IL-31, produced mainly by activated CD4+?T cells, is a newly discovered helical cytokine belonging to the gp130/IL6 cytokine family. IL-31 is closely related in structure to IL-6, IL-11, and IL-27. Binding of IL-31 to its receptor activates JAK/STAT, PI3K/AKT, and MAPK pathways. IL-31 acts on a broad range of immune and non-immune cells and thus possesses potential pleiotropic physiological functions, such as regulating hematopoiesis and immune responses. Human IL-31 is also involved in inflammatory bowel disease, airway hypersensitivity, and dermatitis.