1. An antigen is any substance that causes the immune system to produce antibodies against it. Antigens can be external substances like viruses, bacteria, and pollen that enter the body, or they can be generated internally through infections or metabolism. 2. There are different types of antigens including exogenous antigens from outside the body, endogenous antigens produced internally, autoantigens that cause autoimmune disorders, and tumor antigens on cancer cells. 3. Antigens have antigenic determinants called epitopes that bind to receptors on lymphocytes and stimulate an immune response. Adjuvants are substances used in vaccines to enhance the immune response to antigens.

1. ANTIGEN
Mrs. Praveen Garg
VITS College, satna

2. INTRODUCTION
• Antigen, substance that is capable of stimulating an immune
response, specifically activating lymphocytes, which are the
body’s infection-fighting white blood cells.
• An antigen is any substance that causes your immune system
to produce antibodies against it.
• An antigen may be a substance from the environment, such as
chemicals, bacteria, viruses, or pollen.
• An antigen that induces an immune response i.e., stimulates
the lymphocytes to produce antibody or to attack the antigen
directly is called an immunogen and process is known as
immunogenecity.

3. Types of antigen
• There are different types of antigens on the basis of origin:
• Exogenous Antigens: Exogenous antigens are the
external antigens that enter the body from outside, e.g. inhalation,
injection, etc. It is known as heteroantigen or foreign antigen.
• Example: viruses or microorganisms (such
as bacteria and protozoa), snake venom, polllen, certain proteins in
foods, and components of serum and red blood cells from other
individuals.
• Endogenous Antigens: Endogenous antigens are generated inside
the body due to viral or bacterial infections or cellular metabolism.
• Autoantigens: Autoantigens are the ‘self’ proteins or nucleic
acids that due to some genetic or environmental alterations get
attacked by their own immune system causing autoimmune
diseases.

4. • Normally, the body is able to distinguish self from nonself, but in
persons with autoimmune disorders, normal bodily substances
provoke an immune response, leading to the generation of
autoantibodies.
• Tumour Antigens: It is an antigenic substance present on the
surface of tumour cells that induces an immune response in the
host, e.g. MHC-I and MHC-II. Many tumours develop a
mechanism to evade the immune system of the body.
• On the basis of the immune response:
• Immunogen
• These may be proteins or polysaccharides and can generate an
immune response on their own.
• Hapten
• These are non-protein, foreign substances that require a carrier
molecule to induce an immune response.

6. • On the surface of antigens are regions, called antigenic
determinants, that fit and bind to receptor molecules of
complementary structure on the surface of the lymphocytes.
• The binding of the lymphocytes receptors to the antigens surface
molecules stimulates the lymphocytes to multiply and to initiate
an immune response.
• The amount of antibody formed in response to stimulation
depends on the kind and amount of antigen involved, the route of
entry to the body, and individual characteristics of the host.
Structure of antigen

7. Epitope
• Epitope, also called antigenic determinant, portion of a
foreign protein, or antigen, that is capable of stimulating an
immune response.
• An epitope is the part of the antigen that binds to a specific
antigen receptor or antibodies on the surface of a B cell. Which
remove the antigen from the body.
• Many antigens have a variety of distinct epitopes on their surfaces.
Each epitope is capable of reacting with a different B cell antigen
receptor.
• It is possible for two or more different antigens to have an epitope
in common. In these cases, antibodies targeted to one antigen are
able to react with all other antigens carrying the same epitope.
Such antigens are known as cross-reacting antigens.

8. Properties of Antigens
• The properties of antigens are as follows:
• The antigen should be a foreign substance to induce an
immune response.
• The antigens have a molecular mass of 14,000 to 6,00,000 Da.
• They are mainly proteins and polysaccharides.
• The more chemically complex they are, the more
immunogenic they will be.
• Antigens are species-specific.
• The age influences the immunogenicity. Very young and very
old people exhibit very low immunogenicity.

9. • In pharmacology, an adjuvant is a drug or other substance, or a
combination of substances, that is used to increase the efficacy or
potency of certain drugs.
• An adjuvant is a substance that enhances the immune system's
response to the presence of an antigen.
• They are commonly used to improve the effectiveness of a
vaccine.
• They are injected alongside an antigen to help the immune
system generate antibodies that fight the antigen.
Adjuvant

10. • Aluminum adjuvants are used in vaccines such as hepatitis A,
hepatitis B, diphtheria-tetanus-containing vaccines,
Haemophilus influenzae type b, and pneumococcal vaccines,.
• They are not used in the live, viral vaccines, such as measles,
mumps, rubella, varicella and rotavirus.
• Mineral salts, emulsions, microparticles, saponins, cytokines,
microbial components/products, and liposomes have all been
evaluated as adjuvants

11. Thank you