Immunoglobulins, also known as antibodies, are Y-shaped proteins produced by plasma cells in response to antigens. They consist of two heavy chains and two light chains. The variable regions of the light and heavy chains determine antigen binding specificity. There are five major classes of immunoglobulins - IgG, IgM, IgA, IgD, and IgE - which differ in structure and function. IgG is the most common antibody and provides primary defense. IgM is the first antibody produced during initial exposure and activates the complement system. IgA protects mucosal surfaces from pathogens.

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