1. بسم الله الرحمن الرحيم B AND T LYMPHOCYTES
MEDIATERS OF ADAPTIVE IMMUNE RESPONSE
Dr.Mohammed Sharique Ahmed Quadri
Assistant professor Physiology
Al Maarefa College

2. Objectives Describe the different types of lymphocytes
Discuss the formation and preprocessing of the different types of lymphocytes
Define clonal selection theory
Explain the concept of humoral(antibody mediated ) immunity .
Describe mechanism of action of antibodies
Emphasis the importance of memory cell ( primary and secondary response)

3. Immunity
Body’s ability to resist or eliminate potentially harmful foreign materials or abnormal cells
Immune system activities
Defends against invading pathogens
Removes “worn-out” cells and tissue damaged by trauma
Identify and destroy abnormal or mutant cells
Immune surveillance
Identifies and destroys abnormal or mutant cells that have originated in the body
Mounts inappropriate immune responses that lead either to allergies or to autoimmune diseases

4. Leukocytes Effectors of the immune system 5 Types Neutrophils
Highly mobile phagocytes that engulf and destroy unwanted materials
Eosinophils
Secrete chemicals that fight parasites
Involved in allergic reactions
Basophils
Release histamine and heparin
Monocytes
Transformed into macrophages (tissue-bound phagocytic specialists)
Lymphocytes
Β lymphocytes (β cells)
Transformed into plasma cells that secrete antibodies
T lymphocytes (T cells)
Responsible for cell-mediated immunity

5. Lymphocytes Mainly produced from lymphoid colonies in lymphoid tissues
Tissues that produce, store, or process lymphocytes
Include
Bone marrow
Lymph nodes
Spleen
Thymus
Tonsils
Adenoids
Appendix
Peyer’s patches (GAIT)

6. IMMUNITY
Mechanism by which the body is able to resist or overcome disease causing micro-organisms.
Broadly there are 2 types -
I. Innate/Non-specific/Natural Immunity
II. Acquired /Specific/Adaptive Immunity

7. I. Innate/Non-specific/Natural Immunity.
Provides first line of defense against infections.
Intact skin & mucous membranes.
Secretions such as tears, saliva, HCl acid.
Phagocytes & Natural Killer Cells.
Complement system,(a group of 20 proteins activated by immune complexes)

8. Immune Responses Innate immune system Nonspecific
Responses work immediately when body is exposed to threatening agent
Nonselectively defend against foreign invaders
First line of defense
Rapid but limited responses
Neutrophils, macrophages, several plasma proteins are important in innate defense

9. Immune Responses Adaptive or acquired immune system
Specifically targets foreign material to which body has already been exposed
Body has taken time to prepare to attack
Ultimate weapon against most pathogens
Responses are mediated by β and T lymphocytes
Formation of memory cells allows system to react more swiftly against specific invaders in the future

10. Adaptive Immunity 2 classes of adaptive immunity
Antibody-mediated or humoral immunity
Involves production of antibodies by B lymphocyte derivatives known as plasma cells
Cell-mediated immunity
Involves production of activated T lymphocytes
Directly attack unwanted cells

11. Adaptive Immunity Origins of β and T Cells
After early childhood most new lymphocytes are derived from peripheral lymphocyte colonies rather than from bone marrow

12. Lymphocytes

13. Adaptive Immunity Antigen Large, foreign, unique molecule
Induces an immune response against itself
In general, the more complex a molecule is, the greater its antigenicity

14. β Lymphocytes: Antibody-Mediated Immunity
Each lymphocyte has surface receptors for binding with one particular type of possible antigens- named as BCRs- B-cell receptors
These are eyes of adaptive immune system

15. T-Dependent and T-independent Antigen
Binding with Antigens stimulate B cells to convert into plasma cells that produce antibodies
T-independent: after binding with polysaccharide antigen B cells are activated without assistance from T- helper cells
T-dependent: polypeptide antigen cannot stimulate B cells without the help of T- helper cells
The majority of antigens to which B cell respond are T-dependent

16. β Lymphocytes: Antibody-Mediated Immunity
On binding with processed and presented antigen
Most B cells differentiate into active plasma cells
Other B cells become dormant memory cells
A mature plasma cell then produces antibodies rapidly (2000 antibodies/sec)
All antibodies eventually enter blood where they are known as gamma globulins or immunoglobulin's

17. B -Lymphocytes

18. Plasma Cells Antibody (Immunoglobulin) subclasses IgM IgG IgE IgA IgD
Serves as the β cell surface receptor for antigen attachment
Secreted in early stages of plasma cell response
IgG
Most abundant immunoglobulin in blood
Produced in large amounts when body is exposed to same antigen
IgE
Helps protect against parasitic worms
Antibody mediator for common allergic responses
IgA
Found in secretions of digestive, respiratory, and genitourinary systems; also in milk and tears
IgD
Present on surface of many β cells
Function is uncertain

19. Antibodies Y-shaped molecules
Composed of 4 interlinked polypeptide chains
Two long, heavy chains
Two short, light chains
Properties of tail portion determine functional properties of the antibody( what it will do after binding with antigen)
Identical antigen-binding fragments (Fab) at tip of each arm (unique for each different antibody)
Tail (constant region) regions within each subclass are identical
Antibodies

20. Mechanism of Action of Antibodies
Can physically hinder antigens
By neutralization, they prevent harmful chemicals from interacting with susceptible cells
Can bind to foreign cells by agglutination
Enhance activity of other defense systems by
Activating complement system
Enhancing phagocytosis
Stimulating natural killer (K) cells

21. Mechanism of Action of Antibodies

22. Mechanism of Action of Antibodies

23. Immune Complex Disease
Occurs when overzealous antigen-antibody response causes damage to normal and invading foreign cell
Antigen-antibody complex normally form in response to foreign invasion and are removed by phagocytic cells
If large numbers of these complexes are continuously produced, phagocytes can’t clear away all immune complexes formed
Antigen-antibody complexes not removed continue to activate complement system
Excessive activated complement damage normal cells
Can occur in bacterial, viral, or parasitic infections

24. Clonal Selection Theory (how matching B cell responds to its antigen)
During fetal life B cells are genetically preprogrammed to produce antibody against particular antigen , before ever being exposed to it.
All offspring of particular b lymphocyte form family of identical cells, on exposure to specific antigen . i.e ( clonal expansion ).

25. Clonal Selection Theory (how matching B cell responds to its antigen)

26. Primary and Secondary Response
Memory cells
Small percentage of β lymphocytes become memory cells
Remain dormant
Upon re exposure to same antigen, they are more ready for immediate action than the original lymphocytes of the clone
Secondary response is quicker, more potent, and longer-lasting
Can be induced by disease or vaccination
Formation of memory cell can occurs through the person either actually having disease or being vaccinated

27. Primary and Secondary Immune Responses

28. Active and Passive Immunity
Active immunity
“self-generated”
Results from exposure to an antigen
Passive immunity
“borrowed immunity”
Results from transfer of preformed antibodies
Can provide immediate protection
Example of passive immunity is transfer of IgG antibodies from mother to fetus
Tetanus toxins, anti snake venom, rabies virus

29. References Human physiology by Lauralee Sherwood, seventh edition
Text book physiology by Guyton &Hall,11th edition
Text book of physiology by Linda .s contanzo,third edition