title: IL-17-producing γδ T cells and innate lymphoid cells.
abstract: The inflammatory cytokine IL-17 plays a critical role in immunity to infection and is involved in the inflammatory pathology associated with certain autoimmune diseases, such as psoriasis and rheumatoid arthritis. While CD4(+) and CD8(+) T cells are important sources of this cytokine, recent evidence has suggested that γδ T cells and a number of families of innate lymphoid cells (ILCs) can secrete IL-17 and related cytokines. The production of IL-17 by γδ T cells appears to be largely independent of T-cell receptor activation and is promoted through cytokine signalling, in particular by IL-23 in combination with IL-1β or IL-18. Therefore IL-17-secreting γδ T cells can be categorised as a family of cells similar to innate-like lymphoid cells. IL-17-secreting γδ T cells function as a part of mucosal defence against infection, with most studies to date focusing on their response to bacterial pathogens. γδ T cells also play a pathological role in certain autoimmune diseases, where they provide an early source of IL-17 and IL-21, which initiate responses mediated by conventional IL-17-secreting CD4(+) T cells (Th17 cells). ILCs lack an antigen receptor or other lineage markers, and ILC subsets that express the transcriptional factor RORγt have been found to secrete IL-17. Evidence is emerging that these newly recognised sources of IL-17 play both pathological and protective roles in inflammatory diseases as discussed in this article.
authors.affiliation: Immune Regulation Research Group, School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin, Ireland.
authors.forename: Caroline E
authors.initials: CE
authors.lastname: Sutton
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Mielke
authors.forename: Kingston H G
authors.initials: KH
authors.lastname: Mills
mesh_terms: D000818:Animals; D006801:Humans; D007249:Inflammation / Q000276:immunology; D020381:Interleukin-17 / Q000096:biosynthesis* / Q000276:immunology; D008214:Lymphocytes / Q000276:immunology*; D016692:Receptors, Antigen, T-Cell, gamma-delta / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000276:immunology*
chemical_list: D020381:Interleukin-17; D016692:Receptors, Antigen, T-Cell, gamma-delta