Medical Microbiology

400 7 GeneralVirology

NonspecificImmuneDefenses

Thenonspecificimmunedefensemechanismsareactivatedimmediately

whenpathogenspenetratethebody’souterbarriers.Oneofthemostimpor-

tantprocessesinthesebasicdefensesisphagocytosis,i.e.,ingestionandde-

structionofpathogens.Granulocytesandnaturalkillercellsbearmostofthe

responsibilityinthesemechanisms.ChangesinpHandionbalanceaswellas

feveralsoplayarole,forexample,certaintemperature-sensitivereplication

stepscanbeblocked.Themostimportanthumoralfactoristhecomplement

system.Interferons,whicharedescribedbelow,arealsopotenttoolsfor

fightingoffviralinfections.Theothermechanismsofnonspecificimmune

defensearedescribedinChapter2,(PrinciplesofImmunology,p.43ff.).

Interferons(IFN)arecell-codedproteinswithamolecularweightofabout 20

kDa.Threetypesaredifferentiated(leukocyteinterferon=IFNa,fibroblast

interferon=IFNb,andimmuneinterferon=IFNc)ofwhichtheaminoacid

sequencesareknownandwhich,thankstogeneticengineering,cannow

beproducedinpracticallyunlimitedamounts.Whereastheprincipalbiolog-

icaleffectsofinterferonsonbothnormalandmalignantcellsareantiviraland

antimitotic,thesesubstancesalsoshowimmunomodulatoryeffects.Their

clinicalapplicationsaredesignedaccordingly.Inkeepingwiththescope

ofthissection,thefollowingdescriptionoftheirantiviralactivitywillbere-

strictedtothesalientvirologicalaspects(Fig. 7. 8 ):

Anumberofsubstancescaninducetheproductionofinterferoninacell,

forexampledouble-strandedRNA,syntheticornaturalpolynucleotides,bac-

teria,variouslow-molecularcompoundsand,aboveall,viruses.Allofthese

SynthesisandEffectsofInterferon

Derepression Interferon

Immun-

modulation

Growth

Antiviral

proteins

Derepression

Fig. 7. 8 Aninterferon-inducingsubstanceinitiatesproductionofinterferoninthe

firstcell.Inthesecondcell,interferoninduces,forinstance,productionofantiviral

proteins.

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Kayser, Medical Microbiology © 2005 Thieme