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**** Function chiefly in the defence against extracellular bacteria.  
 
**** Function chiefly in the defence against extracellular bacteria.  
 
** Therefore, one of the major biological functions of the activation of either TH subset is cytokine-controlled reactive haematopoiesis.
 
** Therefore, one of the major biological functions of the activation of either TH subset is cytokine-controlled reactive haematopoiesis.
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==Cytotoxic T-Cells==
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* Viruses are intracellular pathogens that use the host cell machinery for pathogen protein synthesis.
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** Viral peptides associate with MHC class I and are expressed on the cell surface.
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*** CD8+ cytotoxic T-lymphocytes (CTL) recognise the antigen-MHC complex.
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* Cytotoxic T-cells secrete a pattern of cytokines similar to that of TH<sub>1</sub> cells.
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** I.e. IFN&gamma; but not IL-2.
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*** The IFN&gamma; shifts the balance of the immune response in favour of TH<sub>1</sub> cells.
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**** There is therefore an increased level of T-cell proliferation.
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***** The initiation of the immune response via CTL leads to the selective proliferation of CTL - enhances the main mechanism of killing of virally-infected cells.
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===Killing Mechanism===
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* The CTl killing mechanism is initiated by direct CTL-target cell contact. 
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* The cells involved bind by antigen/MHC class I-TcR interaction.
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** This results in the CTL's intracellular granules becoming localised to the area of contact.
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*** These granules contain most of the molecules responsible for cytotoxicity.
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* Direct cell contact stimulates the release of the granule contents into the area of contact between the two cells.
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* The granules contain two groups of cytotoxic molecules.
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** Perforin.
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*** Structurally related to the [[Complement - WikiBlood|complement]] component, C9.
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*** Forms pores in the cell membrane.
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** Granzymes.
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*** Proteolytic enzymes.
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*** Target cell nucleases.
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*** Cause programmed cell death.
    
==T-Cell Activation==
 
==T-Cell Activation==
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[[B cell differentiation - WikiBlood|B Cell Development]]
 
[[B cell differentiation - WikiBlood|B Cell Development]]
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[[Lymphocytes - WikiBlood#Cytotoxic CD8+|Lymphocytes - WikiBlood]]
    
<big><center>[[Leukopoiesis - WikiBlood|'''BACK TO LEUKOPOIESIS''']]</center></big>
 
<big><center>[[Leukopoiesis - WikiBlood|'''BACK TO LEUKOPOIESIS''']]</center></big>
 
<big><center>[[Immunology - WikiBlood|'''BACK TO IMMUNOLOGY''']]</center></big>
 
<big><center>[[Immunology - WikiBlood|'''BACK TO IMMUNOLOGY''']]</center></big>
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