Does allergy impair innate immunity? Leads and lessons from atopic dermatitis

Risk factors for atopic diseases and recurrent respiratory tract infections in children

INTRODUCTION

The simultaneously increased prevalence of atopic diseases and decreased prevalence of infectious diseases might point to a link between the two entities. Past work mainly focused on either atopic diseases or recurrent infections. We aim to investigate whether risk factors for atopic diseases (ie, asthma, allergic rhinitis, atopic dermatitis, and/or food allergy) differ from risk factors for recurrent respiratory tract infections (RRTIs) in children.

METHODS

Cross-sectional data were used from 5517 children aged 1 to 18 years who participated in an Electronic Portal for children between 2011 and 2019. Univariable/multivariable logistic regression analyses were performed to determine risk factors for any atopic disease and RRTIs.

RESULTS

Children aged ≥5 years were more likely to have any atopic disease (adjusted odds ratio [OR]: 1.50-2.77) and less likely to have RRTIs (OR: 0.68-0.84) compared to children aged less than 5 years. Female sex (OR: 0.72; 95% confidence interval [CI]: 0.63-0.81), low birth weight (OR: 0.74; 95% CI: 0.57-0.97) and dog ownership (OR: 0.79; 95% CI: 0.66-0.95) reduced the odds of any atopic disease, but not of RRTIs. Daycare attendance (OR: 1.22; 95% CI: 1.02-1.47) was associated with RRTIs, but not with atopic diseases. A family history of asthma, allergic rhinitis, atopic dermatitis, and RRTIs was significantly associated with the same entity in children, with OR varying from 1.58 (95% CI: 1.35-1.85) in allergic rhinitis to 2.20 (95% CI: 1.85-2.61) in asthma.

CONCLUSION

Risk factors for atopic diseases are distinct from risk factors for RRTIs, suggesting that the changing prevalence of both entities is not related to shared risk factors.

Asthma, other atopic conditions and risk of infections in 105 519 general population never and ever smokers

BACKGROUND

Individuals with atopic conditions may have increased susceptibility to infections outside the organs directly affected by their atopic condition.

OBJECTIVE

We tested the hypothesis that atopic conditions overall, and stratified by smoking history, are associated with increased risk of hospitalization for infections.

METHODS

We collected information on smoking history and self-reported atopic conditions from 105 519 individuals from the general population and followed them for up to 23 years for infectious disease hospitalizations and deaths. For asthma, we focused on never smokers with asthma diagnosed before age 50 (early asthma) to minimize confounding by chronic obstructive pulmonary disease.

RESULTS

During follow-up, 11 160 individuals had infections. Never smokers with early asthma versus no atopic conditions had significantly increased risks of any infection (hazard ratio 1.65; 95% confidence interval 1.40-1.94), pneumonia (2.44; 1.92-3.11) and any non-respiratory tract infection (1.36; 1.11-1.67); results were similar in ever smokers. Never smokers with any asthma had significantly increased risks of any infection (1.44; 1.24-1.66) and pneumonia (1.99; 1.62-2.44). Neither atopic dermatitis (1.00; 0.91-1.10) nor hay fever (1.00; 0.93-1.07) was associated with risk of any infection. In never smokers, risk estimates for any infection were comparable between asthma and diabetes, as were the population attributable fractions of 2.2% for any asthma and 2.9% for diabetes.

CONCLUSION

Early asthma was associated with significantly increased risks of any infection, pneumonia and any non-respiratory tract infection in never and ever smokers. In never smokers, risk estimates as well as population attributable fractions for any infection were comparable between asthma and diabetes, suggesting that asthma may be a substantial risk factor for infections in the general population.

Association of prevalence of rhinitis, atopic eczema, rhinoconjunctivitis and wheezing with mortality from infectious diseases and with antibiotic susceptibility at a country level

BACKGROUND

It was previously reported that there is a positive correlation between incidence of type 1 diabetes and prevalence of asthma and atopic eczema. A negative correlation between the prevalence of type 1 diabetes and mortality from infectious diseases as well as a positive correlation with antibiotic susceptibility at a country level have also been reported.

OBJECTIVE

The aim of this study was to investigate the association between country prevalence of rhinitis, atopic eczema, rhinoconjunctivitis, and wheezing with mortality from infectious diseases and also with antibiotic susceptibility at a country level.

METHODS

Data for prevalence of rhinitis, eczema, rhinoconjunctivitis, and wheezing was obtained from the International Study of Asthma and Allergies in Childhood study (ISAAC). ISAAC Phase one was a multicentre multicountry cross sectional study involving over 700,000 children in 2 age groups of school children, 13-14 years old (adolescents) and 6-7 years old (children) in 156 centres from 56 countries. Mortality from infectious diseases was taken from World Health Organisation data. The Alexander project was used to identify antibiotic susceptibilities to common bacteria.

