PROJECT SUMMARY/ABSTRACT Microsurgical models of murine organ transplantation have played a critical role in advancing our understanding of immunological pathways that regulate graft rejection and tolerance. Such models are important tools to develop therapies for transplant patients. As substantial differences exist between immune responses to various grafts, insights gained in one organ cannot be translated to other organs. Our laboratories have developed clinically relevant models of lung transplantation and re-transplantation in the mouse as well as novel approaches to image immune cell interactions in the murine pulmonary graft in real time. We and others have used these approaches to investigate clinically relevant lung-specific alloimmune responses. A dedicated microsurgery core was established at the initiation of this program project in 2015. The microsurgery core has proven instrumental in facilitating the execution of the experiments. In aim 1 we will continue to standardize the quality of microsurgical and imaging procedures for all three projects in the proposal. In aim 2 we will continue to standardize assessment of graft function and tissue harvest for all three projects. In aim 3 we will maintain a system that provides unfettered access to microsurgical transplants and coordinates intravital imaging procedures for Projects 1 and 3.