Dendritic cells are essential for Th2 differentiation of naïve CD4 + T cells in response to aeroallergens, and in recent years it has been well established that these cells play a pivotal role in the initiation phase of allergic asthma. Dendritic cells are also crucial for maintaining eosinophilic airway inflammation by controlling the recruitment and activation of primed Th2 cells in the lung. A picture is emerging wherein the balance of pathogenic Th2 cells and regulatory T cells is tuned by dendritic cells not only at the initiation but also at the effector stage of the allergic immune response.