IMMUNE RESPONSE TO INFECTIOUS DISEASES
Immune Response to Bacterial Infection
Characteris*csofBacteria
① X② X③ X④ X
⑤ X⑥ X⑦ X
AnypartofthebodycanbeinfectedbymanyInfec;ousagentsandmanybacterialdiseasesandcausingadiseasedueto:① Growthofthemicrobeina;ssue② ProduceBacterialfactorsthatareharmfultohost③ EliciteaninflammatoryresponsethatcausesdamageButalsoleadstoacquiredimmunity
BacterialDiseases
① AHachmentofbacteriumtohost;ssue•Persistenceandgrowthcalledcoloniza;on
StepsofBacterialInfec*on
StepsofBacterialInfec*on2
② Invasionintodeeperhost;ssuesandproduc;onoftoxinsandleadstoinjurytohostcelland;ssue
StepsofBacterialInfec*on3
③ Inflamma;onatsiteofinvasion•Ini;atedbyan;bodybindingtobacterium•Ini;atedbycomplementac;va;onatbacterialsurface•Ini;atedbywoundhealingmechanisms•Allcanac;vatecomplementpathwaysthataltersvascularpermeabilityandac;vateslocalmacrophageandneutrophils(PMNs)
Inflamma*onatsiteofinvasion
Thedefencemechanismsuseddependon:-
Ø Siteofinfec;onØ Structureoftheinvadingbacteria
Ø Howtheycausedamage
Ø Intracellularvs.extracellularloca;on
Immunitytobacteria
Both
Most bacteria
Mycobacteria Clostridium tetani
Toxin production Tissue invasion
HowCanBacteriaCauseDamage?
Immunitytobacteria
• Innateandadap;veimmunesystemsworktogether.
• Ingeneral,theinnateresponseisimportantinpreven;nganinfec;onbecomingestablished,theadap;vesubsequentlyincomba;nganestablishedinfec;on.
Innateimmunesystemcanrecogniseandrespondtocommonbacterial
components① X
② X③ X④ X⑤ X⑥ X⑦ X
InnateImmuneEffectorsandBacterialInfec*on
Adap*veImmunity:I. An*bodymediatedresponse
Action How
Block adhesion Ab to surface proteins
Block proliferation Ab to surface receptors eg. iron
Cause phagocytosis Bind bacterial surface and allow phagocytes to bind bacteria
Lysis, phagocytosis and inflammation
Activate complement
Neutralise toxic products Bind toxins
Prevent tissue invasion and damage
Neutralise bacterial products and proteases
Immunitytoextracellularbacteriaby
an*bodies:
Immunitytoextracellularbacteriaby
an*bodies:
① An*bodiesandcomplementresultinopsonisa;onvia FcRorCRon MØandPMN.
② An*bodycanac;vateclassicalcomplementpathway
resul;ngMACforma;onand opsonisa;on.
③ An*bodiescanalsotriggeran;body-dependentcellmediated cytotoxicity(ADCC)byPMNwithFcRand CRandthatleadstoreleaseproteases,nucleases,lipases.
MechanismsofImmunitytointracellularbacteriabyCMI
II. Cellmediatedimmunityvsintracellularbacteria
1. CD8+Tcells(Tc)cytotoxicTlymphocytes(CTLs).
2. CD4+helperTcells(TH1).
3. NKcellsusingADCC
DoTLymphocytesHaveaRoleintheResponsetoBacteria?
① Tcytotoxiclymphocytescankillinfectedcells(intracellularpathogensegMycobacteriumtuberculosis)
② ThelpercellsproducecytokinesorinterleukinsA. morean*bodyproduc*onB. Interferonγac;vatesmacrophagesandincreasesbacterial
killing,increasesproduc;onofIgGusedbyphagocytes,increasescytotoxicityandCD8Tcellac;vity
HowbacteriaevadeHostImmunity?
① Avoidingan;body② Preventphagocytosis③ Avoidingcomplement④ Down-regulatetheexpressionofMHC-Iand
MHC-II.⑤ Impedethefunc;onoflymphocytesand
granulocytes(toxin,enzymeandproteins).⑥ Overs;mulateinflamma;on