Antigens & immunogensF.ppt

Antigens & ImmunogensAntigens & Immunogens

Professor Md. Professor Md. AkramAkram HossainHossain

November 2010November 2010

12/21/201312/21/2013 11Professor Md. Akram HossainProfessor Md. Akram Hossain

Lession planLession plan

•• Antigen, Immunogen, haptenAntigen, Immunogen, hapten

•• Criteria for antigenicityCriteria for antigenicity

•• Classification of antigensClassification of antigens•• Classification of antigensClassification of antigens

•• Antigenic determinantAntigenic determinant

•• Epitope, ParatopeEpitope, Paratope

•• superantigensuperantigen


Review questionsReview questions

1.1. What is antigen and immunogen?What is antigen and immunogen?

2.2. What are the criteria for immunogenicty? What are the criteria for immunogenicty? Which one is most essential and why?Which one is most essential and why?

3.3. How can you classify antigens?How can you classify antigens?

4.4.4.4. What are the differences between TWhat are the differences between T--dependant and Tdependant and T--independent antigens? independent antigens? Which will give long term immunity?Which will give long term immunity?

5.5. What is super antigenWhat is super antigen

6.6. What is epitope and paratope? Where What is epitope and paratope? Where paratope is located?paratope is located?





DefinitionsDefinitions

•• LiterallyLiterally AntiAnti--gengen meansmeans anyany agentagentwhichwhich cancan generategenerate antibodyantibody

•• ImmunoImmuno--gengen meansmeans anyany agentagent whichwhichgeneratesgenerates immuneimmune responseresponse.. (Antibody(Antibodymediatedmediated oror CellCell mediatedmediated


••ImmunogenImmunogen:: aa stimulusstimulus thatthat producesproduces aa

humoralhumoral oror cellcell--mediatedmediated immuneimmune responseresponse

––HumoralHumoral immuneimmune responseresponse –– byby antibodyantibody

––CellCell mediatedmediated immuneimmune responseresponse –– byby TT cellscells

••AntigenAntigen:: anyany substancesubstance thatthat bindsbinds••AntigenAntigen:: anyany substancesubstance thatthat bindsbinds

specificallyspecifically toto anan antibodyantibody oror aa TT--cellcell receptorreceptor

••ByBy definitiondefinition allall immunogensimmunogens areare antigensantigens butbut allall

antigensantigens areare notnot immunogensimmunogens..

••ForFor simplicity,simplicity, bothboth antigensantigens andand immunogensimmunogens areare

usuallyusually referredreferred toto asas antigensantigens..12/21/201312/21/2013 88Professor Md. Akram HossainProfessor Md. Akram Hossain

•• AntibodyAntibody -- aa diseasedisease fightingfighting proteinproteindevelopeddeveloped byby thethe bodybody inin responseresponse totothethe presencepresence ofof anan antigenantigenthethe presencepresence ofof anan antigenantigen


Historical and Biochemical Evidence for Immunoglobulin Historical and Biochemical Evidence for Immunoglobulin structure.structure.

• Electrophoretic separation of serumproteins yieldsalbumin, ,α β γ globulin, in that order.γ globulinlevels were increased in immunized animals andcould be decreased by incubation with specificantigens.

• Kabat & Tiselius in 1939 showed thatγ globulinfraction of serumcontain antibody.

• Porter proposed of a Y-shaped structure in 1962,after discovering Fc & Fab fragment in 1959.

• Edelman discovered 4 chains of Immunoglobulin.

• Porter & Edelman Won noble prize in 1972.12/21/201312/21/2013 1010Professor Md. Akram HossainProfessor Md. Akram Hossain

γ α

Globulin

Albumin

Electrophoretic mobility of serum proteins

γβ

α


AntigensAntigens��Most are proteins or large polysaccharides Most are proteins or large polysaccharides

from a foreign organism.from a foreign organism.

–– MicrobesMicrobes: Capsules, cell walls, toxins, viral : Capsules, cell walls, toxins, viral

capsids, flagella, etc.capsids, flagella, etc.

–– NonmicrobesNonmicrobes: Pollen, egg white , red blood : Pollen, egg white , red blood

cell surface molecules, serum proteins, and cell surface molecules, serum proteins, and cell surface molecules, serum proteins, and cell surface molecules, serum proteins, and

surface molecules from transplanted surface molecules from transplanted

tissue. tissue.

