PROJECT SUMMARY: Solitary chemosensory cells are rare specialized epithelial cells scattered in the airway (referred to as brush cells) and intestinal mucosa (named tuft cells), recently found to be initiators of type 2 immune responses at least partially through the generation of the proinflammatory cytokine IL-25. In the airways, activation of brush cells by bitter tasting bacterial metabolites also triggers sensory neurons leading to protective airway reflexes. The full effector potential of chemosensory cells and activating receptors beyond taste receptors have not been defined. We have found that epithelial cells sharing the transcriptional profile of chemosensory cells from the trachea and intestine are enriched in the nasal mucosa. We generated a nasal brush cell RNA-seq data set to determine their possible activating receptors and developed an ex vivo system to test the ligand receptor pairs that lead to activation of airway brush cells. We found that brush cells generate large quantities of pro- inflammatory lipid mediators among them cysteinyl leukotrienes (CysLTs). We then generated a new mouse strain with genetic deletion of the terminal CysLT generating enzyme in brush cells to define the contribution of brush cell-derived CysLTs to the pro-inflammatory and protective responses in the airways. In Aim 1, we will define the subsets of nasal brush cells from the respiratory and olfactory mucosa using single cell RNA sequencing. In Aim 2, we will define the brush cell activating pathways triggered in response to aeroallergen sensing, the autocrine loops enhancing this response and the full effector potential of brush cells. In Aim 3, we will define the role of brush cell-derived CysLTs in epithelial cell activation in the airways using mice with genetic deletion of brush cells, CysLTs and brush cell-specific deletion of CysLTs. Findings here will clarify the contribution of brush cell-derived CysLTs to protective and inflammatory responses in the airways and lay the foundation to define their function in human airway mucosa. Results from the proposed experiments will provide critical insights into how protective airway responses designed to expel environmental insults can be diverted to initiate and propagate inflammatory responses leading to allergic airway diseases.