T helper 17 cell
They create inflammation and tissue injury in autoimmune disease such as multiple sclerosis (which was previously thought to be caused by Th1 cells), psoriasis, autoimmune uveitis, juvenile diabetes, rheumatoid arthritis, and Crohn's disease.
Their normal role is to provide anti-microbial immunity at epithelial / mucosal barriers. They produce cytokines (such as interleukin 22) which stimulates epithelial cells to produce anti-microbial proteins to clear out certain types of microbe (such as Candida and Staphylococcus). Thus, a lack of Th17 cells leaves the host susceptible to opportunistic infections.
It has recently been questioned, however, whether TGF-β is involved at all in humans, and it is assumed that interleukin 1β may also play a role. Other proteins involved in their differentiation are signal transducer and activator of transcription 3 (STAT3) and the retinoic-acid-receptor-related orphan receptors alpha (RORα) and gamma (RORγ). Effector cytokines associated with this cell type are IL-17, IL-21 and IL-22.
Activation of precursor T helper cells in the presence of TGF-β and IL-6 is thought to drive differentiation of Th17 cells in the mouse. Aside from a cytokine environment, it is unclear whether any other elements of the initial activation of Th17 cells differ from those of other T helper cells. It has been suggested that IL-23 is involved in the expansion of established Th17 populations, but this cytokine alone does not induce differentiation of naive T-cell precursors into this cell type. IL-21, a cytokine produced by Th17 cells themselves, has also been shown to initiate an alternative route for the activation of Th17 populations. In humans, a combination of TGF-β, IL-1β and IL-23 induces Th17 differentiation from naive T cells. Both interferon gamma (IFNγ) and IL-4, the main stimulators of Th1 and Th2 differentiation, respectively, have been shown to inhibit Th17 differentiation.
Th17 cells, particularly auto-specific Th17 cells, are associated with autoimmune disease. Th17 cells may attack cancers, but this is debated.
The original function of Th17 cells is to protect the body against bacteria and fungi. Though Th17 cells are implicated in anti-fungal immunity, it is thought to be limited to particular sites with detrimental effects observed. Th17 cells produce two main members of the IL-17 family, IL-17A and IL-17F, which cause recruitment, activation and migration of neutrophils. They also secrete IL-21 and IL-22. Th17 cells mediate the regression of tumors in mice.
- Steinman L (February 2007). "A brief history of T(H)17, the first major revision in the T(H)1/T(H)2 hypothesis of T cell-mediated tissue damage". Nat. Med. 13 (2): 139–145. doi:10.1038/nm1551. PMID 17290272.
- Harrington LE, Hatton RD, Mangan PR et al. (November 2005). "Interleukin 17-producing CD4+ effector T cells develop via a lineage distinct from the T helper type 1 and 2 lineages". Nature Immunology 6 (11): 1123–1132. doi:10.1038/ni1254. PMID 16200070.
- Stockinger B, Veldhoen M (June 2007). "Differentiation and function of Th17 T cells". Current Opinion in Immunology 19 (3): 281–286. doi:10.1016/j.coi.2007.04.005. PMID 17433650.
- Dong C (May 2008). "TH17 cells in development: an updated view of their molecular identity and genetic programming". Nature Reviews Immunology 8 (5): 337–348. doi:10.1038/nri2295. PMID 18408735.
- Manel N, Unutmaz D, Littman DR (June 2008). "The differentiation of human T(H)-17 cells requires transforming growth factor-beta and induction of the nuclear receptor RORgammat". Nature Immunology 9 (6): 641–649. doi:10.1038/ni.1610. PMC 2597394. PMID 18454151.
- Ouyang W, Kolls JK, Zheng Y (April 2008). "The biological functions of T helper 17 cell effector cytokines in inflammation". Immunity 28 (4): 454–467. doi:10.1016/j.immuni.2008.03.004. PMID 18400188.
- Bettelli E, Carrier Y, Gao W et al. (May 2006). "Reciprocal developmental pathways for the generation of pathogenic effector TH17 and regulatory T cells". Nature 441 (7090): 235–238. doi:10.1038/nature04753. PMID 16648838.
- Korn T, Bettelli E, Gao W et al. (July 2007). "IL-21 initiates an alternative pathway to induce proinflammatory T(H)17 cells". Nature 448 (7152): 484–487. doi:10.1038/nature05970. PMID 17581588.
- Wu S, Rhee KJ, Albesiano E et al. (September 2009). "A human colonic commensal promotes colon tumorigenesis via activation of T helper type 17 T cell responses". Nature Medicine 15 (9): 1016–1022. doi:10.1038/nm.2015. PMC 3034219. PMID 19701202.
- Vautier, S; da Glo´ ria Sousa, M, Brown, G. "C-type lectins, fungi and Th17 responses". Cytokine & Growth Factor Reviews 21 (6): 405–412.
- Muranski P, Boni A, Antony PA et al. (July 2008). "Tumor-specific Th17-polarized cells eradicate large established melanoma". Blood 112 (2): 362–373. doi:10.1182/blood-2007-11-120998. PMC 2442746. PMID 18354038.
- Martin-Orozco N, Muranski P, Chung Y et al. (November 2009). "T helper 17 cells promote cytotoxic T cell activation in tumor immunity". Immunity 31 (5): 787–798. doi:10.1016/j.immuni.2009.09.014. PMC 2787786. PMID 19879162.
There are some open access Network Protocols for studying Th17 cells at Nature Protocols:
- Egwuagu, Charles; Yu, Cheng-Rong; Amadi-Obi, Ahjoku; Liu, Xuebin; Mahdi, Rashid; Lee, Yun Sang (2007). "TH17 cells contribute to uveitis and scleritis and are inhibited by IL-27/STAT1 in the retina (3) Western Blot Analysis". Nature Protocols. doi:10.1038/nprot.2007.382.
- Egwuagu, Charles; Yu, Cheng-Rong; Amadi-Obi, Ahjoku; Liu, Xuebin; Mahdi, Rashid; Lee, Yun Sang (2007). "TH17 cells contribute to uveitis and scleritis and are inhibited by IL-27/STAT1 in the retina (4) Confocal microscopy". Nature Protocols. doi:10.1038/nprot.2007.383.
- Egwuagu, Charles; Yu, Cheng-Rong; Amadi-Obi, Ahjoku; Liu, Xuebin; Mahdi, Rashid; Lee, Yun Sang (2007). "TH17 cells contribute to uveitis and scleritis and are inhibited by IL-27/STAT1 in the retina (5) Chromatin immunoprecipitation". Nature Protocols. doi:10.1038/nprot.2007.384.