Endotoxin levels in Estonian and Swedish house dust and atopy in infancy

Genetics of Asthma and Allergic Diseases

Asthma genes have been identified through a range of approaches, from candidate gene association studies and family-based genome-wide linkage analyses to genome-wide association studies (GWAS). The first GWAS of asthma, reported in 2007, identified multiple markers on chromosome 17q21 as associates of the childhood-onset asthma. This remains the best replicated asthma locus to date. However, notwithstanding undeniable successes, genetic studies have produced relatively heterogeneous results with limited replication, and despite considerable promise, genetics of asthma and allergy has, so far, had limited impact on patient care, our understanding of disease mechanisms, and development of novel therapeutic targets. The paucity of precise replication in genetic studies of asthma is partly explained by the existence of numerous gene-environment interactions. Another important issue which is often overlooked is that of time of the assessment of the primary outcome(s) and the relevant environmental exposures. Most large GWASs use the broadest possible definition of asthma to increase the sample size, but the unwanted consequence of this is increased phenotypic heterogeneity, which dilutes effect sizes. One way of addressing this is to precisely define disease subtypes (e.g. by applying novel mathematical approaches to rich phenotypic data) and use these latent subtypes in genetic studies.

Airway Microbiota and the Implications of Dysbiosis in Asthma

The mucosal surfaces of the human body are typically colonized by polymicrobial communities seeded in infancy and are continuously shaped by environmental exposures. These communities interact with the mucosal immune system to maintain homeostasis in health, but perturbations in their composition and function are associated with lower airway diseases, including asthma, a developmental and heterogeneous chronic disease with various degrees and types of airway inflammation. This review will summarize recent studies examining airway microbiota dysbioses associated with asthma and their relationship with the pathophysiology of this disease.

Inducing maternal inflammation promotes leptin production in offspring but does not improve allergic symptoms in a mouse model of allergic rhinitis

AIMS

The intrauterine environment is considered to affect immunological development in fetus, leading to an increased risk of developing allergy. In particular, maternal lipopolysaccharides (LPS) administration might regulate the development of allergic disease in offspring. Several studies have shown that being obese relates to a higher prevalence of allergic diseases compared to normal weight. The present study explored the effects of inducing maternal inflammation with LPS before pregnancy on body weight, physical composition including body fat, adipokine production, and pathology of allergic rhinitis in offspring.

MAIN METHODS

Female mice received a single intraperitoneal injection of LPS (2 μg/g BW). After 5 days of LPS administration, female mice were mated with males, and experimental allergic rhinitis was induced in female offspring. Immunization and nasal challenge with ovalbumin (OVA) were performed at 7 and 8 weeks of age. Allergic rhinitis-like symptoms, OVA-specific IgE and adipokines in sera, body weight, fat pad weight, and cytokine production by splenocytes in these 9-week-old offspring.

KEY FINDINGS

Maternal LPS administration results in a significant increase in body weight, visceral fat accumulation, and serum leptin concentration, and the dominance of Th1 in Th balance. Nevertheless, there was no statistical difference in OVA-specific IgE titer and allergic-like symptoms between the groups.

SIGNIFICANCE

In conclusion, maternal LPS promoted leptin production and altered Th balance in mice offspring, but not improved allergic symptoms in a mouse model of allergic rhinitis. It might suggest that inflammation during pregnancy plays a role in the adipose tissue function which could diversely influence allergic inflammation in offspring.

The gut microbiota and its role in the development of allergic disease: a wider perspective

The gut microbiota are critical in the homoeostasis of multiple interconnected host metabolic and immune networks. If early microbial colonization is delayed, the gut-associated lymphoid tissues (GALT) fail to develop, leading to persistent immune dysregulation in mice. Microbial colonization has also been proposed as a major driver for the normal age-related maturation of both Th1 and T regulatory (Treg) pathways that appear important in suppressing early propensity for Th2 allergic responses. There is emerging evidence that resident symbionts induce tolerogenic gut-associated Treg cells and dendritic cells that ensure the preferential growth of symbionts; keeping pathogenic strains in check and constraining proinflammatory Th1, Th2, and Th17 clones. Some effects of symbionts are mediated by short-chain fatty acids, which play a critical role in mucosal integrity and local and systemic metabolic function and stimulate the regulatory immune responses. The homoeostatic IL-10/TGF-β dominated tolerogenic response within the GALT also signals the production of secretory IgA, which have a regulating role in mucosal integrity. Contrary to the 'sterile womb' paradigm, recent studies suggest that maternal microbial transfer to the offspring begins during pregnancy, providing a pioneer microbiome. It is likely that appropriate microbial stimulation both pre- and postnatally is required for optimal Th1 and Treg development to avoid the pathophysiological processes leading to allergy. Disturbed gut colonization patterns have been associated with allergic disease, but whether microbial variation is the cause or effect of these diseases is still under investigation. We are far from understanding what constitutes a 'healthy gut microbiome' that promotes tolerance. This remains a major limitation and might explain some of the inconsistency in human intervention studies with prebiotics and probiotics. Multidisciplinary integrative approaches with researchers working in networks, using harmonized outcomes and methodologies, are needed to advance our understanding in this field.

Nutritional influences on epigenetic programming: asthma, allergy, and obesity

Observational studies show consistent links between early-life nutritional exposures as important risk factors for the development of asthma, allergy, and obesity. Reliance on increasing use of dietary supplementation and fortification (eg, with folate) to compensate for increased consumption of processed foods is also influencing immune and metabolic outcomes. Epigenetics is providing substantial advances in understanding how early-life nutritional exposures can effect disease development. This article summarizes current evidence linking the influence of early-life nutritional exposures on epigenetic regulation with a focus on the disease outcomes of asthma, allergy, and obesity.

Antibiotics in the first week of life is a risk factor for allergic rhinitis at school age

BACKGROUND

Heredity as well as external factors influences the development of allergic rhinitis. The aim of this study was to analyse early risk factors and protective factors for allergic rhinitis at school age.

METHODS

This is a prospective, longitudinal study of children born in western Sweden in 2003 where 50% of the birth cohort was randomly selected. The parents answered questionnaires at 6 months, 12 months, 4.5 yr and 8 yr. At 8 yr, 5044 questionnaires were distributed. Of these, 4051 responded, that is, 80.3%. Current allergic rhinitis was defined as symptoms and use of medication during the past 12 months.

RESULTS

Current allergic rhinitis at 8 yr was reported by 10.9%. Mean onset age was 5.7 yr, and 61.9% were boys. In a multivariate analysis, antibiotics in the first week of life increased the risk of allergic rhinitis (adjusted odds ratio 1.75, 95% confidence interval (1.03, 2.97)). Increased risk was also seen with parental allergic rhinitis (aOR 2.73 (2.12, 3.52)), food allergy first year (aOR 2.45 (1.61, 3.73)), eczema first year (aOR 1.97 (1.50, 2.59)) and male gender (aOR 1.35 (1.05, 1.74)). Living on a farm at 4.5 yr reduced the risk (aOR 0.31 (0.13, 0.78)).

CONCLUSION

Antibiotics in the first week of life increased the risk of allergic rhinitis at school age, while living on a farm at preschool age reduced the risk. Both findings are compatible with the hygiene hypothesis.