��Lipids and nucleic acids are only antigenic Lipids and nucleic acids are only antigenic

when combined with proteins or when combined with proteins or

polysaccharides.polysaccharides.


•• HaptenHapten:: SmallSmall foreignforeign moleculemolecule thatthatisis notnot antigenicantigenic.. MustMust bebe coupledcoupled totoaa carriercarrier moleculemolecule toto bebe antigenicantigenic..OnceOnce antibodiesantibodies areare formedformed theythey willwillOnceOnce antibodiesantibodies areare formedformed theythey willwillrecognizerecognize haptenhapten..

•• KarlKarl LandsteinerLandsteiner discovereddiscovered Hapten,Hapten,whowho alsoalso discovereddiscovered bloodblood groupgroupantigenantigen andand gotgot noblenoble prizeprize


Substances that act as antigensSubstances that act as antigens

InfectiousInfectious materialsmaterialsaa.. microbialmicrobial structuresstructures(cell(cell walls,walls, capsules,capsules, flagella,flagella, pili,pili, viralviral capsids,capsids, envelopeenvelope--associatedassociated glycoproteins,glycoproteins, etcetc..bb.. microbialmicrobial toxinstoxins

NoninfectiousNoninfectious materialsmaterialsNoninfectiousNoninfectious materialsmaterialsaa.. allergensallergens (dust,(dust, pollen,pollen, hair,hair, foods,foods, dander,dander, beebeevenom,venom, drugs,drugs, andand otherother agentsagents causingcausing allergicallergicreactions)reactions);;bb.. foreignforeign tissuestissues andand cellscells (from(from transplantstransplants andandtransfusions)transfusions);; andandcc.. thethe body'sbody's ownown cellscells thatthat thethe bodybody failsfails totorecognizerecognize asas "normal"normal self"self" (cancer(cancer cells,cells, infectedinfectedcells,cells, cellscells involvedinvolved inin autoimmuneautoimmune diseases)diseases)..


Classification of antigensClassification of antigens•• According to chemical natureAccording to chemical nature

1.1. ProteinsProteins-- virtually all virtually all

2.2. Polysaccharides Polysaccharides –– potentially but not alwayspotentially but not always

3.3. Nucleic acids Nucleic acids –– poor antigenspoor antigens

4.4. LipidsLipids-- may act as haptensmay act as haptens

•• According to mode of actionAccording to mode of action

1.1. Thymus dependent Thymus dependent –– Protein antigensProtein antigens

2.2. Thymus independent Thymus independent -- Polysaccharides Polysaccharides 2.2. Thymus independent Thymus independent -- Polysaccharides Polysaccharides

•• According to epitopeAccording to epitope

1.1. Unideterminant univalentUnideterminant univalent

2.2. Unideterminant multivalentUnideterminant multivalent

3.3. multdeterminant multvalentmultdeterminant multvalent

•• According to SourceAccording to Source

1.1. ExogenousExogenous

2.2. EndogenousEndogenous


Types of AntigensTypes of Antigens

•• TT--independentindependent antigensantigens–– ComplexComplex carbohydratescarbohydrates

–– DoDo notnot requirerequire processingprocessing

–– CanCan directlydirectly interactinteract withwith BB cellscells

–– NoNo memorymemory–– NoNo memorymemory

•• TT--dependentdependent antigensantigens–– RequireRequire macrophagesmacrophages oror otherother APCAPC

–– RequireRequire TT--helperhelper cellscells

–– RequireRequire majormajor histocompatibilityhistocompatibility antigensantigens

–– MostlyMostly proteinsproteins


ExogenousExogenous::External antigens e.g. bacterial infection External antigens e.g. bacterial infection

EndogenousEndogenous::

Types of Antigens…Types of Antigens…

Typically peptides derived Typically peptides derived from from anyany protein; e.g. protein; e.g. viral infections an infected viral infections an infected cell cell


The basis of immunogenicity…The basis of immunogenicity…

1.1. Foreignness Foreignness –– most essential most essential

2.2. Molecular sizeMolecular size

3.3. Chemical composition and Chemical composition and

heterogeneityheterogeneityheterogeneityheterogeneity

4.4. DegradabilityDegradability

5.5. Adequate dose & routeAdequate dose & route

6.6. Genetic constitution of hostGenetic constitution of host


•Epitope: the portion of an antigen that isrecognized and bound by an Ab or TCR/MHCcomplex (aka antigenic determinant)

•Paratope: “The site in the variable (V) domain•Paratope: “The site in the variable (V) domainof an antibody or T-cell receptor that binds toan epitope on an antigen


Epitopes: Antigen Regions that Epitopes: Antigen Regions that Interact with AntibodiesInteract with Antibodies


Fig. 1: Epitopes of an Antigen Fig. 1: Epitopes of an Antigen (Polysaccharide) (Polysaccharide)

PolysaccharidesPolysaccharides havehave manymany epitopesepitopes butbut ofof similarsimilarspecificitiesspecificities..


