CD8+ T cells

Definition

CD8+ T cells, also known as cytotoxic T lymphocytes, are a subset of T cells that play a crucial role in the immune response by directly killing infected or cancerous cells. They recognize antigens presented by Major Histocompatibility Complex (MHC) class I molecules and are essential for the adaptive immune response, helping to maintain the body's defenses against intracellular pathogens and tumors.

5 Must Know Facts For Your Next Test

1. CD8+ T cells develop from precursor cells in the bone marrow and mature in the thymus, where they undergo selection to ensure self-tolerance.
2. Upon activation by recognizing a specific antigen presented on MHC class I molecules, CD8+ T cells can proliferate and differentiate into effector and memory T cells.
3. Effector CD8+ T cells utilize perforin and granzymes to induce apoptosis in target cells, effectively eliminating infected or malignant cells.
4. Memory CD8+ T cells provide long-lasting immunity, allowing for a quicker and stronger response upon re-exposure to the same antigen.
5. CD8+ T cell dysfunction can contribute to various autoimmune disorders, where they may attack healthy tissues instead of just infected or abnormal cells.

Review Questions

• How do CD8+ T cells recognize their target antigens, and what role do MHC class I molecules play in this process?
  • CD8+ T cells recognize their target antigens through the T cell receptor (TCR), which specifically binds to peptide fragments presented by MHC class I molecules on the surface of nearly all nucleated cells. This interaction is critical for the activation of CD8+ T cells because it allows them to identify and respond to intracellular infections or malignancies. The presence of MHC class I is essential for CD8+ T cell recognition, as it serves as the platform for displaying the processed antigens derived from pathogens or abnormal cell processes.
• Discuss the differences between effector and memory CD8+ T cells in terms of function and longevity within the immune system.
  • Effector CD8+ T cells are activated T lymphocytes that actively seek out and destroy infected or cancerous cells through mechanisms like apoptosis induction using perforin and granzymes. In contrast, memory CD8+ T cells arise after the resolution of an infection and persist long-term in the body. They remain vigilant for future encounters with the same antigen, allowing for a faster and more robust immune response upon re-exposure. While effector CD8+ T cells have a short lifespan due to their role in immediate defense, memory CD8+ T cells provide lasting immunity.
• Evaluate how dysfunction in CD8+ T cell activity can lead to autoimmune disorders and what mechanisms are involved.
  • Dysfunction in CD8+ T cell activity can result in an inappropriate immune response where these cytotoxic T cells mistakenly target and attack healthy tissues rather than solely infected or malignant cells. This misdirection may be influenced by factors such as molecular mimicry, where foreign antigens closely resemble self-antigens, leading to confusion in recognition. Additionally, chronic activation due to persistent antigen presence can drive autoreactivity. The consequences of such dysfunction manifest in various autoimmune disorders, where tissue damage occurs as a result of misguided immune attacks.

Related terms

MHC Class I:

A type of Major Histocompatibility Complex molecule found on nearly all nucleated cells, responsible for presenting endogenous antigens to CD8+ T cells.

Antigen-Presenting Cells (APCs):

Cells that process and present antigens to T cells, including dendritic cells, macrophages, and B cells, facilitating T cell activation.

Cytokines:

Signaling molecules produced by immune cells that mediate and regulate immune responses, including the activation and differentiation of CD8+ T cells.