Antigen and immunogens, types and mitogens .ppt

antigens and immunogens

1. Antigens & Immunogens

2. Antigen
An antigen is a molecule that stimulates an immune
response.
The word originated from the notion that they can
stimulate antibody generation

3. Immunogen
*Aforeignsubstance,whenintroducedinto
hostbody,stimulateformationofspecific
antibodiesorsensitizedlymphocytes
Antigen
*Antigenshavetheabilitytocombine
specificallywithantibodiesproducedor
sensitizedT-lymphocytesinduced

4. Immunogenicity:abilitytoinduceimmune
responseinthebody(bothhumoraland/orcell
mediated)
Antigenicity:abilitytocombinespecificallywith
thefinalproductsofspecificimmuneresponse
(antibodiesand/orTcell-surfacereceptors)
Allimmunogensareantiges,butalltheantigens
arenotimmunogens

5. Epitopeorantigenicdeterminant
Smallareapresentontheantigencomprisingoffew(fourto
five)aminoacidsormonosaccharideresidues,thatis
capableofsensitizingTandBcells&reactingwithspecific
siteofTcellreceptororanantibody
Smallpartofanantigenthatinteractswithanantibody
•Anygivenantigenmayhaveseveralepitopes.
•Eachepitopeisrecognizedbyadifferentantibodyor
TCR

6. Types of epitope

7. Antigenic epitopes

8. Haptens
Lowmolecularweightmoleculesthatlackimmunogenicity
(cannotinduceimmuneresponse)butretainantigenicityor
immunologicalreactivity(i.e.canbindtotheirspecific
antibodyorTcellreceptor)
Haptenscanbecomeimmunogenicwhencombinedwitha
largerproteinmoleculecalled‘carrier’
Thehapten-carriercomplexiscapableofinducingimmune
responseinthebody
-Examples:
simplechemicalsanddrugs:penicillin,sulphonamide,
aspirin,cosmetic,tranquillizers,neomycinskinointment

9. Animalsimmunizedwithsuchahapten-
carrierconjugateproduceantibodies
specificfor-
oEpitopesofhapten
oUnalteredepitopesonthecarrierprotein
&
oNewepitopesformedbycombinedparts
ofboththehaptenandcarrier

10. Factors influencing Immunogenicty

14. 5-Method of administration:
a-Antigen dose:
Appropriate dose optimum antigenicty
Low dose low-zone tolerance
High dose high-zone tolerance
Repeated Number of doses of antigens
Multiple antigens
Effect of prior administration of antibody
b-Adjuvant:
Substance when injected with an antigen
enhance immunogenicty

15. 6. Susceptibility of antigen to tissue enzymes
Phagocytosis& intracellular enzymes break the
antigen into immunogenic fragments. D amino acids
are not antigenic (not metabolised) while
polypeptides consisting L amino acids are
antigenic.
7. Genetic factor
Different individuals of a given species show different
types of immune responses towards the same antigen.
Responders, Slow responders & Non-responders
MHC

16. Heterophile antigens

17. Diagnostic application-

19. Y
T dependent Ag -T cell help to B cells
B
Signal 1
antigen & antigen
receptor
Th
1. T cell antigen receptor
2. Co-receptor (CD4)
3.CD40 Ligand
Th
Signal 2 -T cell help IL-2 and other cytokines

20. T-independent antigens
polysaccharides and proteins with many identical
polypeptides
Many bacterial capsules & bacterial flagellar proteins
This stimulates the B cell to generate antibody-secreting
plasma cells without the help of IL-2.
While this response is an important defense against many
bacteria, it generates a weaker response than T-dependent
antigens and generates no memory cells.

