Immunoglobulin, also known as antibodies, are Y-shaped glycoprotein molecules that are produced by plasma cells in response to antigens. There are five major classes of immunoglobulins (IgG, IgM, IgA, IgD, IgE) which differ in their structure, function, and location. IgG makes up 80% of antibodies in serum and provides protection against toxins and viruses. IgM is the first antibody produced during infection and is effective against microbes. IgA is found in secretions where it provides localized protection of mucosal surfaces.

1. By S.D.Mankar
Assistant Professor
Department Of Pharmaceutics
Pravara Rural College Of Pharmacy,Pravaranagar
Immunoglobulin

2.  Definition:-
 Antibodies are globulin
proteins(Compact/globular form) therefore we
have come to use the term
immunoglobulin(Ig) for antibodies.
 Globulin protein are relatively soluble.
 Immunoglobulin is a glycoprotein that is made
in response to an antigen and can recognize
and bind to the antigen that caused its
production.

3.  Each antibody has at least two identical sites
that bind to epitopes.
 These sites are known as antigen-binding
sites.
 The number of antigen-binding sites on an
antibody is called valence of that antibody.
 E.g most of human Ab have two binding sites
therefore they are bivalent.

4.  Structure:-
 Bcz a bivalent antibody has simplest
molecular structure, is called monomer.
 A typical antibody monomer has four protein
chains-
 Two identical light chains & two identical
heavy chains.
 ( as per molecular wt)
 The chains are joined by disulfide links &
other bonds to form Y shaped molecule.
 It is flexible & can assume a T shape.
 The two sections located at the end of the Y’s

5.  These binds to epitopes.
 Their structure reflects the nature of the
antigen for which they are specific-they are
specific to the two antigen-binding sites found
on each antibody monomer.
 The stem of the antibody monomer and the
lower parts of the arms of the Y are called
constant(C) regions.
 They are the same for particular class of
immunoglobulin.
 There are five major type of C regions, which
account for the five major classes of
immunoglobulins.

6.  The stem of the Y shaped antibody monomer
is called the Fc region, so named bcz when
antibody structure was first being identified, it
was a fragment(F) that crystallized(c) in cold
storage.
 The Fc region are often important for
immunological reactions.

8. CLASSES (ISOTYPES) OF
IMMUNOGLOBULINS
• Classes based on constant region of heavy chains
– Immunoglobulin A (IgA)
– Immunoglobulin D (IgD)
– Immunoglobulin E (IgE)
– Immunoglobulin G (IgG)
– Immunoglobulin M (IgM)
• Differentiation of heavy chains
– Length of C region, location of disulfide bonds, hinge
region, distribution of carbohydrate
• Classes have different effector functions
Dr.T.V.Rao
MD 8

9. Immunoglobulin Classes
I. IgG
Structure: Monomer
Percentage serum antibodies: 80%
Location: Blood, lymph, intestine
Half-life in serum: 23 days
Complement Fixation: Yes
Placental Transfer: Yes
Known Functions: Enhances
phagocytosis, neutralizes toxins and
viruses, protects fetus and newborn.
Dr.T.V.Rao
MD 9

10. Immunoglobulin Classes
II. IgM
Structure: Pentamer
Percentage serum antibodies: 5-10%
Location: Blood, lymph, B cell surface (monomer)
Half-life in serum: 5 days
Complement Fixation: Yes
Placental Transfer: No
Known Functions: First antibodies produced
during an infection. Effective against microbes
and agglutinating antigens.
Dr.T.V.Rao
MD
1
0

11. Immunoglobulin Classes
III. IgA
Structure: Dimer
Percentage serum antibodies: 10-15%
Location: Secretions
(tears, saliva, intestine, milk), blood and lymph.
Half-life in serum: 6 days
Complement Fixation: No
Placental Transfer: No
Known Functions: Localized protection of
mucosal surfaces. Provides immunity to infant
digestive tract. Dr.T.V.Rao
MD
1
1

12. Immunoglobulin Classes
IV. IgD
Structure: Monomer
Percentage serum antibodies: 0.2%
Location: B-cell surface, blood, and lymph
Half-life in serum: 3 days
Complement Fixation: No
Placental Transfer: No
Known Functions: In serum function is unknown.
On B cell surface, initiate immune response.
Dr.T.V.Rao
MD
1
2

13. Immunoglobulin Classes
V. IgE
Structure: Monomer
Percentage serum antibodies: 0.002%
Location: Bound to mast cells and basophils
throughout body. Blood.
Half-life in serum: 2 days
Complement Fixation: No
Placental Transfer: No
Known Functions: Allergic reactions. Possibly
lysis of worms.
Dr.T.V.Rao
MD
1
3

14. Properties and biological activities of Immunoglobulins
Ig G Ig A Ig M Ig D Ig E
1. Structure Monomer Monomerin
serum/
Dimer in
secretion
Pentamer /
monomer
Monomer Monomer
2.Heavy chain
CH domain
3. Mol. Wt.
4. Serum concentration (mg/ml)
Gamma
Three
1,50,000
12
Alfa
Three
1,60,000
2
Mu
Four
9,00,000
1.2
Delta
Three
1,80,000
0.03
Epsilon
Four
1,90,000
0.00004
_ _ + + _
45 42 80 75 50
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5. Present on membrane of mature B
cell
5.Intravascular
Distribution (%)
6. Crosses placenta
7. Present in milk
8.Selective secretion by seromucous
glands
9.Activation of complement
Classical
Alternate
10 Binds to FC receptor of phagocytes
11 Induces mast cell degranulation -
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