Eosinophils are classically known as proinflammatory cells, as they are equipped with a variety of preformed cytotoxic mediators and have been shown to definitively contribute to asthma. The connection between eosinophils and asthma development has led to a new class of asthma therapeutics based on blocking eosinophils with humanized antibodies that neutralize IL-5, a potent eosinophil growth, activation, and survival factor. Yet, recent studies have led to an increasing appreciation that eosinophils have a variety of homeostatic functions, including immunomodulation. In this issue of the
Marc E. Rothenberg
Schematic diagram of the homeostatic roles of eosinophils.
Eosinophils transit through the blood stream and home into various tissues at baseline. This schematic focuses on three tissues — adipose, small intestine, and lung. In adipose tissue, eosinophils regulate glucose levels and metabolism via eosinophil-derived IL-4, which regulates macrophage polarization and subsequent generation of insulin-sensitizing agents. In the small intestine, eosinophils regulate secretory IgA, mucus production and microbiota composition. A study in this issue by Mesnil et al. (