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==Cytotoxic T-Cells==
 
==Cytotoxic T-Cells==
Cytotoxic T cells kill virus infected cells where the organisms are contained in the cell cytoplasm. Viruses are obligate intracellular pathogens that use the host cell machinery for pathogen protein synthesis; viral peptides associate with MHC class I and are expressed on the cell surface. [[Lymphocytes#Cytotoxic CD8+|CD8+ cytotoxic T-lymphocytes (CTL)]] recognise the antigen-MHC complex.
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Cytotoxic T cells kill virus infected cells where the organisms are contained in the cell cytoplasm. Viruses are obligate intracellular pathogens that use the host cell machinery for pathogen protein synthesis; viral peptides associate with MHC class I and are expressed on the cell surface. [[T_cells#Cytotoxic_CD8.2B|CD8+ cytotoxic T lymphocytes (CTL)]] recognise the antigen-MHC complex. Cytotoxic T-cells secrete a pattern of cytokines similar to that of TH<sub>1</sub> cells:
* Cytotoxic T-cells secrete a pattern of cytokines similar to that of TH<sub>1</sub> cells.
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*IFN&gamma; but not IL-2. The IFN&gamma shifts the balance of the immune response in favour of TH<sub>1</sub> cells and there is therefore an increased level of T-cell proliferation. The initiation of the immune response via CTL leads to the selective proliferation of CTL which enhances the main mechanism of killing virally-infected cells.  
** 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 cells|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.  
      
===Killing Mechanism===
 
===Killing Mechanism===
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