Pre- and postnatal administration of Lactobacillus reuteri decreases TLR2 responses in infants

Background

Mice models indicate that intact Toll like receptor (TLR) signaling may be essential for the allergy protective effects of diverse bacterial exposure observed in clinical trials and epidemiological studies. Probiotic supplementation with Lactobacillus reuteri from pregnancy week 36 and to the infant through the first year of life decreased the prevalence of IgE-associated eczema at two years (ClinicalTrials.gov NCT01285830). The effect of this supplementation on innate immune responses to bacterial products and the expression of associated TLRs were explored.

Methods

Blood mononuclear cells were collected at birth, 6, 12 and 24 months from 61 infants and cultured with TLR2, 4 and 9 ligands. Cytokine and chemokine secretion was determined as well as TLR2, 4 and 9 mRNA expression.

Results

Probiotic supplementation was associated with decreased LTA (lipoteichoic acid) induced CCL4, CXCL8, IL-1β and IL-6 responses at 12 months and decreased CCL4 and IL-1β secretion at 24 months. TLR2 mRNA expression was not affected by probiotic treatment.

Conclusions

Decreased responses to TLR2, the main receptor for LTA from Gram positive bacteria, in probiotic treated children seem to be dependent on factors downstream of TLR mRNA expression.

Epidemiology of Respiratory Allergies and Asthma

Asthma has puzzled and confused physicians from the time of Hippocrates to the present day. The word “asthma” comes from a Greek word meaning “panting” (Keeney 1964), but reference to asthma can also be found in ancient Egyptian, Hebrew, and Indian medical writings (Ellul-Micallef 1976; Unger and Harris 1974). There were clear observations of patients experiencing attacks of asthma in the second century and evidence of disordered anatomy in the lung as far back as the seventeenth century (Dring et al. 1689).

Innate immune response to LPS in airway epithelium is dependent on chronological age and antecedent exposures

The immune mechanisms for neonatal susceptibility to respiratory pathogens are poorly understood. Given that mucosal surfaces serve as a first line of host defense, we hypothesized that the innate immune response to infectious agents may be developmentally regulated in airway epithelium. To test this hypothesis, we determined whether the expression of IL-8 and IL-6 in airway epithelium after LPS exposure is dependent on chronological age. Tracheas from infant, juvenile, and adult rhesus monkeys were first exposed to LPS ex vivo, and then processed for air-liquid interface primary airway epithelial cell cultures and secondary LPS treatment in vitro. Compared with adult cultures, infant and juvenile cultures expressed significantly reduced concentrations of IL-8 after LPS treatment. IL-8 protein in cultures increased with animal age, whereas LPS-induced IL-6 protein was predominantly associated with juvenile cultures. Toll-like receptor (TLR) pathway RT-PCR arrays showed differential expressions of multiple mRNAs in infant cultures relative to adult cultures, including IL-1α, TLR10, and the peptidoglycan recognition protein PGLYRP2. To determine whether the age-dependent cytokine response to LPS is reflective of antecedent exposures, we assessed primary airway epithelial cell cultures established from juvenile monkeys housed in filtered air since birth. Filtered air-housed animal cultures exhibited LPS-induced IL-8 and IL-6 expression that was discordant with age-matched ambient air-housed animals. A single LPS aerosol in vivo also affected this cytokine profile. Cumulatively, our findings demonstrate that the innate immune response to LPS in airway epithelium is variable with age, and may be modulated by previous environmental exposures.

The hygiene hypothesis in allergy and asthma: an update

PURPOSE OF REVIEW

It has been hypothesized that increased cleanliness, reduced family size, and subsequent decreased microbial exposure could explain the increases in global asthma prevalence. This review considers the recent evidence for and against the 'hygiene hypothesis'.

RECENT FINDINGS

Recent evidence does not provide unequivocal support for the hygiene hypothesis: the hygiene hypothesis specifically relates to atopic asthma, but some of the protective effects (e.g. farm exposures) appear to apply to both atopic and nonatopic asthma; asthma prevalence has begun to decline in some western countries, but there is little evidence that they have become less clean; Latin American countries with high infection rates have high asthma prevalence and the hygiene hypothesis relates to early-life exposures, but exposures throughout life may be important.

SUMMARY

There is a considerable body of evidence which warrants scepticism about the hygiene hypothesis. However, these anomalies contradict the 'narrow' version of it in which microbial pressure early in life protects against atopic asthma by suppressing T-helper 2 immune responses. It is possible that a more general version of the hygiene hypothesis is still valid, but the aetiologic mechanisms involved are currently unclear.

The pathophysiology of the hygiene hypothesis

There has been a considerable increase in the diagnosis of allergic diseases over the last decades. Prevalence of allergies in high-income countries and urban areas appears higher than in rural environments. While environmental factors like pollution or nutrition can be important, it is more likely that in the end they have a small association with allergies. Childhood infections and exposure to certain microbial antigens on the other hand seem to present a strong negative correlation with allergies, and therefore the increase of the allergic burden in the Western world has been frequently related to a decline of childhood infections giving birth to the "Hygiene Hypothesis". We address the issue with emphasis on the associated pathophysiology tightrope walking between the skepticism of the critics, which cast doubt on it, and the pilgrims' belief of having discovered allergy's Holy Grail.

Are cats and dogs the major source of endotoxin in homes?

Previous studies have suggested that exposure to cats and dogs during early childhood reduces the risk of allergic disease, possibly by increasing home endotoxin exposure. This study asked the question of whether cats and dogs are the dominant influence on dust endotoxin concentrations in homes after considering other variables reportedly associated with endotoxin. The presence of cats or dogs in homes, household and home characteristics, and dust endotoxin concentrations from 5 locations were assessed in 966 urban and suburban homes. Whether considered together as pets or as cats and dogs separately, the presence of cats and dogs significantly contributed to living room and bedroom floor endotoxin concentrations, but not to bed endotoxin concentrations. However, the two variables consistently related to endotoxin in all home sites were the home occupant density (occupants/room) and cleanliness of the home. Our data suggest that reducing occupant density and improving home cleanliness would reduce home endotoxin concentrations more than removing pet cats or dogs from the home.

PRACTICAL IMPLICATIONS

Many studies have shown that early childhood exposure to indoor cats or dogs is associated with a reduced risk of later allergic disease and asthma. An important question is whether alteration in allergic risk associated with cat and dog exposure results from increased endotoxin exposure or from some other associated exposure. Our findings show that cats and dogs are not the dominant source of endotoxin in homes; rather, the density of human occupation and poor cleaning contribute more consistently to higher home endotoxin concentrations especially in the beds.

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').

House dust bioactivities predict skin prick test reactivity for children with high risk of allergy

BACKGROUND

Although evidence suggests that ambient exposures to endotoxin and other immunostimulants during early life influence allergic risk, efforts to understand this host-environment relationship have been hampered by a paucity of relevant assays.

OBJECTIVES

These investigations determined whether parameters of house dust extract (HDE) bioactivity were predictive of allergen skin prick test (SPT) reactivity for infants at high risk of allergy participating in the Cincinnati Childhood Allergy and Air Pollution Study (CCAAPS).

METHODS

We conducted a nested case-control study, selecting 99 CCAAPS children who had positive SPT results to at least 1 aeroallergen at age 3 years and 101 subjects with negative SPT results. HDEs were prepared from dust samples collected from the subjects' homes at age 1 year. Murine splenocytes and bone marrow-derived dendritic cells were incubated with HDEs, and supernatant cytokine concentrations were determined by means of ELISA. Alternatively, bone marrow-derived dendritic cells were preincubated with HDEs, and then LPS-induced IL-6 responses were assessed. HDE endotoxin levels were determined by using the limulus amebocyte lysate assay.

