Cytotoxic T cells

Definition

Cytotoxic T cells, also known as CD8+ T cells, are a subset of T lymphocytes that play a critical role in the immune response by directly killing infected or cancerous cells. They recognize specific antigens presented by major histocompatibility complex (MHC) class I molecules on the surface of target cells, leading to cell death through various mechanisms, including the release of perforin and granzymes. These cells are essential for eliminating intracellular pathogens and maintaining cellular integrity.

5 Must Know Facts For Your Next Test

1. Cytotoxic T cells are activated when their T Cell Receptors (TCRs) recognize specific antigens bound to MHC class I molecules on infected or abnormal cells.
2. Once activated, cytotoxic T cells proliferate and differentiate into effector cells that can effectively kill target cells.
3. They use perforin to create pores in the target cell membrane, allowing granzymes to enter and induce apoptosis, or programmed cell death.
4. Cytotoxic T cells have memory capabilities, enabling a faster and more robust response upon re-exposure to the same antigen in future infections.
5. The balance between cytotoxic T cell activity and regulatory mechanisms is crucial to prevent autoimmunity while ensuring effective immune responses.

Review Questions

• How do cytotoxic T cells recognize and eliminate target cells during an immune response?
  • Cytotoxic T cells recognize target cells through their T Cell Receptors (TCRs), which bind to specific antigens presented by MHC class I molecules on the surface of infected or abnormal cells. Once binding occurs, this activates the cytotoxic T cell, leading to its proliferation and differentiation into effector cells. The activated cytotoxic T cells then release perforin to create pores in the target cell membrane, allowing granzymes to enter and trigger apoptosis, effectively eliminating the infected or cancerous cell.
• Discuss the role of antigen-presenting cells in the activation of cytotoxic T cells.
  • Antigen-presenting cells (APCs), such as dendritic cells, play a vital role in activating cytotoxic T cells by processing and presenting antigens on their surface using MHC class I molecules. When these APCs encounter pathogens, they internalize them, process the proteins, and present fragments as peptides on MHC class I. This interaction is crucial because it provides the necessary signals for naïve CD8+ T cells to become activated, leading them to proliferate and differentiate into effector cytotoxic T cells that can kill infected or malignant targets.
• Evaluate the importance of memory cytotoxic T cells in long-term immunity against infections.
  • Memory cytotoxic T cells are essential for long-term immunity because they allow for a quicker and more efficient response during subsequent exposures to the same pathogen. After an initial infection, some activated cytotoxic T cells differentiate into memory cells that persist in the body. If the same pathogen is encountered again, these memory cytotoxic T cells can rapidly expand and respond more effectively than during the first exposure. This rapid response is crucial for preventing reinfection and controlling infections more effectively, demonstrating the importance of adaptive immunity in protecting against recurring threats.

Related terms

T Cell Receptor (TCR): A molecule found on the surface of T cells that recognizes specific antigens presented by MHC molecules, crucial for T cell activation and function.

Antigen-Presenting Cells (APCs): Cells that process and present antigens to T cells, facilitating the activation of cytotoxic T cells and other immune responses.

Perforin: A protein released by cytotoxic T cells that forms pores in the membranes of target cells, leading to cell lysis and death.