BackgroundInformation | CD4T-helpercellsaremajorplayersinadaptiveimmunity.Basedontheirexpressionprofileoftranscriptionfactorsandsecretedcytokines,thesecellsaredividedintothemajorsubsetsTh1,Th2,Th17andTregulatory(Treg)cells.Th1cells,inducedbyIL-12andenhancedbyIFN,secreteIFNthatactivatesmacrophages.InducedbyIL-4,Th2cellsprimarilyproduceIL-4,IL-5,IL-13,IL-25andIL-17E,playingaroleinallergy.Tregcells,inducedbyTGFβ,producetheanti-inflammatorycytokinesIL-10andTGFβandfunctiontocontrolT-cellresponsestopreventautoimmunereactions.Th17cells,amorerecentlydiscoveredsubsetcharacterizedbytheproductionofIL-17,areinducedbyTGFβcombinedwithIL-23andIL-1βinhumans,andTGFβ,IL-6andIL-21inmice.ActivatedTh17cellssecreteIL-17A,IL-17F,IL-21,IL-22andTNFαtopromotetissueinflammation.
Th17cellsareinvolvedintheclearanceofextracellularbacteriaandfungi.TheyareabundantintheintestinallaminapropriaandfunctionasabarrieragainstinvADIngpathogens.ExcessiveamountsofTh17cellshavebeenimplicatedinthepathogenesisofseveralautoimmunediseases,includingmultiplesclerosis,psoriasis,juvenilediabetes,rheumatoidarthritis,Crohn"sdiseaseandautoimmuneuveitis.InadditionTh17cellsplayanimportantroleintumordevelopment,progressionandmetastasis,potentiallyinbothpromotingandinhibitingtumorgrowth. |