Lesson from the farm environment.
OBJECTIVE
Several population-based studies have replicated the finding that exposure to a farm environment is protective against the development of atopic diseases. From these studies, novel insights into potential allergy-protective mechanisms were retrieved. This review focuses on consistent and novel findings of immune mechanisms involved in the 'farm effect'.


RESULTS
The most recent studies suggest that the 'farm effect' mediated by microbial exposure may be attributed to both microbial diversity and species specificity. There is convincing evidence that farm milk components and grass arabinogalactan, commonly found in cowshed, may be important. Furthermore, early exposure to a farming environment, in particular in utero, showed stronger effects than exposure later in life, potentially through modulation of the immature immune system by microbes, also involving epigenetic changes. This protective 'farm effect' remains in later adulthood. Regarding gene-environment interactions, polymorphisms in GRM1 interacted with farming in a genome-wide interaction scan for asthma.


CONCLUSIONS
The novel studies strengthen the role of microbial exposure and farm milk and grass components, especially early in life, in the modulation of the immune system towards a Th1/Treg predominance. This may subsequently lead to a long-lasting lower risk of developing atopic diseases.
Department of Pulmonary & Allergy, University Children's Hospital Munich, LMU, Munich, Germany.
Anna
A
Lluis
Bianca
B
Schaub
D000383:Agriculture; D000818:Animals; D000829:Animals, Domestic; D001249:Asthma / Q000453:epidemiology / Q000209:etiology / Q000235:genetics / Q000517:prevention & control*; D004781:Environmental Exposure; D005260:Female; D005685:Galactans / Q000008:administration & dosage; D059647:Gene-Environment Interaction; D055106:Genome-Wide Association Study; D006801:Humans; D006967:Hypersensitivity; D008297:Male; D051379:Mice; D008892:Milk; D011110:Polymorphism, Genetic; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced / Q000453:epidemiology / Q000235:genetics; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics
D005685:Galactans; D018094:Receptors, Metabotropic Glutamate; C005653:arabinogalactan