RESULTS

HDEs derived from the homes of children with positive (cases) and negative (control subjects) SPT results had similar bioactivities. However, when cases were considered in isolation, HDEs with higher levels of bioactivity were significantly associated with children who had lower numbers of positive SPT results. Analogous statistical analyses did not identify any association between HDE endotoxin levels and the aeroallergen sensitization profiles of children included in this study.

CONCLUSION

HDE immunostimulatory activities predicted the aeroallergen sensitization status of CCAAPS subjects better than HDE endotoxin levels. These results provide the first published evidence that HDE bioassays have clinical relevance in predicting atopic risk.

Geographical variation and the determinants of domestic endotoxin levels in mattress dust in Europe

Endotoxin exposures have manifold effects on human health. The geographical variation and determinants of domestic endotoxin levels in Europe have not yet been extensively described. To investigate the geographical variation and determinants of domestic endotoxin concentrations in mattress dust in Europe using data collected in the European Community Respiratory Health Survey follow-up (ECRHS II). Endotoxin levels were measured in mattress dust from 974 ECRHS II participants from 22 study centers using an immunoassay. Information on demographic, lifestyle, and housing characteristics of the participants was obtained in face-to-face interviews. The median endotoxin concentration in mattress dust ranged from 772 endotoxin units per gram (EU/g) dust in Reykjavik, Iceland, to 4806 EU/g in Turin, Italy. High average outdoor summer temperature of study center, cat or dog keeping, a high household crowding index, and visible damp patches in the bedroom were significantly associated with a higher endotoxin concentrations in mattress dust. There is a large variability in domestic endotoxin levels across Europe. Average outdoor summer temperature of study center, which explains only 10% of the variation in domestic endotoxin level by center, is the strongest meteorological determinant. The observed variation needs to be taken into account when evaluating the health effects of endotoxin exposures in international contexts.

PRACTICAL IMPLICATIONS

The incoherent observations of the health effects of endotoxin may be partly owing to the geographical heterogeneity of endotoxin exposure. Therefore, the observed variation should be considered in further studies. Measurements of indoor endotoxin are recommended as an indicator for the level of exposures of individual domestic environments.

A 10-year serological follow-up of celiac disease in an Estonian population

BACKGROUND

Celiac disease (CD) is induced by wheat gluten and related prolamines. Its prevalence may be underestimated in many geographic regions and populations, and has recently increased in several countries. In 1998 and 1999, a random sample of Estonian schoolchildren was screened with IgA-type tissue transglutaminase antibodies (IgA-tTG) for CD. The results revealed a CD prevalence of 0.34%, which is lower compared with many other European countries.

OBJECTIVE

We rescreened the same population for CD using IgA-tTG after a 10-year interval.

MATERIALS AND METHODS

A total of 891 patients from the initial sample were rescreened using the IgA-tTG assay for a participation rate of 76.8% (median age, 24.3 years). As in the initial study, the IgA-tTG results were evaluated by ImmunoCAP EliA Celikey using an IgG-tTG and deamidated gliadin antibody assay for IgA-deficient cases.

RESULTS

No new cases of CD were found in this follow-up study. Of note, 75% of patients with initial IgA-tTG-positive results and biopsy-proven CD remained seropositive. One patient with a negative seroconversion at the time of rescreening followed a strict gluten-free diet during the follow-up years.

CONCLUSION

In a 10-year follow-up period, no new cases of CD were found in this Estonian population of school-children and young adults. Therefore, we presume no increase in CD during the last decade among this age group in Estonia. Additional studies are needed to determine whether similar results would be obtained in other age groups, because of differences in the CD prevalence between Estonian and other European populations.

Importance of allergy in asthma: an epidemiologic perspective

There has been a global epidemic of asthma during the past half-century. More recently, the prevalence has leveled off or declined in many Western countries, whereas the prevalence in less affluent nations is still increasing. The reasons for this and the different geographical patterns of asthma prevalence remain unclear. This paper provides an epidemiologic perspective on whether allergen exposure and allergies can explain these trends. In particular, the paper discusses 1) geographical and temporal trends in asthma and the role of allergens and allergy, 2) the importance of nonallergic mechanisms, 3) nonallergenic exposures that may modify the risk of allergies and asthma, and 4) new and emerging risk and protective factors. Although allergy and asthma are closely related, allergen exposure and allergy alone cannot explain current time trends and geographical patterns of asthma. Population-based studies focusing on recently identified risk and protective factors may provide further insight.

Low diversity of the gut microbiota in infants with atopic eczema

BACKGROUND

It is debated whether a low total diversity of the gut microbiota in early childhood is more important than an altered prevalence of particular bacterial species for the increasing incidence of allergic disease. The advent of powerful, cultivation-free molecular methods makes it possible to characterize the total microbiome down to the genus level in large cohorts.

OBJECTIVE

We sought to assess microbial diversity and characterize the dominant bacteria in stool during the first year of life in relation to atopic eczema development.

METHODS

Microbial diversity and composition were analyzed with barcoded 16S rDNA 454-pyrosequencing in stool samples at 1 week, 1 month, and 12 months of age in 20 infants with IgE-associated eczema and 20 infants without any allergic manifestation until 2 years of age (ClinicalTrials.gov ID NCT01285830).

RESULTS

Infants with IgE-associated eczema had a lower diversity of the total microbiota at 1 month (P = .004) and a lower diversity of the bacterial phylum Bacteroidetes and the genus Bacteroides at 1 month (P = .02 and P = .01) and the phylum Proteobacteria at 12 months of age (P = .02). The microbiota was less uniform at 1 month than at 12 months of age, with a high interindividual variability. At 12 months, when the microbiota had stabilized, Proteobacteria, comprising gram-negative organisms, were more abundant in infants without allergic manifestation (Empirical Analysis of Digital Gene Expression in R [edgeR] test: P = .008, q = 0.02).

CONCLUSION

Low intestinal microbial diversity during the first month of life was associated with subsequent atopic eczema.

Slow salivary secretory IgA maturation may relate to low microbial pressure and allergic symptoms in sensitized children

It is unknown why allergic symptoms do not develop in all sensitized children. We analyzed prospectively the postnatal secretory IgA (SIgA) development and whether high SIgA levels would protect sensitized infants from developing allergic symptoms. Salivary total IgA and SIgA levels were determined by ELISA, and allergy development was investigated at 3, 6, and 12 mo and at 2 and 5 y in two birth cohorts in Estonia (n = 110) and Sweden (n = 91), two geographically adjacent countries with different living conditions and allergy incidence. Total and SIgA levels increased with age, reaching adult levels at the age of 5. Virtually, all salivary IgA in Estonian children was in the secretory form, while a major part of IgA in Swedish saliva lacked the secretory component up to 2 y of age. In Sweden, high levels of salivary IgA without secretory component correlated inversely with house dust endotoxin levels. High SIgA levels were associated with less development of allergic symptoms in sensitized Swedish children. In conclusion, postnatal maturation of the salivary SIgA system proceeds markedly slower in Swedish than Estonian children, possibly as a consequence of low microbial pressure. SIgA may limit allergy-mediated tissue damage at mucosal surfaces in sensitized individuals.