RESULTS

There were significant positive correlations between atopic eczema and mortality from all infectious diseases studied, diarrhoeal illness, tropical infections, and childhood infections. A negative correlation exists between the prevalence of rhinitis and Streptococcus pneumoniae susceptibility to penicillin and to erythromycin, rhinitis and Haemophilus influenzae susceptibility to ampicillin and between rhinoconjunctivitis and H. influenzae susceptibility to ampicillin.

CONCLUSION

Th1/Th2 responses might influence the pathogenesis of infectious disease mortality, while antibiotic overprescription could explain the negative association between atopy and antibiotic susceptibility.

The impact of pulmonary tuberculosis treatment on the prevalence of allergic rhinitis

Atopy is a syndrome characterized by immediate hypersensitivity reactions to common environmental antigens. The "hygiene hypothesis" stipulates that childhood infections are associated with a lower risk of allergies. Not much has been published about the effects that the treatment of pulmonary tuberculosis (TB) has on allergies, specifically allergic rhinitis. We conducted a study to investigate the prevalence of allergic rhinitis in patients with pulmonary TB before and after treatment of their TB. Our initial study group was made up of 121 patients with confirmed pulmonary TB who were followed up by questionnaire. In addition to demographic data, they provided information about their personal and family history of atopy and their current status with regard to allergic rhinitis. After providing informed consent, all patients underwent skin-prick testing with Dermatophagoides pteronyssinus, Dermatophagoides farinae, and Blomia tropicalis allergens before and after TB treatment. Stool samples were obtained to identify patients with worm infestation, and they were excluded from the study. In all, 94 patients completed treatment and follow-up, and their data were included in the final analysis. Of this group, 31 patients (33.0%) exhibited symptoms of allergic rhinitis prior to TB treatment, and 26 (27.7%) had a positive skin-prick test. Following treatment, only 12 patients (12.8%) reported allergic rhinitis symptoms (p = 0.004), but there was no significant reduction in the number of patients with a positive skin-prick test (n = 20 [21.3%]; p = 0.555). We conclude that the treatment of pulmonary TB results in significant relief of atopy, particularly allergic rhinitis symptoms.

Expression of genes related to anti-inflammatory pathways are modified among farmers' children

Background

The hygiene hypothesis states that children exposed to higher loads of microbes such as farmers’ children suffer less from allergies later in life. Several immunological mechanisms underpinning the hygiene hypothesis have been proposed such as a shift in T helper cell balance, T regulatory cell activity, or immune regulatory mechanisms induced by the innate immunity.

Objective

To investigate whether the proposed immunological mechanisms for the hygiene hypotheses are found in farmers’ children.

Methods

We assessed gene expression levels of 64 essential markers of the innate and adaptive immunity by quantitative real-time PCR in white blood cells in 316 Swiss children of the PARSIFAL study to compare farmers’ to non-farmers’ expressions and to associate them to the prevalence of asthma and rhinoconjunctivitis, total and allergen-specific IgE in serum, and expression of Cε germ-line transcripts.

Results

We found enhanced expression of genes of the innate immunity such as IRAK-4 and RIPK1 and enhanced expression of regulatory molecules such as IL-10, TGF-β, SOCS4, and IRAK-2 in farmers’ children. Furthermore, farmers’ children expressed less of the T_H1 associated cytokine IFN-γ while T_H2 associated transcription factor GATA3 was enhanced. No significant associations between the assessed immunological markers and allergic diseases or sensitization to allergens were observed.

Conclusion

Farmers’ children express multiple increased innate immune response and immune regulatory molecules, which may contribute to the mechanisms of action of the hygiene hypothesis.

Polyunsaturated Fatty Acid-derived lipid mediators and T cell function

Fatty acids are involved in T cell biology both as nutrients important for energy production as well as signaling molecules. In particular, polyunsaturated fatty acids are known to exhibit a range of immunomodulatory properties that progress through T cell mediated events, although the molecular mechanisms of these actions have not yet been fully elucidated. Some of these immune activities are linked to polyunsaturated fatty acid-induced alteration of the composition of cellular membranes and the consequent changes in signaling pathways linked to membrane raft-associated proteins. However, significant aspects of the polyunsaturated fatty acid bioactivities are mediated through their transformation to specific lipid mediators, products of cyclooxygenase, lipoxygenase, or cytochrome P450 enzymatic reactions. Resulting bioactive metabolites including prostaglandins, leukotrienes, and endocannabinoids are produced by and/or act upon T leukocytes through cell surface receptors and have been shown to alter T cell activation and differentiation, proliferation, cytokine production, motility, and homing events. Detailed appreciation of the mode of action of these lipids presents opportunities for the design and development of therapeutic strategies aimed at regulating T cell function.

