Asthma and the Hygiene Hypothesis

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Abstract
With reference to the review article by Busse and Lemanske on asthma (Feb. 1 issue),1 we would like to raise the following points. Figure 4 fails to make it clear that several serious diseases, including type 1 diabetes,2 are mediated by a type 1 helper-T-cell (Th1) response; for this reason, any immunotherapy aimed at manipulating the helper-T-cell response in favor of a Th1 response may have unwanted effects, such as the development of Th1-mediated diseases. Type 1 diabetes, like atopy, commonly presents early in life, is also rising in incidence in Europe, and is most common in first-born children and children whose families are well off.3-5 Thus, the epidemiologic features of type 1 diabetes have much in common with those of atopic disease. This evidence contradicts the hypothesis that a change in the balance between Th1 and type 2 helper-T-cell responses is occurring in children.