The primary function of the lung is gas exchange. Immune cells and airway nerves orchestrate interoceptive defensive responses and adjustments to homeostatic function that preserve airway patency, eliminate noxious irritants and pathogens from air spaces, clear airway mucus, and optimize the work of breathing. Dysfunction or dysregulation of these systems directly contribute to the emergence of the physiological and pathophysiological attributes of respiratory diseases and their associated symptoms. Sensory nerves often rely on specialized chemosensory signaling mechanisms at their nerve terminals to transduce mucosal irritation. In the airways, we have described the chemosensory functions of brush cells, their association with the peripheral terminals of vagal afferent nerves and the reflex effects resulting from their activation. The central hypothesis of this research proposal is that brush cells orchestrate both immune and reflex responses in the airways and lungs. We further hypothesize that brush cell dysfunction may contribute to the emergence of symptoms associated with both acute and chronic diseases of the airways and lungs. Studies proposed herein aim to: 1) characterize the mechanisms by which brush cells are activated, how they transmit their activation to adjacent sensory nerves, and the reflexes initiated upon their activation; and 2) determine the role of ATP and the unique expression of carbonic anhydrase by airway brush cells in transducing airway mucosal irritation, acidification of airway surface liquid and the accumulation of carbon dioxide in the airway lumen. We will utilize the innovative techniques that are unique to our laboratories, including transgenic approaches enabling optical recordings of afferent neurons and brush cells, reflex physiological recordings, single afferent neuron recording and our molecular approaches to studying both neurons and brush cells. Our focus on brush cell interactions with afferent nerves is a logical direction for our group, and our plans for hypothesis testing will be enabled by intriguing recent discoveries summarized below in our Research Strategy. We anticipate that the results of these proposed studies will reveal novel roles for brush cells and ATP in transducing reflexes resulting from mucosal irritation in the airways of patients with chronic diseases of the airways and lungs.