Innate Lymphoid Cells

Innate lymphoid cells (ILCs) represent a novel family of developmentally related hematopoietic effectors with central roles in innate immune responses to infections, lymphoid organogenesis, intestinal homeostasis, and wound healing.1 The prototypes of the ILC family are natural killer cells and lymphoid tissue–inducer cells. In 2010, 4 independent laboratories have identified previously unrecognized ILC populations that promote the development of CD4+ T-helper type 2 (Th2) cell–dependent immunity and inflammation at mucosal sites. These cell populations, now collectively termed group 2 ILC2, include natural helper (NH) cells, multipotent progenitor type 2 cells, and nuocytes or innate type 2 helper cells.2–5 They are retinoic-acid-receptor-related orphan receptor-γ-independent Lin−CD90+CD127+GATA3+ and require Id2, interleukin (IL)-7, retinoic-acid-receptor-related orphan receptor-α, and the common cytokine receptor γ chain. ILC2 cells are capable of producing Th2 cytokines, most notably IL-5 and IL-13 but not IL-4, in response to IL-25 and IL-33, 2 predominantly epithelial cell–derived cytokines whose increased expression at mucosal surfaces is associated with exposure to allergens or helminth parasites. Recent characterization of ILC2 cell biology has underscored their major role in asthma, allergies, and parasitic infections, but nothing was known about the role of ILC2 cells in …