Stringent environmental control in pregnancy and early life: the long-term effects on mite, cat and dog allergen

Inverse association between the molecular spreading of IgE to grass pollen and the IgE response to Dermatophagoides pteronyssinus among children with seasonal allergic rhinitis

Background

Seasonal allergic rhinoconjunctivitis (SAR) is a worldwide health problem, especially in Westernized countries. Previous studies of the "Panallergens in Pediatrics" (PAN-PED) cohort found that molecular spreading (ie, the progressive increase in serum specific IgE antibody levels) of the IgE response to the grass pollen, Phleum pratense, molecules is directly associated with polysensitization to pollen in general.The research question is aimed at verifying whether this association can also be detected for non-pollen allergens, specifically Dermatophagoides pteronyssinnus (D.pt), to better understand the relationship between a perennial allergen (D.pt) and a seasonal allergen (Phleum pratense).To this end, our first objective was to analyze the biobank of the PAN-PED cohort serum by measuring the IgE levels to D.pt and its major recombinant molecules (Der p1, Der p2, Der p23); subsequently we investigated their correlation towards Phleum pratense IgE response, studying also the relationship between the molecular spreading of these 2 different allergens.

Methods

Among 1120 patients positive to Phleum pratense, 638 were also sensitized to D.pt. Patients underwent skin prick tests (SPT) for inhalant extracts, and their serum was tested for total IgE (tIgE), and sIgE to pollen and perennial allergens. Considering the molecular allergen detection through the component resolved diagnosis (CRD), out of 638 patients, 146 were further investigated by performing IgE tests of the 3 major D.pt. molecules: Der p1, Der p2, and Der p23.

Results

We found that a broader molecular response to Phleum pratense molecules, assessed by CRD, was associated with higher tIgE levels, polysensitization to pollens, and higher IgE levels to pollens, but also to lower IgE levels to D.pt and lower degree of sensitization to rDer p1, r Der p2, and rDer p23. In a multivariate linear model, the number of Phleum pratense molecules recognized by IgE was still inversely associated with the IgE level to D.pt extract.

Conclusions

The main finding of this study was the detection of an inverse association, never described in the literature, between the molecular spreading of the IgE response to Phleum pratense and the IgE response to D.pt. This led us to speculate on the etiopathogenetic hypothesis according to which, among the majority of pollen allergic patients, a strong and molecularly diversified IgE response may be limited to pollen allergens and may be preventing or contrasting the development of an equally strong and diversified IgE sensitization to D.pt molecules. The biological mechanisms underlying this phenomenon deserve to be investigated.

Dog ownership in infancy is protective for persistent wheeze in 17q21 asthma-risk carriers

BACKGROUND

Asthma-associated single nucleotide polymorphisms from large genome-wide association studies only explain a fraction of genetic heritability. Likely causes of the missing heritability include broad phenotype definitions and gene-environment interactions (GxE). The mechanisms underlying GxE in asthma are poorly understood. Previous GxE studies on pet ownership showed discordant results.

OBJECTIVES

We sought to study the GxE between the 17q12-21 locus and pet ownership in infancy in relation to wheeze.

METHODS

Wheezing classes derived from 5 UK-based birth cohorts (latent class analysis) were used to study GxE between the 17q12-21 asthma-risk variant rs2305480 and dog and cat ownership in infancy, using multinomial logistic regression. A total of 9149 children had both pet ownership and genotype data available. Summary statistics from individual analyses were meta-analyzed.

RESULTS

rs2305480 G allele was associated with increased risk of persistent wheeze (additive model odds ratio, 1.37; 95% CI, 1.25-1.51). There was no evidence of an association between dog or cat ownership and wheeze. We found significant evidence of a GxE interaction between rs2305480 and dog ownership (P = 8.3 × 10-4) on persistent wheeze; among dog owners, the G allele was no longer associated with an increased risk of persistent wheeze (additive model odds ratio, 0.95; 95% CI, 0.73-1.24). For those without pets, G allele was associated with increased risk of persistent wheeze (odds ratio, 1.61; 95% CI, 1.40-1.86). Among cat owners, no such dampening of the genetic effect was observed.

CONCLUSIONS

Among dog owners, rs2305480 G was no longer associated with an increased risk of persistent wheeze (or asthma). Early-life environmental exposures may therefore attenuate likelihood of asthma in those carrying 17q12-21 risk alleles.

The equine asthma model of airway remodeling: from a veterinary to a human perspective

Human asthma is a complex and heterogeneous disorder characterized by chronic inflammation, bronchospasm and airway remodeling. The latter is a major determinant of the structure-function relationship of the respiratory system and likely contributes to the progressive and accelerated decline in lung function observed in patients over time. Corticosteroids are the cornerstone of asthma treatment. While their action on inflammation and lung function is well characterized, their effect on remodeling remains largely unknown. An important hindrance to the study of airway remodeling as a major focus in asthma research is the lack of reliable non-invasive biomarkers. In consequence, the physiologic and clinical consequences of airway wall thickening and altered composition are not well understood. In this perspective, equine asthma provides a unique and ethical (non-terminal) preclinical model for hypothesis testing and generation. Severe equine asthma is a spontaneous disease affecting adult horses characterized by recurrent and reversible episodes of disease exacerbations. It is associated with bronchoalveolar neutrophilic inflammation, bronchospasm, and excessive mucus secretion. Severe equine asthma is also characterized by bronchial remodeling, which is only partially improved by prolonged period of disease remission induced by therapy or antigen avoidance strategies. This review will focus on the similarities and differences of airway remodeling in equine and human asthma, on the strengths and limitations of the equine model, and on the challenges the model has to face to keep up with human asthma research.

LPS-induced modules of co-expressed genes in equine peripheral blood mononuclear cells

BACKGROUND

Lipopolysaccharide (endotoxin, LPS) is a strong inducer of the innate immune response. It is widespread in our environment, e.g. in house dust and contributes to asthma. Compared to humans, horses are even more sensitive to LPS. However, data on LPS effects on the equine transcriptome are very limited. Using RNA-seq we analysed LPS-induced differences in the gene expression in equine peripheral blood mononuclear cells at the gene and gene-network level in two half-sib families and one group of unrelated horses.

