Lec6.Immunogenes or Antigens

8/18/2019 Lec6.Immunogenes or Antigens

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الرح

الرحمن

الة

الرح بس

الرحمن

الة

بس


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Immunogens Or AntigensImmunogens Or Antigens


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Immunogens or AntigenImmunogens or Antigenss

Immunogen or antigen:Immunogen or antigen:

** A foreign substance, when introduced intoA foreign substance, when introduced into

human body, stimulate formation of specifichuman body, stimulate formation of specific

antibodies or sensitized lymphocytesantibodies or sensitized lymphocytes

* Antigens have the ability to combine* Antigens have the ability to combinespecifically with antibodies produced orspecifically with antibodies produced or

sensitized T-lymphocytes inducedsensitized T-lymphocytes induced


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aptens:aptens:- !ow molecular weight substances- !ow molecular weight substances

- These substances not immunogenic by itself - These substances not immunogenic by itself

- If couple to a larger carrier molecule "albumin,- If couple to a larger carrier molecule "albumin,

globulins#, they become immunogenicglobulins#, they become immunogenic

- $%amples :- $%amples :

simple chemicals and drugs:simple chemicals and drugs:

penicillin, sulphonamid, aspirin, cosmetic,penicillin, sulphonamid, aspirin, cosmetic,

ttran&uillizers, neomycin s'in ointmentran&uillizers, neomycin s'in ointment


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$pitopes or Antigenic determinants:$pitopes or Antigenic determinants:

* (ites on or within antigen with which* (ites on or within antigen with whichantibodies reactantibodies react

* Antibodies are specific for epitopes* Antibodies are specific for epitopes


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Types of AntigensTypes of Antigens

$%ogenous Antigens$%ogenous Antigens

)- acterial antigens:)- acterial antigens:

a- Antigens related to bacterial cellsa- Antigens related to bacterial cells

- (omatic antigen "O#: part of cell wall gm +ve bacter- (omatic antigen "O#: part of cell wall gm +ve bacter

- apsular antigen: usually polysaccharide- apsular antigen: usually polysaccharide

- .lagellar Ag "# : a protein made of flagellin- .lagellar Ag "# : a protein made of flagellin

- .imbrial Ag: surface antigens in fimbriated bacilli- .imbrial Ag: surface antigens in fimbriated bacilli

b- Antigen secreted by bacteria:b- Antigen secreted by bacteria: - $%oto%ins- $%oto%ins

- $nzymes- $nzymes

/- 0iral antigens:/- 0iral antigens:

a- protein coat viral antigensa- protein coat viral antigens b- (oluble antigens "soluble nucleoproteins as in influenza#b- (oluble antigens "soluble nucleoproteins as in influenza#


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Types Of AntigensTypes Of Antigens

$ndogenous antigens$ndogenous antigens

uman tissue antigens:uman tissue antigens:

a- lood group antigens:a- lood group antigens:

A, and 1h antigensA, and 1h antigens

b- istocompatibility antigens:b- istocompatibility antigens: 2lycoprotein molecules on all nucleotide cells:2lycoprotein molecules on all nucleotide cells: - 3a4or histocompatibility comple% antigens "3#- 3a4or histocompatibility comple% antigens "3#

- uman leucocyte antigen "!A#- uman leucocyte antigen "!A#


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Major Histocompatibility ComplexMajor Histocompatibility Complex

Antigens (MHC) Antigens (MHC)** 33 has an important function inhas an important function in presentationpresentation ofof

antigens toantigens to T-cellsT-cells

** elper T-cellselper T-cells recognizerecognize foreign antigens on surfaceforeign antigens on surfaceofof A5s,A5s, only when these antigens areonly when these antigens are presentedpresented inin

the groove ofthe groove of 3 II3 II moleculemolecule

** ytoto%ic T-cellsytoto%ic T-cells will onlywill only recognizerecognize antigens, on theantigens, on thesurfaces of virus infected cells or tumor cells onlysurfaces of virus infected cells or tumor cells only

when these antigens arewhen these antigens are presentedpresented in the groove ofin the groove of

lass I moleculelass I molecule "3 restriction#"3 restriction#


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Superantigens (SAgs)Superantigens (SAgs)

* They* They activateactivate multiple clones ofmultiple clones of T-lymphocytesT-lymphocytes

** acterial to%ins:acterial to%ins:

Staph. aureusStaph. aureus to%ic shoc' syndrome to%into%ic shoc' syndrome to%in "T((T#"T((T#

andand enteroto%insenteroto%ins Strpt. pyogenesStrpt. pyogenes pyrogenic to%in Apyrogenic to%in A

* They have the ability to* They have the ability to bindbind bothboth class II 3class II 3

molecules andmolecules and T1T1 66 chainchain

* They act as* They act as a clampa clamp betweenbetween the twothe two, providing a, providing a

signalsignal forfor T-cell activationT-cell activation


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Superantigens (SAgs)Superantigens (SAgs)

* They are* They are activeactive atat very low concentrationvery low concentration causingcausing

release ofrelease of largelarge amounts ofamounts of cyto'inescyto'ines

* The* The massive T-cellmassive T-cell activation and release ofactivation and release of largelargeamounts of cyto'inesamounts of cyto'ines causecause systemic to%icitysystemic to%icity

* This method of* This method of stimulationstimulation isis not specificnot specific for thefor the

pathogenpathogen

* It does* It does notnot lead tolead to ac&uired immunityac&uired immunity ie no memoryie no memory


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Antigen Bining An !ecognition Molecules Antigen Bining An !ecognition Molecules

Antigens are recognized by and bind to:Antigens are recognized by and bind to:

)# -cell receptors "1# :)# -cell receptors "1# :

- These are membrane-bound immunoglobulins- These are membrane-bound immunoglobulins

"Ig3 and Ig7# on -cells"Ig3 and Ig7# on -cells

- 1s can be secreted in plasma as antibodies- 1s can be secreted in plasma as antibodies

/# T-cell receptors "T1#/# T-cell receptors "T1#

-- 88 andand 66 chains anchored to T-cellschains anchored to T-cells

- There is a groove which binds small peptides- There is a groove which binds small peptides

presented by 3 on surface of A5spresented by 3 on surface of A5s

9# 3 molecules9# 3 molecules

They are essential for presentation of peptides soThey are essential for presentation of peptides sothat they can be recognized and bind to T1sthat they can be recognized and bind to T1s


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"actors influencing Immunogenicty"actors influencing Immunogenicty

)-.oreigness :)-.oreigness :

.oreign substances are immunogenic.oreign substances are immunogenic

/- 3olecular size:/- 3olecular size:

igh molecular weight increase immunogenictyigh molecular weight increase immunogenicty

9- hemical structure comple%ity:9- hemical structure comple%ity:

igh comple%ity increase immunogenictyigh comple%ity increase immunogenicty

- 1oute of administration:- 1oute of administration:

5arenteral routes are more immunogenic to oral route5arenteral routes are more immunogenic to oral route


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"actors influencing Immunogenicty"actors influencing Immunogenicty

;- 3ethod of administration:;- 3ethod of administration:

a- Antigen dose:a- Antigen dose:

AAppropriate dose optimum antigenictyppropriate dose optimum antigenicty

!ow dose low- zone tolerance!ow dose low- zone tolerance

igh dose high-zone toleranceigh dose high-zone tolerance

b- Ad4uvant:b- Ad4uvant: (ubstance when in4ected with an antigen(ubstance when in4ected with an antigen

enhance immunogenictyenhance immunogenicty


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Lec6.Immunogenes or Antigens

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