Medical Microbiology

Host–PathogenInteractions 23

— Mechanismsthatrequireoxygen.Halogenationofessentialbacterialcom-

ponentsby themyeloperoxidase-H 2 O 2 –halidesystem;productionof

highlyreactiveO 2 radicals(oxidativeburst)suchassuperoxideanion

(O 2 – ),hydroxylradical(OH),andsingletoxygen(^1 O 2 ).

SpecificDefenseMechanisms..........................

Specificimmunity,basedonantibodiesandspecificallyreactiveTlympho-

cytes,isacquiredinaprocessofimmunesystemstimulationbythecorre-

spondingmicrobialantigens.Humoralimmunityisbasedonantitoxins,op-

sonins,microbicidalantibodies,neutralizingantibodies,etc.Cellularimmu-

nityisbasedoncytotoxicTlymphocytes(Tkillercells)andThelpercells.See

Chapter 2 ontheprinciplesofspecificimmunity.

PhagocytosisofBacteria

Bacteria +

serum factors

(antibodies, C3b,

fibronectin)

Killing and

digestion Fusion to

form phagolysosome

Phagosome

formation

Phagocytosis

Attachment

= Nonspecific

receptor

= Fc receptor

= C3b receptors

CR1 and CR3

Polymorphonuclear

leukocyte

Lysosome

Fig. 1. 6 EncapsulatedbacteriacanonlybeeffectivelyphagocytosedifIgG-class

antibodies(Fcligand)orthecomplementcomponentC3b,orboth,arelocatedon

theirsurfaces.TheFcandC3bligandsbindtotheirspecificreceptorsonthepha-

gocytesurface.

1

Kayser, Medical Microbiology © 2005 Thieme