Fig. 2: Epitopes of an Antigen (Protein)Fig. 2: Epitopes of an Antigen (Protein)

Proteins have many epitopes of different specificities. Proteins have many epitopes of different specificities.


Fig. 3: Antigens and Fig. 3: Antigens and EpitopesEpitopes of a Virus of a Virus

EachEach differentdifferent proteinprotein andand glycoproteinglycoprotein ofof aa virusvirus constitutesconstitutes aadifferentdifferent antigenantigen.. EachEach differentdifferent antigenantigen containscontains aa numbernumber ofofdifferentdifferent epitopesepitopes..


EpitopeEpitope--Specific Specific Receptors on the Receptors on the Surface of BSurface of B-- and Tand T--LymphocytesLymphocytes

BB--lymphocyteslymphocytes havehave BB--cellcellreceptorsreceptors (sIg)(sIg) thatthat recognizerecognizereceptorsreceptors (sIg)(sIg) thatthat recognizerecognizeepitopesepitopes directlydirectly onon antigensantigens..TT--lymphocyteslymphocytes havehave TCRTCRmoleculesmolecules thatthat recognizerecognizeepitopesepitopes onlyonly afterafter theythey havehave

beenbeen placedplaced onon thethe body'sbody'sownown cellscells byby wayway ofof MHCMHCmoleculesmolecules..



HaptenHapten•• HaptenHapten:: AA moleculemolecule tootoo smallsmall toto bebe

immunogenicimmunogenic alone,alone, butbut whichwhich cancan bebeimmunogenicimmunogenic ifif coupledcoupled toto aa largerlarger moleculemolecule

referredreferred toto asas aa carriercarrier..

ByBy itself,itself, aa haptenhapten cancan reactreact withwith anan AbAb

ExampleExample:: PenicillinPenicillin actsacts asas aa haptenhapten



Haptens…Haptens…


Haptens…


AntibodyAntibody--Antigen Antigen InteractionsInteractions•• BindingBinding ofof antigenantigen toto antibodyantibody

•• OccursOccurs inin variablevariable regionregion ofof antibodyantibody moleculemolecule

•• InstantaneousInstantaneous

•• ExothermicExothermic•• ExothermicExothermic

•• MayMay formform complexescomplexes

•• CytotoxicityCytotoxicity mediatedmediated byby complementcomplement (lysis)(lysis)


The key event…The key event…



AA processedprocessed antigenantigen inin anan MHCMHC isis seenseen byby aaTCRTCR..

TheThe TCRTCR asksasks thethe MHC,MHC, “Are“Are youyou me?”me?” andandreceivesreceives anan affirmativeaffirmative answer,answer, “Yes“Yes..””

TheThe TCRTCR asksasks thethe processedprocessed antigen,antigen, “Are“Are youyouTheThe TCRTCR asksasks thethe processedprocessed antigen,antigen, “Are“Are youyoume?”me?” andand receivesreceives thethe negativenegative answer,answer, “No!”“No!”

Thus,Thus, thethe processedprocessed antigenantigen isis seenseen asas “not“not--self,”self,” ii.. ee..,, “foreign“foreign..””


The key event…The key event…A processed antigen in an MHC is seen by a A processed antigen in an MHC is seen by a TCR.TCR. This “viewing” occurs in the This “viewing” occurs in the ternary ternary complex.complex.

The TCR asks the MHC, “Are you me?” and receives an affirmative The TCR asks the MHC, “Are you me?” and receives an affirmative

answer, “Yes.” answer, “Yes.” Here the TCR looks at the MHC Here the TCR looks at the MHC answer, “Yes.” answer, “Yes.” Here the TCR looks at the MHC Here the TCR looks at the MHC histotope.histotope.

