Cell mediated immune response Primary immune response Secondary immune response

1. IMMUNORESPONSE
VASEEM AKRAM PV
2nd MSC Microbiology

2. INTRODUCTION
• Immune responseisareactionwhich occurwithinanorganism forthe purposeofdefending againstforeign substance
• This substanceis commonlywide varietyofdifferentmicro-organismsincluding virus,bacteria,parasitesandfungi whichcould
couseserioushealth issuestothe hostorganism
• Thereare2 typesofimmune response
• Humoralimmune response
• Cell mediatedimmune response
• Theinnateimmuneresponseis anorganism’sfirstresponseagainstthe foreign Body
• The innateimmune systemconsistsof physicalbarrierssuch asskinandmucousmembranes,variouscell typeslike neutrophils,
macrophages,andmonocytes,andsolublefactorsincluding cytokinesandcomplement.
• The adaptiveimmune responseis thebody’ssecond lineof defense

3. Supplements to the Immune Response
• Threeimportantagents areusedin medicine tosupplementthe immune response:
• Antibiotics:arechemicals thatareharmfultobacteriaorefficient againstbacterialattack
• Vaccines:aresubstancesthatstimulatetheproductionofmemorycell. Inactivatedviruses orfragmentsof viruses,bacteria,or
othermicroorganismsareusedasvaccines.
• Passiveimmunity:is obtainedbytransferringantibodiesfromanindividualwho previouslyhadadiseasetoa newlyinfected
individual.Newborninfantsareprotectedbypassiveimmunitythroughthe transferofantibodiesacrosstheplacentaandby
antibodiesin breastmilk.

4. Cell-mediated immune response
• It is animmune responsethatdoesnotinvolve antibodies
• Cell mediatedimmune responseinvolves the activationofmacrophagesandNK-cells, theproductionofantigen-specificcytotoxic
T-lymphocytes
• It releases variouscytokinesin responsetoanantigen .Cellular immunityprotectsthe body
• Cell-mediatedimmunityis targetedprimarilymicrobes thatsurvive in phagocytesandmicrobes thatinfect non-phagocyticcells
• It is moreeffectiveagainstintracellularorganismslike virus, parasites,fungi, intracellularbacteria,andcancercells
• In amannersimilar toB-lymphocytes,T-lymphocytesareabletorandomlycut outandsplice togetherdifferentcombinationsof
genes alongtheir chromosomesthrougha processcalledGene translocation
• This isknownascombinatorialdiversity andresults in eachT-lymphocytegenerating aunique T-cell receptor(TCR).

5. • T-lymphocytesproducedbystem cells ofbonemarrowpassthroughliver andspleen beforereaching the thymuswheretheyare
processed,hence called thymus-dependent(T) lymphocytes.
• T-cell responses,whicharepartofcell-mediatedimmunity,playavital rolein controllingviral infections
• Modeofaction
• Whenanantigen entersthebody,themacrophagesfirstattacktheantigen andfragmentit intopieces
• It thenpresentsa piece ofantigentothe T-helpercells
• The Thelpercells recognizethe antigenandtrigger offaseries ofcell mediatedresponse
• A clone ofT-lymphocytesis firstformedafterbeing activatedbythe T-helpercells
• TherearedifferentkindsofT-cells,which aremorphologicallysimilarbutdifferfunctionally.

6. The actions of the different types of T-cell are
1. Helper cells:- reactbyproducingsmall peptidemolecules called lymphokines.Thelymphokinespromoteproliferationofmore
T-cells, stimulateBcells toproduceantibodiesandalso help in accumulatingmacrophagesin theinflamed tissuesandby
promotingphagocytosis.
2. Cytotoxiccells:- or Killer cellskill cells infectedbyviruses, cancerouscells andtransplants
3. Suppressor cells:- The thirdtypeofT-cells producelymphokinesthatsuppresstheactionofthe phagocytesandthedifferent
typesofWBCcells. Theyplayanimportantrolein immunotolerance.
4. Memorycells:-It is remaining in the lymphoidtissuethroughoutthe body.It is very effectivein the secondaryimmune
response.Thatis theseonsubsequentexposuretothe sameantigencancauseanimmune responsemorerapidlythanthe first
exposure.

8. T Cell Activation
• All threetypesofT cells mustbeactivatedbyanantigenbeforetheycanfightaninfectionor cancer
• Whena Bcell ornonspecificleukocyteengulfs a virus anddisplaysits antigens.Thenthe Tcell encountersthematchingantigen
ona leukocyte,itbecomes activated
• T cell activationrequiresanotherleukocyteto engulf avirus anddisplayits antigen
• Andit activateHelper T cells andCytotoxicTcells
• Helper T Cellsarelikethe “managers”of theimmune response.Theysecrete cytokines,which activateor controlthe activitiesof
otherlymphocytes
• Most helper T cellsdie outonceapathogenhas been cleared fromthe body,buta fewremain asmemorycells.
• Thesememorycells arereadytoproducelargenumbersof antigen-specifichelperTcells like themselves if theyareexposedto
the sameantigen in thefuture.

9. Cytotoxic T Cells
• Destroyvirus-infectedcells andsomecancer cells.
• Onceactivated,acytotoxicTcell divides rapidlyandproducesan“army”ofcells identical toitself
• Thesecells travel throughoutthe body“searching”formorecells todestroy
• T cell releases toxinsthatformporesin themembrane ofthe infectedcell. This causesthe cell toburst,destroyingboththe cell and
theviruesesinside it.
• Afteraninfectionmost cytotoxicT cells dieoff
Regulatory T Cells
• Responsibleforending thecell-mediatedimmune responseafteraninfectionhasbeen destroyed
• TheyalsosuppressT cells thatmistakenlyreactagainstself antigens

10. T cell activation Cytotoxic T cell function

11. Primary immune response
• Boththymus-dependentandthymus-independentantibodiesareinvolvedin theprimaryimmune responseresponseappears
mainlyin thelymphnodesandspleen
• Theantibodielevel reachesmaximumin 7-10days
• Antibodieshavelow affinitytotheir antigen
• The respondingcells arenativeBcells andT cells
• Boththymus-dependentandthymus-independentantibodiesareinvolvedin theprimaryimmune response
• A largeamountofIgM anda small amountofIgG areproducedduringthe primaryimmuneresponse.
• The primaryimmune responseisusuallyweakerthanthesecondaryimmune response.Becausethe lag phaseis long(4-7 days)
alsoFew antibodiesareproducedin theprimaryimmune response.

12. Secondary immune response
• It is thereactionofthe immune system whenit contactsanantigen forthe second andsubsequenttimes.
• The secondaryimmune responseis stronger.
• It appearsmainlyin the bonemarrowandthen,in the spleen andlymphnodes.
• The antibodylevel reachesits peakin 3-5days
• Antibodeishavehigh affinitytotheirantigens
• RespondingCell is MemoryB cells
• Onlythymus-dependentantibodiesareinvolved in the secondaryimmuneresponse
• The IgMis replacedbyA large amountofIgG, asmall amountof IgM, IgA, andIgE areproducedduring thesecondaryimmune
response.

13. A schematic diagram showing a primary and secondary response