Cytotoxic T Cells-mediated Immune Response

Cytotoxic T cells target body cells infected by viruses, intracellular bacteria, or parasites. They also eliminate cancerous cells and foreign cells introduced during transplants. Their ability to monitor, identify, and eliminate cells presenting non-self antigens is termed immunological surveillance, a critical function in maintaining immune defense.

Cytotoxic T cells recognize infected cells through T cell receptors (TCRs) that bind to target antigens presented on MHC-I molecules, which are expressed on all nucleated cells. This TCR-MHC-I-antigen complex creates a secure connection that initiates the cytotoxic process, enabling precise immune surveillance and cell elimination.

Dendritic cells engulf dying virus-infected cells or tumor cells and display these antigens complexed with MHC-I molecules. This antigen presentation is essential for activating naive CD8 T cells, allowing them to recognize and respond to intracellular threats through the adaptive immune response.

Perforin is a protein released by cytotoxic T cells that attaches to the infected cell's plasma membrane and creates pores. These pores disrupt the cell's internal environment and serve as entry points for granzymes, which trigger apoptosis and ensure controlled destruction of infected cells.

Granzymes are enzymes released by cytotoxic T cells that enter infected cells through perforin-created pores. Once inside, granzymes trigger apoptosis, or programmed cell death, rupturing the cell and preventing infection from spreading to neighboring cells. This process ensures controlled elimination of threats.

After binding an infected cell, naive CD8 T cells receive cytokine co-stimulatory signals from helper T cells. These signals are essential for the T cell to differentiate into an effector cytotoxic T cell capable of releasing granules containing perforin and granzymes to destroy target cells.

Cytotoxic T cells destroy cancer cells through multiple mechanisms. They release granules containing perforin to create membrane pores and granzymes to trigger apoptosis. Additionally, they may release cytokines that activate apoptotic genes or lymphotoxins, ensuring controlled elimination of cancerous cells.