Changes

*One pathway uses the CD95 (death receptor) which  triggers apoptosis in the target cell (usually other T cells)

*One pathway uses the CD95 (death receptor) which  triggers apoptosis in the target cell (usually other T cells)

*The other pathway uses perforins and granzymes which form pores in the target cell membrane causing cell lysis

*The other pathway uses perforins and granzymes which form pores in the target cell membrane causing cell lysis

**Perforins are structurally related to [[Complement*MAC|complement factor C9]]

**Perforins are structurally related to [[Complement#MAC|complement factor C9]]

**Granzymes are proteolytic enzymes that target cell nucleases and cause apoptosis  

**Granzymes are proteolytic enzymes that target cell nucleases and cause apoptosis  

In both cases direct contact is required between the T cell and target cell, and cell killing can take several minutes.</p><p> Cytotoxic T cells secrete a pattern of cytokines similar to that of TH₁ cells i.e. IFN-γ but not IL-2. IFN-γ shifts the balance of the immune response in favour of TH₁ cells giving an increased level of T cell proliferation. The initiation of the immune response via cytotoxic T cells leads to the selective proliferation of cytotoxic T cells enhancing the main mechanism of killing infected cells.</p>

In both cases direct contact is required between the T cell and target cell, and cell killing can take several minutes.</p><p> Cytotoxic T cells secrete a pattern of cytokines similar to that of TH₁ cells i.e. IFN-γ but not IL-2. IFN-γ shifts the balance of the immune response in favour of TH₁ cells giving an increased level of T cell proliferation. The initiation of the immune response via cytotoxic T cells leads to the selective proliferation of cytotoxic T cells enhancing the main mechanism of killing infected cells.</p>