Fig. 1.

The heterogeneity of macrophages in the development of adipose tissue inflammation. In the lean state, M2 ATMs predominate. As obesity progresses, monocytes accumulate in adipose tissue and differentiate into inflammatory M1 or anti-inflammatory M2 macrophages. Since the number of M1 ATMs increases dramatically, whereas there is only a modest increase in the number of M2 ATMs, M1 ATMs predominate in obese adipose tissue. M1 ATMs produce inflammatory cytokines and promote insulin resistance. M2 ATMs, on the other hand, secrete anti-inflammatory cytokines, including IL-10 and TGF-β, and suppress inflammation, suggesting that M2 ATMs are associated with insulin sensitivity