Medical Microbiology

intheinductionofantigen-antibodycomplexes—someofwhichwereformed

inthepresenceofantigenexcess—andoccasionallyinducedastateofshock.

&Immunecomplexesinthepresenceofantibodyexcess.Theso-called

Arthusreactionisobservedwhenanindividualisexposedtorepeatedsmall

dosesofanantigenoveralongperiodoftime,resultingintheinductionof

complexesandanantibodyexcess.Furtherexposuretotheantigen,particu-

larlydermalexposure,inducesatypicalreactionofedemaanderythema

whichpeaksafterthreetoeighthoursanddisappearswithin 48 hours,

butwhichsometimesleadstonecrosis.Arthus-typereactionsoftenrepresent

occupationaldiseasesinpeopleexposedtorepeateddosesofenvironmental

antigens:farmer’slung(thermophilicActinomycesinmoldyhay),pigeon

breeder’slung(proteininthedustofdriedfecesofbirds),cheeseworker’s

lung(sporesofPenicilliumcasei),furrier’slung(proteinsfrompelthairs),

malt-worker’slung(sporesofAspergillusclavatusandA.fumigatus).

TypeIV:HypersensitivityorDelayedType,

Cell-MediatedHypersensitivity

Intracutaneousinjectionofasolubleantigenderivedfromaninfectious

pathogeninducesadelayeddermalthickeningreactioninthosepeople

whohavesufferedapreviousinfection.Thisdelayedskinreactioncanserve

asatesttoconfirmimmunityagainstintracellularbacteriaorparasites.

Formostcases,thetimebetweenadministrationoftheantigenandthe

swellingreactionis 48 – 72 hours—asdescribedaboveforcellulardelayedtype

hypersensitivity(DTH)reactionsintheskin(p.99).Asobservedforantibody-

dependenthyper-reactionsoftypesI-III,thetypeIVresponseispathogenic

anddiffersfromprotectiveimmuneresponsesonlyintermsoftheextentand

consequencesofthetissuedamage,butnotintermsofthemechanismofaction.

ThebalancebetweenautoimmunediseaseandtypeIVimmunopathologyin

suchcasesisreadilyillustratedbytypeIVreactions(e.g.,aggressivehepatitis

inhumansorlymphocyticchoriomeningitisinmice).Shouldthecausal

infectiouspathogenbeknown,theresponseistermedatypeIVreaction,

ifthecausalagentisunknown(ornotyetdetermined)thesamecondition

maybetermed“autoimmunedisease.”Thereaderisreferredtothemany

examplesoftypeIVresponsesalreadydiscussedwithinvariouschapters

(DTH[p.99],immuneprotectionandimmunopathology[Tables2. 9 and

2. 10 ,pp. 104 and 1 05],transplantationimmunology[seebelow],andauto-
   immunity[p. 11 0ff.]).
   AutoimmuneTcellsareusuallydirectedagainstautoantigensthatwould
   otherwisebeignored(sincetheyareonlyexpressedintheextralymphatic
   periphery).AutoaggressiveCD4+Tcellsapparentlyrespondagainstmyelin

114 2 BasicPrinciplesofImmunology

2

All rights reserved. Usage subject to terms and conditions of license

Kayser, Medical Microbiology © 2005 Thieme

All rights reserved. Usage subject to terms and conditions of license.