The development of Th2 responses to inhaled proteins represents a malfunction of the adaptive immune system in that protein antigens are not microbial in nature and should not elicit an adaptive immune reaction. This derailing of the immune system may result from false alarms generated by the innate immune system, resulting in unexpected dendritic cell (DC) maturation after exposure to allergens. Conditions in the local microenvironment during DC maturation may also result in the preferential induction of Th2 responses. Recent progress has been made in our understanding of the role of DCs in both Th2 sensitization to aeroallergens and the regulation of Th2 and Th1 immunity.