Inflammation and macrophage modulation in adipose tissues.

The adipose tissue is an active endocrine organ that harbours not only mature and developing adipocytes but also a wide array of immune cells, including macrophages, a key immune cell in determining metabolic functionality. With adipose tissue expansion, M1 pro-inflammatory macrophage infiltration increases, activates other immune cells, and affects lipid trafficking and metabolism, in part via inhibiting mitochondrial function and increasing reactive oxygen species (ROS). The pro-inflammatory cytokines produced and released interfere with insulin signalling, while inhibiting M1 macrophage activation improves systemic insulin sensitivity. In healthy adipose tissue, M2 alternative macrophages predominate and associate with enhanced lipid handling and mitochondrial function, anti-inflammatory cytokine production, and inhibition of ROS. The sequence of events leading to macrophage infiltration and activation in adipose tissue remains incompletely understood but lipid handling of both macrophages and adipocytes appears to play a major role.