Asthma is an important disease of which the underlying mechanism of disease susceptibility and pathogenesis is poorly understood. We have developed a mouse model that resembles the human disease for asthma studies. The focus of the laboratory is to elucidate the steps in airway allergen stimulation and the function of various lung cell types in the inflammatory response. Our studies have centered on lung dendritic cell functions. Dendritic cells are the primary cell type responsible for handling airway allergens and ultimately presenting the active allergen fragment to the T cells which then are activated and respond specifically to the allergen by producing growth factors to initiate and promote inflammatory responses in the lung. We have determined that there are three main dendritic cell types in the lung, the conventional CD11b+ dendritic cells, the regulatory plasmacytoid dendritic cells, and a lymphoid-like CD103+ dendritic cell that activate regulatory T cells. The CD11b+ dendritic cells preferentially produce high levels of chemokines and increase markedly in allergic lung inflammation and thus may function as a major proinflammatory cell type. CD103+ dendritic cells, on the other hand, may play major regulatory roles. Our laboratory has been determining the phenotypic and functional differences among the lung dendritic cells types, how they may mediate the transition from a toleragenic to an inflammatory response in lungs in response to allergens, and how they interact with various T cell subsets. The studies will provide the understanding of asthma pathogenesis in finer detail and may identify novel targets or agents for asthma therapy.