Antibodies, also known as immunoglobulins, are Y-shaped proteins produced by plasma cells in response to antigens in the body. They are made of two heavy chains and two light chains that form sites to bind to antigens. There are five main antibody isotypes - IgA, IgD, IgM, IgG, and IgE - that have different functions. Antibodies can neutralize pathogens, agglutinate cells for phagocytosis, activate the complement system, and trigger allergic reactions. Medical applications of antibodies include disease diagnosis, blood typing, pregnancy tests, and cancer imaging.

1. AntibodiesAntibodies
Ioulios Konstantelos, Giannis Mparounis, Nikolas Manaras,
Dionisis Kontodimopoulos,
Xenophon Logothetis & Ilias Kouris
Varvakeio Model Gymnassium

2. The antibodies
• An antibody (Ab) is a large, Y- shaped protein
produced mainly by plasma cells. The antibodies are
produced as a response to the immune system to a
unique molecule of a pathogen, called antigen.
• Antibodies are also known as immunoglobulins (Ig),
as they are spherical structured proteins due to the
specific folding of their chains.
• Antibodies are secreted by B cells of the adaptive
immune system, mostly by differentiated B cells, called
plasma cells.

3. Structure of the antibodies
• An antibody is consisted of four polypeptide chains,
two identical heavy chains and two identical, called
light chains.
• These chains are connected with covalent, disulfide
bonds and they form a structure similar to a sling or
to the letter Y.
• Each chain, heavy or light, is consisted of two
regions, called constant and variable domains.
• The variable domains of the chains consist the
antigen binding site of the antibody.

4. Structure of an antibody

5. Antibody Isotypes
There are 5 different classes of antibodies also known as isotypes
depending on the type of their heave chain
 IgA (isotypes IgA1 & IgA2), found in mucosal areas
 IgD, expressed on the surface of B cells that have not been
exposed to the antigen
 IgM, expressed on the surface of B cells and in a secreted
form
 IgG (Ig1-2-3-4), provides the majority of antibody-based
immunity against invading pathogens.
 IgE, binds to allergens and triggers histamine release by mast
cells and baseophils.

6. Antibody Isotypes

7. Antibody complexes

8. Antibody Function
The main categories of antibody action include the following:
 Neutralization, in which neutralizing antibodies block parts of the
surface of a bacterial cell or a virus to render its attack ineffective
 Agglutination, in which antibodies “glue together” foreign cells into
clumps that are attractive targets for phagocytosis
 Precipitation, in which antibodies “glue together” serum-soluble
antigens, forcing them to precipitate out of solution in clumps that are
attractive targets for phagocytosis.
 Complement activation (fixation) in which antibodies that are
latched on a foreign cell encourage complement to attack it with a
membrane attack complex, which leads to lysis of the foreign cell and
encouragment of inlammation by chemotactically attracting
inflammatory cells.

9. Antigen-Antibody binding

10. Allergies
 Allergies, also known as allergic diseases, are a number of
conditions caused by hypersensitivity of the immune system to
something in the environment that usually causes little or no problem in
most people.
 Allergens, the factors that cause allergies, are usually pollen, insect
stings, medication or certain food.
 The immune system reacts to allergens producing specific antibodies.
The underlying mechanism The underlying mechanism involves
immunoglobulin E antibodies (IgE), part of the body's immune
system, binding to an allergen and then to a receptor on mast cells or
basophils, where it triggers the release of inflammatory chemicals,
such as histamine.
 Diagnosis is typically based on a person's medical history. Further
testing of the skin or blood may be useful in certain cases. Well known
tests are RAST and immunoCAP.

11. Medical Applications
➔
Detection f particular antibodies is a very common form of medical
diagnostics. For example, in biochemical essays for disease diagnosis a
titer of antibodies detected against Epstein-Barr virus or Lyme disease is
estimated from the blood.
➔
In clinical immunology, levels of individual classes of immunoglobulins
are measured to characterize the antibody profile of the patient. Elevations
in different types of IgA indicate alcoholic cirrhosis, elevated IgM indicates
viral hepatitis and primary biliary cirrhosis, while IgM is elevated in viral
hepatitis, autoimmune hepatitis and cirrhosis.
➔
Autoimmune disorders can often be traced to antibodies that bind the
body’s own epitopes. Many of them can be detected through blood tests.
The Coombs test is also used for antibody screening in blood tranfusion
preparation and in antibody screening in antenatal women.
➔
Several immunodiagnostic methods based on detection of complex
antigen-antibody are used to diagnose infectious diseases, for example
ELISA, immunofluoresence, Western blotting, immunodiffusion,
immunoelectrophorsis and magnetic immunoessay.
➔
Antibodies raised against human chorionic gonadotropin are used in over
the counter pregnancy tests.
➔
New dioxaborolane chemistry enables radioactive fluoride (18F) labeling of
antibodies, which allows for positron emission tomography (PET) imaging
of cancer.