RESULTS

24 h-LPS challenge of equine immune cells resulted in substantial changes in the transcriptomic profile (1,265 differentially expressed genes) showing partial overlap with human data. One of the half-sib families showed a specific response different from the other two groups of horses. We also identified co-expressed gene modules that clearly differentiated 24 h-LPS- from non-stimulated samples. These modules consisted of 934 highly interconnected genes and included genes involved in the immune response (e.g. IL6, CCL22, CXCL6, CXCL2), however, none of the top ten hub genes of the modules have been annotated as responsive to LPS in gene ontology.

CONCLUSIONS

Using weighted gene co-expression network analysis we identified ten co-expressed gene modules significantly regulated by in vitro stimulation with LPS. Apart from 47 genes (5%) all other genes highly interconnected within the most up- and down-regulated modules were also significantly differentially expressed (FDR < 0.05). The LPS-regulated module hub genes have not yet been described as having a role in the immune response to LPS (e.g. VAT1 and TTC25).

Dust mite avoidance for the primary prevention of atopic dermatitis: A systematic review and meta-analysis

BACKGROUND

Dust mite sensitization plays a controversial role in the development of atopic dermatitis. Despite a lack of evidence for its efficacy, dust mite avoidance is commonly recommended for the prevention and treatment of atopic dermatitis. We aimed to evaluate whether dust mite avoidance strategies reduce the risk of developing atopic dermatitis in high-risk infants compared to randomized controls.

METHODS

Studies were obtained by searching MEDLINE, PubMed, Scopus, The Cochrane Library, and The Global Resource of Eczema Trials databases. We included randomized, controlled trials of high-risk infants treated with a dust mite avoidance intervention and assessed for atopic dermatitis. Data were extracted independently by two reviewers using predefined criteria.

RESULTS

Seven randomized controlled trials met our inclusion criteria (total n = 3040). Studies were largely unblinded but otherwise of reasonable quality. Three trials utilizing a dust mite avoidance approach but not additional interventions were combined in a meta-analysis. Dust mite avoidance provided no benefit in the prevention of atopic dermatitis (relative risk (RR) = 1.08, 95% confidence interval (CI) = 0.78-1.49, I(2) = 73%).

CONCLUSIONS

Dust mite avoidance strategies alone or in combination with additional allergen avoidance modalities do not decrease the risk of developing atopic dermatitis and, given the current state of the evidence, should not be recommended for this purpose. The utility of dust mite avoidance for the treatment of atopic dermatitis or for the prevention and treatment of asthma or seasonal rhinoconjunctivitis are outside the scope of this review.

Childhood Asthma Management and Environmental Triggers

Asthma is the most common chronic disease among children. It cannot be prevented but can be controlled. Industrialized countries experience high lifetime asthma prevalence that has increased over recent decades. Asthma has a complex interplay of genetic and environmental triggers. Studies have revealed complex interactions of lung structure and function genes with environmental exposures such as environmental tobacco smoke and vitamin D. Home environmental strategies can reduce asthma morbidity in children but should be tailored to specific allergens. Coupled with education and severity-specific asthma therapy, tailored interventions may be the most effective strategy to manage childhood asthma.

Effect of inhaled hydrosoluble curcumin on inflammatory markers in broncho-alveolar lavage fluid of horses with LPS-induced lung neutrophilia

Background

Horses commonly suffer from chronic respiratory disease and are also used in large animal models of spontaneous or induced airway inflammation. The anti-inflammatory properties of curcumin are largely described but its low bioavailability precludes its clinical use. NDS27, a lysin salt of curcumin incorporated in beta-cyclodextrine, has high bioavailability and can be administered by inhalation. The aim of this study was to investigate the effects of inhaled NDS27 on inflammatory cytokines and proteins in the broncho-alveolar lavage fluid using a model of neutrophilic airway inflammation.

Methods

Airway neutrophilia was induced in eight horses by inhalation of lipopolysaccharides (LPS). Horses were treated with either inhalation of NDS27 or with placebo in a randomized cross-over design. Broncho-alveolar lavages were performed 6 hours after stimulation with LPS. Percentage of neutrophils, concentrations of IL-1β, TNF-α, IL-6, Club cell secretory protein, myeloperoxidase (MPO) and elastase (ELT) concentrations were determined.

Results

LPS stimulation induced significant increases in neutrophil counts and concentrations of IL-6 (70.2 ± 66.0 pg/ml), TNF-α (43.9 ± 31.2 pg/ml), MPO (580.9 ± 327.0 ng/ml) and ELT (27.6 ± 16.7 ng/ml). Treatment with NDS27 significantly prevented the increase in active and total MPO (216.4 ± 118.1 ng/ml) and ELT (5.9 ± 3.2 ng/ml) while there was a trend towards reduced IL-6 concentration.

Conclusions

Results show that, although not reducing neutrophil recruitment, NDS27 largely abolishes LPS-induced neutrophil degranulation. Reduced levels of ELT and MPO, as well as reduced MPO activity may have beneficial effects via a reduced production of reactive oxygen species implicated in chronic inflammation and airway remodeling.

Trajectories of lung function during childhood

RATIONALE

Developmental patterns of lung function during childhood may have major implications for our understanding of the pathogenesis of respiratory disease throughout life.

OBJECTIVES

To explore longitudinal trajectories of lung function during childhood and factors associated with lung function decline.

METHODS

In a population-based birth cohort, specific airway resistance (sRaw) was assessed at age 3 (n = 560), 5 (n = 829), 8 (n = 786), and 11 years (n = 644). Based on prospective data (questionnaires, skin tests, IgE), children were assigned to wheeze phenotypes (no wheezing, transient, late-onset, and persistent) and atopy phenotypes (no atopy, dust mite, non-dust mite, multiple early, and multiple late). We used longitudinal linear mixed models to determine predictors of change in sRaw over time.

