The role of allergens in the induction of asthma.

Despite the strong and consistent association between immediate hypersensitivity and asthma, there is still controversy about the role inhaled allergens play and about the timing of events related to sensitization. Recent studies have provided further evidence on the nature of the immune response to allergens, the timing of this response, and, in particular, whether any response to allergens occurs in utero. Some of the studies also provide a better explanation for why there is not a simple dose response relationship between allergens and asthma. The new studies also raise major issues about the nature of the immune response in nonallergic individuals. Taken together, the findings do not support a simple view about the balance between TH1 and TH2 responses, but strongly support the relevance of IgE to the risk of asthma.