✔ [ Ссылка ]
✔ [ Ссылка ]
✔ Ask questions here: [ Ссылка ]
Follow us:
▶ Facebook: [ Ссылка ]
▶ Review Us: [ Ссылка ]
• Most cells which have CD8 on their surface become cytotoxic T cells (Tc cells).
• CD8 T cells recognize a foreign antigen when it is presented in conjunction with the protein, MHC-I.
• Nearly all nucleated cells in the body express MHC-I molecules.
• T cells that recognize self-peptides expressed by MHC-I on the surface of healthy cells don't survive in the thymus gland.
• The surviving T cells can therefore recognize:
• Certain tumor cells expressing abnormal proteins that are seen as foreign.
• Transplanted cells that express foreign MHC-I with their specific proteins.
• Body cells infected by viruses which have viral antigen on their surface.
• Binding to antigen presented to it by a foreign, tumor or viral infected cell is not enough for activation.
• Costimulation needed for activation of a cytotoxic T cell is provided by the close association of molecules on the two cell membranes and cytokines released by a Th cell.
• Once the Tc cell is activated, it will proliferate into a clone of identical Tc cells, each expressing the Tc cell receptor of the original cell.
• Most of the offspring cells will differentiate into effector Tc cells.
• The receptors on these cells will bind to the same antigen as the receptor on the original Tc cell.
• Some Tc clones will not become effector cells but will differentiate into memory cells.
• Memory Tc cells will respond rapidly to future exposure to the same antigen.
• Tc cells can therefore eliminate cells which are infected or have become cancerous. They can also act against foreign cells.
• Tc cells kill target cells using two major mechanisms:
• Perforin induced cytolysis
• Tc cells release perforin which creates holes in target cell membranes, causing a target cell to burst.
• Lymphotoxin induced cell death - Tc cells can also secrete lymphotoxin which starts a cascade of events in the target cell, leading to degradation of its DNA and cell death.
