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IMMUNOLOGY. Immunoglobulin. immunoglobulin. Introduction the basic structure of immunoglobulins Fuction of immunoglobulins the structures and properties of immunoglobulin classes Monoclonal antibody. immunoglobulin. Introduction. Immunoglobulins (Ig)

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IMMUNOLOGY

Immunoglobulin

immunoglobulin
immunoglobulin
  • Introduction
  • the basic structure of immunoglobulins
  • Fuction of immunoglobulins
  • the structures and properties of immunoglobulin classes
  • Monoclonal antibody
introduction

immunoglobulin

Introduction

Immunoglobulins (Ig)

- Glycoprotein molecules which are produced by plasma cells in response to an immunogen and which function as antibodies. The immunoglobulins derive their name from the finding that when antibody-containing serum is place in an electrical field the antibodies, which were responsible for immunity, migrated with the globular proteins

- secreted Ig(sIg) ; membrane Ig(mIg)

introduction2

immunoglobulin

Introduction

Antibody(Ab)

- Serum protein formed in response to immunization; antibodies are generally defined in terms of their specific binding to the immunizing antigen.

basic structure of the immunoglobulins1

immunoglobulin

basic structure of the immunoglobulins

1.Heavy Chain and Light Chain

heavy chain (H chain)

50-75Kd 450-550aa

isotype:IgM,IgD,IgA,IgE,IgG

H chain: μ δ α ε γ

light chain (L chain)

25Kd 214aa

classes of L chain: κ λ

basic structure of the immunoglobulins2

immunoglobulin

basic structure of the immunoglobulins

2.variable region and constant region

variable region(V region)

Light Chain - VL (110 aa)

Heavy Chain - VH (110 aa)

HRV(hypervariable region)

CDR(complementarity-determining region)

FR(framework region)

basic structure of the immunoglobulins4

immunoglobulin

basic structure of the immunoglobulins

2.variable region and constant region

constant region(C region)

Light Chain - CL (110 aa)

Heavy Chain - CH (330-440 aa)

CH1, CH2, CH3,( CH4)

basic structure of the immunoglobulins5

immunoglobulin

basic structure of the immunoglobulins

3. Hinge Region

- between the CH1 and CH2 region of the H chain

- be made of cysteine and proline residues

cysteine:be involved in formation of interchain

disulfide bonds

proline residues:prevent folding in a globular

structure

  • flexibility: allow the two Fab arms to open;

close to accommodate binding to epitope;

be cleaved by proteases.

- IgM and IgE have no hinge region

domains of immunoglobulin

immunoglobulin

Domains of immunoglobulin

Domains

- 3D images of the immunoglobulin molecule shows that it is not straight as depicted in Figure. Rather, it is folded into globular regions each of which contains an intra-chain disulfide bond. These regions are called domains.

1. Light Chain Domains - VL and CL

2. Heavy Chain Domains - VH, CH1,CH2, CH3 (or CH4)

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immunoglobulin

Domains of the Ig

j chain and sp

immunoglobulin

J chain and SP

Joining chain

-J chain

a ploypeptide chain

Join the units together

j chain and sp1

immunoglobulin

J chain and SP

Secretory piece

-SP,SC

function of immunoglobulins

immunoglobulin

Function of immunoglobulins

Functions of V regions

- recognition and binding to antigen

- HVR (CDR)

- neutralization of toxins; immobilization

of microorganisms; neutralization of

viral activity

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immunoglobulin

Function of C regions (Fc portion)

1. Activation of complement: IgM,

IgG1,3; IgA

2. Binding to Fc receptor of cell

  • opsonization, enhancement of Ag uptake by DC and M
  • ADCC
  • Participation in type I hypersensitivity

3. Passage through the placenta (IgG)

and mucosa (sIgA)

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immunoglobulin

Opsonization of antibody

slide22

immunoglobulin

Antibody-dependent cell-mediated cytotoxicity (ADCC)

slide23

immunoglobulin

IgG
  • IgG is the major Ig in serum - 75% of serum Ig
  • IgG is the major Ig in extra vascular spaces

c) Fixes complement - Not all subclasses fix equally

well; IgG4 does not fix complement

d) Binding to cells - Macrophages, monocytes, PMN's and some lymphocytes have Fc receptors for the Fc region of IgG.

slide24

immunoglobulin

IgM

a) IgM is the 3rd most common serum Ig.

b) IgM is the first Ig to be made by the fetus and the first Ig to be made by a virgin B cells when it is stimulated by antigen.

c) As a consequence of its pentameric structure, IgM is a good complement fixing Ig. Thus, IgM antibodies are very efficient in leading to the lysis of microorganisms

d) As a consequence of its structure, IgM is also a good agglutinating Ig .

e) IgM binds to some cells via Fc receptors.

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immunoglobulin

IgA

a) IgA is the 2nd most common serum Ig.

b) IgA is the major class of Ig in secretions –

tears, saliva, colostrum, mucus. Since it is

found in secretions secretory IgA is

important in local (mucosal) immunity.

c) Normally IgA does not fix complement,

unless aggregated.

d) IgA can binding to some cells - PMN's and

some lymphocytes.

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immunoglobulin

IgD

a) IgD is found in low levels in serum; its role

in serum uncertain.

b) IgD is primarily found on B cell surfaces

where it functions as a receptor for

antigen. IgD on the surface of B cells has

extra amino acids at C-terminal end for

anchoring to the membrane. It also

associates with the Ig-alpha and Ig-beta

chains.

c) IgD does not bind complement.

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immunoglobulin

IgE
  • IgE is the least common serum Ig

since it binds very tightly to Fc receptors on basophils and mast cells even before interacting with antigen.

b) Involved in allergic reactions

c) IgE also plays a role in parasitic

helminth diseases

d) IgE does not fix complement

slide29

immunoglobulin

Monoclonal antibody