Project Summary/Abstract: Type 2 allergic immunity is a specialized subtype of immune response that limits multicellular helminths and protozoa. However, recent work also implicates type 2 immunity in physiologic tissue remodeling, which in excess can drive allergy, asthma, atopy, and tissue fibrosis. Type 2 immunity is coordinately driven by tissue type 2 innate lymphoid cells (ILC2s) and type 2 CD4+ T helper cells (Th2s). Tissue-resident ILC2s and Th2s have a high degree of transcriptional and functional similarity, secreting high levels of the cytokines IL-5 and IL- 13 to organize downstream immune and non-hematopoietic cells. Although diverse tissue signals regulate these cells, it remains unclear how their broad localization (i.e. topography) within organs is controlled and how this may impact immune pathology. In many tissues, ILC2s and Th2s localize to fibroblast-rich adventitial areas around larger blood vessels and lung airways. Our preliminary data show that type 2 inflammation drives their expansion into de novo parenchymal niches (e.g. near alveoli in lung, hepatocytes in liver). We find that ILC2s require trafficking-associated pathways to expand into parenchymal niches, whereas type 1 lymphocytes (T1Ls) are broadly distributed in tissues and produce IFNγ+ that confine ILC2s and Th2 subsets to adventitial niches. In models of mixed type 1/type 2 inflammation, enforced ILC2s and Th2s in parenchymal sites inhibit effective T1L- mediated responses leading to increased mortality. Our central hypothesis is that ILC2 and Th2 localization to tissue parenchymal niches occurs via trafficking from blood pools and must be tightly controlled to balance immune risks and benefits to organs. Aim 1 will define the mechanism(s) and impact of IFNγ repression of ILC2 and Th2 cell parenchymal distribution. We will test the hypothesis that IFNγ produced by T-cells restricts cell trafficking into parenchymal niches during mixed inflammation. We will use genetic tools to eliminate IFNγ- signaling on ILC2s and Th2 subsets and determine functional consequences in models of mixed inflammation. Aim 2 will determine the routes and signals that control ILC2 and Th2 parenchymal localization. Here we will test the hypothesis that type 2 immunity activates tissue type 2 lymphocyte expansion and ‘retrograde trafficking’, with transitory residency in the blood allowing for tissue-specific re-entry in parenchymal sites and ultimate type 2 niche expansion. We will use multimodal approaches, including organ transplantation, photoconversion, parabiosis, and cell transfers to determine the required trafficking molecules, kinetics, dwell time, and ultimate fate in parenchymal sites. Aim 3 will define functional impacts and targets of ILC2 and Th2 parenchymal localization. Here we will test how production of IL-13 and other signals target discrete tissue immune and stromal subsets, potentially impairing effective type 1 immunity and leading to context-dependent beneficial o...