DEPARTMENT OF IMMUNOBIOLOGY

Antibody (Ab)Antibody (Ab)

Xiaowu Hong

xiaowuhong@fudna.edu.cn021-54237093

Department of ImmunologyShanghai Medical College of Fudan University

Emil von Behring, 1901, antitoxins

Georeges Kohler and Cesar Milstein, 1984, monoclonal antibody

Susumu Tonegama,1987, structure of Ig gene

Gerald Edelman and Rodney Porter, 1972, structure of antibody

Paul Ehrlich , 1908, production of antibody

Nobel Prize winners

Emil von Behring (1845-1917)

Emil von Behring, 1901, antitoxins

I Definition of antibodyI Definition of antibody

II Structure of antibody II Structure of antibody

III Function of antibody III Function of antibody

IV Biological characteristics of different antibodies IV Biological characteristics of different antibodies

Contents

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.

All antibodies are immunoglobulins, but it is not certain that all immunoglobulins have antibody function.

The relationship between Ab & Ig

Antibody molecules are found in serum

(account for approximately 20% of the t

otal plasma protein ), in extravascular flui

ds, in exocrine secretions, and on the suon the su

rfacerface of some lymphocytes.

Distribution of antibody

Section 1 Structure of Ig

* 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 Basic four chain structure

(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)

CLCH1CH2CH3(CH4)

(complimentarity

determining re

gion, CDR) :

formation of the Ag binding site

Framework region （ FR ) :

maintaining the 3- dimensional configuration

(3) hypervarible region (HVR)

(complimentarity determining region,) CDR

purple : HV CDR ( in both the ribbon and ball and stick views)

green : antigen

HV sequences contact the antigen.

antibody

antigen antigen-antibody complex:

Representation of the disassociation of an antibody (top) and antigen (botton) molecule.

CDR

Epitope

antibody

antigen

(4) Hinge region

VH

CH1

CH2

CH3

CH4

VL

CL

Hinge region

COO–

NH3+

Properties:1) Flexible2) Rich in proline

Function:1) Facilitating the interaction between Ag and Ab2) Facilitating complement

fixation

(IgM CH3 ， IgG CH2)

IgG Molecule Conformational Changes Induced by Antigen Binding

Fab

Fc

PREBINDING

CH1

CH2

Barricaded C1q-bindingsite

POSTBINDING

Exposed C1q-bindingsite

Flexibility of immunoglobulins

domains: polypeptide chains folded by disulfide bonds into globular regions.

domains:

FcR binding (mast, basophil)(IgE)CH2+CH3

C1q binding(IgM)CH3

FcR binding (MC, M, B,NK)(IgG)CH3

C1q binding(IgG)CH2

Allotypic markerCH1+CL

a Ag- binding siteVH+VL

Figure 3-3 part 1 of 2

3 Enzymatically generated Ab fragments

(1) Papain:

Fab (Ag-binding Fragment )

Fc (Crystallizable Fragment ) : complement fixation, FcR

Figure 3-3 part 2 of 2

( 胃蛋白酶 )(2) Pepsin( Fab’ ) 2

pFc ( peptides of Fc )

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

C region:Fixation of complement

2 Role of antibodies in complement activation

C region:Binding cells Opsonization Mediating ADCC

3 Role of antibodies binding to effector cells

(1) Opsonization:

The process of attaching opsonins , such as IgG or complement fragments, to microbial surfaces to target the microbes for phagocytosis.

antibody

complement

CD16 CD16 （（ FcFcR IIR IIII ））

CD11b/CD18

CD25

CD28

CD32 （ Fc R II ）

CD35 （ CR1）

CD64 （ Fc R I ）

CD71

B7-2

IL-2

antibody

antibody

Recognition of microbes by neutrophils and macrophages

complement

Lacto

ferrin

Surface receptor on

macrophage

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.

FcR and Complement Receptors Cooperate To Induce Greater Phagocytosis

FcRIII CD16

Antibody Marks Target Cells For NK Cell Attack

(ADCC)

(2) ADCC

Figure 1-24 part 2 of 3

Section 5 Biological characteristics of different antibodies

7.4.1

11 interchain disulfide bonds.

1 IgG

(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 place

ntal transfer of IgG.

(1) StructureSecreted IgM (sIgM): pentamerMembrane-bound IgM (mIgM): monomer

J chain

IgIg

IgIg

2 IgM

(1)Chemical nature: polypeptide chain secreted by plasma cell

(2) Presence: polymeric Igs such as IgM (pentamer), sIgA (dimer).

Joining chain

J CHAIN

IgM

IgA

Secrete piece

Joining chain

(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 typeblood type antibody(E) Binding to cells –

Opsonization.

mediating ADCC

3 IgA(1) Structure

Secretory Piece ( SC )synthesized by nonmotible epithelial cells near the mucosal membrane

Function:i. Enabling IgA to be transported across mucosal tissues into secretions.

ii. Protecting sIgA from being proteolytic attack.

IgA dimer

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

A) The least common Ig

B) Binds to basophils & mast cells (FcR)

(2) Properties

Involved in allergic reactions( hypersensitivity I)

(2) Properties

a. On the surface of mature B cell serving as BC

R mature marker of B cell

b. In serum (uncertain Ab

activity)

Immunoglobulin Isotypes Are Distributed To

Different Parts Of The Body

IgM – BloodIgG – TissuesIgA – MucosaIgE - Surfaces

• 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.

Emphases

School of Medicine

Fudan University