Respiratory infections in adults with atopic disease and IgE antibodies to common aeroallergens

Background

Atopic diseases, including allergic rhinitis, allergic dermatitis and asthma, are common diseases with a prevalence of 30–40% worldwide and are thus of great global public health importance. Allergic inflammation may influence the immunity against infections, so atopic individuals could be susceptible to respiratory infections. No previous population-based study has addressed the relation between atopy and respiratory infections in adulthood. We assessed the relation between atopic disease, specific IgE antibodies and the occurrence of upper and lower respiratory infections in the past 12 months among working-aged adults.

Methods and Findings

A population-based cross-sectional study of 1008 atopic and non-atopic adults 21–63 years old was conducted. Information on atopic diseases, allergy tests and respiratory infections was collected by a questionnaire. Specific IgE antibodies to common aeroallergens were measured in serum. Adults with atopic disease had a significantly increased risk of lower respiratory tract infections (LRTI; including acute bronchitis and pneumonia) with an adjusted risk ratio (RR) 2.24 (95% confidence interval [CI] 1.43, 3.52) and upper respiratory tract infections (URTI; including common cold, sinusitis, tonsillitis, and otitis media) with an adjusted RR 1.55 (1.14, 2.10). The risk of LRTIs increased with increasing level of specific IgE (linear trend P = 0.059).

Conclusions

This study provides new evidence that working-aged adults with atopic disease experience significantly more LRTIs and URTIs than non-atopics. The occurrence of respiratory infections increased with increasing levels of specific IgE antibodies to common aeroallergens, showing a dose-response pattern with LRTIs. From the clinical point of view it is important to recognize that those with atopies are a risk group for respiratory infections, including more severe LRTIs.

Risk factor-dependent dynamics of atopic dermatitis: modelling multi-scale regulation of epithelium homeostasis

Epithelial tissue provides the body with its first layer of protection against harmful environmental stimuli by enacting the regulatory interplay between a physical barrier preventing the influx of external stimuli and an inflammatory response to the infiltrating stimuli. Importantly, this interdependent regulation occurs on different time scales: the tissue-level barrier permeability is regulated over the course of hours, whereas the cellular-level enzymatic reactions leading to inflammation take place within minutes. This multi-scale regulation is key to the epithelium's function and its dysfunction leads to various diseases. This paper presents a mathematical model of regulatory mechanisms in the epidermal epithelium that includes processes on two different time scales at the cellular and tissue levels. We use this model to investigate the essential regulatory interactions between epidermal barrier integrity and skin inflammation and how their dysfunction leads to atopic dermatitis (AD). Our model exhibits a structure of dual (positive and negative) control at both cellular and tissue levels. We also determined how the variation induced by well-known risk factors for AD can break the balance of the dual control. Our model analysis based on time-scale separation suggests that each risk factor leads to qualitatively different dynamic behaviours of different severity for AD, and that the coincidence of multiple risk factors dramatically increases the fragility of the epithelium's function. The proposed mathematical framework should also be applicable to other inflammatory diseases that have similar time-scale separation and control architectures.

Low vitamin D serum level is inversely associated with eczema in children and adolescents in Germany

BACKGROUND

Recent studies have yielded heterogeneous results regarding the relationship between vitamin D and atopic conditions. The aim of this study was to investigate the association between serum vitamin D level and the prevalence of eczema in German children and adolescents.

METHODS

Data were drawn for children aged 1-17 from the German Health Interview and Examination Survey for Children and Adolescents (KiGGS), a nationwide cross-sectional representative survey. 25-hydroxyvitamin D (25(OH)D) serum concentration was measured in 9838 individuals with eczema and categorized into quartiles. We investigated the association of vitamin D level and eczema by means of logistic regression models.

RESULTS

Weighted prevalence of eczema was 13.5% (95% confidence interval (CI) 12.6-14.4%). Mean vitamin D level was significantly higher in those with eczema compared with those without (P < 0.0001). Logistic regression revealed an inverse association between low levels of vitamin D and eczema (multivariate OR for quartile 1 vs quartile 2: 0.76 (95% CI 0.61-0.94)).

CONCLUSIONS

This study suggests that low serum vitamin D level is inversely associated with eczema in German children and adolescents. Prospective studies are required to confirm this result, to discuss a potential opportunity for prevention of eczema.