MEASUREMENTS AND MAIN RESULTS

Contrary to the assumption that sRaw is independent of age and sex, boys had higher sRaw than girls (mean difference, 0.080; 95% confidence interval [CI], 0.049-0.111; P < 0.001) and a higher rate of increase over time. For girls, sRaw increased by 0.017 kPa ⋅ s(-1) per year (95% CI, 0.011-0.023). In boys this increase was significantly greater (P = 0.012; mean between-sex difference, 0.011 kPa ⋅ s(-1); 95% CI, 0.003-0.019). Children with persistent wheeze (but not other wheeze phenotypes) had a significantly greater rate of deterioration in sRaw over time compared with never wheezers (P = 0.009). Similarly, children with multiple early, but not other atopy phenotypes had significantly poorer lung function than those without atopy (mean difference, 0.116 kPa ⋅ s(-1); 95% CI, 0.065-0.168; P < 0.001). sRaw increased progressively with the increasing number of asthma exacerbations.

CONCLUSIONS

Children with persistent wheeze, frequent asthma exacerbations, and multiple early atopy have diminished lung function throughout childhood, and are at risk of a progressive loss of lung function from age 3 to 11 years. These effects are more marked in boys.

Impermeable dust mite covers in the primary and tertiary prevention of allergic disease: a meta-analysis

BACKGROUND

Up to 40% of the world's population has been diagnosed with an allergic disease. The most prevalent allergy is to house dust mites. Impermeable mattress covers are often the first treatment in the prevention and decrease of symptoms of allergic disease.

OBJECTIVE

To perform a meta-analysis evaluating the effectiveness of impermeable mattress covers in the primary prevention of allergic disease and as a single intervention in the tertiary prevention of allergic disease symptoms.

METHODS

MEDLINE, Embase, Web of Science, and CINAHL were systematically searched for relevant publications. Seven primary prevention trials (n = 3,461) and 17 tertiary prevention trials (n = 1,671) met the inclusion criteria and were included in the review. All article reviews and abstractions were performed in duplicate.

RESULTS

No significant pooled relative risks were found for the prevention of allergic disease. The pooled relative risks were 0.97 (95% confidence interval [CI] 0.62-1.51) for house dust mite sensitization, 0.92 (95% CI 0.81-1.05) for wheeze, 0.85 (95% CI 0.70-1.02) for asthma, 1.03 (95% CI 0.90-1.19) for allergic rhinitis, and 1.05 (95% CI 0.84-1.32) for allergic dermatitis. Likewise, no significant pooled standardized mean differences were found in the tertiary prevention of symptoms. The pooled standardized mean differences were -0.03 (95% CI -0.15 to 0.09) for peak flow, -0.06 (95% CI -0.32 to 0.20) for asthma symptom score, and -0.39 (95% CI -0.88 to 0.11) for nasal symptom score. A significant effect was seen in the decrease of house mite dust level in the mattress (-0.79, 95% CI -0.98 to -0.60).

CONCLUSION

No evidence was found to support the use of impermeable mattress covers in the primary prevention of allergic disease or in the tertiary prevention of allergic disease symptoms.

Pediatric asthma and development of atopy

PURPOSE OF REVIEW

There is ongoing controversy about the relationship between atopy and asthma.

RECENT FINDINGS

In clinical practice, specific IgE and skin test results should not be reported as 'positive' or 'negative', but as the level of IgE and the size of skin test wheal diameter. In assessment of children with severe asthma, these tests are not mutually exclusive but complementary, and both should be carried out and quantified. In the near future, their diagnostic accuracy in children with wheezing may be improved by the measurement of allergen-specific IgG. It is becoming increasingly clear that asthma is not a single disease, but a collection of several diseases with similar/same symptoms. These distinct disease entities (endotypes) may share similar observable characteristics (phenotypes), but arise via different pathophysiological mechanisms. Observable phenotypic features (e.g. sputum inflammatory phenotypes) are not stable in children with asthma. The discovery of novel, latent endotypes of asthma will require integration of a time component to take into account the phenotype instability and longitudinal changes. Not only asthma, but also 'atopy' encompasses a number of different endotypes which differ in their association with asthma.

SUMMARY

Novel endotypes of atopy and asthma which better reflect the unique pathophysiological processes underlying different diseases in the atopy and asthma syndromes can be defined through the fusion of computational thinking and novel mathematical approaches with biomedical science. These novel endotypes may be more relevant for epidemiological, genetic and therapeutic studies.

Gene-environment interactions in the development of asthma and atopy

Asthma is a complex multifactorial disorder involving a variety of different mechanisms. Little has changed in asthma treatment over the past five decades. There is evidence for a strong genetic component of asthma, but genetic studies have produced heterogeneous results with little replication, with most of the heritability remaining unexplained. The rapid increase in asthma prevalence over a short time period suggests that environmental exposures play an important role, but there is a considerable heterogeneity in the results describing the effect of different environmental exposures. There are many reasons for the lack of replication in genetic association studies and those of environmental exposures. These include the failure to consider that asthma may arise as a consequence of environmental factors, modulating the risk in genetically susceptible individuals via gene-environment interactions. In addition, many studies rely on oversimplified phenotypes often derived through aggregation of several heterogeneous conditions (e.g., 'physician-diagnosed asthma').

Atopic dermatitis in a high-risk cohort: natural history, associated allergic outcomes, and risk factors

BACKGROUND

Atopic dermatitis (AD) is commonly associated with asthma and other atopic disorders in childhood.

OBJECTIVE

To evaluate the natural history of AD and its association with other allergic outcomes in a high-risk cohort through the age of 7 years.

METHODS

A total of 373 high-risk infants, who had undergone a randomized controlled trial with intervention measures for primary prevention of asthma applied during the first year of life, were assessed for asthma, AD, and allergic sensitization at 1, 2, and 7 years.

