2. Immunoglobulin define
• A protein that is made by B cells
and plasma cells (types of white
blood cells ) and helps the body
to fight infection .
3. Structure of immunoglobulin
consists of
four polypeptide chains (two heavy chains and two
light chains) joined together by disulfide bridges
(shown in red).
The light chain consists of a variable light (VL) and
constant light (CL) region, and the heavy chain
consists of one (VH) chain linked to three constant
regions (CH1,CH2, and CH3).
The (Fab) is a region on an antibody that binds
to antigens
The(Fc) is the tail of the antibody, which
interacts with effector cell surface This
property allows antibodies to activate the
immune system.
5. • Immunoglobulin G (IgG) is the most common and abundant antibody present in the body.
• Blood plasma consists of 75-80% of IgG antibodies.
• Of all antibodies, IgG has the longest lifespan of about 23 days.
• IgG is the only antibody that can cross the placental barrier and provide passive immunity to a
developing fetus.
IgG antibodies remember the pathogens that have previously entered the body and caused an
infection. IgG also provides some immunity to infants when ingested through breast milk.
The function of IgG is to enhance the phagocytosis of pathogens, neutralize bacterial or viral toxins,
and trigger the activation of the complement system.
IgG has four isotypes:
IgG1
IgG2
IgG3
IgG4
immunoglobulin [ G ]
6. immunoglobulin [ M ]
is the first antibody that interacts with new bacteria that enter the body,
and it initiates a primary immune response.
IgM is also called a natural antibody because it serves as the first line of
defense of the immune system and provides short-term protection.
IgM has a gigantic pentamer structure above all other antibodies and
consists of 10 antigen-binding sites, making them more effective than
IgG in killing bacteria or viruses.
The life span of the IgM antibody in our body is about five days, and
it makes up 5% – 10% of the antibodies in blood plasma.
IgM also causes agglutination (formation of clumps) of bacteria when
binding to its surface epitope. The IgM antibody is known as a potent
agglutinin and is also found on the surface of naïve B-cells and red blood
cells in its monomeric form
7. immunoglobulin [ A ]
is the most common antibody after IgG. IgA is present in the blood,
lymph, and other body secretions such as saliva, tears, and milk. It can
also be found in the genital lining, respiratory tract, and intestine lining.
IgA antibodies protect the body from bacterial growth and colonization.
However, it is less stable than IgG and can be found in a lower
quantity, accounting for about 10% – 15% of the total
immunoglobulins in the blood.
IgA is often called a secretory antibody because it has an attached
secretory component that protects it from enzymatic digestion. Every
day, a human secretes about 5 g to 15 g of secretory IgA into mucous
secretions to prevent pathogenesis .
8. immunoglobulin [ D ]
Immunoglobulin D (IgD) makes up less than 0.5% of serum
antibodies.
IgD is found in lesser amounts in lymphatic fluids and blood.
The function of IgD is still unknown, but it is present on
the surface of immature B-cells as receptors,
and it is also a part of the innate immune system. Researchers
believe that IgD regulates the B-cells’ activation and
differentiation into plasma cells.
9. immunoglobulin [ E ]
Immunoglobulin E (IgE) makes up less than 0.01% of serum
antibodies. Even though it is present in the lowest amount in the
blood and has a shorter lifespan, it is still a potent antibody.
IgE is the most effective antibody against parasitic infections,
including helminths.
A high level of IgE in the blood can sometimes cause
hypersensitivity toward non-harmful substances such as pollen or
dust particles. Recently, immunologists have begun formulating new
anti-IgE antibodies for the treatment of allergy and asthma.
