A Paracrine Loop Between Adipocytes and Macrophages Aggravates Inflammatory Changes. Role of Free Fatty Acids and Tumor Necrosis Factor α

Objective— Weight gain is associated with infiltration of fat by macrophages, suggesting that they are an important source of inflammation in obese adipose tissue. Here we developed an in vitro coculture system composed of adipocytes and macrophages and examined the molecular mechanism whereby these cells communicate. Methods and Results— Coculture of differentiated 3T3-L1 adipocytes and macrophage cell line RAW264 results in the marked upregulation of proinflammatory cytokines, such as tumor necrosis factor α (TNF-α), and the downregulation of the antiinflammatory cytokine adiponectin. Such inflammatory changes are induced by the coculture without direct contact, suggesting the role of soluble factors. A neutralizing antibody to TNF-α, which occurs mostly in macrophages, inhibits the inflammatory changes in 3T3-L1, suggesting that TNF-α is a major macrophage-derived mediator of inflammation in adipocytes. Conversely, free fatty acids (FFAs) may be important adipocyte-derived mediators of inflammation in ...