RESULTS

The multifaceted intervention program did not reduce AD despite reducing the prevalence of asthma significantly. Sixty-two children (16.6%) had AD during the first 2 years (early-onset AD); of these, 26 continue to have AD at the age of 7 years (persistent), whereas 36 no longer had the disease (nonpersistent) at the age of 7 years. Twenty-three children (6.2%) developed AD only after the age of 2 years (late-onset AD). Early-onset AD, persistent or nonpersistent, was associated with increased risk of allergic sensitization to food allergens within the first 2 years of life and asthma diagnosis at year 7. However, only persistent AD was associated with an increased risk of other atopic diseases and allergic sensitization to food and aeroallergens at year 7. Late-onset AD was not associated with atopic diseases or allergic sensitization at year 7 with the exception of Alternaria alternans.

CONCLUSION

In this cohort of infants at high risk of asthma, early-onset persistent AD, which was highly associated with atopic sensitization, increased the risk of atopic diseases in later childhood and thus appears to be part of the atopic march.

Increased hypoxia-inducible factor 1α expression in lung cells of horses with recurrent airway obstruction

Background

Recurrent airway obstruction (RAO, also known as equine heaves) is an inflammatory condition caused by exposure of susceptible horses to organic dusts in hay. The immunological processes responsible for the development and the persistence of airway inflammation are still largely unknown. Hypoxia-inducible factor (Hif) is mainly known as a major regulator of energy homeostasis and cellular adaptation to hypoxia. More recently however, Hif also emerged as an essential regulator of innate immune responses. Here, we aimed at investigating the potential involvement of Hif1-α in myeloid cells in horse with recurrent airway obstruction.

Results

In vitro, we observed that Hif is expressed in equine myeloid cells after hay dust stimulation and regulates genes such as tumor necrosis factor alpha (TNF-α), interleukin-8 (IL-8) and vascular endothelial growth factor A (VEGF-A). We further showed in vivo that airway challenge with hay dust upregulated Hif1-α mRNA expression in myeloid cells from the bronchoalveolar lavage fluid (BALF) of healthy and RAO-affected horses, with a more pronounced effect in cells from RAO-affected horses. Finally, Hif1-α mRNA expression in BALF cells from challenged horses correlated positively with lung dysfunction.

Conclusion

Taken together, our results suggest an important role for Hif1-α in myeloid cells during hay dust-induced inflammation in horses with RAO. We therefore propose that future research aiming at functional inactivation of Hif1 in lung myeloid cells could open new therapeutic perspectives for RAO.

Quantification of atopy, lung function and airway hypersensitivity in adults

BACKGROUND

Studies in children have shown that concentration of specific serum IgE (sIgE) and size of skin tests to inhalant allergens better predict wheezing and reduced lung function than the information on presence or absence of atopy. However, very few studies in adults have investigated the relationship of quantitative atopy with lung function and airway hyperresponsiveness (AHR).

OBJECTIVE

To determine the association between lung function and AHR and quantitative atopy in a large sample of adults from the UK.

METHODS

FEV1 and FVC (% predicted) were measured using spirometry and airway responsiveness by methacholine challenge (5-breath dosimeter protocol) in 983 subjects (random sample of 800 parents of children enrolled in a population-based birth cohort enriched with 183 patients with physician-diagnosed asthma). Atopic status was assessed by skin prick tests (SPT) and measurement of sIgE (common inhalant allergens). We also measured indoor allergen exposure in subjects' homes.

RESULTS

Spirometry was completed by 792 subjects and 626 underwent methacholine challenge, with 100 (16.0%) having AHR (dose-response slope>25). Using sIgE as a continuous variable in a multiple linear regression analysis, we found that increasing levels of sIgE to mite, cat and dog were significantly associated with lower FEV1 (mite p = 0.001, cat p = 0.0001, dog p = 2.95 × 10-8). Similar findings were observed when using the size of wheal on skin testing as a continuous variable, with significantly poorer lung function with increasing skin test size (mite p = 8.23 × 10-8, cat p = 3.93 × 10-10, dog p = 3.03 × 10-15, grass p = 2.95 × 10-9). The association between quantitative atopy with lung function and AHR remained unchanged when we repeated the analyses amongst subjects defined as sensitised using standard definitions (sIgE>0.35 kUa/l, SPT-3 mm>negative control).

CONCLUSIONS

In the studied population, lung function decreased and AHR increased with increasing sIgE levels or SPT wheal diameter to inhalant allergens, suggesting that atopy may not be a dichotomous outcome influencing lung function and AHR.

Does allergen avoidance work?

Allergic rhinitis affects a large portion of the population. Patients are frequently sensitized to indoor allergens. The most important contributors are house dust mites, pets, and fungi. In very controlled environments where allergen exposure is significantly reduced, individuals have been shown to have clinical improvement in allergic rhinitis and/or asthma symptoms. Achieving sufficient exposure reduction in the home has proven difficult. Nonetheless, evidence exists that demonstrates exposure avoidance can be useful as an adjunct to other therapies, such as pharmacotherapy and immunotherapy, for the treatment of allergic rhinitis.

Allergen-specific IgG antibody levels modify the relationship between allergen-specific IgE and wheezing in childhood

BACKGROUND

An increase in IgE antibody levels to inhalant allergens is associated with an increased likelihood of wheezing. The role of allergen-specific IgG and IgG4 in relation to wheezing is yet to be determined.

OBJECTIVE

We sought to investigate whether Fel d 1-specific IgG and IgG4 antibodies modify the association between cat allergen-specific IgE and childhood wheezing.

METHODS

We used data from 2 population-based birth cohorts (United Kingdom [UK], n = 473; Australia, n = 1336). Current wheeze was defined as wheezing in the previous 12 months at age 5 (UK) and 14 (Australia) years. We determined cat allergen-specific IgE (whole extract) and IgG and IgG4 antibody (purified rFel d 1) levels and used logistic regression to estimate the relationship between wheeze and the quantitative allergen antibody levels.

