Eosinophils in fat: pink is the new brown.

Subcutaneous white adipose tissue can be induced to undergo "browning" and acquire thermogenic capacity in response to physiological stimuli such as cold exposure or exercise. In this issue of Cell, Qiu et al. and Rao et al. demonstrate that pink-staining eosinophils and alternatively activated macrophages play key roles in an immune cascade mediating this metabolic switch.