Receptor for advanced glycation endproducts mediates allergic airway inflammation via group 2 innate lymphoid cells

Half of all asthmatics suffer from allergic airway inflammation driven by type 2 immune responses in the lung, yet the molecular mechanisms that control early, initiating events in allergic asthma are poorly understood. Recently, scientists have discovered a new subset of innate cells that can trigger rapid type 2 allergic inflammation, even in the absence of an adaptive immune system. These cells, termed group 2 innate lymphoid cells (ILC2s), are activated by the epithelial alarmin, interleukin (IL)-33, and secrete copious amounts of the type 2 cytokines IL-5 and IL-13 to drive tissue eosinophilia, mucus hypersecretion, and airway hyperresponsiveness (AHR). It is unknown how these cells are recruited to the lung to promote allergic airway inflammation (AAI).\ud The receptor for advanced glycation endproducts (RAGE) is a proinflammatory receptor abundantly expressed in the lung. Previous studies have found that, in the absence of RAGE, IL-5 and IL-13 cytokine responses are impaired, and mouse lungs are completely protected from development of AAI and AHR. It was therefore hypothesized that RAGE was necessary for recruitment of type-2-cytokine-producing ILC2s to the lung during allergen challenge to initiate AAI.\ud The data presented here demonstrate that RAGE is, in fact, necessary for ILC2 accumulation in the lung after allergen challenge. Furthermore, this mechanism appears to be lung-specific and independent of RAGE expression on ILC2s themselves: tissues that do not normally express RAGE (i.e. gastrointestinal tract) mount normal ILC2-driven allergic responses even in RAGE KO mice. The ILC2-activating cytokine, IL-33, was also dependent on RAGE signaling, both upstream to trigger its release from epithelial cells and also downstream to mediate its inflammatory effects.\ud This is the first study examining a parenchymal factor in the recruitment of ILC2s to a specific organ. The exact mechanism by which this is occurring is still under investigation, but it may lead to the discovery of important new therapeutic targets early in the development of AAI.\u