antibody IgM,igG,IgA,IgE,IgD

1. Antibody
Chanderhash – ASU2017010100041 | 5th Semester | School of Bioscience
BSBT 303
Fundamentals of Immunobiology
Session 2019-2020
Presented by:-

2. Barriers of Invasion
1st line defence
Physical barriers
Physiological barriers
Cytokine barriers
Cellular barriers
P1
3rd line defence
2nd line defence
Cellular barriers
Humoral barriers
T-
lymphocyt
es cell
mediated
Antibody
(B-
lymphocyt
es
mediated)

3. What is an antibody?
• Produced by Plasma cell (B-lymphocytes producing Ab)
• Essential part of adaptive immunity
• Specifically bind a unique antigenic epitope (also called an
antigenic determinant)
• Possesses antigen binding sites
• Members of the class of proteins called immunoglobulins

4. Structure of antibody

5. Antibody Structure
• Antibodies Are Made Up Of:
• 2 Light Chains (identical) ~25 KDa
• 2 Heavy Chains (identical) ~50 KDa
• Each Light Chain Bound To Heavy Chain By Disulfide (H-L)
• Heavy Chain Bound to Heavy Chain (H-H)
• First 100 a/a Of Amino Terminal Vary of Both H and L Chain Are
Variable
• Referred To As VL , VH, CH And CL
• CDR (Complementarity Determining Regions) Are What Bind Ag
• Remaining Regions Are Very Similar Within Same Class

6. Fab – fragment
antigen binding
 Specificity of antigen
binding determined by
VH and VL
Fc- Fragment constant
Can bind cell receptors
and complement
proteins
Antibody

7. • Six loops of the VH (H1, H2 and H3) and VL
(L1, L2 and L3) domains create a great variety
of surfaces
• Deep binding cavities: such as those seen in
some antibody-hapten complexes
• Wide pockets : seen in certain antibody-peptide
complexes
• Flat surfaces : seen in antibody-protein
interactions
• H3 is the most variable of the loops and in all
crystallographically solved antibody-antigen
complexes makes several contacts with antigen
The Complementarity Determining Regions

8. Antigen-antibody interactions regions come in many shapes
including: pockets, grooves, or extended flat surfaces.

9. • Epitope: the portion of an antigen that is recognized and bound by an
antibody (Ab) or a T-cell receptor (TCR)
• epitope = antigenic determinant
Epitope

10. •Epitope: the portion of an antigen that is recognized and bound by an Ab or a T Cell receptor
One protein may have multiple antigenic determinant
Epitope

11. • B-cell Epitopes – recognized by B-cells
• T-cell Epitopes – recognized by T cells
Epitope

12. • Antibodies occur in 2 forms
• Soluble Ag: secreted in blood and tissue
• Membrane-bound Ag: found on surface of B-cell, also known
as a B-cell receptor (BCR)
Antibodies exist in two forms

13. • IgG
• IgM
• IgA
• IgD
• IgE
Five kinds of antibodies

15. IgG = IgG1,2,3,4
• Most abundant immunoglobin 80% of serum
• IgG1, IgG3 and IgG4 cross placenta
• IgG3 Most effective complement activator
• IgG1 and IgG3 High affinity for FcR on phagocytic cells, good for
opsonization
• neutralize microbes and toxins
• opsonize antigens for phagocytosis
• activate the complement
• protect the newborn
•

16. IgM
• Secreted initially during primary infection
• Cannot cross the placenta
• secreted first during primary
exposure
• activates the complement
• used as a marker of recent
infection
•Presence in
newborn means
infection
•Single positive
sample in
serum or CSF
indicates recent
or active
infection
•Used to detect
early phase of
infection

17. IgA
• Monomeric in serum
• Dimeric with secretory component in the lumen of the
gastro-intestinal tract and in the respiratory tract
• neutralizes microbes and toxins
• Help’s in secretion such as Saliva and Milk
•Sero-
diagnosis
of
tuberculo
sis
•Synthici
al
respirator
y virus
tests

18. IgD
• Monomeric
• present on the surface of B lymphocytes
• functions as membrane receptor
• role unclear
• has a role in antigen stimulated lymphocyte
differentiation (B cell activation)
•B cell
activati
on
•Can’t
cross
placent
a

19. Serodiagnosis
of infectious
and non
infectious
allergies
(e.g., allergic
bronchopulmo
nary
aspergillosis,
parasitic
diseases)
IgE
• Mediates type I hypersensitivity
• Monomeric
• Major functions / applications
• associated with anaphylaxis
• plays a role in immunity to
helminthic parasites
• Responsible for allergic reaction

21. Antibodies as Receptors
• Antibodies can attach
to B cells, and serve
to recognize foreign
antigens.

22. Antigens as Effectors
• Free antibodies can
bind to antigens,
which “tags” the
antigen for the
immune system to
attack and destroy.

23. What Do Antibodies Recognize?
1. Proteins (conformational determinants, denatured or
proteolyzed determinants)
2. Nucleic acids
3. Polysaccharides
4. Some lipids
5. Small chemicals (haptens)

24. • Antibodies bind to antigens by
recognizing a large surface, and
through surface complementarity.
• Thus, these complexes have a very
high affinity for each other.
Antigen:Antibody complex

25. Quantitating antibody-antigen interactions:
Strength is determined by the sum of multiple non-covalent bonds.
Strength of interaction between a single epitope and
antigen binding site is called its affinity. Each antibody-antigen interaction
has a distinct affinity.

26. Effects of Antigen-Antibody Interactions

27. 1. Opsonization

28. • Haptens, having a limited total surface area, deeply embed themselves into the VL/VH
dimer interface
• Hapten binding antibodies frequently show a deep central cavity, long CDR L1 loops and a
CDR H3 loop with an "open" conformation, allowing the hapten to bind as much as 80%
of its total surface in the interaction.
Antibody-Hapten Complex

29. Intimate interaction between Ab and Hapten

30. Peptide Antibody Complex

31. • In contrast, proteins preferentially to a relatively flat binding surface
• In a "closed" CDR H3 conformation, the CDR H3 loop packs down onto the central
cavity, and the protein antigen binds on top of it.
Protein Antibody Complex

32. The Fc-Fc Receptor complex
• FcR plays important role in antibody mediated immune responses
• Ig and FcR binding activates effector functions
• Fc Receptor interacts with the CH2 and CH3 domains of Immunoglobulins