Medical Microbiology

44 2 BasicPrinciplesofImmunology

phenomenacausingmainlypathologicaleffects,i.e.,tissuedamagedueto

inadequate,misguided,orexcessiveimmuneresponses.However,afailed

immuneresponsemayalsobecausedbyanumberofotherfactors.For

instance,certainviralinfectionsormedicationscansuppressorattenuate

theimmuneresponse.Thiscondition,knownasimmunosuppression,can

alsoresultfromraregeneticdefectscausingcongenitalimmunodeficiency.

Theinabilitytoinitiateanimmuneresponsetothebody’sownselfanti-

gens(alsotermedautoantigens)isknownasimmunologicaltolerance.

Anergyisthetermusedtodescribethephenomenoninwhichcellsin-

volvedinimmunedefensearepresentbutarenotfunctional.

Animmuneresponseisareactiontoanimmunologicalstimulus.The

stimulatingsubstancesareknownasantigensandareusuallyproteinsor

complexcarbohydrates.Thestericcounterpartsoftheantigensaretheanti-

bodies,i.e.,immunoreceptorsformedtorecognizesegments,roughly 8 – 15

aminoacidslong,ofthefoldedantigenicprotein.Thesefreelyaccessible

structuralelementsareknownasepitopeswhenpresentontheantigens,

orasantigen-bindingsites(ABS)fromthepointofviewoftheimmuno-

receptors.Presentedalone,anepitopeisnotsufficienttostimulateanimmu-

nologicalresponse.Insteadresponsivenessisstimulatedbyepitopescon-

TheComponentsofAnti-InfectionDefense

Physical

barriers

Skin, mucosa

Innate,

nonspecific

defenses

Cellular

defenses

Granulocytes

Macrophages

NK cells

Chemical barriers

pH, lipids, enzymes,

complement factors,

interleukins, acute

phase proteins,

antimicrobial peptides

surfactants

Cellular

defenses

Humoral

defenses

Lymphokines,

cytokines Antibodies

B cells

Cytotoxic T cells

T helper cells

Acquired,

specific

immunity

Fig.2. 1 Theinnateimmunedefensesystemcomprisesnonspecificphysical,

cellular,andchemicalmechanismswhicharedistinctfromtheacquiredimmune

defensesystem.Thelattercomprisescellular(T-cellresponses)andhumoral(anti-

bodies)components.SpecificTcells,togetherwithantibodies,recruitnon-specific

effectormechanismstoareasofantigenpresence.

2

Kayser, Medical Microbiology © 2005 Thieme