Adipose tissue macrophages (abbr. ATMs) comprise tissue resident macrophages present in adipose tissue. Adipose tissue apart from adipocytes is composed of the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells and variety of immune cells. The latter ones are composed of mast cells, eosinophils, B cells, T cells and macrophages. The number of macrophages within adipose tissue differs depending on the metabolic status. As discovered by Rudolph Leibel and Anthony Ferrante et al. in 2003 at Columbia University, the percentage of macrophages within adipose tissue ranges from 10% in lean mice and humans up to 50% in extremely obese, leptin deficient mice and almost 40% in obese humans. Increased number of adipose tissue macrophages correlates with increased adipose tissue production of proinflammatory molecules and might therefore contribute to the pathophysiological consequences of obesity (e.g. insulin resistance, type 2 diabetes).