Cytotoxic T Lymphocyte (CTL)

Definition

Cytotoxic T lymphocytes, also known as CD8+ T cells, are a specialized subset of T cells that play a crucial role in the adaptive immune response by directly killing infected or cancerous cells. They are a key component in the major histocompatibility complex (MHC) and antigen-presenting cell (APC) pathways.

5 Must Know Facts For Your Next Test

1. Cytotoxic T lymphocytes recognize and kill cells that display foreign or abnormal peptides on their surface, such as those infected with viruses or transformed by cancer.
2. CTLs undergo a process of clonal selection and expansion, where they proliferate and differentiate upon recognition of their specific antigen presented by MHC class I molecules.
3. The binding of the T cell receptor (TCR) on the CTL to the MHC-peptide complex on the target cell triggers the release of cytotoxic granules, containing perforin and granzymes, which induce apoptosis in the target cell.
4. CTLs play a crucial role in the clearance of intracellular pathogens, such as viruses, and the elimination of cancerous cells that have evaded other immune mechanisms.
5. The activation and function of CTLs are tightly regulated to prevent autoimmunity, with co-stimulatory and inhibitory signals controlling their response.

Review Questions

• Explain the role of cytotoxic T lymphocytes (CTLs) in the adaptive immune response.
  • Cytotoxic T lymphocytes (CTLs) are a specialized subset of T cells that play a crucial role in the adaptive immune response by directly killing infected or cancerous cells. They recognize foreign or abnormal peptides presented on the surface of target cells by MHC class I molecules. Upon recognition of their specific antigen, CTLs undergo clonal selection and expansion, and then release cytotoxic granules containing perforin and granzymes, which induce apoptosis in the target cell. This allows CTLs to effectively clear intracellular pathogens, such as viruses, and eliminate cancerous cells that have evaded other immune mechanisms.
• Describe the relationship between cytotoxic T lymphocytes (CTLs) and the major histocompatibility complex (MHC).
  • The major histocompatibility complex (MHC) plays a crucial role in the activation and function of cytotoxic T lymphocytes (CTLs). MHC class I molecules present peptide fragments, including those derived from intracellular pathogens or abnormal self-proteins, to the T cell receptor (TCR) on CTLs. This MHC-peptide complex recognition triggers the activation of the CTL, leading to the release of cytotoxic granules and the subsequent killing of the target cell. The specificity of the CTL response is determined by the unique TCR-MHC-peptide interactions, which allow the immune system to distinguish self from non-self and mount an appropriate cytotoxic response against infected or transformed cells.
• Analyze the importance of the interplay between cytotoxic T lymphocytes (CTLs) and antigen-presenting cells (APCs) in the adaptive immune response.
  • The interplay between cytotoxic T lymphocytes (CTLs) and antigen-presenting cells (APCs) is crucial for the effective functioning of the adaptive immune response. APCs, such as dendritic cells, macrophages, and B cells, are responsible for processing and presenting foreign or abnormal peptides on their surface via MHC class I molecules. These MHC-peptide complexes are then recognized by the T cell receptor (TCR) on CTLs, triggering their activation and proliferation. The activated CTLs can then directly kill the target cells displaying the recognized peptide. This coordinated effort between APCs and CTLs allows the immune system to mount a targeted and efficient cytotoxic response against infected or transformed cells, playing a vital role in the clearance of intracellular pathogens and the elimination of cancerous cells.

Related terms

T Cell Receptor (TCR): The T cell receptor is a protein complex found on the surface of T cells that recognizes specific antigens presented by MHC molecules, triggering the activation of the T cell.

Major Histocompatibility Complex (MHC):

The major histocompatibility complex is a group of genes that encode proteins responsible for presenting antigenic peptides to T cells, allowing the immune system to distinguish self from non-self.

Antigen-Presenting Cell (APC): Antigen-presenting cells, such as dendritic cells, macrophages, and B cells, are responsible for processing and presenting foreign antigens to T cells, activating the adaptive immune response.