21. Thymus independent antigens…
Principal example:
LPS

22. Principal example(s):
Bacterial capsules
Bacterial flagella
Mechanism:
extensivecross-linking of mIg

23. T
Dependent
Antigens
TI-1
Antigens
TI-2
Antigens
Induce responses in athymics No Yes Yes
Polyclonally activate B cellsNo Yes No
Require repeating epitopes No No Yes
Affinity maturation Yes No No
Isotype switching Yes No Limited
Immunological memory Yes No No
T Dependent & Independent Antigens

24. Superantigens

25. Superantigens
Directlybridgenon-specificallybetween
majorhistocompatibilitycomplex(MHC)-II
ofAPCsandTcells.
Non-specificactivationofTcellsleadsto
massivereleaseofcytokines

26. Conventional Ag
Superantigens

27. Bacterialsuperantigen
Staphylococcaltoxin-
Toxicshocksyndrometoxin-1(TSST-1);Exfoliative
toxin;Enterotoxins
Streptococcal toxin-Streptococcal pyrogenic exotoxin (SPE)-
A and C
Mycoplasmaarthritidismitogen-I
Yersinia enterocolitica
Yersinia pseudotuberculosis
Viralsuperantigen
Epstein-Barrvirusassociatedsuperantigen
Cytomegalovirusassociatedsuperantigen
Rabiesnucleocapsid
HIV encoded superantigen(nef-negative regulatory factor)
Fungalsuperantigen
Malasseziafurfur

28. Disease associated with superantigens
Conditions associated with staphylococcal
toxins are as follows-
oToxic shock syndrome
oFood poisoning
oScalded skin syndrome
oRare conditions such as-Atopic dermatitis,
Kawasaki syndrome, psoriasis, acute
disseminated encephalomyelitis.

29. Cross reacting antigen
Ags sharing identical/similar epitope
Sometimes, Ab can “cross-react” with unrelated Ag….
 Often seen with polysaccharide Ag’s
 e.g. ABO Blood groups –glycoproteins
 -persons lacking one or both of the blood (AB)
Ag’s will have serum Ab’s vs.the missing Ag’s
 -these Ab’s produced from cross-reactive MO
Ag’s!!
-provides basis for blood typing tests

30. -
The outer layer of RBCs membrane contain certain
antigens which are chemically glycoproteins &
called agglutinogens.
-According to the presence of these antigens ,
human blood can be classified into many groups.

31. ABO system
-This system includes 2 types of antigens A and B agglutinogens.
-According to the presence of A and B antigens there are 4 groups of
human blood :
1-Group A (about 41% ) : when only type A antigen is present.
2-Group B (about 9 % ) : when only type B antigen is present.
3-Group AB (about 3 % ): when both types A and B antigens are present.
4-Group O (about 47 % ): when both types A and B antigens are absent.

32. A: adds N-acetylgalactosamineto the terminal sugar of the H
antigen
B: adds D-galactoseto the terminal sugar of the H antigen

35. Rh system (Rh factor)
-This is system of agglutinogens normally present in the red
cells of Rhesus monkey (hence the name Rh)
-There are 6 varieties known as(dominant C , D and E)
(antigens and recessive c , d and e ) antigens.
-These antigens were also found in the human red cells.
-Antigen D has the strongest antigenic effect So :
If D antigen is present →Rh +ve.
If D antigen is absent →Rh -ve.

36. Significances of blood grouping:
1-Blood transfusion.
2-Marriage ( Rh incompatibility).
3-Disputed paternity.
4-Detection of criminals(Medico-legal).

37. Determination of ABO system
-Mix one drop of blood with 1 ml of isotonic saline in
a test tube.
-Put 2 separate drops of the diluted blood on a glass
slide.
-Add one drop of anti-A serum (blue coloured) to
one blood drop and one drop of anti-B (yellow
coloured) to the other drop.
-Mix the blood with anti-A and anti-B sera gently
using the blunt end of two separate pins.

38. -After 2 minutes examine for agglutination :
a-If agglutination occurs with anti-A serum only , the
blood group is type A.
b-If agglutination occurs with anti-B serum only , the
blood group is type B.
c-If agglutination occurs with both anti-A and anti-B sera ,
the blood group is type AB.
d-If no agglutination occurs with either anti-A or anti-B ,
the blood group is type O.

39. Determination of Rh group
-Put 2 drops of diluted blood on a glass slide.
-Add one drop of anti-D serum to the blood and mix
gently with the blunt end of a pin.
-Examine for agglutination :
a-If agglutination occurs , the blood group is
Rh +ve.
b-If no agglutination occurs , the blood group
is Rh –ve.

41. Mitogen