RESULTS

In the univariate analysis risk of wheezing increased significantly with increasing cat-specific IgE levels (UK: odds ratio [OR], 1.56; 95% CI, 1.28-1.90; Australia: OR, 1.29; 95% CI, 1.19-1.40). rFel d 1-specific IgG or IgG4 had no significant effect on wheeze in either population. However, a different pattern of the relationship between antibody levels and wheezing emerged in the multivariate analysis. In the UK cat-specific IgE increased the risk of wheeze (OR, 2.01; 95% CI, 1.29-3.12; P = .002), whereas rFel d 1-specific IgG decreased the risk (OR, 0.46; 95% CI, 0.21-0.99; P = .05). This finding was replicated in Australia (IgE: OR, 1.46; 95% CI, 1.28-1.68; P < .001; IgG: OR, 0.66; 95% CI, 0.44-0.99; P = .049). There was no significant association between IgG4 antibody levels and wheezing in either population.

CONCLUSIONS

rFel d 1-specific IgG but not IgG4 antibody levels significantly modify the association between cat-specific IgE and childhood wheezing, with the risk of symptoms decreasing with increasing IgG levels.

Human allergy to environmental pet danders: a public health perspective

The prevalence of human allergy to pet danders has increased rapidly over the past six decades, as a consequence of lifestyle changes that have enhanced ambient exposure to pet allergens. This is a problem of global public health importance, as the morbidity associated with allergic diseases disproportionately affects socio-economically disadvantaged populations, particularly children. Although the public often seeks advice from veterinary health-care professionals regarding healthy pet ownership practices, including strategies for reducing residential pet dander exposure, many misconceptions persist in the public domain regarding pet dander allergy, such as the belief that certain dog and cat breeds are 'hypoallergenic' due to their hair/coat type. This review considers the epidemiology of human exposure to the major cat and dog dander allergens, Fel d 1 and Can f 1 respectively, and the sensitization mechanisms to them, including the hygiene hypothesis and the putative role of bacterial endotoxin. The literature regarding primary and secondary exposures in different ambient environments is explored including threshold effects that influence allergen sensitization and elicitation of symptoms, and environmental intervention strategies that seek to reduce allergen exposure. Pet-specific factors, including the aetiopathogenesis of the several cat and dog allergens that have been characterized to the molecular level, individual animal characteristics that influence Fel d 1 and Can f 1 shedding, and pet-directed interventions intended to reduce allergen dispersal, are discussed.

Prevention of allergic sensitization by environmental control

For about 20 years, investigators have been attempting to design studies to reduce exposure to allergens in order to prevent the development of allergic sensitization and thus prevent the onset of allergic disease, particularly asthma. Seven such studies-environmental control studies-have attempted to accomplish this by changing the domestic environment into which a high-risk child is born. Some of these studies also included a dietary intervention aimed at reducing the risk of development of sensitization to food allergens. In this review, we summarize the seven studies, compare study designs, and evaluate the effectiveness of the environmental control measures adopted. We present published results, focusing on the most recent. There is great heterogeneity of results that cannot be explained by the variety of study designs alone. We propose that the next generation of primary prevention studies will be informed by epidemiologic studies of gene-environment interactions and will investigate the effects of tailor-made measures targeting individuals with specific susceptibilities who may benefit from specified interventions.

Strategies for primary prevention of atopy in children

In recent decades, the prevalence of atopic diseases such as asthma, hayfever, food allergy, and atopic dermatitis has been steadily increasing. Unfortunately, more advances have been made in secondary prevention of symptoms and exacerbations than in primary prevention. One barrier to adopting prevention strategies is uncertainty regarding the cause of atopy. A genetic predisposition has been well documented. However, other factors, including diet, environment, infections, medications, and gastrointestinal flora, all play a role in the development of atopic disease. Modifying these factors holds promise for stopping the atopic march in the future. This paper reviews advances that have been made in the primary prevention of atopic disease.

Early environmental determinants of asthma risk in a high-risk birth cohort

Environmental exposures during early life have been suggested to have the greatest impact on childhood asthma. Our aim was to evaluate the risk factors associated with asthma at age 7 yr in a high-risk cohort that participated in a randomized controlled study on the primary prevention of asthma. Indoor exposures were characterized before birth and at 2 weeks, 4, 8, 12, 18, and 24 months after birth and again at 7 yr. Nasal scrapings for respiratory viruses were done at the same intervals during the first 2 yr. At age 7, the children were assessed by a pediatric allergist and had allergy skin tests. Logistic regression analysis was undertaken to evaluate the effect of exposures on asthma for the entire cohort with adjustment for group allocation. In addition to the lower risk of asthma in the intervention group, we found a higher prevalence of asthma at age 7 for males, those having a positive history of asthma in mother, father, or older siblings, for children residing in Winnipeg and for atopic subjects. Upon adjustment for intervention group assignment and baseline factors, significant environmental risk factors during year 1 included dog ownership and respiratory syncytial viral infection detected at 12 months while maternal smoking was protective. Dog ownership was a significant risk factor in year 2, but highly correlated with dog ownership in year 1. Indoor environmental exposures during year 7 were not associated with asthma at age 7. Maternal smoking at year 7 was associated with a reduced risk of asthma at 7 yr. Early-life exposures were more important determinants than those in later years. A 'window of opportunity' exists for intervention measures to be applied.

Allergen avoidance

The systematic avoidance of indoor allergens by modification of houses, furnishings, or hygiene practices has long been advocated to reduce both the incidence of allergic diseases in at-risk infants and exacerbations or symptoms in those previously sensitized with such a disease. However, such advocacy is now under challenge, due to both a lack of evidence of clinical efficacy of avoidance measures and rapidly changing models of disease causation and pathology. This article reviews the current dilemmas in understanding the complexity of allergen sources, disease risks, nature of bioaerosol exposure, and the inadequacies of many available methods.

