Theoretical lecture (4) Third Class Microbiology Department (2015-2016)
Assist.Prof.Dr. Ikram Abbas Aboud Al-Samarraae
T-Cell, Activation , Proliferation and Cell Mediated Immunity:The success of immune response depands on the ability of the lymphocytes to recognize
an antigen which have entered into the host .T- cells after activation begins to divide . Itis
divided 2 to 3 times / day for 4 – 5 days generating alarge number of T- cells . The
daughter cell differentiate into effector T- cells and other differentiate into memory T- cells
. lymphocytes that undergo maturation within the Thymus are known as T- Lymphocytes
or T-Cells , Leave the thymus accumulate within paracortex of lymph nodes , lymphoid
sheath of spleen and peyerʼs patches . T-Cells are predominant circulating T- lymphocytes
in peripheral blood .
Among the T- cells , there are two functionally different sub population and each
population has itʼs own surface markers .
1- Helper T- cell promote the immunologic functions of other cell types such as B cell ,
T cytotoxic cells and macrophages .
2- Cytotoxic T-cellplay an important role in killing virus –infected cells and cancer
cells.
Funtions of activated T-Helper( TH) cells :1-Activation and proliferation of T-Cytotoxic cells .
2-Help in the activation of B-cells to produce plasma cells which secrete
immunoglobulins .
3- Regulate the activaties of monocytes , macrophages and other cells of the immune
response .
Cytotoxic T- Cell (TC) activation :Cytotoxic T- (TC) Cells or cytolytic T-Lymphocytes (CTLs) , they play amajor role in
defense against infection .
Funtions of Cytotoxic T (CT) cells :1-Destruction of virus infected cell , leading to the elimination of virus from the host .
2- Destruction of cancer cells .
4- Destruction of cells transplanted organ .
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MemoryT- Lymphocytes :The T cell is activated by itʼs content with the antigen , the Tcell continues to live and
divide many times , some daughter cells become effector T cells . while other daughter cells
become memory T cells . The effector T cells functions are required for the immediate
action against the antigen where as the memory T cell functions are reseved for future
encounters with the similar antigen , if the antigen happens to enter into the host again .
SuppressorT-Lymphocyte :Apart from T- Lymphocytes ,Helper and Cytotoxic subpopulation of T cells , another
subpopulation of T cells
called SuppressorT-Lymphocyte exists ,that suppress the
humoral and cell medi ated immune response .
Natural Killed Cells:Natural Killed Cells alarge granuler Lymphocytes , it is 15% of peripheral blood
Lymphocytes , it is derived from the stem cells in bone marrow , it is donʼt required
thymus for their development , their activity doesnʼt require any exposure to antigen .
T-Cell Proliferation and Differentiation :T cells activation depends on a variety of events , naïve T-cells are activated when they
encounter antigen alone or antigen presenting cell (APC) .Resting T cell must receive 2
signals for activation to occur , signal comes from the T-cell receptor interacting with an
antigen presented on another cell .
Recognition of antigen triggers a set of biochemical pathways in the cell that results in
DNA synthesis and mitosis . Release of IL-2 results in activation of other T cell bearing IL2 receptors . once T cells exposure to antigen , activated then secrete IL-2 and express IL-2
receptor . T cell proliferate and differentiate into effector cells . Proliferating CD4 cells that
can become inflammatory TH1 cells or TH2 cells .
T-Helper 2 (TH2) activated B-cells to make antibody and stimulate humoral immunity ;
in latter case , IL-2 released from the T-Helper cells may help drive the final stages of
activation of CD8T cells :1-Cytotoxic T cells that recognize a foreign peptide (viruses ) . 2-Inflammatory (TH1) T
cell . 3-Helper (TH2) T cells that activated B-cells to secrete antibodies and initiate a
humoral immune response .
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T-Cell Functions in cell mediated immune response:T-Cells have both effectors and regulatory functions:A – Effectors Functions:Cell Mediated Immunity (CMI) reactions are produced mainly against antigen of
intracellular parasite including viruses , fungi ; some protozoa and bacteria .
B- Regulatory Functions:T-Cells play acentral role in regulatory of both humoral ( antibody ) and cell mediated
immunity (cellular ) .
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