Type IV hypersensitivity reaction, or delayed-type hypersensitivity, is a cell-mediated response to antigen exposure.Learn.Apply.Retain.Yourpathtoachievemedicalexcellence.StudyformedicalschoolandboardswithLecturioUSMLEStep1  |  USMLEStep2  |  COMLEXLevel1  |  COMLEXLevel2  |  ENARM  |  NEET  CreateyourfreeaccountContinueLearningTheLecturioMedicalConceptLibraryTypeIVHypersensitivityReactionTypeIVHypersensitivityReactionTypeIVhypersensitivityreaction,ordelayed-typehypersensitivity,isacell-mediatedresponsetoantigenexposure.ThereactioninvolvesTcells,notantibodies,anddevelopsoverseveraldays.PresensitizedTcellsinitiatetheimmunedefense,leadingtotissuedamage.Acytokine-mediatedprocessisactivatedbyT-helpercellswhilecytotoxicTcellsdirectlyreleasecytotoxinstoinfectedordysfunctionalcells,causingcelllysis.Clinicalmanifestationsdependonthesysteminvolved,sodiagnostictestsrelyonhistoryandfindings.Treatmentincludescontrollingtheeffectsoftheimmuneresponsewithglucocorticoidsandimmunosuppressivetherapywhilemanagingtheassociateddiseasecomplications.Lastupdate:September24,20204:27pmTableofContentsSharethisconcept:ShareonfacebookShareontwitterShareonlinkedinShareonredditShareonemailShareonwhatsappOverviewHypersensitivityreactionA“hyper”orexaggeratedresponsetowhatshouldbeconsideredharmlessenvironmentalantigensTypesI,II,andIIIareimmediatereactionsoccurringwithin24hours.TypeIVreactiondevelopsoverseveraldays.TypeIVhypersensitivityreactionCell-mediatedhypersensitivityreactionUnliketheotherhypersensitivityreactions,whicharemediatedbyantibodies(Abs),typeIVinvolvesantigen-specificeffectorTcells.Doesnotoccuruntil24–72hoursafterexposureofasensitizedindividual (thus,delayed-typehypersensitivity)ThedelayisduetothetimerequiredforTcelldifferentiation,cytokineandchemokinesecretion,andaccumulationofleukocytesatthesite.Relatedvideos1:42IntroductiontoHypersensitivity4:42Hypersensitivity:TypesPathophysiologyTcellfunctionTypeIVhypersensitivityreactionsdonotinvolveantibodies.Instead,Tcellsareinvolved.Majortype