Medical Microbiology

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repeatedinaregularpattern(lineare.g.,flagella,ortwo-dimensionale.g.,
viruses)withintervalsof 5 – 10 nm.Theseparacrystalline-patternedantigens
arecapableofinducingB-cellresponseswithoutcontact-dependentTcell
help.ThisprobablyoccursbymeansofmaximumIgreceptorcross-linking.
SuchB-cellresponsesareusuallyoftheIgMtype,sinceswitchingtodifferent
isotypeclassesiseitherimpossibleorveryinefficientintheabsenceofTcell
help.TheIgMresponseisofarelativelybriefduration(exhibitingahalf-lifeof
about 24 h),butcannonethelessbehighlyefficient.Examplesofthiseffi-
ciencyincludeIgMresponsesinducedbymanyviralenvelopeantigenswhich
bearneutralizing(“protective”)determinantsaccessibletothecorresponding
antibodies,andresponsestobacterialsurfaceantigens(e.g.,flagellae,lipo-
polysaccharides)orparasites.


TCells.......................................................


T-CellActivation........................................


TherearetwoclassesofTcells;Thelpercells(CD4+)andcytotoxicTcells
(CD8+).Table2. 5 summarizestherelianceofT-cellresponsesonthedose,
localization,anddurationofpresenceofantigen.T-cellstimulationviathe
TCR,accessorymoleculesandadhesionmoleculesresultsintheactivation


ImmuneResponsesandEffectorMechanisms 71

Table2. 5 DependenceofT-CellResponseonAntigenLocalization,Amount,
andDurationofPresence


Antigen T-cellresponse

Localization Amount Durationof
presence


Thymus Small-large Always Negativeselectionby
deletion


Blood,spleen,
lymphnodes
(secondary
lymphoid
organs)


Small
Small

Large
Large

Short(1day)
Long(7days)

Short
Long(> 10 days)

Noinduction
Induction

Noinduction
Exhaustiveinduction/
deletion(anergy?)

Peripheralnon
lymphoidtissue


Largeorsmall Alwaysorshort Ignorance,indifference

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Kayser, Medical Microbiology © 2005 Thieme
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