The document discusses the concepts of immunity and the organs of the immune system, defining antigens and their classification based on origin and immune response types. It explains the differences between immunogens and haptens, as well as T cell-dependent and independent antigens. Additionally, it covers the terms immunogenicity and antigenicity, highlighting their roles in the immune response.

1. 1: IMMUNITY AND ORGANS OF THE IMMUNE
SYSTEM
Dr. Vividha Raunekar

2. Dr. Vividha Raunekar
ANTIGEN/IMMUNOGENS
Definition- A substance when introduced in body, evokes immune response to produce a
specific antibody with which antigen reacts in an observable manner
Chemical Nature-
1. mostly protein- present on pathogen surface- good immunogens
2. Polysac and Lipopolysac (LPS)
3. Nucleic acids- poor immunogens but can be immunogenic when complexed with proteins
4. Lipids- non- immunogenic but can act as haptens

3. Dr. Vividha Raunekar
EPITOPE/ ANTIGENIC DETERMINANTS
A specific site where antibody binds to the antigen
Types- Bcell epitopes- conformational- when heat denatured; not recognized by Ab;
thus vaccines are not heat denatured
T cell epitopes- linear

4. Dr. Vividha Raunekar
CLASSIFICATION OF AGS- 1. ON BASIS OF THEIR
ORIGIN
Exogenous- that comes inside the body from outside- pathogens, pollutants, pollens,
etc
Endogenous- present inside the body – Blood grp Ags, autoimmune diseases

5. Dr. Vividha Raunekar
2. ON BASIS OF THEIR IMMUNE RESPONSE
Types- 1. Immunogen/ Complete Ag- Induce Ab formation by themselves and react
specifically with Abs; mostly proteins
2. Incomplete Ag/ Haptens- Unable to Induce Ab formation by themselves Induce Ab
formation by themselves , so need help of carrier proteins; e.g., polysac of
pneumococci, streptococci, etc

6. Dr. Vividha Raunekar
Hapten+ carrier prot.= induce Ab formation; generates specific reaction
Types of hapten- simple and complex
Simple hapten- Univalent- react with Ab and does not produce precipitation
Complex hapten- Polyvalent- react with Ab and does produce precipitation

7. Dr. Vividha Raunekar
3. T (THYMUS) DEPENDENT AGS
Requires help of T cells to induce B cell response to produce Abs.

8. Dr. Vividha Raunekar
T (THYMUS) INDEPENDENT AGS
They stimulate B cells to generate Abs without help of T cells
They are polysac that contain repeating epitopes/ LPS derived from Gram negative
bacteria
Do not stimulate Immunological memory

9. Dr. Vividha Raunekar
IMMUNOGENICITY
Ability of a substance to Induce immune response (humoral/ cell mediated) is
immunogenicity
Substance are called immunogenic

10. Dr. Vividha Raunekar
ANTIGENICITY
Ability of a substance to bind the product of immune response
Substance are called antigenic

11. Dr. Vividha Raunekar
THANK YOU