Project Summary Neurotransmitters and hormones serve as a link between the nervous and immune systems. Among them, norepinephrine and epinephrine are synthesized in the postganglionic neurons of the sympathetic nervous system and the adrenal medulla. Upon release, they engage the β2-adrenergic receptor (β2AR) expressed on immune cells. Notably, β2AR abnormal expression and gene polymorphisms are associated with several types of autoimmune diseases. However, mechanisms by which β2AR signaling dysfunction contribute to these diseases remain largely unknown. In this context, our studies with mouse models have uncovered previously unappreciated major dichotomous roles of β2AR in immune development and reconstitution: 1) Under specific pathogen free (SPF) condition, β2AR deficiency causes significantly reduced T cell development in thymus in contrast to increased CD115+ myeloid cell development in bone marrow (BM); 2) Both thymic and myeloid development phenotypes are remarkably more manifested during immune reconstitution following allogeneic hematopoietic cell transplantation (allo-HCT); 3) β2AR plays differential roles in in mature peripheral T cell subsets and myeloid cell subsets that result in different outcome in graft-versus-host disease (GVHD). Together, these findings highlight the critical and fundamental role of β2AR signaling in maintaining immune homeostasis and regulating immune response. Therefore, this study will pursue three specific aims to test an overarching hypothesis that β2AR signaling regulates immune development and reconstitution via cross-talking with canonical immune signaling pathways and/or fine-tuning metabolic fitness of immune cells. Aim 1 will determine mechanisms by which β2AR signaling regulates T cell development, reconstitution and GVHD. Aim 2 will define mechanisms by which β2AR signaling regulates CD115+ myeloid cell development, reconstitution and GVHD. Aim 3 will study the translational potential and mechanisms of pharmacologic β2AR intervention. We will use unbiased RNA-seq transcriptomic approach along with flow cytometry, CyTOF mass cytometry and Seahorse metabolic assay combined with cell type-specific β2AR knockout (Cre-LoxP) to define the molecular mechanisms for T cell and myeloid cell differentiation and function. In the setting of allo-HCT, we will also examine the impact of these mechanisms on GVHD and GVT effect. This project will not only improve our understanding of the fundamental mechanisms of β2AR signaling in adaptive and innate immune cells in central and peripheral immune organs, but it may also explain how β2AR signaling contributes to immunologic disorders and allo-HCT based immunotherapy. Therefore, this study may have important ramifications on therapeutic rationale based upon manipulation of β2AR signaling. Since β2AR agonists and antagonists are already widely available, new clinical trials emanating from this research could be rapidly implemented for patients receiving allo-HCT for t...