Cytotoxic T cells, called T killer cells in the Edexcel specification, are the effector cells of the cell-mediated response. They destroy body cells that display a specific non-self antigen, such as virus-infected cells and some cancer cells.How they kill:
1. A T killer cell is activated when its receptor binds a complementary antigen and it receives cytokines from T helper cells. It divides to form a clone.
2. The T killer cells circulate and bind to any body cell displaying the same antigen fragment on its MHC proteins.
3. The T killer cell releases a protein called perforin, which inserts into the cell surface membrane of the target cell and forms pores.
4. Enzymes called granzymes enter through the pores and trigger apoptosis (programmed cell death) of the infected cell. Water and ions also move through the pores, and the cell may burst.
5. The T killer cell detaches and moves on to kill another infected cell.
Killing the infected cell destroys the virus's means of reproduction, because viruses can only replicate inside living cells. Virus particles released from the dying cell are exposed to antibodies and phagocytes. Cells dying by apoptosis break into small fragments that macrophages engulf, so their contents do not leak out and cause inflammation.Because T killer cells destroy the body's own cells, their activity must be controlled. T regulatory cells shut the response down once the infection is cleared.
1. A T killer cell is activated when its receptor binds a complementary antigen and it receives cytokines from T helper cells. It divides to form a clone.
2. The T killer cells circulate and bind to any body cell displaying the same antigen fragment on its MHC proteins.
3. The T killer cell releases a protein called perforin, which inserts into the cell surface membrane of the target cell and forms pores.
4. Enzymes called granzymes enter through the pores and trigger apoptosis (programmed cell death) of the infected cell. Water and ions also move through the pores, and the cell may burst.
5. The T killer cell detaches and moves on to kill another infected cell.
Killing the infected cell destroys the virus's means of reproduction, because viruses can only replicate inside living cells. Virus particles released from the dying cell are exposed to antibodies and phagocytes. Cells dying by apoptosis break into small fragments that macrophages engulf, so their contents do not leak out and cause inflammation.Because T killer cells destroy the body's own cells, their activity must be controlled. T regulatory cells shut the response down once the infection is cleared.