This document provides information about immunoglobulins and their classification. It defines immunoglobulins as glycoproteins produced in response to antigens that can recognize and bind to antigens. The document discusses the occurrence, general chemistry including structure, functions such as antigen binding and complement fixation, digestion, and classification of immunoglobulins. It provides details on the subclasses of immunoglobulin G and the properties and functions of immunoglobulin D.

1. Biochemistry presentation
Class : Bs honors 7th Semester
Roll No : 085674/ 390

2. Immunoglobulin and its classification
• CONTENT :
1. Definition
2. Occurrence
3. General chemistry
4. General functions
5. Digestion of immunoglobulin
6. Classification
a - Ig G
b - Ig D

3. Immunoglobulin
• Definition
Immunoglobulin is a glycoprotein that is
made in response to an antigen and can recognize
and bind to the antigen that caused its production .

4. CONTINUE …….
The immunoglobins
derive their name
from the finding that
they migrate in the
region of globulins
when antibody
containing serum is
placed in an electric
field

5. Occurence:
1. Antibodies are present in serum, tissue fluids and mucosal
surfaces .
2. Constitute 25-30% of total serum proteins
3. Synthesized by plasma cells in response to an antigen and
which function as antibodies .
4. Immunoglobulin are gamma globulins
5. All antibodies are immunoglobulin ,but all immunoglobulin
may not be antibodies

6. Basic structural Characteristics of Immunoglobulin
A. Heavy and Light Chains
• All immunoglobulin
have a four chain
structure as their basic
unit .
• They are composed
of two identical light
chains (23KD) and two
identical heavy chains
(50-70KD)

7. B-Disulfide Bonds
• Inter-chain disulfide bonds
The heavy and light chains
and the two heavy chains are
held together by inter-chain
disulfide bonds and by non-
covalent interactions .
• The number of inter-chain
disulfide bonds varies among
different immunoglobulin
molecules.
• Intra-chain disulfide bonds
Within each of the
polypeptide chains there are
also intra-chain disulfide
bonds

8. C-Variable (V) and constant(C) Regions
Both the heavy and light chain
can be divided into two
regions based on variability in
the amino acid sequence
These are the
• Light chain VL(110 Amino Acid )
CL(110 amino acids)
• Heavy Chain VH(110 Amino Acid )
CH (330-440 Amino Acid)

9. D-Hinge Region
• This is the region at which the arms of the antibody molecule
form a Y
• It is called the hinge region because there is some flexibility in
the molecule at this point
E –Domains
Three dimensional images of the immunoglobulin molecule
show that it is not a straight molecule 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

10. F-Oligosaccharides
• Carbohydrates are attached to the CH2 domain in most
immunoglobulin.
• However, in some cases carbohydrates may also be attached
at other location.

12. Digestion of immunoglobulin with proteolytic enzymes
Papain Enzyme
• Peptide bonds in the
hinge region are broken
• Produces 3 fragments
• 2 identical fragments
called Fob fragments –
antigen binding activity .
• Other fragment called Fc
fragment (Fraction
Crystallizable) –
Complement binding

13. Pepsin digestion
• Produces a single fragment composed of two Fab like subunits F(ab)2 binds
antigen
• Fc fragment is not recovered digested to small numerous peptides

14. GENERAL FUNCTION OF IMMUNOGLOBULIN
1. Antigen Binding
• Antigen binding by
antibodies is the
primary function of
antibodies and can
result in protection of
the host
• Each immunoglobulin
binds to a specific
antigenic determinant .

15. Complement
fixation
Binding to
various cell types
Placental
transfer
Opsonization
2. EFFECTOR FUNCTION

16. 3. Binding to various cell types
• Phagocytic cells,
lymphocytes, platelets ,
most cells and basophils
have receptors that bind
immunoglobulins
• The binding can activate
the cells to perform some
function .

