Antibodies, also known as immunoglobulins, are Y-shaped proteins produced by B cells that recognize and bind to specific antigens. They have a basic structure consisting of two light polypeptide chains and two heavy chains connected by disulfide bonds. The variable regions of the heavy and light chains come together to form the antigen binding site. The five main classes of antibodies in humans are IgG, IgM, IgA, IgD, and IgE, which have different structures and functions such as complement activation, opsonization, and mediating allergic reactions.

1. Antibody
(Immunoglobulin)
By: Prof. Shashank
Chaurasiya
Bansal College of Pharmacy, Bhopal

2. Antibod
y
• glycoprotein that is made in
response to antigen.
• shed from B cell into surrounding fluid
following antigenic stimulation.
• specialised serum proteins that are formed
in a response to antigen
• react specifically with that particular antigen
or one very closely related to it in some
observable manner.

3. Structure of
antibody:
• All immunoglobulin
molecules have basic
structure (roughly Y- shaped
molecules)
• composed of four polypeptide
chain connected to each-other
by disuphide bond.
• The four polypeptide chain
includes two light (L) chain
and two heavy (H) chain,
• the longer chains are called
heavy and the shorter ones
are light chain.

4. Light
chain
• Each light chain usually
consists of about 220 amino
acids
• the molecular weight 25000
dalton
• The light chain are of two
types namely kappa and
lambda and only one type is
found in each antibody.
• Each light chain consists of two
domains of 110 amino acids.
• The amino acid sequence of
C- terminus domain is
constant (CL) where as
sequence of N- terminus is
variable (VL).
• The amino acid sequence in
VL domain of each light
chain is different.

5. Heavy
chain
• Each heavy chain consists of
about 440 amino acids
• has molecular weight of
about 50-70 kilodalton.
• The type of heavy chain
present determine the
immunoglobulin serotypes,
which determines the class of
antibody such as IgA, IgD,
IgE, IgG, and IgM antibodies
respectively.
• The variable region of each
heavy chain is approximately
110 amino acids long and is
composed of a single Ig
domain .
• Consists of single variable
region and three constant
regions but heavy chains μ
and ε have a constant region
composed of four domains.

6. • The variable regions of
heavy chain and light
chain folded together to
form antigen binding site.
• When antibody is cleave
with papain enzyme, it will
give two fractions
• a) fab fragment
• b) fc fragment.
• The hinge region is the
region that links the Fc
and Fab portions of
antibody molecule .

7. Functions of
Antibody

8. Types of
Antibody
• All classes are named using the convention
Ig*, where Ig stands for immunoglobulin
and * is the designation for the specific
isotype.
• There are five different antibody isotypes
seen in humans:
• IgG,
• IgM,
• IgA,
• IgD
and
• IgE.
Go
d
MAD
E

10. Ig
G
• Structure
All IgG's are monomers and has
two heavy γ chains and two light
chains of either κ or λ types but
not both.
• Fc region has CH1, CH2
and CH3 domains.
• IgG is 7S immunoglobulin with
• molecular weight of 160 KDa
• found highest concentration in
blood.
• subclasses of IgG in humans are
IgG1 (65-70%), IgG2 (23-28%),
IgG3 (4-7 %) and IgG4 (3-4%)

11. Ig
G
• Properties
• a) major immunoglobulin in serum – 75-80 % of
serum immunoglobulin is IgG
• b) major immunoglobulin in extra vascular spaces.
• c) Placental transfer - only class of immunoglobulin
that crosses the placenta.
• Transfer is mediated by a receptor on placental cells
for the Fc region of IgG. Not all subclasses cross
equally well; IgG2 does not cross well.
• d) Fixes complement - Not all subclasses fix equally
well; IgG4 does not fix complement
• e) Binding to cells - Macrophages, monocytes,
PMNs and some lymphocytes have Fc receptors
for the Fc region of IgG.
• f) produced later to IgM but provide long lasting

12. Ig
M
• Structure
• Normally exists as a pentamer
• 19S immunoglobulin
• an also exist as a monomer.
• On B cell surface, IgM is single monomer
(180KDa) but the secreted IgM is a
pentamer
.
• Five monomers of IgM are linked in a
circular fashion by disulphide bonds
between heavy chains and one-addition
chain rich in cysteine and asparagine
called J Chain
• In the pentameric form all heavy chains
are identical and all light chains too are
identical. Thus, the valence is
theoretically 10.
• Each IgM monomer has two heavy μ
chains
and 2 light chains of either κ or λ.
• Each heavy chain has an additional
domain (CH4) at the C terminus of FC
region.

13. Ig
M
• Properties
• IgM is predominantly present
intravascularly (80%).
• IgM is the first immunoglobulin to
be made by the fetus or
• the first immunoglobulin to be made
by a virgin B cells when it is
stimulated by antigen.
• As a consequence of its
pentameric structure, IgM is a
good complement fixing
immunoglobulin.
• IgM is also a good agglutinating
immunoglobulin. Thus, IgM
antibodies are very good in
clumping microorganisms for
eventual elimination from the body.
• IgM binds to some cells via Fc
receptors.

14. Ig
A
• Structure
• occurs in two forms -Serum IgA and
Secretary IgA. T
• he Serum IgA is a monomer (7S
with molecular weight 160 KDa).
• But secretary IgA usually found in
mucosal surfaces and in secretions
is a dimer.
• It is formed by two 7S IgA
monomer joined at their carboxy
terminus of Fc region by “J” chain
and also with a secretary
component .
• The dimer IgA is much longer (11S
with
molecular weight of 360KDa).
• IgA molecule has two α
heavy
chains containing 3 constant

15. Ig
A
• Properties
• major class of Ig in secretions - tears, saliva,
colostrum, mucus.
• Since it is found in secretions secretory IgA is important
in
local (mucosal) immunity
• Normally IgA does not fix complement, unless
aggregated.
• IgA can binding to some cells - PMN's and some
lymphocytes.
• It helps in phagocytosis and intracellular
killing of microorganisms.
• It is a minor component in systemic humoral immunity
but plays a major role in mucosal immunity.

16. Ig
D
• Structure
• IgD exists only as a monomer.
• Properties
• a) is found in low levels in
serum; its role in serum
uncertain.
• b) 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.
• c) IgD does not bind
complement.

17. Ig
E
• Structure
• IgE exists as a monomer and has an
extra
domain in the constant region.
• Properties
• It mediates immediate hypersensitivity
reaction (Type-1) e.g. anaphylactic
shock, hay fever, asthma etc.
• 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.
• Involved in allergic reactions
• IgE also plays a role in parasitic
helminth diseases. Since serum IgE
levels rise in parasitic diseases,
measuring IgE levels is helpful in
diagnosing parasitic infections.