Project Summary/Abstract Monocytes and macrophages function in diverse processes, from homeostatic maintenance to immune responses and tissue regeneration. These functions are coordinated with and strongly influenced by cellular metabolism via mechanisms that are increasingly studied and characterized in populations of macrophages. However, such studies mask the cell-to-cell variation which is an inherent property of macrophage diversity. Indeed, single-cell transcriptomics data have demonstrated that macrophage polarization is better described by continuous gradients rather than by discrete states amenable to isolation and population analysis. Yet, transcriptional measurements are insufficient to characterize the metabolic and protein networks that shape monocyte and macrophage diversity. To understand how these networks control macrophage polarization and functions, we propose to directly quantify proteins and regulatory signals (such as localization of key regulators, e.g., NF-κB) in primary human monocytes and macrophages responding to physiologically relevant metabolic environments. Furthermore, we will extend this single-cell analysis to the responses of these cells to pathogen-associated molecular patterns and damage-associated molecular patterns. These data will enable us to identify likely regulatory networks driving monocyte and macrophage responses to metabolic states and molecular patterns. Subsequently, we will test these networks via pharmacological and genetic perturbations. We are uniquely positioned to perform this research since we recently pioneered methods for quantifying thousands of proteins across many single cells. Furthermore, we have the required expertise in analyzing metabolic systems (including aerobic glycolysis, which is frequently associated with macrophage activation) and developing new algorithms for data analysis. This project will advance our understanding of macrophage immunometabolism and polarization, will introduce methods for more sensitive and accurate single-cell analysis, and will provide a proof-of-principle demonstration of the possibility to identify protein-mediated molecular mechanisms at single-cell resolution. We strongly believe that attaining these goals will have a transformative impact on biomedical research and will inform new and better therapeutic strategies.