This document discusses antigens, self-tolerance, and the mechanisms by which the immune system avoids attacking self-antigens. It explains that lymphocytes can recognize virtually any antigen due to random rearrangement of gene segments. While autoreactive lymphocytes are constantly generated, the immune system remains tolerant of self-antigens through central and peripheral tolerance mechanisms. Central tolerance eliminates many autoreactive T and B cells early in development in primary lymphoid organs. Peripheral tolerance then controls responses of mature lymphocytes to self-antigens in secondary lymphoid organs.

2. ANTIGEN
Recognized by the bodyas
foreign.
Stimulatesan immune
response.
Can be foreign or self.

3. SELF ANTIGENS

4. • FIRST LINE OF DEFENSE
• (Skin and mucous membranes)
• SECOND LINE OF DEFENSE
• (Defensive cells,Antimicrobial substances,Inflammation,Fever)
• THIRD LINE OF DEFENSE
• (T cells,B cells and Antigen presenting cells)

5. B andT cell receptors areencodedby random
rearrangement of pre-existing genesegments.
Occursin the early development of lymphocytes.
Antigen specefic receptors aregenerated priortothe
encounter of lymphocytes with the specific antigens.
Ourimmune system generates lymphocytes clones
that can virtually recognizeany antigen in the
universe.

6. LYMPHOCYTES HAVING RECEPTORS AGAINST SELF-ANTIGENS
ARE CONSTANTLY BEING GENERATED IN OUR BODY.
SELF ANTIGENS
Auto antigens
Own cells andmolecules
AUTOREACTIVE (SELF-
REACTIVE)
LYMPHOCYTES
“STILL WE AVOID
ATTACK ON OUR OWN
CELLS AND TISSUES.”

7. Our immune
system has the
ability to react with
enormous and
diverse foreign
antigenswhileit is
tolerantto theself-
antigens.

8. Thestate of unresponsiveness of the immune system toantigens
Thestate of unresponsivness ofthe immune system toself-antigens
SELF-TOLERANCE

9. If fails(i.e. starts
respondingtoself-
antigens)

10. How immune responseto self-antigens
arepreventedin human body?

11. Achieved by variousmechanismsand processes
operatingon the cellsof the immune system.
SELF-TOLERANCE
CENTRAL
TOLERANCE
PERIPHERAL
TOLERANCE

12. 1.CENTRAL TOLERANCE
“Central” refers to the primary or
central lymphoid organs where
development of lymphocytes
takesplace.
T and B lymphocytes first express
antigen receptors.

13. 1.CENTRAL TOLERANCE
“TOLERANCE INDUCED DURING EARLY DEVELOPMENT
OF LYMPHOCYTES.”
Comprises of mechanisms that eliminate most auto-reactive T and B
cells during their early development.
Central tolerance is NOT FULL PROOF.

14. 2.PERIPHERAL TOLERANCE
“Peripheral” refers to the
secondary or peripheral lymphoid
organs.
Lymphocytes responses to foreign
antigens are initiated to develop.

15. 2.PERIPHERAL TOLERANCE
“Tolerance inducedin mature
lymphocytes.
Prevent auto-reactive mature
lymphocytes from attackingself-
antigens.

16. REGULATION OF
IMMUNE
RESPONSE