Early colonization with a group of Lactobacilli decreases the risk for allergy at five years of age despite allergic heredity

Background

Microbial deprivation early in life can potentially influence immune mediated disease development such as allergy. The aims of this study were to investigate the influence of parental allergy on the infant gut colonization and associations between infant gut microbiota and allergic disease at five years of age.

Methods and Findings

Fecal samples were collected from 58 infants, with allergic or non-allergic parents respectively, at one and two weeks as well as at one, two and twelve months of life. DNA was extracted from the fecal samples and Real time PCR, using species-specific primers, was used for detection of Bifidobacterium (B.) adolescentis, B. breve, B. bifidum, Clostridium (C.) difficile, a group of Lactobacilli (Lactobacillus (L.) casei, L. paracasei and L. rhamnosus) as well as Staphylococcus (S.) aureus. Infants with non-allergic parents were more frequently colonized by Lactobacilli compared to infants with allergic parents (p = 0.014). However, non-allergic five-year olds acquired Lactobacilli more frequently during their first weeks of life, than their allergic counterparts, irrespectively of parental allergy (p = 0.009, p = 0.028). Further the non-allergic children were colonized with Lactobacilli on more occasions during the first two months of life (p = 0.038). Also, significantly more non-allergic children were colonized with B. bifidum at one week of age than the children allergic at five years (p = 0.048).

Conclusion

In this study we show that heredity for allergy has an impact on the gut microbiota in infants but also that early Lactobacilli (L. casei, L. paracasei, L. rhamnosus) colonization seems to decrease the risk for allergy at five years of age despite allergic heredity.

Breast milk cytokine and IgA composition differ in Estonian and Swedish mothers-relationship to microbial pressure and infant allergy

The immune system of the neonate is influenced by maternal immunity during pregnancy and lactation. An altered microbial exposure, possibly underlying the increase of allergic diseases in affluent societies, may affect maternal breast milk immune composition. Secretory IgA (SIgA), IL-4, IL-10, IL-13, IFN-[gamma], TGF-[beta]1, and TGF-[beta]2 were analyzed with ELISA in colostrum and 1-mo mature milk from mothers from Estonia (n = 39) and Sweden (n = 60), the two geographically adjacent countries with different living conditions and allergy incidence. The IL-10 and IFN-[gamma] levels were higher in colostrum from Estonian than Swedish mothers, whereas the opposite was true for TGF-[beta]2. In mature milk, higher SIgA and IFN-[gamma] levels but lower TGF-[beta]1 and TGF-[beta]2 levels were observed in Estonian than Swedish mothers. Interestingly, in Sweden but not Estonia, the TGF-[beta]1 and TGF-[beta]2 levels correlated inversely with environmental endotoxin concentrations, whereas positive correlations to microbial load were observed for IL-4, IL-10, and IFN-[gamma]. High colostral IL-13 levels were associated with allergic sensitization during infancy in Sweden. In conclusion, Estonian mothers have lower breast milk levels of TGF-[beta], particularly TGF-[beta]2, but higher levels of SIgA, IL-10, and IFN-[gamma] than Swedish mothers, possibly because of differences in microbial load.

Variation of dust endotoxin concentrations by location and time within homes of young children

Endotoxin may affect the development of allergic disease in childhood but little is known about endotoxin variation within homes. We sought to determine endotoxin concentration agreement within homes when five locations were each sampled twice 5 months apart. Endotoxin was measured using the recombinant Limulus factor C assay in dust samples from 585 homes of children enrolled in a prospective study and again in 335 homes 5 months later. The five locations sampled in each home were the child's bedroom floor, child's bed, mother's bedroom floor, mother's bed and living room floor. Concentrations of 4 allergens (Can f 1, Fel d 1, Der f 1 and Bla g 2) were also measured from the child's bedroom floor. In pair-wise comparisons, endotoxin concentrations in all locations within each home were significantly different from all other locations (p < 0.001) except for the child's and mother's bedroom floors (p = 0.272). Spearman correlations between endotoxin concentrations from the different locations were all statistically significant (p < 0.05) but of modest magnitude (r = 0.24-0.54). Similarly, correlations at each site over the 5 month observation interval were statistically significant but modest (r = 0.17-0.44). Pets and season of the year did not affect correlations, although correlations were lower if the floor was not carpeted. Endotoxin concentrations at all locations were minimally correlated with allergen concentrations in both negative and positive directions (r = -0.12 to 0.12). We conclude that a single measurement of endotoxin from a home dust sample provides an imprecise estimate of dust endotoxin concentrations in other locations within the home and over a relatively short observation interval.

The role of lipopolysaccharide in the development of atopy in humans

Atopy is a highly prevalent condition and remains the single biggest risk factor for asthma. Although atopy has a heritable component, the time frame of the increase in the prevalence indicates that it is not due to genetic factors alone. The relationship between allergen exposure and sensitization is complex. Lipopolysaccharide (LPS) and its bioactive moiety endotoxin are common to all gram-negative bacteria, and have been used as a surrogate of microbial load. Endotoxin can be readily measured in dust collected from homes. Some studies have demonstrated a clear inverse dose-response relationship between exposure to endotoxin and the risk of atopy but this finding has not been reproduced in all studies. Our innate immune system recognizes LPS readily via the LPS signal transduction pathway, which has the trimolecular complex of CD14/TLR4/MD2 at the core. A common single-nucleotide polymorphism in the promoter region of CD14 rs2569190 C to T (CD14/-260 or CD14/-159) has been associated with elevated sCD14. Although early studies suggested that this variant was associated with more severe atopy, this finding was not uniformly replicated. It has now been demonstrated in four independent populations that high exposure to endotoxin in the domestic environment is protective against the development of atopy, but only among carriers of the C allele, that is, the environmental exposure is only relevant when taken in the context of the genotype. Furthermore, this interaction is biologically plausible. We propose that neither the environmental exposure nor the genotype in isolation is sufficient to cause complex diseases like asthma and atopy, but disease results from the one acting in the context of the other, of which CD14 and endotoxin is one example contributing to the risk for atopy.

Microbial content of house dust samples determined with qPCR

This study was designed to produce information about microbial concentrations using qPCR and their variation in different seasons and home environments with analyses of two types of house dust samples. Also the correlations between the two types of samples and the reproducibility of the parallel subsamples were studied. Two types of vacuumed house dust samples, rug dust and vacuum cleaner bag dust, were collected in 5 normal urban homes in four different seasons (N=20+20). From all dust samples, five parallel subsamples were subjected to qPCR analyses of 17 microbial species or assay groups of microbes. The highest fungal concentrations were found for the Penicillium/Aspergillus/Paecilomyces variotii group, and for the species Aspergillus penicillioides, Aureobasidium pullulans, Cladosporium cladosporioides and Cladosporium herbarum. These species/groups were present in almost all samples. The two types of dust samples gave similar results for most microbial species or groups analyzed, but in general, concentrations were slightly higher in rug dust than in dust from vacuum cleaner bag. Microbial concentrations varied significantly between different seasons and hence the similarity of samples within home was mainly low. The concentrations varied significantly also between different home environments. The reproducibility of the parallel subsamples was good or moderate for most of the analyzed species or assay groups. However, further studies are needed to fully understand the factors causing variation in these methods. Nevertheless, in order to show actual differences in fungal concentrations between urban homes with no known microbial sources, all dust samples to be compared should be taken during the same season.

