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

•The three major type of antigen presenting cells

1. Macrophages2. B Lymphocyte3. Dendritic cells

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

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

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

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

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

T Cells Only Recognize Antigen Associated with MHC Molecules on Cell

Surfaces

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.

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

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

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

Humoral Response to T Dependent Antigens

Central Role of Helper T Cells

Antibody Mediated (Humoral) Immunity

Review of Immune Response

Overview of the Immune Response

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

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

Cytotoxic T Cells Lyse Infected Cells

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