PROJECT SUMMARY/ABSTRACT This proposal details a two-year plan to allow the candidate, Daniel Dwyer, PhD, to transition to a stable independent research career. The focus of this study is on characterizing a novel regulatory axis capable of mediating the recruitment and activation of mast cells (MCs) during type 2 inflammation (T2I). MCs are potent effector cells that play key pathogenic roles in type 2 inflammatory diseases through the generation and release of a broad range of inflammatory mediators, including histamine, proteases, lipid mediators, and cytokines. The specific mechanisms underlying the expansion of MC during type 2 inflammation or the persistent activation of these cells associated with these diseases are unclear. This proposal identifies novel expression of a G protein-coupled receptor (GPCR) in both human and mouse MCs. Ligation of this receptor elicits mediating MC migration in vitro and additionally induces MC activation both in vivo and in vitro. Further, this proposal further identifies upregulation of a necessary enzyme for synthesis of the ligand across a spectrum of human T2I disease and finds that murine MC progenitor recruitment during allergic pulmonary inflammation is virtually absent in mice lacking the enzyme. Aim 1 of this proposal will utilize two murine models of allergic lung inflammation to assess which cells express and upregulate the enzyme in the context of T2I, followed by in vitro approaches to determine the mechanism driving this upregulation. Aim 2 of this proposal details the generation of a novel mouse strain in which the GPCR is specifically deleted in MC. After an initial confirmation of specific deletion and characterization of the MC compartment across tissues, the specific role of this GPCR in regulating constitutive MC activation and MC progenitor recruitment will be assessed in two inflammatory models.