Type I hypersensitivity (or immediate hypersensitivity) is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an ...TypeIhypersensitivityFromWikipedia,thefreeencyclopediaJumptonavigationJumptosearchMedicalconditionTypeIhypersensitivityOthernamesImmediatehypersensitivitySEMofmiscellaneousplantpollens:Pollensareverycommonallergens.SpecialtyImmunologyTypeIhypersensitivity(orimmediatehypersensitivity)isanallergicreactionprovokedbyre-exposuretoaspecifictypeofantigenreferredtoasanallergen.[1]TypeIisdistinctfromtypeII,typeIIIandtypeIVhypersensitivities.Exposuremaybebyingestion,inhalation,injection,ordirectcontact.Contents1Pathophysiology2Treatmentandprognosis3Examples4Seealso5References6ExternallinksPathophysiology[edit]Intype1hypersensitivity,B-cellsarestimulated(byCD4+TH2cells)toproduceIgEantibodiesspecifictoanantigen.Thedifferencebetweenanormalinfectiousimmuneresponseandatype1hypersensitivityresponseisthatintype1hypersensitivity,theantibodyisIgEinsteadofIgA,IgG,orIgM.Duringsensitization,theIgEantibodiesbindtoFcεRIreceptorsonthesurfaceoftissuemastcellsandbloodbasophils.[2]MastcellsandbasophilscoatedbyIgEantibodiesare"sensitized".Laterexposuretothesameallergencross-linkstheboundIgEonsensitizedcells,resultinginanaphylacticdegranulation,whichistheimmediateandexplosivereleaseofpharmacologicallyactivepre-formedmediatorsfromstoragegranulesandconcurrentsynthesisofinflammatorylipidmediatorsfromarachidonicacid;[3]someofthesemediatorsincludehistamine,leukotriene(LTC4andLTD4andLTB4),andprostaglandin,whichactonproteins(e.g.,G-proteincoupledreceptors)locatedonsurroundingtissues.[3]Theprincipaleffectsoftheseproductsarevasodilationandsmooth-musclecontraction.Type1hypersensitivitycanbefurtherclassifiedintoimmediateandlate-phasereactions.Theimmediatehypersensitivityreactionoccursminutesafterexposureandincludesreleaseofvasoactiveaminesandlipidmediators,whereasthelate-phasereactionoccurs2–4hoursafterexposureandincludesthereleaseofcytokines.[4]Listofaf