Antigen

Antigens are any foreign compound that generate immune response

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.

5. 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

6. 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.

7. 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.

8. 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

9. 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  

10. Thank you