Many genetic risk factors have been reported to modify susceptibility to asthma and allergy, but the dramatic increase in the prevalence of these conditions in westernized countries in the past half-century suggests that the environment also plays a critical role. The importance of environmental exposures in the development of asthma is most exquisitely illustrated by epidemiologic studies conducted in Central Europe that show significant protection from asthma and allergic disease in children raised on traditional dairy farms.
- Donata Vercelli, M.D.
- Fernando D. Martinez, M.D.
- Raina M. Maier, Ph.D.
- Despite the similar genetic ancestries and lifestyles of Amish and Hutterite children, the prevalence of asthma and allergic sensitization was 4 and 6 times as low in the Amish.
- Median endotoxin levels in Amish house dust was 6.8 times as high.
- Differences in microbial composition were also observed in dust samples from Amish and Hutterite homes.
- Profound differences in the proportions, phenotypes, and functions of innate immune cells were also found between the two groups of children.
- In a mouse model of experimental allergic asthma, the intranasal instillation of dust extracts from Amish but not Hutterite homes significantly inhibited airway hyperreactivity and eosinophilia.
- These protective effects were abrogated in mice that were deficient in MyD88 and Trif, molecules that are critical in innate immune signaling.
- The results of the studies in humans and mice indicate that the Amish environment provides protection against asthma by engaging and shaping the innate immune response.