Braun-Fahrländer C, Riedler J, Herz U, et al. N Engl J Med. 2002;347:869–877
Purpose of the Study.
The “hygiene hypothesis” has been proposed as a major factor underlying the rapid increase in asthma and allergy over the past 20 to 30 years. This purpose of this study was to investigate whether exposure to microbial products in early life had any effect on the future development of asthma or allergy.
Eight hundred twelve children between the ages of 6 and 13 years living in rural areas of Germany, Austria, and Switzerland where there were both farming and nonfarming households.
Parents completed a standardized questionnaire on asthma and hay fever. Blood samples were obtained from the children and tested for atopic sensitization; peripheral-blood leukocytes were also harvested from the samples for testing. The levels of endotoxin in the bedding used by these children were examined in relation to clinical findings and to the cytokine-production profiles of peripheral-blood leukocytes that had been stimulated with lipopolysaccharide and staphylococcal enterotoxin B.
Endotoxin levels in samples of dust from the children’s mattress were inversely related to the occurrence of hay fever, atopic asthma, and atopic sensitization. Nonatopic wheeze was not significantly associated with endotoxin levels. Cytokine production by leukocytes (production of tumor necrosis factor-α, interferon-γ, interleukin-10, and interleukin-12) was inversely related to the endotoxin level in the bedding, indicating a marked downregulation of immune responses in exposed children.
A child’s environmental exposure to endotoxin may have a crucial role in the development of tolerance to ubiquitous allergens found in natural environments.
This is a fascinating study on a timely and important topic. Although the final answer on the hygiene hypothesis is still far from complete, this is another piece of evidence in support of this theory.