T Lymphocytes

Definition

T lymphocytes, or T cells, are a type of white blood cell that play a critical role in the immune response by recognizing and responding to antigens. These cells originate from stem cells in the bone marrow but mature in the thymus gland, where they acquire the ability to distinguish between self and non-self antigens. The recognition of antigens is facilitated by T cell receptors (TCRs) on their surface, which bind to specific antigens presented by Major Histocompatibility Complex (MHC) molecules on other cells.

5 Must Know Facts For Your Next Test

1. There are two main types of T lymphocytes: CD4+ T helper cells, which assist other immune cells, and CD8+ cytotoxic T cells, which directly kill infected or cancerous cells.
2. T cells undergo a process called positive and negative selection in the thymus, ensuring that only those that recognize foreign antigens and do not react strongly to self-antigens are allowed to mature.
3. Upon activation by antigen recognition and co-stimulatory signals, T cells proliferate and differentiate into effector cells that carry out specific immune functions.
4. Memory T cells are generated after an initial infection and remain in the body long-term, enabling a faster and more effective response upon re-exposure to the same antigen.
5. T lymphocytes play a pivotal role not only in fighting infections but also in the pathogenesis of autoimmune diseases when they mistakenly target self-antigens.

Review Questions

• How do T lymphocytes recognize antigens, and what role do MHC molecules play in this process?
  • T lymphocytes recognize antigens through their T cell receptors (TCRs), which bind specifically to antigens presented on the surface of other cells by Major Histocompatibility Complex (MHC) molecules. There are two classes of MHC: Class I molecules present antigens to CD8+ cytotoxic T cells, while Class II molecules present to CD4+ T helper cells. This interaction is crucial for T cell activation and subsequent immune response.
• Discuss the importance of positive and negative selection during T cell maturation in the thymus.
  • Positive and negative selection during T cell maturation is critical for developing a functional and self-tolerant T cell repertoire. Positive selection ensures that only T cells with receptors capable of recognizing self-MHC molecules survive, while negative selection eliminates those that strongly bind to self-antigens, reducing the risk of autoimmunity. This process creates a diverse population of T cells ready to respond to foreign pathogens while minimizing harmful reactions against the body's own tissues.
• Evaluate the role of memory T cells in adaptive immunity and their significance in vaccine responses.
  • Memory T cells are essential for providing long-lasting immunity after an initial exposure to an antigen. They persist in the body and can rapidly respond to subsequent encounters with the same pathogen, leading to a quicker and more effective immune response compared to naive T cells. This characteristic makes them particularly important in vaccine strategies, as vaccines aim to generate memory T cell populations that can protect against future infections by eliciting robust immune responses upon re-exposure.

Related terms

Antigen: A substance that triggers an immune response, typically a foreign protein or polysaccharide found on pathogens or infected cells.

Major Histocompatibility Complex (MHC): A set of molecules displayed on cell surfaces that present antigens to T lymphocytes, essential for T cell activation.

Cytokines:

Signaling molecules produced by immune cells, including T cells, that facilitate communication and coordination of the immune response.