IgE-bearing cells in bronchoalveolar lavage fluid and allergen-specific IgE levels in sera from RAO-affected horses

Recurrent airway obstruction (RAO) is a common condition in stabled horses characterized by small airway inflammation, airway neutrophilia and obstruction following exposure of susceptible horses to mouldy hay and straw and is thus regarded as a hypersensitivity reaction to mould spores. However, the role of immunoglobulin E antibodies (IgE) in the pathogenesis of RAO is unclear. We hypothesized that the number of cells with receptor-bound IgE in bronchoalveolar lavage fluid (BALF) and IgE levels in serum would be higher in RAO-affected than in healthy horses living in the same environment. Therefore, IgE-positive (+) cells were identified by immunocytochemistry on cytospins from BALF and counted. IgE levels against the mould extracts Aspergillus fumigatus (Asp. f.) and Alternaria alternata (Alt. a.) and the recombinant mould allergen Aspergillus fumigatus 8 (rAsp f 8) were measured by enzyme-linked immunosorbent assay (ELISA) in the sera of seven RAO-affected and 22 clinically healthy mature horses housed in the same conventional stable environment. After correcting for the number of neutrophils, there were no significant differences in IgE+ cells on cytospins from BALF between both groups of horses (5% versus 7%, P > 0.1). Serum IgE levels against the mould extracts were significantly higher in RAO-affected than in clinically healthy horses [median = 119 versus 66 relative ELISA units (REU), P < 0.05]. Furthermore, significantly more RAO-affected than healthy horses had detectable serum IgE against the recombinant allergen rAsp f 8 (4/7 and 3/22, respectively, P < 0.05). Age had no significant effect on BALF cell ratios or on specific serum IgE levels. These results show that high IgE levels against mould antigens are associated with RAO under controlled environmental conditions but ranges of mould-specific serum IgE levels overlapped too much between diseased and clinically healthy animals to be of any diagnostic value. Further studies are needed to assess whether IgE-mediated reactions contribute to the pathogenesis of RAO.

Rhinoconjunctivitis in 5-year-old children: a population-based birth cohort study

BACKGROUND

There is a paucity of data on the prevalence, risk factors and natural history of rhinitis in early childhood.

OBJECTIVE

Within the context of a whole-population birth cohort we investigated the prevalence of and risk factors for current rhinoconjunctivitis (CRC) at age 5 years.

METHODS

Children were followed prospectively to age 5 years [questionnaires (n = 815), skin testing (n = 717), specific immunoglobulin E (n = 478), lung function (n = 711), dry air challenge (n = 556)]. Endotoxin and allergen exposures were measured in dust samples.

RESULTS

The prevalence of rhinitis ever, current rhinitis and rhinoconjunctivitis was 28.2%, 26.1%, and 12.1%, respectively. Asthma, wheeze and eczema coexisted with CRC (P < or = 0.01). In a multivariate model, maternal asthma (OR 2.38, 95% CI: 1.30-4.38, P = 0.005), paternal hay fever (1.96, 1.11-3.46, P = 0.02) and sensitization to grass (3.46, 1.86-6.42, P < 0.001) and cat (2.42, 1.14-5.18, P = 0.02) remained significant and independent associates of CRC. Whilst almost half of children with CRC were nonatopic, there was little difference in risk factors between atopic and nonatopic CRC. Amongst children with current wheeze, the presence of concurrent CRC had no effect on either severity or frequency of wheezy episodes. There was no difference in specific airway resistance, forced expiratory volume in 1 second (FEV(1)) or airway reactivity between children with and without CRC after adjustment for the presence of wheeze.

CONCLUSION

Family history of allergic disease and sensitization to inhalant allergens are risk factors for rhinoconjunctivitis in preschool children. In this age group, there is no association between the presence of rhinoconjunctivitis and severity of wheeze, increased airway reactivity and reduced lung function.

Dust mite allergen avoidance as a preventive and therapeutic strategy

Asthma is a global health problem with genetic and environmental components. Indoor allergens have a major impact on asthma, and exposure in sensitized subjects can compromise lung function. A reduction in allergen exposure would seem a logical facet to treatment. Methods for reducing mite allergen levels that are effective in the laboratory may not work in the home and may not result in a clinical benefit. Six ongoing studies are investigating the effects of environmental control on the primary prevention of asthma and allergies. Although the Isle of Wight and Canadian studies provide encouraging results at age 8 and 7 years, respectively, it will be some time before a definitive public health message emerges. For secondary prevention, there is little evidence to support the use of mite-proof encasings as a single intervention in adults. In children, however, single or multifaceted interventions appear to be of some benefit.

Endotoxin Exposure, CD14, and Allergic Disease

RATIONALE

High endotoxin exposure may reduce the risk of allergic sensitization.

OBJECTIVE

To determine the relationship between a promoter polymorphism in the CD14 gene (CD14/-159 C to T) and endotoxin exposure in relation to the development of allergic sensitization, eczema, and wheeze within the setting of a birth cohort.

METHODS

We genotyped 442 children (CD14/-159 C to T; rs2569190). We assessed children for allergic sensitization (IgE > 0.2 kU/L to at least one of seven allergens), eczema (physical examination), and parentally reported wheeze. Endotoxin was measured in house dust.

MAIN RESULTS

Genotype frequencies were consistent with other populations (TT, 25%; CT, 47%; CC, 28%). Sensitization (present in 33% of children) was not associated with genotype. For children with TT and CT genotypes, there was no association between endotoxin and sensitization (odds ratio [OR], 0.95; 95% confidence interval [CI], 0.71-1.23; p = 0.7; and OR, 0.90; 95% CI, 0.77-1.04; p = 0.16, respectively) or endotoxin and eczema (OR, 0.99; 95% CI, 0.81-1.20; p = 0.89; and OR, 1.38; 95% CI, 0.83-2.30; p = 0.22, respectively). In children with the genotype CC, increasing endotoxin load was associated with a marked and significant reduction in the risk of sensitization (OR, 0.70; 95% CI, 0.55-0.89; p = 0.004) and eczema (OR, 0.73; 95% CI, 0.56-0.95; p = 0.02). However, we observed an increased risk of nonatopic wheeze with increasing endotoxin exposure in children with the CC genotype (OR, 1.42; 95% CI, 1.01-1.99; p = 0.04) but not other genotypes. No effect was seen for atopic wheeze.

