Medical Microbiology

&IgE-mediateddefenseisimportant,alongwithIgA,inenhancingtheeli-
minationofgastrointestinal,pulmonary,anddermalparasites.Althoughde-
tailsoftheprocessarestillsketchy,IgE-dependentbasophilandeosinophil
defensemechanismshavebeendescribedformodelschistosomalinfections.

ImmuneDefensesagainstInfectionandTumorImmunity 101

GeneralSchemesofInfectiousDiseases

Fig.2. 19 Thedegreeofhostsurvivaldependsonboththerateofproliferation,

andtheextentofspread,ofaninfectiousagent–aswellastheintensityofthe

host’scytotoxicT-cellresponse.Infectionbycytopathicpathogenscanonlybe

controlledifpathogenicproliferationisslowandthepathogenremainslocalized;

otherwisetheoutcomeisusuallyfatal.Inthecaseofnoncytopathicpathogens,

thecytotoxicT-cellresponseisthecriticalparameter.Pathogenswhichproliferate

slowlyarequicklyeradicated.TheT-cellresponsecanbehaltedbypathogens

whichproliferaterapidlyandspreadwidelyduetothedeletionofresponding

Tcells.Thedegreeofsurvivalforhostsishighinbothofthesecases.Forpathogens

whichexhibitmoderateratesofproliferationandspread,theT-cellresponsemay

causeextensiveimmunopathologicaldamage,andthusreducetheproportionof

survivinghosts,someofwhichwillcontrollvirus,somenot.

Aweakenedimmunedefensesystemmaynotprogressbeyondanunfavorable

virus-hostbalance,evenwhenconfrontedwithastaticorslowlyreplicatingpatho-

genwhichrepresentsaninitiallyfavorablebalance.

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.