Comparisons of computer-controlled chamber measurements for soil-skin adherence from aluminum and carpet surfaces

A computer-controlled mechanical chamber was used to control the contact between carpet and aluminum sheet samples laden with soil, and human cadaver skin and cotton sheet samples for the measurement of mass soil transfer. The contact parameters of pressure (10-50 kPa) and time (10-50s) were varied for 768 experiments of mass soil transfer, where two soil types (play sand and lawn soil) and two soil particle sizes (<139.7 and 139.7<381 microm) were used. Mean soil mass transfer to cadaver skin was higher than mean transfer to cotton sheets for both carpet and aluminum transfers, and also generally higher pressure was associated with larger amounts of soil transfer for all contact scenarios. The mean soil adherence from carpet was 0.37+/-0.4 mg/cm(2), while the mean soil adherence from aluminum was 0.42+/-0.6 mg/cm(2). For aluminum, smaller soil particle size was associated with more transfer (p=0.0349), while for carpet, larger soil size was associated with more transfer (p<0.0001). Soil type was significant but only for aluminum surface, where sand was associated with higher adherence (p<0.0001). This data set can be used to improve estimates of dermal exposure to contaminants found in soils and dust present in indoor environments.

The low prevalence of allergic disease in Eastern Europe: are risk factors consistent with the hygiene hypothesis?

BACKGROUND

The prevalence of allergic disease is known to be low in Eastern Europe.

OBJECTIVE

To assess the association of suspected risk factors, including several closely linked to the hygiene hypothesis, with allergic symptoms and atopic sensitization in young school-aged children.

METHODS

Observational study of 13 889 Belarusian children followed up at age 6.5 years in the Promotion of Breastfeeding Intervention Trial (PROBIT). Allergic symptoms and diseases were based on parental responses to the International Study of Asthma and Allergy in Childhood questionnaire, and prick tests to five common inhalant allergens were performed using standard methods.

RESULTS

Significantly increased risks of wheezing and hayfever symptoms in the past 12 months, and of recurrent itchy rash were observed in boys, children with a positive first-degree family atopic history, and those who had received probiotics (especially as prophylaxis with antibiotic use). Pet ownership, contact with farm animals, the presence and number of younger and (especially) older siblings, and residency in rural areas of Western Belarus were associated with reduced risks. Maternal postnatal smoking was associated with wheezing and hayfever symptoms, while the duration of exclusive breastfeeding was not protective against any of the studied outcomes. The risk factors for allergic symptoms were similar in children with positive skin-prick tests to those in the overall cohort.

CONCLUSION

Many of the risk and protective factors we identified are consistent with those reported in Western countries and with the hygiene hypothesis. Further research on dietary and other environmental and genetic factors is necessary to understand the low prevalence of allergic disease in Belarus and other Eastern European countries.

Altered early infant gut microbiota in children developing allergy up to 5 years of age

BACKGROUND

Early colonization with bifidobacteria and lactobacilli is postulated to protect children from allergy, while Clostridium (C.) difficile colonization might be associated with allergic disease. Previous studies of infant gut microbiota in relation to subsequent allergy development have mostly employed culture-dependent techniques, studied genera of bacteria and the follow-up period was limited to 2 years.

OBJECTIVE

To relate gut microbiota in early infancy, notably bifidobacteria and lactobacilli at species level, to allergy development during the first 5 years of life and study if environmental factors influence the early infant gut microbiota.

METHODS

Fecal samples were collected at 1 week, 1 month and 2 months after birth from 47 Swedish infants, followed prospectively to 5 years of age. Bacterial DNA was analysed with real-time PCR and related to allergy development, family size as well as endotoxin and Fel d 1 levels in house dust samples. Primers binding to C. difficile, four species of bifidobacteria, two lactobacilli groups and Bacteroides fragilis were used. Children regarded as allergic manifested allergic symptoms and were skin prick test positive during their first 5 years while non-allergic children were neither.

RESULTS

Children who developed allergy were significantly less often colonized with lactobacilli group I (Lactobacillus (L.) rhamnosus, L. casei, L. paracasei), Bifidobacterium adolescentis and C. difficile during their first 2 months. Infants colonized with several Bifidobacterium species had been exposed to higher amounts of endotoxin and grew up in larger families than infants harbouring few species.

CONCLUSION

A more diverse gut microbiota early in life might prevent allergy development and may be related to the previously suggested inverse relationship between allergy, family size and endotoxin exposure.

Allergen tolerance versus the allergic march: the hygiene hypothesis revisited

In addition to genetics, several environmental variables appear to impact allergic risk. Meta-analyses of epidemiologic studies presented in this article demonstrate a correlation between specific ambient exposures (eg, livestock, pets, endotoxin, and unpasteurized milk ingestion) and reduced allergic risk during childhood. Additional laboratory investigations discussed in this review characterized the intrinsic immunostimulatory activities of living environments. Considered together, results of these investigations suggest a novel paradigm by which early-life home exposures to microbial products and other allergen-nonspecific immunostimulants modify allergic risk.

Domestic and farm-animal exposures and risk of non-Hodgkin's lymphoma in a population-based study in the San Francisco Bay Area

OBJECTIVE

To assess the association between animal exposures and non-Hodgkin's lymphoma (NHL).

METHODS

Exposure data were collected from 1,591 cases and 2,515 controls during in-person interviews in a population-based case-control study of NHL in the San Francisco Bay Area. Odds ratios (OR) and 95% confidence intervals (95% CI) were adjusted for potential confounders.

RESULTS

Pet owners had a reduced risk of NHL (OR, 0.71; 95% CI, 0.52-0.97) and diffuse large-cell lymphoma large cell (DLCL; OR, 0.58; 95% CI, 0.39-0.87) compared with those who never had owned a pet. Ever having owned dogs and/or cats was associated with reduced risk of all NHL (OR, 0.71; 95% CI, 0.54-0.94) and of DLCL (OR, 0.60; 95% CI, 0.42-0.86). Longer duration of cat ownership (P(trend) = 0.008), dog ownership (P(trend) = 0.04), and dog and/or cat ownership (P(trend) = 0.004) was inversely associated with risk of NHL. Ownership of pets other than cats and dogs was associated with a reduced risk of NHL (OR, 0.64; 95% CI, 0.55-0.74) and DLCL (OR, 0.58; 95% CI, 0.47-0.71). Exposure to cattle for >or=5 years was associated with an increased risk of NHL (OR, 1.6; 95% CI, 1.0-2.5) as was exposure to pigs for all NHL (OR, 1.8; 95% CI, 1.2-2.6) and for DLCL (OR, 2.0; 95% CI, 1.2-3.4).

CONCLUSIONS

The association between animal exposure and NHL warrants further investigation in pooled analyses.

Soil-skin adherence from carpet: use of a mechanical chamber to control contact parameters

A computer-controlled mechanical chamber was used to control the contact between carpet samples laden with soil, and human cadaver skin and cotton sheet samples for the measurement of mass soil transfer. Mass soil transfers were converted to adherence factors (mg/cm2) for use in models that estimate dermal exposure to contaminants found in soil media. The contact parameters of pressure (10 to 50 kPa) and time (10 to 50 sec) were varied for 369 experiments of mass soil transfer, where two soil types (play sand and lawn soil) and two soil sizes (< 139.7 microm and > or = 139.7 < 381) were used. Chamber probes were used to record temperature and humidity. Log transformation of the sand/soil transfers was performed to normalize the distribution. Estimated adjusted means for experimental conditions were exponentiated in order to express them in the original units. Mean soil mass transfer to cadaver skin (0.74 mg/cm2) was higher than to cotton sheets (0.21 mg/cm2). Higher pressure (p < 0.0001), and larger particle size (p < 0.0001) were also all associated with larger amounts of soil transfer. The original model was simplified into two by adherence material type (i.e., cadaver skin and cotton sheets) in order to investigate the differential effects of pressure, time, soil size, and soil type on transfer. This research can be used to improve estimates of dermal exposure to contaminants found in home carpets.

