Transcript Document 7145999

DEPARTMENT OF IMMUNOBIOLOGY
Antibody (Ab)
Xiaowu Hong
[email protected]
021-54237093
Department of Immunology
Shanghai Medical College of Fudan University
Nobel Prize winners
Emil von Behring,
1901, antitoxins
Paul Ehrlich , 1908,
production of antibody
Georeges Kohler and Cesar Milstein,
1984, monoclonal antibody
Gerald Edelman
and Rodney Porter,
1972, structure of
antibody
Susumu Tonegama,1987,
structure of Ig gene
Emil von Behring (1845-1917)
Emil von Behring,
1901, antitoxins
Contents
I Definition of antibody
II Structure of antibody
III Function of antibody
IV Biological characteristics of different antibodies
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.
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.
The relationship between Ab & Ig
All antibodies are
immunoglobulins, but
it is not certain that
all immunoglobulins
have antibody function.
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.
Section 1 Structure of Ig
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
(1)Heavy chain (H):
① Composed of about 500 aa, oligosaccharide(+)
② Class :
heavy chain
,  ,  , ,
.
immunoglobulin(Ig) IgA, IgG, IgM IgD, IgE
(2) Lght chain (L):
① Composed of about 214 aa, oligosaccharide(-)
② Type:  ,
2 Variable (V) and Constant (C) regions
(1) V region
① N-terminal
1/2L+1/4(1/5)H;
VL, VH
(2) Constant region
(C-terminal 1/2L+3/4(4/5)H)
CL
CH1
CH2
CH3
(CH4)
(3) hypervarible region (HVR)
(complimentarity
determining
region,
CDR) :
formation of the
Ag binding
site
Framework
region（ FR ) :
maintaining the
3- dimensional
configuration
CDR
(complimentarity determining region,)
antibody
antigen
purple : HV CDR
( in both the ribbon and
ball and stick views)
green : antigen
HV sequences contact
the antigen.
antigen-antibody
complex:
antibody
CDR
Epitope
antigen
Representation of
the disassociation
of an antibody (top)
and antigen (botton)
molecule.
(4) Hinge region
NH3+
VH
VL
CH1
CL
Hinge region
CH2
CH3
CH4
COO–
Properties:
1) Flexible
2) Rich in proline
Function:
1) Facilitating the
interaction
between Ag and Ab
2) Facilitating complement
fixation
IgG Molecule Conformational
Changes Induced by Antigen Binding
PREBINDING
CH1
CH2
Fc
Barricaded
C1q-binding
site
(IgM CH3，IgG CH2)
POSTBINDING
Exposed
C1q-binding
site
Flexibility of immunoglobulins
domains:
polypeptide chains folded by disulfide
bonds into globular regions.
domains:
VH+VL
a Ag- binding site
CH1+CL
Allotypic marker
(IgG)CH2
C1q binding
(IgG)CH3
(IgM)CH3
(IgE)CH2+CH3
FcR binding (MC, M, B,NK)
C1q binding
FcR binding (mast, basophil)
3 Enzymatically generated Ab fragments
Figure 3-3 part 1 of 2
(1) Papain:
Fab (Ag-binding Fragment )
Fc (Crystallizable Fragment ) : complement fixation, FcR
Figure 3-3 part 2 of 2
(2) Pepsin
( Fab’ ) 2
pFc ( peptides of Fc )
(胃蛋白酶)
Section 2 Biological functions of antibodies
1 Antibody function in the absence of
other factors
V region: Ag binding
•Neutralizing toxin & virus
•Agglutination microbes,
•Prevention adhesion
Neutralization By
Antitoxin
Antibodies
Neutralization By
Antiviral
Antibodies
Bacterial ‘Neutralization’ By Ab
2 Role of antibodies in complement
activation
C region:
Fixation of complement
3 Role of antibodies binding to
effector cells
C region:
Binding cells
Opsonization
Mediating ADCC
(1) Opsonization:
The process of attaching
opsonins , such as IgG or
complement fragments, to
microbial surfaces to target the
microbes for phagocytosis.
Recognition of microbes by
neutrophils and macrophages
CD16
（FcR III）
Lactoferrin
Surface receptor on macrophage
CD11b/CD18
IL-2
CD25
CD71
B7-2
CD28
CD64
（Fc  R I）
CD35
（CR1）
CD32 （Fc  R II）
complement
Adherence of bacteria via receptors
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.
FcR and Complement Receptors Cooperate To
Induce Greater Phagocytosis
(2) ADCC
FcRIII CD16
Antibody Marks
Target Cells For NK
Cell Attack (ADCC)
Figure 1-24 part 2 of 3
Section 5 Biological characteristics of
different antibodies
1 IgG7.4.1
11 interchain disulfide bonds.
(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.
2 IgM
(1) Structure
Secreted IgM (sIgM): pentamer
Membrane-bound IgM (mIgM): monomer
J chain
Ig Igb
Ig Igb
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).
(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
(E) Binding to cells –
Opsonization.
mediating ADCC
type antibody
3 IgA
(1) Structure
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.
ii. Protecting sIgA from being
proteolytic attack.
Secrete piece
Joining chain
(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)
4 IgE
(1) Structure
(2) Properties
A) The
least common Ig
B) Binds to basophils & mast cells (FcR)
Involved in allergic reactions
( hypersensitivity I)
(2) Properties
a. On the surface of mature B cell serving as
BCR mature marker of B cell
b. In serum (uncertain Ab
activity)
Immunoglobulin Isotypes
Are Distributed To
Different Parts Of The
Body
IgM – Blood
IgG – Tissues
IgA – Mucosa
IgE - Surfaces
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.
Fudan University
School of Medicine