Antibody (Ab)

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Antibody (Ab) Xiaowu Hong xiaowuhong_at_fudna.edu
.cn 021-54237093 Department of Immunology Shanghai
Medical College of Fudan University
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Nobel Prize winners
Emil von Behring, 1901, antitoxins
Georeges Kohler and Cesar Milstein, 1984,
monoclonal antibody
Paul Ehrlich , 1908, production of antibody
Gerald Edelman and Rodney Porter, 1972, structure
of antibody
Susumu Tonegama,1987, structure of Ig gene
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Emil von Behring (1845-1917)
Emil von Behring, 1901, antitoxins
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Contents
I Definition of antibody II Structure of
antibody III Function of antibody IV
Biological characteristics of different
antibodies
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Antibody (Ab) A globulin which is
produced by plasma cell as a result of the
introduction of an antigen and which has
the ability to combine with the antigen
that stimulated its production.
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Immunoglobulins (Ig) Globulins composed
of H and L chains, or globulins function as
antibody.
Immunoglobulins Antibody-containing serum is
place in an electrical field Antibodies
migrated with the globular proteins.
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The relationship between Ab Ig
All antibodies are immunoglobulins,
but it is not certain that all
immunoglobulins have antibody function.
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Distribution of antibody
Antibody molecules are found in serum
(account for approximately 20 of the total
plasma protein ), in extravascular fluids, in
exocrine secretions, and on the surface of
some lymphocytes.
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Section 1 Structure of Ig
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1 Basic four chain structure
A four polypeptide chains two identical
light chains two identical heavy chains ,
held by disulfide bonds. Y-shape
structure, symmetric. NH2 terminal, -COOH
terminal. variable constant
regions. domains
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(1)Heavy chain (H) ? Composed of about 500
aa, oligosaccharide() ? Class heavy
chain ?, ? , ? , ?,
?. immunoglobulin(Ig) IgA, IgG, IgM IgD,
IgE (2) Lght chain (L) ? Composed of about
214 aa, oligosaccharide(-) ? Type ? ,?
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2 Variable (V) and Constant (C) regions
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(1) V region

• ? N-terminal 1/2L1/4(1/5)H
• VL, VH

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(2) Constant region (C-terminal 1/2L3/4(4/5)H)
CL CH1 CH2 CH3 (CH4)
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• (complimentarity determining region, CDR)
• formation of the Ag binding site
• Framework region( FR )
• maintaining the 3- dimensional configuration

(3) hypervarible region (HVR)
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CDR
(complimentarity determining region,)
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antibody
antigen-antibody complex
antigen
purple HV CDR ( in both the ribbon and ball
and stick views) green antigen HV
sequences contact the antigen.
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antibody
CDR
Epitope
Representation of the disassociation of an
antibody (top) and antigen (botton) molecule.
antigen
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(4) Hinge region
NH3
VH

• Properties
• 1) Flexible
• 2) Rich in proline
• Function
• 1) Facilitating the
• interaction
• between Ag and Ab
• 2) Facilitating complement fixation

VL
CH1
CL
Hinge region
COO
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IgG Molecule Conformational Changes Induced by
Antigen Binding
POSTBINDING
PREBINDING
Fab
CH1
Exposed C1q-binding site
Barricaded C1q-binding site
CH2
Fc
(IgM CH3,IgG CH2)
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Flexibility of immunoglobulins
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domains
polypeptide chains folded by disulfide bonds
into globular regions.
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domains
a Ag- binding site
VHVL
Allotypic marker
CH1CL
C1q binding
(IgG)CH2
Fc?R binding (MC, M?, B,NK)
(IgG)CH3
(IgM)CH3
C1q binding
Fc?R binding (mast, basophil)
(IgE)CH2CH3
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3 Enzymatically generated Ab fragments
papain Fab (Ag-binding Fragment ) Fc
(crystallizable Fragment ) Complement
fixation FcR
Fab
papain
(????)
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Figure 3-3
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Figure 3-3 part 1 of 2
3 Enzymatically generated Ab fragments
(1) Papain Fab (Ag-binding Fragment ) Fc
(Crystallizable Fragment ) complement
fixation, FcR
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Figure 3-3 part 2 of 2
(????)
(2) Pepsin
( Fab ) 2 pFc ( peptides of Fc )
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Section 2 Biological functions of antibodies
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1 Antibody function in the absence of other
factors

