune responses were evaluated in vivo or ex vivo. Furthermore, the levels of specific IgG antibodies (an alternative marker for EV quantification) to L. lactis‐EVs were measured by ELISA in the sera of 27 asthmatic patients and 26 healthy controls.ResultsAllergic asthmatic mice showed a lower proportion of Lactococcus compared to healthy mice. L. lactis was cultured and its EVs abundantly contained pyruvate kinase. When allergic asthmatic mice were intranasally treated with EVs, airway hyperresponsiveness, eosinophil number, cytokine secretion, and mucus production were significantly decreased. Moreover, L. lactis‐EV treatment shifted immune responses from Th2 to Th1 by stimulating dendritic cells to produce IL‐12. In addition, significantly lower levels of serum specific IgG4 (but not IgG1) to L. lactis‐EVs were noted in asthmatic patients than in healthy controls. A positive correlation between the levels of EV‐specific IgG4 and FEV₁ (%), but a negative correlation between the levels of EV‐specific IgG4 and IL‐13 were observed.ConclusionThese findings suggest that L. lactis‐EVs may have immune‐regulating effects on airway inflammation mediated by dendritic cell activation, providing a potential benefit for allergic asthma.     

Type 2 immunity is controlled by IL-4/IL-13 expression in hematopoietic non-eosinophil cells of the innate immune system

Nippostrongylus brasiliensis infection and ovalbumin-induced allergic lung pathology are highly interleukin (IL)-4/IL-13 dependent, but the contributions of IL-4/IL-13 from adaptive (T helper [Th]2 cells) and innate (eosinophil, basophils, and mast cells) immune cells remain unknown. Although required for immunoglobulin (Ig)E induction, IL-4/IL-13 from Th2 cells was not required for worm expulsion, tissue inflammation, or airway hyperreactivity. In contrast, innate hematopoietic cell–derived IL-4/IL-13 was dispensable for Th2 cell differentiation in lymph nodes but required for effector cell recruitment and tissue responses. Eosinophils were not required for primary immune responses. Thus, components of type 2 immunity mediated by IL-4/IL-13 are partitioned between T cell–dependent IgE and an innate non-eosinophil tissue component, suggesting new strategies for interventions in allergic immunity.     

Topical hypochlorite ameliorates NF-κB–mediated skin diseases in mice

Nuclear factor-κB (NF-κB) regulates cellular responses to inflammation and aging, and alterations in NF-κB signaling underlie the pathogenesis of multiple human diseases. Effective clinical therapeutics targeting this pathway remain unavailable. In primary human keratinocytes, we found that hypochlorite (HOCl) reversibly inhibited the expression of CCL2 and SOD2, two NF-κB–dependent genes. In cultured cells, HOCl inhibited the activity of inhibitor of NF-κB kinase (IKK), a key regulator of NF-κB activation, by oxidizing cysteine residues Cys114 and Cys115. In NF-κB reporter mice, topical HOCl reduced LPS-induced NF-κB signaling in skin. We further evaluated topical HOCl use in two mouse models of NF-κB–driven epidermal disease. For mice with acute radiation dermatitis, topical HOCl inhibited the expression of NF-κB–dependent genes, decreased disease severity, and prevented skin ulceration. In aged mice, topical HOCl attenuated age-dependent production of p16^INK4a and expression of the DNA repair gene Rad50. Additionally, skin of aged HOCl-treated mice acquired enhanced epidermal thickness and proliferation, comparable to skin in juvenile animals. These data suggest that topical HOCl reduces NF-κB–mediated epidermal pathology in radiation dermatitis and skin aging through IKK modulation and motivate the exploration of HOCl use for clinical aims.     

