Download - Lecture 15
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Cellular Immunity
T lymphocyte respond to antigen when they bond to specific antigen called MHC proteins (major histocompatibility complex proteins) on the surface of the antigen presenting cells
T cells do not recognize free antigen but do recognize antigens combined with an MHC protein
MHC: Cell surface molecule that present antigen to T Cell
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•The three major type of antigen presenting cells
1. Macrophages2. B Lymphocyte3. Dendritic cells
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Release of activated T Cell from lymphoid tissue
Once exposed to antigen, T lymphocyte proliferate and release large number of activated, specifically reacting T cell
Whole activated T cells are formed and release into the lymph and circulated throughout the body
T lymphocyte memory cells are formed same way as that B memory cells
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Antigens
bacteria
viruses
ANTIGENS
bacteria
viruses
SPECIFIC DEFENSES
(Immune response)
CELL MEDIATED IMMUNITY
APC’s phagocytize Ag & activate T cells
Direct physical &
chemical attack
Activated T cells clone & differentiate into: Cytotoxic T cells Helper T cells Memory T cells
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Cellular Immunity
Lymphocyte can be divided into two major classes based on cell surface proteins called CD proteins
One class of lymphocyte has CD4 and the other CD8
About one third of all T cells are CD8 and the other two third have CD4
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Activated CD8 cells become cytotoxic T cells
Activated CD4 become Helper T cells CD8 bind to the class I MHC proteins CD4 bind to class II MHC proteins
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T cell CD8 T cell CD4
Minority Majority
Become cytotoxic T cell Most become T helper cell
Binds MHC class I proteins Binds MHC class II proteins
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T Cells Only Recognize Antigen Associated with MHC Molecules on Cell
Surfaces
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Once a T cell is activated by the presentation of the combined MHC/Antigen, it will clone differentiate into:
Activated CD8 cells become cytotoxic T cells – seek out the specific pathogen/infected cell that contains the targeted Antigen and destroys it by secreting various chemicals
Activated CD4 becomes helper T cells – necessary for coordination of both specific & non-specific defenses, as well as for stimulating both cell-mediated & antibody-mediated immunity.
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Helper T cell
1. The most numerous of T cells2. Help regulate immune system by
forming protein called lymphokines, that act on other cells of the immune system
3. Some of lymphokines are:Interleukin-2Interleukin-3 Interleukin-4 Interleukin-5 Interleukin-6
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T-Helper Cell function
1. Forming lymphokinesImmune system is paralyzed in the
absence of lymphokines2. Stimulation of growth and
proliferation of cytotoxic T cells and suppressor T cells
Interleukin-2 has strong effect in causing growth and proliferation of both cytotoxic and suppressor T cells
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3. Stimulation of B cells growth and differentiation
Have direct effect to cause B- cell growth, proliferation, formation of plasma cells and secretion of antibodies
4. Activate macrophage system
They slow / stop the migration of the macrophages after they have attracted to the inflamed tissue
5. Stimulate effect on the helper cells
Interleukin-2 have direct effect in stimulating activation of helper T cells themselves
T-Helper Cell function
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Humoral Response to T Dependent Antigens
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Central Role of Helper T Cells
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Antibody Mediated (Humoral) Immunity
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Review of Immune Response
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Overview of the Immune Response
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Cytotoxic T Cells
Also called Killer cells Capable of killing microorganism and
even some of the body’s own cells Cytotoxic T cell secret whole forming
proteins called perforins that punch holes in the membrane of attacked cell
Cytotoxic T cell releases cytotoxic substance into the attacked cell causing lysis of infected cell
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Cytotoxic T cell recognize and destroy cancer cells
Recognize and destroy transplanted tissue
Undergo apoptosis when stimulating antigen is gone
ApoptosisProgrammed cell death, eliminate cells
that are unneeded, infected or cancerous
Cytotoxic T Cells
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Cytotoxic T Cells Lyse Infected Cells
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Suppressor T cells
They are capable of suppressing the function of both cytotoxic and helper T cell
They serve functions of preventing the cytotoxic cells from causing excessive immune reactions that may damage the body own tissues, this called immune tolerance
Immune ToleranceThe condition of not mounting an immune
response against the antigens that normally found within one’s own body. Lack of self tolerance underlies autoimmune diseases