CONCLUSIONS

Increasing endotoxin exposure is associated with reduced risk of allergic sensitization and eczema but with increased risk of nonatopic wheeze in children with the CC genotype at -159 of the CD14 gene. The impact of environmental endotoxin may be enhanced in individuals with this genotype.

House dust mite allergen reduction and allergy at 4 yr: follow up of the PIAMA-study

Exposure to high allergen levels in early life is a risk factor for the development of allergy. We previously reported limited effects of mite allergen impermeable mattress covers in the prevention and incidence of asthma and mite allergy (PIAMA) cohort at the age of 1 and 2 yr. We now present the results of follow-up at 4 yr objectives. To examine the effects of early reduction of house dust mite (HDM) allergen exposure by means of mattress covers on the incidence of allergy and asthma symptoms in the PIAMA birth cohort at the age of 4 yr. High-risk children (allergic mother) were prenatally recruited and randomly allocated to three groups; receiving mite allergen impermeable mattress covers (n = 416), placebo covers (n = 394) or no intervention (n = 472). At 4 yr of age, atopy was assessed by questionnaire; specific Immunoglobulin E (IgE) to inhalant and food allergens was measured in serum. Dust samples collected from the children's mattresses were analysed for mite allergens. Dermatophagoides farinae1 allergen (Der f 1) levels in dust were reduced in the active group. However, Dermatophagoides pteronissinus 1 (Der p 1) levels, sensitization and atopic symptoms were similar in all groups. We found no effect of mite allergen impermeable mattress covers on sensitization and atopy at 4 yr. Moreover, the allergen reducing effects of the covers had disappeared for one of the two mite allergens that were measured.

New insights in allergen avoidance measures for mite and pet sensitized patients. A critical appraisal

It is widely acknowledged that avoidance of allergens such as those derived from foods, drugs, latex and stinging insects results in a complete disappearance of symptoms. By contrast, although it has been clearly shown that allergens are an important risk factor for the development of respiratory symptoms and that several avoidance measures reduce allergen levels, whether this gives clinical improvement in symptoms is debatable. Many reasons could be invoked to justify this evident discrepancy. Apart from the intrinsic methodological aspects (e.g. single or combined interventions measure, population studied, severity of respiratory symptoms, outcomes, evaluated parameters, etc.), it is important to outline that a successful approach requires that the avoided allergen is the only and real factor responsible for symptoms, the patient's education and the use of a comprehensive protocol to reduce allergen exposure. Other important factors include the involvement of the patient, the relevance of other allergens/non-specific agents, and exposure to sensitizing agents also outside patient's home. It is likely that the clinical phase of allergic airway disease and the degree of bronchial (and also nasal) remodelling, in each individual, represent relevant factors for the clinical outcome of allergen avoidance procedures. Since the management of respiratory allergy is a complex strategy (including drugs, allergen avoidance, immunological and educational interventions), it is difficult in real life to distinguish the efficacy of a single intervention in comparison to the others. A combined strategy is likely to produce better clinical results.

Domestic allergen and endotoxin exposure and allergic sensitization in Cyprus

We investigated the relationship between domestic allergen and endotoxin exposure and allergic sensitization among children in Cyprus. We skin prick tested 128 children aged 15-16 yr (random samples of 85 children with self-reported asthma and 43 healthy controls) and measured their domestic exposure to endotoxin and allergens (mite, cat, and dog). We analyzed the data using multivariate logistic regression (adjusting for gender, area of residence and parental history) and presented the outcomes as odds ratios (OR) and 95% confidence intervals (CI). Among this selected population, 19% of children were sensitized to mite, 15% to cat and 7% to dog. Male gender (OR 2.74, 95% CI 1.18-6.38, p = 0.02), maternal history of allergic disease (OR 3.53, 95% CI 1.13-11.00, p = 0.03), increasing endotoxin (OR 1.58, 95% CI 1.00-2.49, p = 0.05) and residence in the district of Nicosia (OR 2.48, 95% CI 1.01-6.08, p = 0.05) were independent associates of allergic sensitization. Factors associated with mite sensitization were increasing Der p 1 and endotoxin exposure (OR 1.28, 95% CI 1.01-1.62, p = 0.04 and OR 1.76, 95% CI 1.01-3.08, p = 0.05, respectively) and living in an urban area (OR 6.80, 95% CI 1.37-33.67, p = 0.02). Sensitization to domestic pets was associated only with paternal allergic disease (cat: OR 5.68, 95% CI 1.57-23.56, p = 0.02; dog: OR 13.5, 95% CI 1.79-101.73, p = 0.01), but not with pet ownership or specific allergen or endotoxin exposure. In conclusion, mite allergen exposure was associated with sensitization to mite, but there was no association between cat and dog allergen exposure and specific sensitizations. Surprisingly, in this area, increasing endotoxin exposure was associated with an increased risk of sensitization.

Possible reasons for lack of effect of allergen avoidance in atopy-prone infants and sensitive asthmatic patients

The basic paradigm that allergen exposure produces atopic sensitization, and that continued exposure leads to clinical asthma throughout the development of airway inflammation and bronchial hyperreactivity has been challenged. However, because it was observed that epidemiological evidence suggests that around 40% of asthma cases are attributable to atopy (even using restrictive criteria), the obvious corollary is that if allergen avoidance begins before the onset of sensitization (primary prevention), then it should be associated with a reduced number of new cases of the disease. However, there are conflicting results regarding the effect of allergen avoidance on primary prevention of atopic sensitization and asthma onset. Instead, more uniform and positive results are available from secondary prevention studies. Secondary prevention obviously is an attractive opportunity for pediatricians who may recognize the patients who might benefit from these interventions simply by screening for food allergy in young children with atopic dermatitis. The conflicting results of tertiary prevention are most frequently observed in adult patients and sometimes result from incomplete avoidance of allergens responsible for the sensitization.