Defining a role for ambient TLR ligand exposures in the genesis and prevention of allergic diseases

Environmental variables responsible for the increasing allergic disease burden observed in developed countries over the last century have yet to be adequately characterized. Meta-analyses of epidemiological studies presented in the first half of this paper demonstrate a correlation between farm-associated exposures (i.e., livestock, pets, unpasteurized milk, and endotoxin) and a reduction in allergic risk during childhood. Laboratory investigations discussed in the second half of the paper characterize the intrinsic immunostimulatory activities of living environments. Considered together, experimental findings presented herein suggest a novel paradigm by which early life home exposures to microbial products and other allergen-nonspecific immunostimulants modify allergic risk.

Soluble CD14 and CD83 from human neonatal antigen-presenting cells are inducible by commensal bacteria and suppress allergen-induced human neonatal Th2 differentiation

CD14 is expressed on the cell surface of various antigen-presenting cells, and CD83 is a maturation marker for dendritic cells (DC). CD14 and CD83 are also present as soluble proteins, and both have immunoregulatory functions. We examined whether neonatal cord blood monocytes or DC released soluble CD14 (sCD14) or sCD83 when exposed to the commensal intestinal bacteria Clostridium perfringens, Staphylococcus aureus, Lactobacillus rhamnosus, Escherichia coli, and Bacteroides fragilis. We found that the gram-positive bacteria C. perfringens and S. aureus, but not gram-negative bacteria, induced the release of sCD14 from monocytes. DC, on the other hand, released sCD14 in response to both gram-positive and gram-negative bacteria. Moreover, the expression of the virulence factor staphylococcal protein A seemed to be important for S. aureus-induced sCD14 production from both monocytes and DC. Soluble CD83 was released from DC, but not from monocytes, when exposed to both gram-positive and gram-negative bacteria. Finally, to investigate whether sCD14 or sCD83 could modulate neonatal allergen-induced T-cell differentiation, DC were exposed to birch allergen alone or in the presence of sCD14 or sCD83 and then cocultured with autologous T cells. We demonstrate that sCD14 and sCD83 inhibited the birch allergen-induced Th2 differentiation by suppressing interleukin 13 production. Together, these results suggest that the commensal intestinal flora may be an important stimulus for the developing immune system by inducing the immunoregulatory proteins sCD14 and sCD83, which may be involved in preventing T-cell sensitization to allergens in infants.

Probiotics in prevention of IgE-associated eczema: a double-blind, randomized, placebo-controlled trial

BACKGROUND

An altered microbial exposure may underlie the increase of allergic diseases in affluent societies. Probiotics may alleviate and even prevent eczema in infants.

OBJECTIVE

To prevent eczema and sensitization in infants with a family history of allergic disease by oral supplementation with the probiotic Lactobacillus reuteri.

METHODS

Double-blind, randomized, placebo-controlled trial, which comprised 232 families with allergic disease, of whom 188 completed the study. The mothers received L reuteri ATCC 55730 (1 x 10(8) colony forming units) daily from gestational week 36 until delivery. Their babies then continued with the same product from birth until 12 months of age and were followed up for another year. Primary outcome was allergic disease, with or without positive skin prick test or circulating IgE to food allergens.

RESULTS

The cumulative incidence of eczema was similar, 36% in the treated versus 34% in the placebo group. The L reuteri group had less IgE-associated eczema during the second year, 8% versus 20% (P = .02), however. Skin prick test reactivity was also less common in the treated than in the placebo group, significantly so for infants with mothers with allergies, 14% versus 31% (P = .02). Wheeze and other potentially allergic diseases were not affected.

CONCLUSION

Although a preventive effect of probiotics on infant eczema was not confirmed, the treated infants had less IgE-associated eczema at 2 years of age and therefore possibly run a reduced risk to develop later respiratory allergic disease.

CLINICAL IMPLICATION

Probiotics may reduce the incidence of IgE-associated eczema in infancy.

Variation of biocontaminant levels within and between homes--the AIRALLERG study

Few epidemiological studies report on reliability of exposure measurements even though this significantly influences the results of correlation and regression analysis often used in these studies. Poor reliability of exposure measurement reduces the ability to detect a true association between a certain component and health outcome variables. The aim of this study was to determine the ratio of the within-home and between-home components of variance of a number of biocontaminants measured in house dust in the framework of an international study conducted in the Netherlands, Germany and Sweden (the AIRALLERG study). To this end, duplicate dust samples were collected from children's beds and from living room floors in over 100 homes. Samples were taken at the same point in time. Variables considered were the dust mass collected in mg/m2 and the concentrations of the house dust mite allergens Der p 1 and Der f 1, cat allergen Fel d 1, endotoxin, (1 --> 3)-beta-D-glucan and extracellular polysaccharides, all per gram of dust and per square meter of sampling surface. An analysis of variance showed that the within-home variance was small compared to the between-home variance for most variables (mostly less than half) with the exception of glucan on mattresses, when expressed in mug/g. Investigation of variation over time is needed for a more complete assessment of the use of these variables in epidemiological analyses of exposure-response relationships.

Determinants of house dust endotoxin in three European countries - the AIRALLERG study

The comparison of endotoxin levels between study populations and countries is limited as a result of differences in sampling, extraction, and storage procedures. The objective of this study is to assess the levels and determinants of endotoxin in mattress and living room floor dust samples from three European countries, namely, Germany, the Netherlands, and Sweden, using a standardized sampling, storage, and analysis protocol. The mattress and living room floor dust was collected from the homes of 1065 German, Dutch, and Swedish (pre-)school children. All the samples were collected in the cool season and analyzed for endotoxin in a central laboratory. The determinants were assessed by a standardized questionnaire. The endotoxin concentrations in mattress and living room floor dust were found to be the highest in German homes and lowest in the Swedish ones. Differences between the geometric means were small (factor 1.1-1.7). Most of the associations between endotoxin concentrations and potential determinants were not statistically significant and heterogeneous across countries. However, keeping pets and having more than four persons living in the home were consistently associated with up to 1.7-fold higher endotoxin concentrations in mattress and floor dust. Furthermore, having carpets or rugs, and opening the windows frequently was associated with up to 3.4-fold and 1.3-fold higher endotoxin concentrations in living room floor dust, respectively. The proportion of variance explained by the questionnaire variables was generally low. In conclusion, the data on housing characteristics did not accurately predict the endotoxin concentrations in house dust, and could only partly explain the differences between countries.

PRACTICAL IMPLICATIONS

The differences between the endotoxin concentrations in German, Dutch, and Swedish homes are small. House dust endotoxin concentrations are associated with a number of housing factors, such as pet-ownership, floor cover, number of persons living in the home, and ventilation. The variability of the endotoxin levels between homes and countries can only be partly explained by these factors.

Increased levels of circulating soluble CD14 but not CD83 in infants are associated with early intestinal colonization with Staphylococcus aureus

BACKGROUND

Soluble forms of the monocyte marker CD14 and the mature dendritic cell marker CD83 are plasma proteins with immunoregulatory functions. The physiological stimulus for their production is unclear and their possible role in allergy development is unknown.

