Do only European cattle protect from allergies?

The relationships between environmental bacterial exposure, airway bacterial colonization, and asthma

PURPOSE OF REVIEW

Recent application of advanced culture-independent molecular techniques for the identification of microorganisms has contributed to our knowledge on the role of early-life microbial exposure and colonization in health and disease. The purpose of this review is to present the current perspectives regarding the role of microbial exposure and airway bacterial colonization on the development and the activity of asthma.

RECENT FINDINGS

Recent findings continue to support the protective role of early-life diverse microbial exposure against the development of atopic diseases. However, airway bacterial colonization early in life serves as a risk factor for the development of asthma. Culture-independent molecular techniques for the identification of microorganisms have challenged the traditional paradigm that the lower airway is a sterile compartment. Asthmatics, compared with nonasthmatics, appear to have a different lung microbiome composition and some of these differences might contribute to asthma activity, severity, and corticosteroid response.

SUMMARY

Bacterial presence in the airway appears to influence the inception and may affect the activity of asthma. Complex interactions between different types and routes of bacterial exposures, the airway, and the immune system early in life may determine whether these exposures augment or reduce the risk of asthma development.

Epigenetics in asthma and COPD

Epigenetic mechanisms are likely to play a role in many complex diseases, the extent of which we only beginning to understand. COPD and asthma are two respiratory diseases subject to strong environmental influences depending on underlying genetic susceptibility. Epigenetic mechanisms such as DNA methylation, histone modification and microRNA may be involved in these processes by modulating environmental effects to influence disease development. Given their demonstrated modifiable nature, epigenetic mechanisms may open new possibilities for therapeutic intervention. Here we give an overview of recent developments in the field of respiratory epigenetics in relation to asthma and COPD in the context of our current understanding of mechanisms leading to such diseases.

A polymorphism in CD14 modifies the effect of farm milk consumption on allergic diseases and CD14 gene expression

BACKGROUND

Consumption of farm milk in early life is associated with less asthma and allergies.

OBJECTIVE

We hypothesized that genetic variation in the innate immunity receptor CD14 might modify the association between farm milk consumption and asthma and atopy.

METHODS

Questionnaire data, serum IgE levels, and genotypes for 4 single nucleotide polymorphisms in CD14 were assessed in farmers' and nonfarmers' children from 2 European populations (Allergy and Endotoxin study, n = 576; Prevention of Allergy Risk factors for Sensitization in children related to Farming and Anthroposophic Lifestyle study, n = 1539). In a subsample (n = 222) CD14 gene expression was measured in peripheral blood leukocytes. The effects of farm milk and CD14 genotypes on asthma, allergies, and CD14 expression and their interactions were investigated.

RESULTS

We found a significant interaction between genetic variation in CD14/-1721 and farm milk consumption. Adjusted odds ratios for the association between farm milk and asthma varied between the genotypes: AA, 0.18 (95% CI, 0.07-0.47); AG, 0.47 (95% CI, 0.26-0.86); and GG, 0.98 (95% CI, 0.46-2.08). Similar patterns were observed for symptoms of allergic rhinoconjunctivitis and pollen sensitization. CD14/-1721 also modified the association between farm milk and CD14 gene expression (adjusted geometric means ratios: AA, 1.61 (95% CI, 0.98-2.66); AG, 1.11 (95% CI, 0.71-1.72); and GG, 0.76 (95% CI, 0.39-1.48).

CONCLUSION

The protective effect of farm milk consumption on allergic diseases is stronger in children carrying the A allele in CD14/-1721 than in children homozygous for the G allele. This might be mediated through farm milk-induced upregulated CD14 gene expression.

CLINICAL IMPLICATIONS

Our results support the hypothesis that the inverse association between farm milk consumption and allergic diseases is mediated by CD14-activated innate immune mechanisms.

Bacterial and fungal components in house dust of farm children, Rudolf Steiner school children and reference children--the PARSIFAL Study

BACKGROUND

Growing up on a farm and an anthroposophic lifestyle are associated with a lower prevalence of allergic diseases in childhood. It has been suggested that the enhanced exposure to endotoxin is an important protective factor of farm environments. Little is known about exposure to other microbial components on farms and exposure in anthroposophic families.

OBJECTIVE

To assess the levels and determinants of bacterial endotoxin, mould beta(1,3)-glucans and fungal extracellular polysaccharides (EPS) in house dust of farm children, Steiner school children and reference children.

METHODS

Mattress and living room dust was collected in the homes of 229 farm children, 122 Steiner children and 60 and 67 of their respective reference children in five European countries. Stable dust was collected as well. All samples were analysed in one central laboratory. Determinants were assessed by questionnaire.

RESULTS

Levels of endotoxin, EPS and glucans per gram of house dust in farm homes were 1.2- to 3.2-fold higher than levels in reference homes. For Steiner children, 1.1- to 1.6-fold higher levels were observed compared with their reference children. These differences were consistently found across countries, although mean levels varied considerably. Differences between groups and between countries were also significant after adjustment for home and family characteristics.

CONCLUSION

Farm children are not only consistently exposed to higher levels of endotoxin, but also to higher levels of mould components. Steiner school children may also be exposed to higher levels of microbial agents, but differences with reference children are much less pronounced than for farm children. Further analyses are, however, required to assess the association between exposure to these various microbial agents and allergic and airway diseases in the PARSIFAL population.

Can we prevent allergy?

Allergic conditions continue to increase steeply. The last two decades have seen many prevention trials, studying the effect of dietary and environmental interventions. These trials have yielded invaluable information about the atopic march and also highlighted the need for a clear and commonly used nomenclature as well as a need for better outcome measures. This review discusses primary and secondary prevention studies and their results.