Studies from our laboratory and elsewhere have implicated populations of dendritic cells in lung and airway tissues as key regulators of both qualitative and quantitative aspects of T cell responses to local antigenic challenge. Under steady state conditions, they are specialized for uptake of antigen, and require additional maturation signals for full expression of their T cell-stimulating activity. Their functional phenotype appears to be controlled via a complex series of interactions with both bone marrow-derived, mesenchymal, and possibly neuroendocrine cells; failure(s) in one or more of these regulatory interactions may be important etiologic and/or pathogenic factors in a variety of respiratory immunoinflammatory disease.