Infection of Mice with Mycobacterium bovis–Bacillus Calmette-Guérin (BCG) Suppresses Allergen-induced Airway Eosinophilia

It has been proposed that the increase in prevalence and severity of atopic disorders inversely correlates with exposure to infectious diseases such as tuberculosis. We have investigated this issue by combining an intranasal Mycobacterium bovis–Bacillus Calmette-Guérin (BCG) infection with a murine model of allergen, (ovalbumin [OVA]) induced airway eosinophilia. BCG infection either 4 or 12 wk before allergen airway challenge resulted in a 90–95 and 60–70% reduction in eosinophilia within the lungs, respectively, compared to uninfected controls. The inhibition of airway eosinophilia correlated with a reduced level of IL-5 production by T cells from the lymph node draining the site of OVA challenge. Interestingly, BCG infection of the lung had no effect on IgG1 and IgE OVA-specific serum immunoglobulin or blood eosinophil levels. Furthermore, BCG-induced inhibition of airway eosinophilia was strongly reduced in interferon (IFN)-γ receptor–deficient mice and could be partially reversed by intranasal IL-5 application. Intranasal BCG infections could also reduce the degree of lung eosinophilia and IL-5 produced by T cells after Nippostrongylus brasiliensis infection. Taken together, our data suggest that IFN-γ produced during the T helper cell (Th)1 immune response against BCG suppresses the development of local inflammatory Th2 responses in the lung. Most importantly, this inhibition did not extend to the systemic immunoglobulin response against OVA. Our data support the view that mycobacterial infections have the potential to suppress the development of atopic disorders in humans.     

Contact allergens in moisturizers in preventative emollient therapy – A systematic review

BackgroundResults of preventative emollient therapy on atopic dermatitis and food allergy trials are inconsistent. In addition to the ingredients considered beneficial, the moisturizers may contain potentially harmful haptens. This study aimed to assess the prevalence of haptens in moisturizers used in studies to prevent atopic dermatitis or food allergy and assess their correlations to the trial results.MethodsA systematic search of studies investigating the role of emollient usage in preventing atopic dermatitis or food allergy in infants was performed from inception to December 2020. Haptens were identified based on the nine common patch test series (European, American, and Australian).Results12 clinical trial studies were included in the review. In total, 16 different emollients were applied as an intervention. The vast majority (75%) of preparations contained at least one hapten from which several substances pose high allergic or irritant potential. Quantitative data synthesis of the findings regarding food allergy and atopic dermatitis prevention was not possible due to the significant heterogeneity of preparations used.ConclusionsCareful selection of emollient should consider the absence of potentially harmful ingredients, particularly when used in youngest children. Chronic skin exposure to haptens promotes the development of allergic contact dermatitis and moreover, via deterioration of the skin barrier and subclinical inflammation, may facilitate epicutaneous sensitization and promote atopic dermatitis; however further research is needed to validate our suppositions.     

Inhibition of NK cell activity by IL-17 allows vaccinia virus to induce severe skin lesions in a mouse model of eczema vaccinatum

Threats of bioterrorism have renewed efforts to better understand poxvirus pathogenesis and to develop a safer vaccine against smallpox. Individuals with atopic dermatitis are excluded from smallpox vaccination because of their propensity to develop eczema vaccinatum, a disseminated vaccinia virus (VACV) infection. To study the underlying mechanism of the vulnerability of atopic dermatitis patients to VACV infection, we developed a mouse model of eczema vaccinatum. Virus infection of eczematous skin induced severe primary erosive skin lesions, but not in the skin of healthy mice. Eczematous mice exhibited lower natural killer (NK) cell activity but similar cytotoxic T lymphocyte activity and humoral immune responses. The role of NK cells in controlling VACV-induced skin lesions was demonstrated by experiments depleting or transferring NK cells. The proinflammatory cytokine interleukin (IL)-17 reduced NK cell activity in mice with preexisting dermatitis. Given low NK cell activities and increased IL-17 expression in atopic dermatitis patients, these results can explain the increased susceptibility of atopic dermatitis patients to eczema vaccinatum.The smallpox vaccine consists of live vaccinia virus (VACV) and is considered the gold standard of vaccines, as it has led to the complete eradication of a lethal infectious disease from the human population. Recent fears that smallpox might be deliberately released in an act of bioterrorism have led to renewed efforts to better understand the disease mechanism and to develop a safer vaccine. Approximately 50% of US residents were born after the regular smallpox vaccination was discontinued in 1972. Thus, these unimmunized people are vulnerable to smallpox. The population landscape is very different between now and 36 yr ago, with two-to-three times more frequent incidence of atopic dermatitis in the current population (1). Individuals with atopic dermatitis are excluded from smallpox vaccination because of their propensity to develop eczema vaccinatum, a disseminated vaccinia infection (2).Atopic dermatitis is a chronic inflammatory skin disease (3). The etiology of this disease is multifactorial, and involves complex interactions between genetic and environmental factors. The skin in a preatopic dermatitis state has been postulated to have hypersensitivity to environmental triggers, resulting from a defective skin barrier that allows the penetration of allergens and microbial pathogens (4). The acute phase is characterized by eczematous skin lesions with an infiltration of Th2 cells. The chronic phase is characterized by lichenification of skin and an infiltration of Th1 cells. As recent studies have established IL-17– and IL-22–producing CD4⁺ T cells as a distinct class of helper T cells (Th17), Th17 cells are also implicated in the acute but not the chronic phase (5, 6). Despite the progress in our understanding of atopic dermatitis pathogenesis (7) and immune responses to VACV (8), it is not understood why atopic dermatitis patients are susceptible to developing eczema vaccinatum (9).In this study, we have established a mouse model of eczema vaccinatum using a strain of mice that are prone to develop eczematous skin lesions, characterized their immune responses to VACV infection, and showed the importance of NK cells in early suppression of VACV-induced severe eczema vaccinatum–like skin lesions.     

