1. CELL MEDIATED IMMUNITY
The immune system can mount a cell mediated immune response. This involves the production of special cells that can react with the foreign agent.(T helper cell,cytotoxic and suppressor cell) The reacting cell can either destroy the foreign agents, or it can secrete chemical signals that will activate other cells to destroy the foreign agent.

2. CELL MEDIATED
The T lymphocytes, which are the main effectors of the cell mediated response, mature in the thymus, thus the name T cell.

3. CT…
There are several different types of T cells performing different functions.
Diverse responses of the different T cells are collectively called the “cell-mediated immune responses.”

4. Steps involved in the cell-mediated response.
The pathogen (bacteria, virus, fungi, or a parasite),or foreign agent, enters the body through the blood stream, different tissues, or the respiratory tract.
Once inside the body, the foreign agents are carried to the spleen, lymph nodes, or the mucus-associated lymphoid tissue (MALT) where they will come in contact with specialized cells known as antigen presenting cells (APC).

5. STEPS CT…
When the foreign agent encounters the antigen-presenting cells, an immune response is triggered.
These antigen presenting cells digest the engulfed material,and display it on their surface complexed with certain other proteins known as the Major Histocompatibility Class (MHC) of proteins.

6. STEPS..
The T cells must recognize the antigen. Specialized receptors found on some T cells are capable of recognizing the MHC-antigen complexes as foreign and binding to them.

7. Activated T Cells
Fig Activation of T cells requires interaction of T cell receptors
with an antigen that is transported to the surface of the APC
by a MHC protein.

8. CT..
Each T cell has a different receptor in the cell membrane that is capable of binding a specific antigen. Once the T cell receptor binds to the antigen, it is stimulated to divide and produce large amounts of identical cells that are specific for that particular foreign antigen.

9. The T lymphocytes also secrete various chemicals (cytokines) that can stimulate this proliferation. The cytokines are also capable of amplifying the immune defense functions that can eventually destroy and remove the antigen.

10. A subclass of the T cells mature into cytotoxic T cells that can kill cells having the foreign antigen on their surface, such as virus-infected cells, bacterial-infected cells, and tumor cells.

11. CT..
Another subclass of T cells called helper T cells activates the B cells to produce antibodies that can react with the original antigen.

12. CT..
A third group of T cells called the suppressor T cells is responsible for regulating the immune response by turning it on only in response to an antigen and turning it off once the antigen has been removed

13. Some of the B and T lymphocytes become “memory cells,” that are capable of remembering the original antigen.
This is the reason the body develops permanent immunity to an infectious disease after being exposed to it.
This is also the principle behind immunization

14. HUMORAL IMMUNITY
The immune system responds to pathogens by producing soluble proteins called antibodies. Involves the activation of a special set of cells known as the B lymphocytes. They originate in the bone marrow.

15. CT..
The humoral immune response helps in the control and removal of pathogens such as bacteria, viruses, fungi, and parasites before they enter host cells.
The antibodies produced by the B cells are the mediators of this response.
The antibodies form a family of plasma proteins referred to as immunoglobulins.

16. Ct..
They perform two major functions One function of an antibody is to bind specifically to the molecules of the foreign agent that triggered the immune response. A second antibody function is to attract other cells and molecules to destroy the pathogen after the antibody molecule is bound to it.

17. What is happening?
When a foreign agent enters the body, it is engulfed by the antigen-presenting cells, or the B cells. The B cell that has a receptor (surface immunoglobulin) on its membrane that corresponds to the shape of the antigen binds to it and engulfs it.
Within the B cell, the antigen-antibody pair is partially digested, bound to a special class of proteins - MHC-II, and then displayed on the surface of the B cell. The helper T cells recognize the pathogen bound to the MHC-II protein as foreign and becomes activated.

18. These stimulated T cells then release certain chemicals- cytokines (or lymphokines) that act upon the primed B cells (B cells that have already seen the antigen). The B cells are induced to proliferate and produce several identical cells capable of producing the same antibody.

19. Lymphocyte Clones
Fig. 34.2

20. Ct…
The cytokines also signal the B cells to mature into antibody producing cells. The activated B cells first develop into lymphoblast and then become plasma cells, which are essentially antibody producing factories.

21. Ct..
A subclass of B cell they become memory cells that are capable of producing antibodies at a low rate. These cells remain in the immune system for a long time, so that the body can respond quickly if it encounters the same antigen again

22. Humoral Immunity and the Antibodies
Fig Primary and secondary antibody responses

23. The antibody destroys the pathogen in three different
Neutralization, the antibodies bind to the bacteria or toxin and prevent it from binding and gaining entry to a host cell. Neutralization leads to a second process called opsonization.
The antibody bound to the pathogen, macrophages engulf these cells and destroy them- phagocytosis.

24. CT..
The immunoglobulin IgM or IgG can bind to the surface of the pathogen and activate a class of serum proteins called the complement, which can cause lysis of the cells bearing that particular antigen.

25. Mechanism of Action of Antibodies (Indirect)-the Complement System
Antibodies (cont.)
Mechanism of Action of Antibodies (Indirect)-the
Complement System
Fig. 34.6

26. In the humoral immune response, each B cell produces a distinct antibody molecule.
There are over a million different B lymphocytes in each individual, which are capable of recognizing a corresponding million different antigens.

27. CT..
Each antibody molecule is composed of two different proteins (the light chain and the heavy chain), it can bind two different antigens at the same time.

28. Antibodies (cont.)
Fig Structure of the typical IgG antibody

29. Blood, Lymph, B cell surface Cell bound to mast cells and basophils
Antibodies (cont.)
Classes of Antibodies
Class
Structure
Location MW
Half-Life
In Serum
Function
IgG
Monomer
Blood, Lymph, Intestine
170,000
23 days
Phagocytosis, neutralization, crosses placenta
IgM
Pentamer
Blood, Lymph, B cell surface
970,000
5 days
Primary response, phagocytosis, agglutination
IgA
Dimer
Secretions
405,000
6 days
Mucosal ab
IgD
B cell surface
175,000
3 days
Surface Ig on B cells
IgE
Cell bound to mast cells and basophils
190,000
2 days
Allergic Reactions,parasitic reactions

30. Refferences Word of microbiology and immunology vol1&2,Brighan Narins.
Foundation microbiology ,4th edition ,Kathleen Park Talaro.
Guyton and Hall, Textbook of Medical Physiology, 12th edition.
Review of medical microbiology and immunology 10th edition(Vishal).