17. 4. Major Function of immunoglobulin
• some immunoglobulins
also bind to receptors on
placental trophoblast ,
which result in transfer of
the immunoglobulin across
the placenta.
• As a result ,the
transferred maternal
antibodies provide
immunity to the fetus and
newborn.

18. • The immunoglobulins can be
divided into five different
classes based on differences in
the amino acid sequences in
the constant region of the
heavy chain.
1.IgG- Gamma heavy chains
2. IgA- Alpha heavy chains
3. IgM- Mu heavy chains
4. IgE- Epsilon heavy chains
5. IgD- Delta heavy chains
Classification of Immunoglobulin

19. Properties of IgG
• Major Ig in serum
• Constitutes 80% total immunoglobin
• Present in blood , plasma and tissue fluids
• Produced particularly during secondary immune responses.
• It has a half life of 23 days , the longest of all of the Ig
isotypes
• Major Ig in extra vascular spaces
• The only antibody to cross the placenta
• Complement fixation
• Opsonization

20. Chemistry of IgG
The molecule consists of two light chains and two heavy chains.
1. Each light chain consists of a variable (VL) and a constant (CL)
region .
2. Each heavy chain consists of a variable region (VH) and a constant
region that is divided into three domains (CH1,CH2 and CH3).
3. The CH2 domain contains the complement binding site
4. The CH3 domain contains a site that attaches to receptors on
neutrophils and macrophages .
5. The heavy chains themselves and with light chains are linked
together by disulphide bonds.
6. The antigen – binding site is formed by the hyper variable regions
of both the light and heavy chains

21. A. Structure of IgG B.Schematic model of IgG

22. Subclasses of IgG
• There are four IgG subclasses (IgG1,IgG2,IgG3 and IgG4) in
humans ,named in order of their abundance in serum
Name Percenta
ge
Crosses
Placenta
easily
Comple
ment
Activato
r
Binds to
Fc
receptor
Half life
IgG1 66% Yes Second
highest
High
Affinity
21 days
IgG2 23% No Third
highest
Extremely
low
Affinity
21 days
IgG3 7% Yes Highest High
Affinity
7 days
IgG4 4% Yes No Intermedi
ate
Affinity
21 days

23. Structure of Subclasses of IgG
• Four subclasses of human IgG differ in their structure
because they are encoded by different germ- line CH genes
• They differ in the size of the hinge region and the number
and arrangements of the interchain disulfide bonds linking
heavy chains

24. Biological Function of IgG
• Cross the placenta
• Binds and neutralize microbes and toxins
• Opsonize antigens for phagocytosis
• Activate the complement system
• protect the new born
• Control infection of body tissues
• involved in the regulation of Allergic reactions
• play an important role in antibody dependent cell –
mediated cytotoxity (ADCC) and intracellular antibody –
mediated proteolysis

25. Properties of IgD
• IgD exists only as a monomer
• It is found in low levels in serum ,its role in serum is uncertain
• Serum concentration 30 micrograms per ml
• Constitutes 0.2% of total immunoglobulin
• Half life : 3 days
• IgD does not bind complement
• IgD together with IgM is major membrane bound
immunoglobulin on unstimulated B Lymphocytes .

26. Chemistry of Ig D
• Secreted IgD is a glycoprotein produced as a monomeric
antibody with two identical heavy chains of the Delta class ,
and two identical Ig light chains
• The structure has two identical antigen binding areas
consisting of both light and heavy chains and a valency of 2
• The light chains have two domains , one variable and one
constant .
• The heavy chains have four domains , one variable and three
constant region domains
• IgD molecule has a long hinge region between Fob and Fc

27. Structure of IgD

28. Function of IgD
• act as an antigen receptor on B cells and is probably involved
in regulating B cell function
• Secreted IgD also exists and plays an elusive function in blood
,mucosal secretions and on the surface of innate immune
effector cells such as basophils .
• IgD may have some role in allergic reactions
• It also able to bind to basophils and mast cells and activate
these cells to produce antimicrobial factors that are functional
in respiratory immune defence in humans