Update in clinical allergy and immunology

In the recent years, a tremendous body of studies has addressed a broad variety of distinct topics in clinical allergy and immunology. In this update, we discuss selected recent data that provide clinically and pathogenetically relevant insights or identify potential novel targets and strategies for therapy. The role of the microbiome in shaping allergic immune responses and molecular, as well as cellular mechanisms of disease, is discussed separately and in the context of atopic dermatitis, as an allergic model disease. Besides summarizing novel evidence, this update highlights current areas of uncertainties and debates that, as we hope, shall stimulate scientific discussions and research activities in the field.

Thymic stromal lymphopoietin stimulates the formation of eosinophil extracellular traps

BACKGROUND

Thymic stromal lymphopoietin (TSLP) that is released by epithelial cells upon certain environmental triggers activates cells of the innate and adaptive immune system resulting in a preferential T helper 2 immune response. By releasing eosinophil extracellular traps (EETs), eosinophils achieve an efficient extracellular bacterial killing. Eosinophil extracellular traps release, however, has been observed in both infectious and noninfectious eosinophilic diseases. Here, we aim to investigate whether eosinophils generate functional EETs as a direct response to TSLP, and further to study the extra- and intracellular mechanisms involved in this process as well as TSLP receptor (TSLPR) expression by eosinophils in vitro and in vivo.

METHODS

Thymic stromal lymphopoietin receptor expression on blood and tissue eosinophils was assessed by immunoblotting, flow cytometry, and immunofluorescence staining. Purified eosinophils were stimulated with recombinant human TSLP. The release of extracellular DNA in association with eosinophilic cationic protein (ECP) was detected by fluorescence staining techniques and confocal microscopy. In addition, cell survival, cell adhesion, production of reactive oxygen species (ROS), and the inhibition of bacterial growth by TSLP-stimulated eosinophils were measured.

RESULTS

Thymic stromal lymphopoietin receptor was observed on peripheral blood eosinophils as well as on tissue infiltrating eosinophils in skin diseases. TSLP did not affect eosinophil survival, but induced the formation of EETs consisting of mitochondrial DNA in association with ECP in a concentration- and time-dependent manner. Eosinophil extracellular trap release could be inhibited by blocking either cell adhesion or ROS production. While eosinophils prevented the growth of both Staphylococcus aureus and Staphylococcus epidermidis, the latter were unable to elicit EET formation and eosinophils required additional TSLP stimulation to achieve this antibacterial activity.

CONCLUSIONS

thymic stromal lymphopoietin directly stimulates eosinophils to produce EETs. Our observations link epithelial TSLP expression triggered by environmental factors with pathogen defense mechanisms involving eosinophils.

Decreased serum LL-37 and vitamin D3 levels in atopic dermatitis: relationship between IL-31 and oncostatin M

BACKGROUND

Skin lesions with atopic dermatitis (AD) are associated with dysregulated expression of LL-37 and enhanced expression of IL-22, thymic stromal lymphopoietin (TSLP), IL-25, IL-31, and oncostatin M. Vitamin D3 enhances LL-37 production in keratinocytes. This study aimed to examine the serum levels of LL-37 and vitamin D3 and their regulation of cytokine production in patients with AD.

METHODS

Serum levels of LL-37 and 25-hydroxyvitamin D3 were analyzed by ELISA. The effects of 1,25-dihydroxyvitamin D3 or LL-37 on cytokine production in T cells or keratinocytes were analyzed by ELISA and real-time PCR.

RESULTS

Serum levels of LL-37 and 25-hydroxyvitamin D3 were decreased in patients with AD compared to normal donors and were correlated in both groups. Serum levels of LL-37 correlated with those of oncostatin M and IL-31 in normal donors and patients with AD, while 25-hydroxyvitamin D3 levels did so only in normal donors. 1,25-dihydroxyvitamin D3 increased LL-37 production in human keratinocytes and neutrophils. 1,25-dihydroxyvitamin D3 and LL-37 enhanced the oncostatin M and IL-31 production in CD3/28-stimulated T cells, but did not alter IL-25 and TSLP production in TNF-α-stimulated keratinocytes. In CD3/28-stimulated T cells, 1,25-dihydroxyvitamin D3 reduced the IL-22 production, while LL-37 enhanced it. These effects of 1,25-dihydroxyvitamin D3 and LL-37 were suppressed by vitamin D receptor antagonist and pertussis toxin, respectively.

CONCLUSIONS

Systemic vitamin D3 levels are reduced in patients with AD, which may contribute to decreased systemic LL-37 levels. LL-37 may systemically potentiate the oncostatin M and IL-31 production in normal donors and patients with AD, while vitamin D3 may do so only in normal donors.