Innate lymphoid cells (ILCs) are effectors of innate immunity and regulators of tissue modeling. Recently identified ILC populations have a cytokine expression pattern that resembles that of the helper T cell subsets T(H)2, T(H)17 and T(H)22. Here we describe a distinct ILC subset similar to T(H)1 cells, which we call 'ILC1'. ILC1 cells expressed the transcription factor T-bet and responded to interleukin 12 (IL-12) by producing interferon-γ (IFN-γ). ILC1 cells were distinct from natural killer (NK) cells as they lacked perforin, granzyme B and the NK cell markers CD56, CD16 and CD94, and could develop from RORγt(+) ILC3 under the influence of IL-12. The frequency of the ILC1 subset was much higher in inflamed intestine of people with Crohn's disease, which indicated a role for these IFN-γ-producing ILC1 cells in the pathogenesis of gut mucosal inflammation.

Innate lymphoid cells (ILCs) are emerging as a family of effectors and regulators of innate immunity and tissue remodeling. Interleukin 22 (IL-22)- and IL-17-producing ILCs, which depend on the transcription factor RORγt, express CD127 (IL-7 receptor α-chain) and the natural killer cell marker CD161. Here we describe another lineage-negative CD127(+)CD161(+) ILC population found in humans that expressed the chemoattractant receptor CRTH2. These cells responded in vitro to IL-2 plus IL-25 and IL-33 by producing IL-13. CRTH2(+) ILCs were present in fetal and adult lung and gut. In fetal gut, these cells expressed IL-13 but not IL-17 or IL-22. There was enrichment for CRTH2(+) ILCs in nasal polyps of chronic rhinosinusitis, a typical type 2 inflammatory disease. Our data identify a unique type of human ILC that provides an innate source of T helper type 2 (T(H)2) cytokines.