Eosinophils Forestall Obesity

Eosinophils in adipose tissue maintain metabolic homeostasis by controlling macrophage activity. Most human body fat is stored in adipose tissue, and under healthy conditions, it provides a balanced exchange of triglycerides in response to energy demands. But adipose tissue is also the cardinal locus of the metabolic syndrome, whose hallmarks include the accumulation of abdominal fat and insulin resistance, with cardiovascular consequences. Adipose tissue is dynamically linked with the immune system; indeed, the activity of macrophage cells has a key role in progression to obesity ( 1 – 4 ). On page 243 of this issue, Wu et al. ( 5 ) show that eosinophils, an immune cell typically associated with allergy and worm infection, regulate the macrophage activation state in mammalian adipose tissue and may have an important role in metabolic homeostasis.