Interleukin-10 Is a Natural Suppressor of Cytokine Production and Inflammation in a Murine Model of Allergic Bronchopulmonary Aspergillosis

We have used interleukin-10 (IL-10) gene knockout mice (IL-10^−/−) to examine the role of endogenous IL-10 in allergic lung responses to Aspergillus fumigatus Ag. In vitro restimulated lung cells from sensitized IL-10^−/− mice produced exaggerated amounts of IL-4, IL-5, and interferon-γ (IFN-γ) compared with wild-type (WT) lung cells. In vivo, the significance of IL-10 in regulating responses to repeated A. fumigatus inhalation was strikingly revealed in IL-10^−/− outbred mice that had a 50–60% mortality rate, while mortality was rare in similarly treated WT mice. Furthermore, IL-10^−/− outbred mice exhibited exaggerated airway inflammation and heightened levels of IL-5 and IFN-γ in bronchoalveolar lavage (BAL) fluids. In contrast, the magnitude of the allergic lung response was similar in intranasally (i.n.) sensitized IL-10^−/− and wild-type mice from a different strain (C57BL/6). Using a different route of priming (intraperitoneal) followed by one i.n. challenge we found that IL-10^−/− C57BL/6 mice had heightened eosinophilic airway inflammation, BAL–IL-5 levels, and numbers of αβT cells in the lung tissues compared with WT mice. We conclude that IL-10 can suppress inflammatory Th2-like lung responses as well as Th1-like responses given the constraints of genetic background and route of priming.     

Toll-like receptor and IL-12 signaling control susceptibility to contact hypersensitivity

Allergic contact hypersensitivity (CHS) is a T cell–mediated inflammatory skin disease. Interleukin (IL)-12 is considered to be important in the generation of the allergen-specific T cell response. Loss of IL-12 function in IL-12Rβ2–deficient mice, however, did not ameliorate the allergic immune response, suggesting alternate IL-12–independent pathways in the induction of CHS. Because exposure to contact allergens always takes place in the presence of microbial skin flora, we investigated the potential role of Toll-like receptors (TLRs) in the induction of CHS. Using mice deficient in TLR4, the receptor for bacterial lipopolysaccharide (LPS), IL-12 receptor (R) β2, or both, we show that the concomitant absence of TLR4 and IL-12Rβ2, but not the absence of TLR4 or IL-12Rβ2 alone, prevented DC-mediated sensitization, generation of effector T cells, and the subsequent CHS response to 2,4,6-trinitro-1-chlorobenzene (TNCB), oxazolone, and fluorescein isothiocyanate. Introduction of the TLR4 transgene into the TLR4/IL-12Rβ2 mutant restored the CHS inducibility, showing a requirement for TLR4 in IL-12–independent CHS induction. Furthermore, the concomitant absence of TLR2 and TLR4 prevented the induction of CHS to TNCB in IL-12–competent mice. Finally, CHS was inducible in germ-free wild-type and IL-12Rβ2–deficient mice, but not in germ-free TLR4/IL-12Rβ2 double deficient mice, suggesting that the necessary TLR activation may proceed via endogenous ligands.