METHODS

We measured the plasma levels of soluble CD14 (sCD14) and soluble CD83 (sCD83) in 64 Swedish children in relation to intestinal bacterial colonization pattern in a prospective birth cohort. Soluble CD14 and sCD83 levels were quantified by enzyme linked immunosorbent assay in plasma obtained at birth and at 4, 18 and 36 months of age. All major aerobic and anaerobic bacteria were quantified in faecal samples obtained regularly over the first 8 weeks of life. Clinical allergy and IgE levels were evaluated at 18 months of age.

RESULTS

Soluble CD14 in plasma increased during the first 18 months of life while sCD83 peaked at 4 months of age. Children who were perinatally colonized with Staphylococcus aureus had significantly higher levels of sCD14 in plasma at 4 months of age relative to non-colonized children. The levels of sCD14 were unrelated to colonization with Escherichia coli, other enterobacteria, enterococci, clostridia, Bacteroides, bifidobacteria or lactobacilli. Further, children with food allergy by 18 months tended to have lower levels of sCD14 than healthy children. Plasma levels of sCD83 were not related to either bacterial colonization pattern or allergy development.

CONCLUSIONS

Perinatal colonization with S. aureus may trigger the occurrence of sCD14 in plasma, which may influence development of the infantile immune system and risk of allergy development.

Influence of dog ownership and high endotoxin on wheezing and atopy during infancy

BACKGROUND

Increased exposure to microbial products early in life may protect from development of atopic disorders in childhood. Few studies have examined the relationship of endotoxin exposure and pet ownership on atopy and wheezing during infancy.

OBJECTIVE

Evaluate relationships among high endotoxin exposure, pet ownership, atopy, and wheezing in high-risk infants.

METHODS

Infants (n = 532; mean age, 12.5 +/- 0.8 months) with at least 1 parent with confirmed atopy were recruited. A complete medical history and skin prick testing to foods and aeroallergens were performed at age 1 year. House dust samples were analyzed for endotoxin.

RESULTS

Prevalences of wheezing were not independently associated with dog or cat ownership or endotoxin levels. Percutaneous reactivity to at least 1 allergen was observed in 28.6% of infants. Univariate analyses showed significant associations of any wheezing, recurrent wheezing, and recurrent wheezing with an event with daycare attendance, number of siblings, respiratory infections, maternal smoking, and history of parental asthma. Logistic regression adjusting for the latter variables showed that recurrent wheezing (odds ratio, 0.4; 95% CI, 0.1-0.9) as well as 2 other wheeze outcomes were significantly reduced in homes with high endotoxin exposure in the presence of 2 or more dogs.

CONCLUSION

Pet ownership or endotoxin did not independently modify aeroallergen sensitization or wheezing during infancy. However, high endotoxin exposure in the presence of multiple dogs was associated with reduced wheezing in infants.

CLINICAL IMPLICATIONS

A home environment with many dogs and high levels of endotoxin may be conducive to reduced wheezing in infancy.

Association between exposure to farming, allergies and genetic variation in CARD4/NOD1

BACKGROUND

Caspase recruitment domain protein (CARD) 4 has been recently identified as an intracellular pattern recognition receptor that interacts with muropeptides found in common Gram-negative bacteria. We therefore aimed to explore whether the previously observed inverse association between exposure to microbial products and asthma and allergies in childhood is modified by genetic variation in CARD4.

METHODS

We genotyped 668 children [mean age 9.3 (SD 1.5) years] enrolled in the cross-sectional ALEX study for seven haplotype tagging single nucleotide polymorphisms in CARD4. We studied the association of asthma, hay fever and allergen-specific serum immunoglobulin E with exposure to a farming environment and with levels of endotoxin and muramic acid measured in house dust samples. We tested whether these associations differed between the genotypes of the polymorphisms under study.

RESULTS

A strong protective effect of a farming environment on allergies was only found in children homozygous for the T allele in CARD4/-21596, but not in children carrying the minor allele (C). Among the former, farmers' children had a significantly lower frequency of sensitization against pollen (5.8%), hay fever (1.7%) and atopic asthma symptoms (1.7%) compared with children not living on a farm (19.4%, 13.0% and 7.6%, P<0.01, <0.01 and <0.05, respectively). Conversely, no significant difference in prevalence of these phenotypes by farming status was found among children with a C allele in CARD4/-21596 (14.3%, 7.1% and 8.0%vs 16.5%, 9.0% and 5.7%, respectively).

CONCLUSION

Polymorphisms in CARD4 significantly modify the protective effect of exposure to a farming environment.

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.

Childhood asthma and indoor aeroallergens and endotoxin in Palestine: a case-control study

This study was carried out to evaluate the relationship between wheezing or sensitization and concentrations of mites, cat and dog allergens, and bacterial endotoxin in Palestine. A nested case-control involved analysis of mattress and floor dust from a 110 children's houses with reported wheezing and without wheezing. We found no consistent associations between allergen levels and either wheeze or specific atopic sensitization. Furthermore, no clear associations between mattress endotoxin levels and wheeze or atopy were found. Endotoxin in floor dust was inversely associated with atopic sensitization and wheeze, statistically significant only for atopic wheeze. Finally, a nonsignificant inverse association was observed between living room endotoxin and atopy within the non-wheezing control group. In conclusion, although our study found mostly negative results, it does suggest that endotoxin on living room floors might protect against atopic wheeze. However, this finding should be interpreted with caution due the relatively small sample size of the study and requires further confirmation.

Too clean, or not too clean: the hygiene hypothesis and home hygiene

The 'hygiene hypothesis' as originally formulated by Strachan, proposes that a cause of the recent rapid rise in atopic disorders could be a lower incidence of infection in early childhood, transmitted by unhygienic contact with older siblings. Use of the term 'hygiene hypothesis' has led to several interpretations, some of which are not supported by a broader survey of the evidence. The increase in allergic disorders does not correlate with the decrease in infection with pathogenic organisms, nor can it be explained by changes in domestic hygiene. A consensus is beginning to develop round the view that more fundamental changes in lifestyle have led to decreased exposure to certain microbial or other species, such as helminths, that are important for the development of immunoregulatory mechanisms. Although this review concludes that the relationship of the hypothesis to hygiene practice is not proven, it lends strong support to initiatives seeking to improve hygiene practice. It would however be helpful if the hypothesis were renamed, e.g. as the 'microbial exposure' hypothesis, or 'microbial deprivation' hypothesis, as proposed for instance by Bjorksten. Avoiding the term 'hygiene' would help focus attention on determining the true impact of microbes on atopic diseases, while minimizing risks of discouraging good hygiene practice.

