Overall Summary/Abstract This Asthma and Allergic Disease Cooperative Research Center (AADCRC) continues its focus on the mechanistic basis of respiratory tract type 2 immunopathology (T2I), particularly in aspirin-exacerbated respiratory disease (AERD), a distinctive clinical syndrome that accounts for a disproportionate percentage of individuals with severe asthma and recurrent chronic rhinosinusitis with nasal polyposis (CRSwNP). In the current period of support, we discovered marked epigenetically imprinted abnormailites in epithelial basal cell (BC) function and differentiation underlying CRSwNP and AERD, some of which are driven by strong, persistent signaling through the interleukin 4 receptor alpha (IL-4Rα) and some by altered Wnt/Notch signaling. We identified dramatic hyperplasia of mast cells (MCs) in CRSwNP tissue, especially from individuals with AERD, driven in part by a novel, transcriptionally and cytofluorographically distinct MC population with a high rate of proliferation. We now have strong evidence that MC-stromal interactions drive many pathophysiologic features of respiratory T2I, and that these interactions are regulated by synergistic inputs from IL-4Rα and IL- 33/ST2 signaling axes. A tightly interactive team of accomplished investigators with complementary skills will apply cellular, molecular, and whole animal strategies, combined with a proof-of-concept clincal trial to determine the mechanistic basis for these findings, their relevance to disease pathophysiology, and their amenability to therapy. Project 1 (J. Boyce, PI) focuses on the the developmental origins of respiratory tract MCs, how their interactions with stromal cells dictate MC development and function and are altered by IL-4Rα signaling, and how MCs drive altered stromal cell function through a feed-forward loop involving IL-6 and leukemia inhibitory factor. Project 2 (N. Barrett, PI) focuses on the mechanisms by which epigenetic reprogramming of BCs combines with IL-4Rα signaling to drive BC dysplasia and sensecence as a disease- causing mechanism. Project 3 (T. Laidlaw, PI) will compare the efficacy of IL-4Rα blockade with IL-33 blockade in a proof of mechanism placebo controlled trial, focusing on restoration of BC function and suppression of MC hyperplasia and activation. The Projects are supported by respective Cores for Adminstration (Core A), and Integrative Genomics (Core B).