Allergen avoidance as primary prevention: con

There has been a dramatic increase in the prevalence of atopic diseases, such as atopic dermatitis, food allergy, allergic rhinitis, and allergic asthma. Because environmental factors such as early allergen exposure to nutritional and inhalant allergens have been suspected as potential environmental factors favoring the development of allergic diseases and asthma, primary prevention studies have begun to investigate the effect on sensitization and wheezing. Designs of the studies are different and, therefore, are not completely comparable. Although no clear primary prevention study is available for pets, mite allergen avoidance during infancy can achieve a reduction of specific sensitization and, in some studies, can also produce a slight effect on respiratory symptoms.

Latitude, birth date, and allergy

BACKGROUND

The space and time distribution of risk factors for allergic diseases may provide insights into disease mechanisms. Allergy is believed to vary by month of birth, but multinational studies taking into account latitude have not been conducted.

METHODS AND FINDINGS

A questionnaire was distributed in 54 centres to a representative sample of 20- to 44-y-old men and women mainly in Europe but also including regions in North Africa, India, North America, Australia, and New Zealand. Data from 200,682 participants were analyzed. The median prevalence of allergic rhinitis was 22%, with a substantial variation across centres. Overall, allergic rhinitis decreased with geographical latitude, but there were many exceptions. No increase in prevalence during certain winters could be observed. Also, no altered risk by birth month was found, except borderline reduced risks in September and October. Effect estimates obtained by a multivariate analysis of total and specific IgE values in 18,085 individuals also excluded major birth month effects and confirmed the independent effect of language grouping.

CONCLUSION

Neither time point of first exposure to certain allergens nor early infections during winter months seems to be a major factor for adult allergy. Although there might be effects of climate or environmental UV exposure by latitude, influences within language groups seem to be more important, reflecting so far unknown genetic or cultural risk factors.

Indoor air quality and human health: truth vs mass hysteria

Indoor air quality is an important issue, because anything we breathe can potentially affect our health. To determine if there is a real health risk, well-designed scientifically valid studies must be performed. Although much attention has focused on sick building syndrome, chemical sensitivities, and mycotoxicosis, there actually is very little evidence that these conditions have an adverse effect on human health. In contrast, real health issues have been shown to exist regarding indoor air triggers of allergies and asthma. Outdoor allergens are difficult to avoid because the pollen grains we encounter outdoors, which are the size that can cause allergies, are windborne and can travel for miles. However, indoor allergens can cause severe allergic symptoms and may also have a priming effect on an individual’s susceptibility to simultaneous or subsequent exposure of other outdoor allergens. Therefore, it is important to minimize exposure to indoor allergens. Determination of individual susceptibility can be paired with knowledge of the patient’s indoor exposure pattern to produce a customized management plan of avoidance, which can be used in conjunction with pharmacological treatment of allergies and asthma, as well as immunotherapy.

A preliminary analysis of the process of protein secretion and the diversity of putative secreted hydrolases encoded inAspergillus fumigatus: insights from the genome

The genome sequence of Aspergillus fumigatus has enabled the annotation of genes likely to encode secreted enzymes that may be important in underpinning the natural lifestyle of the fungus and its pathogenicity. We summarize the data from the genome sequence relevant to both the process of protein secretion and the predicted hydrolase enzymes secreted by A. fumigatus.

Allergen avoidance in the primary prevention of asthma

PURPOSE OF REVIEW

Six primary prevention studies trialing environmental modifications to reduce asthma in children have published results of clinical outcomes. All are still in progress.

RECENT FINDINGS

In the Isle of Wight study, mite and food avoidance were evaluated to age 9 months. At 8 years, children in the active group had less current wheeze, wheeze with bronchial hyperresponsiveness and atopy (P < or = 0.05). The Canadian Primary Prevention Study examined avoidance of inhalant and food allergens. At 1 year there was a reduction in probable asthma and rhinitis in the active group. The Study on the Prevention of Allergy in Children in Europe tested avoidance of inhalant and food allergens. At 1 year there was less atopy and sensitization to mites in the active group. In the Childhood Asthma Prevention Study both mite avoidance and a dietary supplement of omega 3 fatty acids were analysed in a factorial design. At age 18 months, children in the dietary intervention group had significantly less wheeze. Eczema was more common amongst children using the mite avoidance measures. The Prevention and Incidence of Asthma and Mite Allergy Study is a placebo-controlled study of mite avoidance. At 2 years, there was a small reduction in nocturnal cough without a cold in the active group. The Manchester Asthma and Allergy Study included stringent environmental control. At 1 year prescribed medication for wheeze and wheeze with shortness of breath were significantly less common in the active group than the control group.

SUMMARY

Although initial results look promising, further follow up of the ongoing cohorts is required before any recommendations can be made within the public health context.

Early life environmental control: effect on symptoms, sensitization, and lung function at age 3 years

We investigated whether environmental control during pregnancy and early life affects sensitization and lung function at the age of 3 years. High-risk children (n = 251) were prenatally randomized to stringent environmental control (active) or no intervention (control). Questionnaires, skin testing, IgE, and specific airway resistance (sRaw) measurement were completed at the age of 3 years. Children in the active group were significantly more frequently sensitized compared with control subjects (at least one allergen by skin tests: risk ratio, 1.61; 95% confidence interval [CI], 1.02-2.55; p = 0.04; mite by IgE: risk ratio, 2.85; 95% CI, 1.02-7.97; p = 0.05). However, sRaw was significantly better in the active group (kiloPascal/second, geometric mean [95% CI]: 1.05 [1.01-1.10] vs. 1.19 [1.13-1.25], p < 0.0001, active vs. control). Maximal flow at functional residual capacity was measured using rapid thoracic compression at the age of 4 weeks in a subgroup. Prospective lung function data (at infancy and 3 years) were obtained in 32 children (14 active and 18 control). There was no difference in infant lung function between the groups, but at 3 years, sRaw was significantly lower in the active compared with control children (p = 0.003). Stringent environmental control was associated with increased risk of mite sensitization but better results for some measurements of lung function in high-risk children at the age of 3 years.