The TCR asks the processed antigen, “Are you me?” and receives The TCR asks the processed antigen, “Are you me?” and receives

the negative answer, “No!” the negative answer, “No!” Here the TCR uses its Here the TCR uses its paratopeparatope and looks at the and looks at the epitope.epitope.



A processed antigen in an MHC is seen by a TCR.A processed antigen in an MHC is seen by a TCR.

The TCR asks the MHC, “Are you me?” and receives an The TCR asks the MHC, “Are you me?” and receives an affirmative answer, “Yes.”affirmative answer, “Yes.”

The TCR asks the processed antigen, “Are you me?” and The TCR asks the processed antigen, “Are you me?” and receives the negative answer, “No!”receives the negative answer, “No!”The TCR asks the processed antigen, “Are you me?” and The TCR asks the processed antigen, “Are you me?” and receives the negative answer, “No!”receives the negative answer, “No!”

But what if the TCR asks the processed antigen,“Are you me?” and receives the answer, “Yes.” TCR’swhich can see “self” are eliminated in a process calledclonal deletion.

Clonal deletion assures that TCR’s don’t see “self.”12/21/201312/21/2013 3434Professor Md. Akram HossainProfessor Md. Akram Hossain




Experimental systems…Experimental systems…


Epitopes for BEpitopes for B--cells cells versus versus TT--cellscells

ByBy examiningexamining myoglobinmyoglobin oneone cancan seesee thatthat thethe Ag’sAg’s seenseen byby BB--cellscells andandTT--cellscells areare differentdifferent.. BB--cellscells seesee aa continuouscontinuous oror discontinuousdiscontinuous seriesseriesofof aminoamino acidsacids;; byby somesome circumstance,circumstance, aminoamino acidacid residueresidue 109109 hashasnevernever beenbeen aa partpart ofof anan epitopeepitope forfor anyany monoclonalmonoclonal antibodyantibody;; yetyetresidueresidue 109109 isis alwaysalways partpart ofof thethe processedprocessed antigenantigen seenseen byby aa TCRTCR..


Presentation of processed antigen…Presentation of processed antigen…


Presentation of processed antigen…Presentation of processed antigen…


There are two classes of TThere are two classes of T--cellscells

TTHH havehave CDCD44 whichwhich interactsinteracts withwithMHCMHC--IIII;; thus,thus, CDCD44++ TT--cellscells areare“MHC“MHC--IIII restrictedrestricted..””

TT cellscells areare “helper“helper cells”cells” thatthat sendsendTTHH cellscells areare “helper“helper cells”cells” thatthat sendsendsignalssignals ((viavia cytokinescytokines andand surfacesurface

proteinsproteins)) toto otherother cellscells ofof thethe immuneimmunesystemsystem.. TheThe TTHH cellscells functionfunction asas thethe“brain”“brain” ofof thethe immuneimmune systemsystem..


There are two classes of TThere are two classes of T--cells…cells…

TTCC havehave CDCD88 whichwhich interactsinteracts withwith MHCMHC--II;;thus,thus, CDCD88++ TT--cellscells areare “MHC“MHC--II restrictedrestricted..””TTCC cellscells becomebecome cytotoxiccytotoxic TT lymphocyteslymphocytes(CTL’s)(CTL’s) whichwhich attackattack “altered“altered selfself--cellscells ((ee..gg..,, infectedinfected cellscells..)) “Altered“Altered selfself--cells”cells” arearegg..,, infectedinfected cellscells..)) “Altered“Altered selfself--cells”cells” arearealsoalso calledcalled “target“target cellscells..”” TheyThey areare thethetargetstargets forfor thethe CTL’sCTL’s cytotoxicitycytotoxicity..


“adjuvants”“adjuvants”

AdjuvantsAdjuvants::

AA substancesubstance thatthat nonnon--specificallyspecificallyenhancesenhances thethe immuneimmune responseresponse toto ananantigenantigen–– ProlongProlong thethe presencepresence ofof thethe antigenantigen–– ProlongProlong thethe presencepresence ofof thethe antigenantigen

–– EnhanceEnhance productionproduction ofof “co“co--stimulatory”stimulatory”signalssignals

–– InduceInduce granulomagranuloma formationformation ((ii..ee..,, ananaccumulationaccumulation ofof macrophages)macrophages)

