The good, the bad, and the ugly of interleukin-6 signaling.

Interleukin-6 (IL-6) is a pleiotropic cytokine with complex roles in inflammation and metabolic disease. While typically regarded as a pro-inflammatory cytokine, multiple studies in the last 20 years have generated conflicting data on the role of IL-6 in inflammation and metabolism. In a recent study in Nature Immunology, Brüning and collaborators demonstrate that IL-6 signaling in myeloid cells attenuates obesity-induced inflammation and insulin resistance by promoting macrophage alternative activation (Mauer et al, 2014). This study unveils a new and surprising anti-inflammatory action of IL-6 and further highlights the complex actions of this cytokine.