Brown adipose tissue plays a key role during cold exposure by generating heat, a process named thermogenesis. Thermogenesis is essential to maintain body temperature and brown fat activation improves the host’s metabolism. Various types of immune cells have been identified in brown adipose tissue and their contribution to thermogenesis has been suggested. Macrophages are the most abundant immune cells in brown fat. We recently identified several brown adipose tissue macrophage subsets co-existing within this tissue. The current proposal aims to investigate the functions and relative contribution of brown fat macrophage subsets to homeostatic tissue maintenance and during cold-induced thermogenesis and stress. Molecular biology (RNAseq, lipidomics) and cell biology (spectral cytometry, confocal microscopy) approaches combined to original mouse lines will be used for this project. This consortium gathers 4 research teams with complementary expertise in immunology, metabolism and lipidomics.