The natural and the inducible interleukin (IL)-17-producing γδ T cells

gamma delta T cells are the major initial interleukin (IL)-17 producers in acute infections. Recent studies have indicated that some gamma delta T cells have IL-17-producing capabilities without explicit induction of an immune response. They are preferentially localized in barrier tissues and are likely to originate from fetal gamma delta thymocytes. In addition, gamma delta T cells present in the secondary lymphoid organs will mature and differentiate to produce IL-17 after antigen encounter in an immune response. Based on these studies, we propose that there are two different sets of IL-17-producing gamma delta T cells (T gamma delta 17) referred to as the 'natural' and the 'inducible' T gamma delta 17 cells. This review focuses on recent publications leading to the delineation of these two types of cells and their implied roles in host immune defense.