Development and function of intestinal innate lymphoid cells.

Innate lymphoid cells (ILCs) are generated from common lymphoid precursors, like lymphocytes, but do not express an antigen receptor. ILCs include Natural Killer (NK) cells, first described 38 years ago, as well as the more recently discovered lymphoid tissue inducer (LTi) cells, NK(22) cells and ILC2s. ILCs reflect many functions of CD4(+) T helper cells by expressing IFNγ, IL-17, IL-22 or IL-13. However, in contrast to T cells, they are not selected on the basis of antigen specificity, and expand and act shortly after stimulation. Therefore, ILCs play fundamental roles early in responses to infection and injury, in the maintenance of homeostasis, and possibly in the regulation of adaptive immunity. Here, we review the recent data on the development and role of RORγt(+) ILCs and ILC2s in intestinal homeostasis and defense.