• V region Ag binding
• Neutralizing toxin virus
• Agglutination microbes,
• Prevention adhesion

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Neutralization By Antitoxin Antibodies
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Neutralization By Antiviral Antibodies
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Bacterial Neutralization By Ab
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2 Role of antibodies in complement activation

C region Fixation of complement
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3 Role of antibodies binding to effector cells
C region Binding cells Opsonization
Mediating ADCC
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(1) Opsonization The process of attaching
opsonins , such as IgG or complement fragments,
to microbial surfaces to target the microbes for
phagocytosis.
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Recognition of microbes by neutrophils and
macrophages
complement
antibody
Surface receptor on macrophage
CD11b/CD18
CD16 (Fc?R III)
IL-2
Lactoferrin
CD25
CD71
B7-2
CD28
CD64 (Fc ? R I)
CD35 (CR1)
CD32 (Fc ? R II)
antibody
complement
antibody
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Adherence of bacteria via receptors
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Opsonin. A macromolecule that becomes attached to
the surface of a microbe and can be recognized by
surface receptors of neutrophils and macrophages
and that increase the efficiency of phagocytosis
of the microbe. Opsonins include IgG
antibodies, which are recognized by the Fc?
receptor on phagocytes, and fragment of
complement proteins, which are recognized by CR1.
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FcgR and Complement Receptors Cooperate To Induce
Greater Phagocytosis
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FcgRIII CD16Antibody Marks Target Cells For NK
Cell Attack (ADCC)
(2) ADCC
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Figure 1-24
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Figure 1-24 part 1 of 3
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Figure 1-24 part 2 of 3
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Figure 1-24 part 3 of 3
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Section 5 Biological characteristics of
different antibodies
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1 IgG
7.4.1
11 interchain disulfide bonds.
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(1) Properties (A) IgG is the major Ig in serum
- 75 (B) The longest half life (t ½
23days) (C) IgG is the major Ig in extravascular
spaces (D) Placental transfer (E) Fixation
complement (F) Binding to cells Opsonization
mediating
ADCC
Immunity is transferred from mother to fetus
through placental transfer of IgG.
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2 IgM
(1) Structure
Secreted IgM (sIgM) pentamer Membrane-bound
IgM (mIgM) monomer
J chain
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Joining chain
(1)Chemical nature polypeptide chain secreted
by plasma cell
Secrete piece
J CHAIN
Joining chain

IgM
IgA
(2) Presence polymeric Igs such as IgM
(pentamer), sIgA (dimer).
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(2) Properties (A) The first Ig made by fetus
and B cells (B) Fixation complement classical
pathway (C) The largest size of molecule (D)
Natural blood type antibody (E) Binding to cells
Opsonization. mediating ADCC
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3 IgA
(1) Structure
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Secretory Piece ( SC )
synthesized by nonmotible epithelial cells
near the mucosal membrane
IgA dimer
Function i. Enabling IgA to be transported
across mucosal tissues into secretions.
Secrete piece
Joining chain

ii. Protecting sIgA from being proteolytic
attack.
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(2) Properties
(A) The major Ig in secretions. (secretory
IgA, sIgA. 5-15g/d)
(B) sIgA transferred to the newborn
through colostrum
(C) The important antibody against mucosal
infections
(Local (Mucosal )immunity)
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4 IgE
(1) Structure
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(2) Properties
A) The least common Ig
B) Binds to basophils mast cells (Fc?R)
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Involved in allergic reactions (
hypersensitivity I)
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5 IgD
(1) Structure
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(2) Properties
a. On the surface of mature B cell serving
as BCR mature marker of B cell b. In
serum (uncertain Ab activity)
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Immunoglobulin Isotypes Are Distributed To
Different Parts Of The BodyIgM BloodIgG
TissuesIgA MucosaIgE - Surfaces
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Emphases

• Master the concepts of Ig and Ab
• Master the relationship between structure and
  functions of Ab
• Master properties and biological activities of
  five classes of Igs.

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Fudan University
Thank you !
School of Medicine