[Roles of RORγt+ innate lymphoid cells in mucosal tissues of mouse and human]

Innate Lymphoid cells (ILCs) are recently defined lymphocytes composed of several subsets such as Natural Killer (NK), Natural Helper (NH) and RORγt(+) cells, which have no antigen receptors but exhibit rapid cytokine production after stimulation. Murine RORγt(+) ILCs can be classified either as CCR6(+)c-kit(high)IL-7Rα(high) or CCR6NK(-)p46(+) cells. The former ones play roles on the formation of secondary lymphoid tissues and the later ones contribute to the maintenance of intestinal epithelial integrity by producing IL-22. Human fetal intestine, tonsil and lympho nodes harbor both NKp44 positive and negative RORγt(+) ILC subsets. Since human Crohn's disease patients have increased number of RORγt(+) ILCs in the inflamed intestine, roles of RORγt(+) ILCs on the pathogenesis of Crohn's disease became of great interest.