TR&D 2 Project Summary Macrophages are innate immune cells present in all major tissues and are responsible for homeostasis. Macrophages sense and respond to pathogens and other environmental challenges and participate in tissue repair after injury. Recent research reveals macrophages as remarkably plastic cells that are epigenetically programmed in response to signals originating from the tissue environment. The macrophage heterogeneity and plasticity is evident from how the microenvironment shapes macrophage phenotype and functional identity that ensures ongoing adaption of macrophages to the environment. Typically, macrophages are defined as M1 macrophages (classically activated pro-inflammatory macrophages) and M2 macrophages (alternatively activated tissue-resident anti-inflammatory macrophages). M1 macrophages are pro-inflammatory and have a central role in host defense against inflammation and infection, while M2 macrophages are associated with responses to anti-inflammatory reactions and tissue remodeling, and they represent two terminals of the full spectrum of macrophage activation. Since the transformation of different phenotypes of macrophages regulates the initiation, development, and cessation of inflammatory diseases, it is critical to track the well-defined macrophages populations with constant expression of surface markers across multiple organs to interrogate their temporal and spatial distribution along the progression and regression of inflammatory diseases or malignancies. Based on our previous work and published data, we have identified chemokine receptor type 2 (CCR2) as a surface biomarker for M1 macrophage and CD163 as a biomarker for M2 macrophage. We have developed the first CCR2 radiotracer imaging inflammation in animal models and malignancies, as well as humans. We have also developed the first CD163 radiotracer for initial evaluation. In this proposal, we plan to further improve the imaging efficiency of CCR2 and thoroughly assess CD163 tracers in order to determine the temporal and spatial distribution of M1 and M2 macrophages in inflammatory diseases and cancers. Therefore, we proposal the following 3 specific aims working closely with our Collaborative Projects. Aim 1. Develop new CCR2 targeted radiotracers imaging M1 pro-inflammatory macrophages. Aim 2. Develop CD163 targeted radiotracer imaging M2 tissue resident macrophages. Aim 3. Validate macrophage-specific radiotracers to detect heterogeneity, temporal and spatial distribution of macrophages in inflammatory diseases and malignancies. These products and those developed in the current grant cycle will be provided to our Service Projects as well.