Do adipose tissue macrophages promote insulin resistance or adipose tissue remodelling in humans?

In diet induced and genetically obese rodent models, adipose tissue is associated with macrophage infiltration, which promotes a low grade inflammatory state and the development of insulin resistance. In humans, obesity is also closely linked with macrophage infiltration in adipose tissue, a pro-inflammatory phenotype and insulin resistance. However, whether macrophage infiltration is a direct contributor to the development of insulin resistance that occurs in response to weight gain, or is a later consequence of the obese state is unclear. There are a number of concomitant changes that occur during adipose tissue expansion, including the number and size of adipocytes, the vasculature and the extracellular matrix. In this review, we will examine evidence for and against the role of macrophage recruitment into adipose tissue in promoting the development of insulin resistance in rodents and humans, as well as discuss the emerging role of macrophages in mediating healthy adipose tissue expansion during periods of caloric excess.