Medical Microbiology

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2 BasicPrinciplesofImmunology

R.M.Zinkernagel

Introduction

&Resistancetodiseaseisbasedoninnatemechanismsandadaptiveor
acquiredimmunity.Acquiredimmunemechanismsactinaspecificmanner
andfunctiontosupplementtheimportantnonspecificornaturalresistance
mechanismssuchasphysicalbarriers,granulocytes,macrophages,and
chemicalbarriers (lysozymes,etc.).The specificimmunemechanisms
constituteacombinationoflessspecificfactors,includingtheactivationof
macrophages,complement,andnecrosisfactors;theearlyrecognitionof
invadingagents,bycellsexhibitingalowlevelofspecificity,(naturalkiller
cells,cd[gamma-delta]Tcells);andsystemsgearedtowardhighlyspecific
recognition(antibodiesandab[alpha-beta]Tcells).
Manycomponentsofthespecificimmunedefensesalsocontributeto
nonspecificornaturaldefensessuchasnaturalantibodies,complement,
interleukins,interferons,macrophages,andnaturalkillercells. &

Inthestrictsense,“immunity”definesanacquiredresistancetoinfectious

diseasethatisspecific,i.e.,resistanceagainstaparticulardisease-causing

pathogen.Forexample,apersonwhohashadmeaslesoncewillnotsuffer

frommeaselsasecondtime,andisthuscalledimmune.However,suchspe-

cificoracquiredimmunemechanismsdonotrepresenttheonlyfactors

whichdetermineresistancetoinfection.Thecaninedistempervirusisaclose

relativeofthemeaslesvirus,butnevercausesaninfectioninhumans.This

kindofresistanceisinnateandnonspecific.Ourimmunesystemrecognizes

thepathogenasforeignbasedoncertainsurfacestructures,andeliminatesit.

Humansarethusbornwithresistanceagainstmanymicroorganisms(innate

immunity)andcanacquireresistancetoothers(adaptiveoracquiredim-

munity;Fig.2. 1 ).Activationofthemechanismsofinnateimmunity,also

knownastheprimaryimmunedefenses,takesplacewhenapathogen

breachestheouterbarriersofthebody.Specificimmunedefensefactors

aremobilizedlatertofortifyandregulatetheseprimarydefenses.Responses

oftheadaptiveimmunesystemnotonlyengenderimmunityinthestrict

sense,butcanalsocontributetopathogenicprocesses.Thetermsimmuno-

pathology, autoimmunity,andallergy designatea groupof immune

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Kayser, Medical Microbiology © 2005 Thieme