Macrophages are core components of the innate immune system. Once activated, they may have either pro- or anti-inflammatory effects that include pathogen killing, safe disposal of apoptotic cells or tissue renewal. The activation state of macrophages is conceptualized by the so-called M1/M2 model of polarization. M2 macrophages are not simply antagonists of M1 macrophages; rather, they represent a network of tissue resident macrophages with roles in tissue development and organ homeostasis. M2 macrophages govern functions at the interfaces of immunity, tissue development and turnover, metabolism, and endocrine signaling.