Antibody structure, immunoglobulin, IgA, IgG, IgD, IgE, IgM, fab region, Fc region

1. IMMUNOLOGY
PRESENTATION
SRISHTI
BSc. Hons. Biochemistry
Department Of Chemistry & Biochemistry
School Of Basic Sciences & Research
Sharda University

2. ANTIBODY
An antibody (immunoglobulin) is a Y-shaped
structure which consists of four polypeptides — two
heavy chains and two light chains.
This structure allows antibody molecules to carry out their dual
functions: antigen binding and biological activity mediation. Each
function is carried out by different parts of the antibody:
1. Fragment antigen-binding (Fab fragment) - region on an antibody
that binds to antigens. It is composed of one constant and one variable
domain of each of the heavy and the light chain. These domains shape
the paratope — the antigen-binding site — at the amino terminal end
of the monomer.
2. Fragment crystallizable region (Fc region) - tail region of an
antibody that interacts with cell surface receptors called Fc
receptors and some proteins of the complement system. This property
allows antibodies to activate the immune system.

3. ANTIBODY STRUCTURE

4. Five Different Types of Antibodies
Distinguished by the type of heavy chain they
contain
1. IgG
2. IgM
3. IgA
4. IgE
5. IgD

5. IgG antibody structure and function
Structure
IgG antibody is large globular protein with molecular weight
of about 150 kDa & made of four peptide chains. It contains
two identical heavy chains of 50 kDa and two identical light
chains of 25 kDa (tetrameric quaternary structure)
functions
• 1) provides long term protection as it persists for months
and years after the presence of the antigen that has
triggered its production.
• 2) IgG protects against bacteria, viruses, neutralises
bacterial toxins
• 3) triggers complement protein systems
• 4)binds antigens to enhance the effectiveness of
phagocytosis.

6. IgM antibody structure and function
structure
• IgM antibodies constitute of five or six units
(mostly as pentamers) which are each comprised
of two heavy-chains and two light chains, bound
together by disulfide bonds.
function
1)IgM is involved in the ABO blood group antigens
on the surface of RBCs.
2) IgM enhances ingestions of cells
by phagocytosis.

7. IgA antibody structure and function
structure
• IgA antibodies consist of heavy (H) and light (L)
chains. Each H chain is comprised of the constant
region, hinge region & the variable (V) region. Light
chains consist of the constant & variable elements.
function
• The main function of IgA is to bind antigens on
microbes before they invade tissues. It aggregates
the antigens and keeps them in the secretions so
when the secretion is expelled, so is the antigen.
• IgA is also first defense for mucosal surfaces such as
the intestines, nose, and lungs.

8. IgE antibody structure and function
structure
• Immunoglobulin E (IgE) antibodies have only been
found in mammals. IgE is synthesized by plasma
cells.
• Monomers of IgE consist of two heavy chains &
two light chains, with the heavy chain containing
4constant domains.
functions
• IgE bind to mast cells and basophils which
participate in the immune response.
• Involved in allergic response.

9. IgD antibody structure and function
• Immunoglobulin D (IgD) antibodies are
expressed in the plasma membranes of
immature B-lymphocytes.
• IgD is also produced in a secreted form that is
found in small amounts in blood serum.
• IgD plays a role in the induction of antibody
production.