IL-31isa24kDand164AAα-helicalproteinwithafour-helixbundlestructure,preferentiallyproducedbyCD4+type2helperTcells(Th4).IL-31iscloselyrelatedtotheIL-6typecytokinessuchasoncostatinM(OSM),Leukemiainhibitoryfactor(LIF)andcardiotrophin1(CT-1).IL-31signalsviabindingtoaheterodimericcomplexthatiscomposedofIL-31receptorA(IL-31RA)thatishighlyhomologouswiththegp30-likereceptorandoncostatinMreceptorsubunits.Thesereceptorsubunitsareexpressedinactivatedmonocytes,inepithelialcells,andkeratinocytesrespectively.OntargetcellsIL-31bindingcaninduceactivationoftheJAK/STAT,AKTandMAPKsignalingpathways.Duetotheubiquitousexpressionofitsreceptorcomplex,IL-31hasnumerousphysiologicalrolesincludingregulationofhematopoiesisandimmuneresponse.Whenoverexpressedintransgenicmice,IL-31inducesseverepruritusresemblingeczemainhumans.SerumIL-31waspreviouslyfoundoverexpressedinadultswithatopicdermatitis(AD).SerummeasurementofIL-31inpaediatricatopicdermatitisrevealedthatelevatedlevelscorrelatewithseverityscoring.ActivatedeffectorTcellsarerecruitedtotheskinbychemokinesandcelladhesionmolecules.ThesecomponentsinthelocalmicroenvironmentprolongTcellsurvivalandcontributetothechronicityofthesediseases.IL-31isassociatedwiththepromotionofallergicandchronicinflammatoryconditionssuchasdermatitis,pruritus,airwayhypersensititvityandinflammatoryboweldisease..