Immunology - Antigens - Immunogenecity and antigenecity, Haptens - Types and Examples & Adjuvants - commonly used adjuvants and mechanism of immune stimulation by adjuvants

1. Dr. S. ASHA., M.Sc., M.Phil., Ph.D., SET,
ASSISTANT PROFESSOR,
DEPARTMENT OF BIOCHEMISTRY,
D.K.M. COLLEGE FOR WOMEN,
SAINATHAPURAM,
VELLORE.

2. Antigens
• An antigen is a molecule capable of inducing an immune system to
produce an antibody in the host organism.
• Most antigens are either Proteins or Polysaccharides. Lipids and
Nucleic acids are usually antigenic only when combined with Proteins
and Polysaccharides.
• Most antigens are large, complex molecules with a molecular weight
generally greater than 10,000 to 6,00,000 Daltons.
• The ability of a molecule to function as an antigen depends on its Size,

3. Structural complexity, Chemical nature and Degree of
foreignness to the host.
• The Antigen may originate from within the body (Self – antigen or
Autoantigens) or from the external environment (Non-self antigen or
Heteroantigens or Foreign antigen).
• Self - antigens: Originate within the human body during Autoimmune
diseases.
• Non - self antigens: Microorganisms, Snake venom, Certain proteins
from foods and Components of Serum & RBCs.

4. • Antigenic compounds are often components of invading microbes, such
as capsules, cell walls, flagella, fimbriae, and toxins of bacteria; the
coats of viruses; or the surfaces of other types of microbes.
• Non-microbial antigens include Pollen, Egg white, Blood cell surface
molecules, Serum proteins, and Surface molecules of transplanted
tissues & organs.
• It satisfies two distinct immunologic properties
1. Immunogenicity
2. Antigenicity

5. Immunogen
• A substance which induces a detectable immune response (either cell –
mediated or humoral) are appropriately called immunogen.
• An immunogen can trigger an immune response and acts as an antigen in
that response.
• All molecules having immunogenicity also show antigenicity. Hence all
immunogens are antigens.
• Despite the fact that all antigens are recognized by specific lymphocytes
or antibodies, not every antigens can evoke an immune response.

6. • Those antigens which are all capable of inducing an immune response
are said to be immunogenic and are called immunogens.
• So all antigens are not immunogens.

7. HAPTENS
• The term Hapten was first coined by Karl Landsteiner.
• Hapens are low molecular weight organic molecules that are not
antigen (incapable of including antibody formation) by themselves but
become antigen if they bon to a larger carrier molecule such as a
protein. These low molecular weight antigen are called Hapten.
• Hence hapten are non immunogenic but antigen nature.
• When hapen combines with a large protein molecule, a carrier it
become immunogenic.

8. • Example of a Hapten is Penicillin, a small molecule and is not
antigenic. However, when it is combined with certain serum proteins of
sensitive individuals, the resulting molecule becomes immunogenic,
activates lymphocytes, and initiates a severe and sometimes fatal
Allergic reaction (a type of immune response).
 Types of Haptens
 Complex Hapten
 Simple Hapten.

9. • Complex Haptens
Polyvalent
Precipitate with Specific antibodies by Hapten-antibody complex.
• Simple Haptens
Univalent
Non – precipitate with Specific antibodies.

10. Examples of Haptens
1) Aniline (an Organic compound) and its derivatives (o-, m, p-benzoic acid)
(First researched Hapten).
2) Urushiol present in Toxicodendron radicans, Poison ivy plant.
3) Hydralzine, a blood pressure lowering drug.
4) Fluorescein, a fluorescent dye.
5) Biotin, a Vitamin – B7 (Formerly Vitamin – H or Coenzyme – R).
6) Penicillin, anAntibiotic.
7) Digoxigenis, a steroid found in the flowers & leaves of the plants Digitalis
purpurea, Digitalis orientalis & Digitalis lanata.
8) 2,4 – Dinitrophenol, an Organic compound.

11. ADJUV
ANTS
• Adjuvants are substances that, when mixed with an antigen and injected
with it, enhance the immunogenicity of that antigen
• The word Adjuvants was derived from the Latin word “Adjuvare” which
means “Tohelp”).
• Adjuvants are often used to boost the immune response when an antigen
has low immunogenicity or when only small amounts of an antigen are
available.
• Adjuvants may be added to a Vaccine to modify the Immune response.

12. • The antibody response of Mice to immunization with Bovine serum
albumin (BSA) can be increased fivefold or more if the BSA is
administered with an adjuvant.
COMMONIY USED ADJUVANTS:
1) Aluminium potassium sulfate (Alum) (First Aluminium salt used as
Adjuvant and now completely replaced by aluminium hydroxide and
aluminium phosphate for commercial vaccines).
2) Freund’s Incomplete Adjuvant (Oil in water emulsions).
3) Freund’s complete Adjuvant (Inactivated and dried Mycobacterium
tuberculosis).

13. 4) Plant Saponins.
5) Cytokines.
6) Quil A (Detergent).
7) Mineral oil and Food based oil (Peanut oil).
8) Squalene (Carbon organic compound obtained from Shark liver oil).
9) Bacterial Products - Toxoids, Lipopolysaccharides and Killed Bordetella
pertussis.
10) Synthetic Polynucleotide.

14. Mechanism of Immune stimulation by Adjuvants
 Extend the presence of antigen in the blood.
 Helps the Antigen presenting cells absorb antigen.
 Activate Macrophages and Lymphocytes.
 Support the production of Cytokines.

15. Haptens - small molecules
Large carrier protein
Hapten-carrier conjugated
(immunogenic)