Medical Microbiology

ImmuneResponsesandEffectorMechanisms 79

AntiviralProtectionbyTCells

Perforin

T cell T cell

Perforin

Noncytopathic

virus

Cytopathic

virus

Perforin mouse:

uncontrolled

viral proliferation

Control mouse:

perforin lyses

infected cells

T cell B cell

IL IFN

Neutralizing

antibody

Diffusion,

protection of

many other cells

Lysis caused by virus

Fig.2. 15 Certainvirusesdestroytheinfectedhostcells(right),othersdonot

(left).CytotoxicTcellscandestroyfreshlyinfectedcellsbydirectcontact(with

thehelpofperforin),thusinhibitingviralreplication(middle).Whethertheresult

ofthislysisisclinicallydesirabledependsonthebalancebetweenprotectionfrom

viralproliferation,andthedamagecausedbyimmunologicallymediatedcellde-

struction.Inperforinknockoutmice(perforino/o),Tcellsareunabletoproduce

perforinandthereforedonotdestroytheinfectedhostcells.Replicationof

non-cytopathicvirusesthuscontinuesunabatedinthesemice.Solubleanti-viral

interleukins(especiallyIFNcandTNFa),andneutralizingantibodies,combatcyto-

pathicviruses(whichreplicatecomparativelyrapidly)moreefficientlythandocy-

tolyticTcells;thisisbecauseinterleukinandantibodymoleculescanreadilydiffuse

throughtissuesandreachagreaternumberofcells,morerapidly,thancankillerT

cells.

2

Kayser, Medical Microbiology © 2005 Thieme