immunoglobulin structure,types

1. Immunoglobulin
By
Swetha smenon
2nd msc

2. • Specialized group of proteins mostly
associated with γ globulin fraction.
• Immunoglobulins is a functional term while γ
globulin is a physical term.
• Abbreviated as Ig
• Ig are produced by plasma cells in response to
an antigen and which function as antibodies.

3. Structure of immunoglobulins
• All immunoglobulin molecules basically consist
of : two identical heavy chains and two identical
light chains held together by disulfide linkages
(Inter-chain and Intra-chain ) and non-covalent
interactions.
• It is Y shaped tetramer (H2L2) Each heavy chain
contains 450 amino acids Light chain has 212
amino acids
• Heavy chain of Ig are linked to carbohydrates
hence Ig are glycoproteins.

5. • Amino acid sequence of variable regions of
light and heavy chains is responsible for
specific binding of immunoglobulin (antibody)
with antigen.
• There are certain hypervariable regions
interspersed between the relatively invariable
regions.
• Light chain has 3 hypervariable regions
• Heavy chain has 4.
• The hypervariable regions more specifically
determine the antigen-antibody binding.

6. Immunoglobulin Classes
• IgG - Gamma heavy chains
• IgM - Mu heavy chains
• IgA - Alpha heavy chains
• IgD - Delta heavy chains
• IgE - Epsilon heavy chains

7. • Two types of light chains : kappa (Κ) and
lambda (λ)
• An Ig contains two Κ or two λ light chain and
never a mixture.
• Kappa chain (60%) is more common in
human.

8. Ig G
• Major serum Ig – 75 -80 % Single Y shaped
unit (monomer)
• It is the antibody seen in secondary immuno
response.
• It can transverse blood vessels readily. IgG is
only Ig that can cross the placenta and
transfer the mothers immunity to developing
fetus

9. Ig M
• J Chain Largest Ig composed of 5 Y shaped
units held together by a J polypeptide chain.
• Pentamer –bind with 5 antigenic sites
• Due to its large size, IgM cannot transverse
blood vesssels, hence it is restricted to the
blood stream.
• IgM is first antibody to be produced in
response to an antigen and is most effective
against invading micro-organism.

10. • IgM Ab cannot cross placenta
• So if the fetus even though it carries an
incompatible Ag , is protected from natural Ab
of the mother

11. IgA
• Single (monomer) or double unit (dimer) held
together by J chain
• Mostly found in body secretions such as saliva,
tears, sweat, milk and the walls of intestine.
• Most predominant Ab in colostrum.
• Ig A molecules bind with bacterial Ag present on
body surface and remove them. So IgA prevents
the foreign substances from entering the body
cells.

12. IgE
• Single Y shaped (Monomer)
• Normally present in minute conc in blood – 0.3g/ml
• IgE levels are elevated in individuals with allergies as it
is associated with the body’s allergic response – Hay
fever, Asthma, Anaphylactic shock.
• IgE tightly binds with Fc receptors on basophils and
mast cells which release histamine and cause allergy.
• Immediate type Hypersensitivity reaction – peak at 30
min

13. IgD
• Single Y shaped unit (Monomer)
• Present in low concentration in circulation.
• Present on surface of B cells
• Their function is not known

15. Immunoglobulin MajorFunctions
IgG •Main antibody in the secondary response.
• Opsonizes bacteria, making them easier
to phagocytose.
• Fixes complement, which enhances
bacterial killing.
• Neutralizes bacterial toxins and viruses.
• Crosses the placenta.
IgA •Secretory IgA prevents attachment of
bacteria and viruses to mucous
membranes.
Does not fix complement
IgM Produced in the primary response to an
antigen.
•Fixes complement.
• Does not cross the placenta
IgD • Found on the surfaces of B cells where it
acts as a receptor for antigen.

16. IgE •Mediates immediate hypersensitivity
(allergy) by causing release of mediators
from mast cells and basophils upon
exposure to antigen (allergen).
• Does not fix complement.
•Main host defense against helminthic
infections.

17. • REFERNCE
• A text of microbiology ,Dr. R.C Dubey & Dr. D.K
Maheswari
• https://www.dianova.com/en/faq/antibody-
structure-what-is-a-secondary-antibody/
• https://www.biologyexams4u.com/2012/11/d
ifferent-types-of-immunoglobulins-igg.html