Medical Microbiology

&Congenitaloracquiredimmunodeficiency—whethercausedbyanti-lym-

phocyticsera,cytostaticdrugs,gammairradiation,UVirradiation,orinfec-

tion—usuallyencouragestumorgrowth,especiallyforlymphohematopoietic

tumors.Carcinomasandsarcomasshowlittleornoincreasedsusceptibility.

Interestingly,experimentalcarcinogensarefrequentlyalsoimmunosuppres-

sive.

&Surgicalremovalofalargeprimarytumormayresultinthedisappearance

(orrarelyinrapidgrowth)ofmetastaseswithinthelymphnodes.

&TumorcellsoftendisplaymodulatedMHCexpression—sometumorslack

MHCclassImoleculesentirely—orinsomecasestumorsselectivelydown-

modulatetheonlyMHCallelecapableofpresentingaspecifictumor-asso-

ciatedpeptide(e.g.,thecolonadenocarcinomas).Othertumorsside-stepim-

munedefensesbydown-regulatingtumor-specificantigens.

&Theimmuneresponsemayfailiftumordifferentiationantigensareex-

pressed,againstwhichthehostexhibitsanimmunologicaltolerance(e.g.,

carcinoembryonicantigen[CEA],T-cellleukemiaantigen).

&Blockadeofthereticuloendothelialsystemmayencouragethedevelop-

mentoflymphohematopoietictumors.Forinstance,chronicparasiticinfec-

tionsorinfectionbymalariacanresultinthedevelopmentofBurkittlym-

phoma,aB-cellmalignancy.

ThePathologicalImmuneResponse................................

&Animmuneresponsecanalsocausedisease.Suchresponsescanbe

classifiedintothefollowingtypes:TypeI:allergicIgE-dependentdiseases;

TypeII:antibody-dependentresponsestocellmembranes,bloodgroupanti-

gensorotherauto-antigens;TypeIII:immunecomplex-initiateddiseases

wherebysurplusantigen-antibodycomplexesaredepositedonbasement

membranes,resultingindevelopmentofchronicdiseaseviacomplement

activationandinflammatoryreactions;TypeIV:cellularimmunopathology

resultingfromexcessiveT-cellresponsesagainstinfectionsthatotherwise

exhibitlowcytopathogenicity,oragainstallogenicorgantransplants. &

TypeI:IgE-TriggeredAnaphylaxis........................

Thistypeofimmediatehypersensitivityreactionoccurswithinminutesin

allergicallysensitizedindividuals.AlthoughserumIgEhasashorthalf-life

(onetotwodays),IgEantibodiesboundtotheFcereceptoronbasophils

108 2 BasicPrinciplesofImmunology

2

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Kayser, Medical Microbiology © 2005 Thieme

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