Cytotoxic T cells are a vital component of the immune system. They have the remarkable ability to identify and target antigens on infected or abnormal cells. These antigens often originate from intracellular pathogens such as viruses or abnormal proteins cancer cells produce.
Immunological surveillance is the ability of immune cells to monitor and eliminate infected cells with intracellular pathogens, neoplastically transformed cells, and cells with non-self antigens. Cytotoxic T cells and NK cells have different ways of performing immune surveillance. NK cells can recognize and kill infected or abnormal cells without prior activation. They identify cells that lack primary histocompatibility complex class I (MHC-I) or display altered MHC-I expression, providing a broader but less specific immune response. In contrast, cytotoxic T cells require prior specific-antigen activation and can identify and eliminate cells with non-self antigens through a more precise process. The antigens are presented on MHC-I molecules located on the surface of all nucleated cells, enabling cytotoxic T cells to recognize and eliminate cells that pose a threat.
When the T cell receptor (TCR) on the cytotoxic T cell identifies an infected cell, it creates a secure connection based on specific antigens that the infected cell presents using MHC-I molecules. The TCR-MHC-I-antigen complex initiates the cytotoxic process. The next step involves the release of cytotoxic substances by the cytotoxic T cell to destroy the infected cell. One of these substances is perforin, a protein that attaches to the infected cell's plasma membrane and creates pores. These pores disrupt the cell's internal environment, compromising its stability and integrity. The pores created by perforin also serve as entry points for another group of proteins called granzymes. These enzymes enter the infected cell through the pores and trigger a process known as apoptosis, or programmed cell death. All these steps ensure the controlled destruction of the infected cell, preventing the infection from spreading to neighboring cells.
In conclusion, cytotoxic T cells are indispensable to our immune system. Their ability to recognize specific antigens and directly induce cell death allows for precise immune surveillance, distinguishing them from other immune cells like NK cells. Understanding these mechanisms deepens our knowledge of the immune response and could inform future therapeutic strategies for infectious diseases and cancer.
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.
For successful activation, TCRs on naive CD8 T cells must meet their target antigens presented on MHC-I molecules expressed on all nucleated cells.
Additionally, dendritic cells engulf dying virus-infected cells or tumor cells and display these antigens complexed with MHC I for these T cells.
After binding the infected cell, the naive CD8 T cell receives cytokine co-stimulatory signals from a helper T cell, eventually differentiating into a cytotoxic T cell.
This effector T cell releases granules with perforin, creating pores in the membrane of infected cells for cytolysis.
Some granules release granzymes, which enter and rupture the cell via apoptosis.
In some cases like cancer, the cytotoxic cells may also release cytokines that activate apoptotic genes or lymphotoxins to destroy the target cell.
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