Abstract
IL-9 has been reported to play dual roles in the pathogenesis of autoimmune disorders and cancers. The collaboration of IL-9 with microenvironmental factors including the broader cytokine milieu and other cellular components may provide important keys to explain its conflicting effects in chronic conditions. In this review, we summarize recent findings on the cellular sources of, and immunological responders to IL-9, in order to interpret the role of IL-9 in the regulation of immune responses. This knowledge will provide new perspectives to improve clinical benefits and limit adverse effects of IL-9 when treating pathologic conditions.