–– NonNon--specificallyspecifically stimulatestimulate lymphocyteslymphocytes


SuperantigensSuperantigens

SuperantigensSuperantigens areare unusualunusual bacterialbacterialtoxinstoxins thatthat interactinteract withwithexceedinglyexceedingly largelarge numbersnumbers ofof TT44--lymphocyteslymphocytes .. ConventionalConventionalantigensantigens areare engulfedengulfed byby antigenantigenpresentingpresenting cellscells (APCs),(APCs), degradeddegraded intointoepitopesepitopes..,, bindbind toto thethe peptidepeptide groovegrooveepitopesepitopes..,, bindbind toto thethe peptidepeptide groovegrooveofof MHCMHC--IIII molecules,molecules, andand areare putput ononthethe surfacesurface ofof thethe APCAPC (see(see FigFig.. 11))..HereHere theythey areare recognizedrecognized bybyspecificspecific TT44--lymphocyteslymphocytes havinghaving aaTCRTCR withwith aa correspondingcorresponding shapeshape(see(see FigFig.. 22)).. SuperantigensSuperantigens,,however,however, bindbind directlydirectly toto thetheoutsideoutside ofof MHCMHC--IIII moleculesmolecules andandactivateactivate largelarge numbersnumbers ofof TT44--lymphocyteslymphocytes (see(see FigFig.. 33))..


SuperantigensSuperantigens

Regular antigenSuper antigen


Actions of superantigensActions of superantigens1.1. ThisThis activationactivation ofof veryvery largelarge numbersnumbers ofof TT44--lymphocyteslymphocytes resultsresults

inin thethe secretionsecretion ofof excessiveexcessive amountsamounts ofof aa cytokinecytokinecalledcalled interleukininterleukin--22 (IL(IL--22)) asas wellwell asas thethe activationactivation ofof selfself--reactivereactive TT--lymphocyteslymphocytes..

2.2. ProductionProduction ofof highhigh levelslevels ofof ILIL--22 cancan resultresult inin circulationcirculation ofof ILIL--22inin thethe bloodblood leadingleading toto symptomssymptoms suchsuch asas fever,fever, nausea,nausea,vomiting,vomiting, diarrhea,diarrhea, andand malaisemalaise..

excessexcess stimulationstimulation ofof ILIL--22 secretionsecretion cancan alsoalso leadlead totoproductionproduction ofof otherother cytokinescytokines suchsuch asas

–– tumortumor necrosisnecrosis factorfactor--alphaalpha (TNF(TNF--alpha),alpha),–– tumortumor necrosisnecrosis factorfactor--alphaalpha (TNF(TNF--alpha),alpha),–– interleukininterleukin--11 (IL(IL--11),),–– inflammatoryinflammatory chemokineschemokines suchsuch asas ILIL--88,,–– plateletplatelet--activatingactivating factorfactor (PAF),(PAF),

cancan leadlead toto thethe samesame endothelialendothelial damage,damage, acuteacute respiratoryrespiratory distressdistresssyndrome,syndrome, disseminateddisseminated intravascularintravascular coagulation,coagulation, shock,shock, andandmultiplemultiple organorgan systemsystem failurefailure seenseen withwith EndotoxinEndotoxin..

33.. ActivationActivation ofof selfself--reactivereactive TT--lymphocyteslymphocytes cancan alsoalso leadlead totoautoimmuneautoimmune attackattack..


Examples of superantigensExamples of superantigens

1.1. ToxicToxic shockshock syndromesyndrome toxintoxin--11 (TSST(TSST--11)),,

2.2. StreptococcalStreptococcal pyrogenicpyrogenic exotoxinexotoxin (Spe)(Spe),,

producedproduced byby rarerare invasiveinvasive strainsstrains andand scarletscarlet feverfever strainsstrains

ofof StreptococcusStreptococcus pyogenespyogenes (group(group AA betabeta streptococci)streptococci)..

3.3. StaphylococcalStaphylococcal enterotoxinsenterotoxins (SE)(SE),,

4.4. SuperantigensSuperantigens associatedassociated withwith StreptococcusStreptococcus pyogenespyogenes

areare alsoalso thoughtthought toto bebe responsibleresponsible forfor psoriasispsoriasis..

5.5. AntigensAntigens associatedassociated withwith MycobacteriumMycobacterium tuberculosistuberculosis,, thethe

rabiesrabies virus,virus, andand possiblypossibly HIVHIV maymay alsoalso functionfunction asas

superantigenssuperantigens


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Antigens & immunogensF.ppt