The PASTURE project: EU support for the improvement of knowledge about risk factors and preventive factors for atopy in Europe

Since January 2002, the European Commission is funding a large project, 'Protection against Allergy--Study in Rural Environments' (PASTURE; contract no. QLK4-2001-00250), under the Fifth Framework Program in the field of epidemiology of allergic diseases. The aim of this paper was to describe the background and design as well as the aims of the project. Asthma and allergic disorders are a major public health problem in many Western countries. The aetiology of asthma and allergic disease remains poorly understood despite considerable research. Epidemiology has the potential to add greatly to the understanding by elucidating the risk factors for asthma and allergic disease and thereby suggesting productive avenues for research into causation and prevention. Several risk factors for the development of asthma and atopic disease in children such as passive smoke exposure during pregnancy and infancy, low birth weight or high body mass index later in life have been described. Furthermore, there is consistent evidence that the prevalence of atopy increases with higher socio-economic status. Levels of air pollution such as ozone, NO2, SO2 and particles are likely to provoke acute exacerbations of pre-existent respiratory disease. Their role in the inception of asthma and allergies remains to be clarified. Allergen exposure has been linked to the development of atopic sensitization to that particular allergen in children as well as in adults with occupational exposures. Exposure to house dust mite or cat allergen is, however, unlikely to contribute to the development of childhood asthma. In turn, pet keeping in the first year of life, particularly, dog keeping, has been inversely related to the development of wheeze and atopic illnesses. Several prospective birth cohort studies found a decreased prevalence of atopic disease in children having daily contact to pets, in particular to cats and dogs, during early infancy. The protective effect might be attributable to allergen or other exposures associated with pet ownership, but may also in part be because of the removal of pets in families with sensitized or symptomatic children or in families with a positive history for atopy at the time the child was born.

Does early indoor microbial exposure reduce the risk of asthma? The Prevention and Incidence of Asthma and Mite Allergy birth cohort study

BACKGROUND

Exposure to microbial agents might inhibit the development of atopy and asthma.

OBJECTIVE

We measured the association between microbial exposure assessed at 3 months and the development of atopic sensitization and doctor-diagnosed (DD) asthma and wheeze in the first 4 years in a birth cohort study of children with atopic mothers.

METHODS

Endotoxin, fungal (1-->3)-beta-D-glucans, extracellular polysaccharides from the genera Penicillium and Aspergillus (EPS-Pen/Asp), and dust on living room floors were measured at 3 months of age. Serum IgE levels against common allergens were determined at 1 and 4 years, and questionnaire information about respiratory morbidity was collected yearly.

RESULTS

Microbial levels in mattresses were low and not associated with serum IgE levels, DD asthma, and wheeze. Floor levels of biocontaminants and dust, on the other hand, were inversely associated with DD asthma, being most pronounced for endotoxin (odds ratio [OR], 0.40; 95% CI, 0.21-0.77) and EPS-Pen/Asp (OR, 0.42; 95% CI, 0.18-0.99). Mutual adjustment for other exposures did not significantly alter the results for endotoxin and only moderately affected the results for EPS-Pen/Asp. Persistent wheeze was also consistently less common in the high-exposure group, being significant only for EPS-Pen/Asp (OR, 0.37; 95% CI, 0.15-0.96). Transient wheeze and wheeze in the past 12 months were also reduced, but effects were smaller and not significant. Relationships with serum-specific IgE levels, which could only be assessed in 41% at age 4 years, were less pronounced and statistically significant only for EPS-Pen/Asp.

CONCLUSIONS

Early exposure to common microbial contaminants, including fungal agents, might protect against asthma.

CLINICAL IMPLICATIONS

Microbial exposure in early life might protect against asthma and might constitute a novel target for prevention.

Dust sampling methods for endotoxin - an essential, but underestimated issue

Exposure to farming environment in early life has been associated with lower risk for allergic diseases possibly caused by increased exposure to endotoxin. The aims of this study were to compare the reproducibility of different sampling methods for endotoxin, and to determine whether environmental characteristics have different effect on endotoxin levels of different sample types. The reproducibility of sampling methods (bed dust, floor dust, vacuum cleaner dust bag dust, settled dust and air samples) was studied with repeated sampling (five visits during 1 year) in five farming and five urban homes. To examine determinants of endotoxin for different types of dust sample, sampling was conducted once in 12 farming and 17 urban homes. Endotoxin was analyzed using Limulus Amebocyte Lysate assay. Bed dust samples had the best reproducibility (intraclass correlation, ICC=66%), but the difference between farming and non-farming homes was not clear with this sample type. The reproducibility of floor (ICC=52%) and settled dust (ICC=51%) was moderate. With these sample types the difference between farming and non-farming homes was clear. Settled dust had some seasonal variation. Based on this study, the best compromise for sampling for endotoxin appears to be floor dust sample followed by bed and settled dust samples. Practical Implications Endotoxins have been widely measured, even though the validity of different sample types to reflect the endotoxin exposure level of an indoor environment is poorly known. This study shows that bed dust samples have the best reproducibility, but they do not reflect the differences in exposure due to environmental factors such as farming. Floor dust samples with moderate reproducibility may be the best choice for sampling of endotoxin in large field studies.

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.

Allergens and endotoxin in settled dust from day-care centers and schools in Oslo, Norway

Allergy to indoor allergens can cause frequent and severe health problems in children. Because little is known about the content of allergens in the indoor environments in Norway, we wanted to assess the levels of cat, dog and mite allergens in schools and day-care centers in Oslo. Allergen levels in dust samples from 155 classrooms and 81 day-care units were measured using commercially available enzyme-linked immunosorbent assay (ELISA) kits. Additionally, we measured the levels of endotoxin in 31 day-care units, using the limulus amebocyte lysate test. Most of the dust samples contained detectable amounts of cat and dog allergens. In mattress and floor dust (day-care centers), and curtain and floor dust (schools) the median Fel d 1 levels were 0.17, 0.002, 0.02 and 0.079 microg/m2, while the median Can f 1 levels were 1.7, 0.03, 0.1 and 0.69 microg/m2, respectively. Levels of cat and dog allergens in school floor dust were associated with the number of pupils with animals at home. In contrast, <1% of the samples had measurable levels of the mite allergen Der p 1. Moreover, the levels of endotoxin tended to be higher in dust from floors (1.4 ng/m2) compared with that from mattresses (0.9 ng/m2).

PRACTICAL IMPLICATIONS

To reduce allergen exposure, allergic individuals should be placed in the classes/rooms with the fewest pet owners. Moreover, mattresses in day-care centers are major reservoirs of cat and dog allergens and should be cleaned frequently.

Prenatal lipopolysaccharide-exposure prevents allergic sensitization and airway inflammation, but not airway responsiveness in a murine model of experimental asthma

BACKGROUND

Epidemiological evidence underlines the impact of prenatal environmental factors on the development of postnatal allergies. In this regard an inverse correlation between lipopolysaccharide (LPS) exposure and development of childhood allergy has been found.

OBJECTIVE

To assess the impact of prenatal LPS exposure on the development of postnatal respiratory allergies in a mouse model of experimental asthma.

METHODS

Female BALB/c mice were exposed to LPS before conception and during pregnancy. Several weeks after birth offspring were sensitized to ovalbumin (OVA) followed by aerosol allergen challenges.

RESULTS

Prenatal, maternal LPS-exposure enhanced neonatal IFN-gamma, but not IL-4 and IL-2 production. OVA sensitization of prenatally LPS-exposed mice was accompanied by a marked suppression in anti-OVA IgG1 and IgE as well as unchanged IgG2a antibody responses, paralleled by a significant reduction in IL-5 and IL-13 levels following mitogenic stimulation of splenic leucocytes. Assessment of bronchoalveolar lavage fluids following allergen challenges revealed a marked reduction in eosinophils and macrophages in these mice. Surprisingly, development of airway hyper-responsiveness, a hallmark of bronchial asthma, was not affected.

CONCLUSION

This study provides first experimental evidence that LPS may already operate in prenatal life in order to modulate the development of allergies in the offspring.