CD8+ T cells

Definition

CD8+ T cells, also known as cytotoxic T cells, are a subset of T lymphocytes that play a crucial role in the adaptive immune response by directly killing infected or cancerous cells. They recognize antigens presented by major histocompatibility complex (MHC) class I molecules on the surface of target cells and initiate a cytotoxic response to eliminate these threats.

5 Must Know Facts For Your Next Test

1. CD8+ T cells recognize peptide antigens presented by MHC class I molecules on the surface of infected or cancerous cells, triggering their cytotoxic response.
2. Upon activation, CD8+ T cells release cytotoxic granules containing perforin and granzymes, which induce apoptosis (programmed cell death) in the target cell.
3. CD8+ T cells play a crucial role in the adaptive immune response against intracellular pathogens, such as viruses, and in the immune surveillance and elimination of transformed (cancerous) cells.
4. The clonal selection of CD8+ T cells with specific T cell receptors (TCRs) allows for the rapid expansion of an effective cytotoxic T cell response against a recognized threat.
5. Dysfunction or dysregulation of CD8+ T cell activity can contribute to the development of autoimmune diseases, chronic infections, and cancer immune evasion.

Review Questions

• Explain the role of CD8+ T cells in the context of major histocompatibility complexes (MHC) and antigen-presenting cells.
  • CD8+ T cells, also known as cytotoxic T cells, play a crucial role in the adaptive immune response by recognizing peptide antigens presented by MHC class I molecules on the surface of infected or transformed cells. MHC class I molecules display peptide fragments, including those derived from intracellular pathogens, to CD8+ T cells, allowing them to identify and initiate a cytotoxic response against these threats. This interaction between CD8+ T cells and MHC class I-presented antigens is a key mechanism by which the immune system can detect and eliminate infected or cancerous cells.
• Describe how the cytotoxic function of CD8+ T cells contributes to organ transplantation and rejection.
  • CD8+ T cells are a major contributor to the rejection of transplanted organs. When a foreign organ is transplanted, the recipient's immune system recognizes the transplanted cells as foreign and activates CD8+ T cells to mount a cytotoxic response. The CD8+ T cells recognize peptide antigens presented by the donor's MHC class I molecules and release cytotoxic granules containing perforin and granzymes, which induce apoptosis in the transplanted cells. This cytotoxic activity of CD8+ T cells is a key mechanism underlying acute and chronic rejection of transplanted organs, highlighting the importance of immunosuppressive therapies to prevent rejection and maintain graft survival.
• Analyze the potential implications of CD8+ T cell dysfunction or dysregulation in the context of autoimmune diseases, chronic infections, and cancer immune evasion.
  • Dysregulation of CD8+ T cell activity can have significant implications in various disease states. In autoimmune diseases, CD8+ T cells may mistakenly recognize self-antigens as foreign, leading to the destruction of healthy tissues and the development of autoimmune pathologies. Conversely, in chronic infections and cancer, CD8+ T cells may become dysfunctional or exhausted, impairing their ability to effectively eliminate the persistent threat. This can contribute to the progression of chronic infections and allow cancer cells to evade immune surveillance and continue proliferating. Understanding the complex role of CD8+ T cells in these contexts is crucial for developing targeted therapies to modulate their function and improve clinical outcomes for patients with autoimmune disorders, chronic infections, and cancer.

Related terms

MHC Class I: Major histocompatibility complex (MHC) class I molecules are cell surface proteins that present peptide fragments, including those derived from intracellular pathogens, to CD8+ T cells, allowing them to recognize and respond to infected or cancerous cells.

Cytotoxicity: Cytotoxicity refers to the ability of CD8+ T cells to induce the death of target cells through the release of cytotoxic granules containing perforin and granzymes, which trigger apoptosis (programmed cell death) in the infected or transformed cells.

Clonal Selection:

Clonal selection is the process by which CD8+ T cells with T cell receptors (TCRs) specific to a particular antigen are selectively activated and proliferate, allowing for the rapid expansion of an effective cytotoxic T cell response against the recognized threat.