Costimulatory Molecules

Definition

Costimulatory molecules are essential proteins found on the surface of antigen-presenting cells (APCs) that provide a second signal necessary for T cell activation and function. This second signal is critical in the immune response, ensuring that T cells are fully activated only when there is a legitimate threat, such as an infection. The interaction between costimulatory molecules on APCs and their receptors on T cells helps to amplify the immune response and maintain tolerance to self-antigens, connecting the innate and adaptive immune systems.

5 Must Know Facts For Your Next Test

1. Costimulatory signals are typically provided by molecules such as CD80/CD86 on APCs binding to CD28 on T cells, essential for full T cell activation.
2. Without costimulatory signals, T cells may become anergic (inactive) or undergo apoptosis (programmed cell death), which prevents unnecessary immune responses.
3. Costimulatory molecules also play a significant role in the development of memory T cells, which are crucial for long-term immunity.
4. Different types of costimulatory molecules can influence the type of immune response that occurs, whether it be Th1, Th2, or regulatory T cell differentiation.
5. Understanding costimulatory molecules has important implications in immunotherapy and vaccine development, as they can enhance or modulate immune responses.

Review Questions

• How do costimulatory molecules influence the activation and differentiation of T cells?
  • Costimulatory molecules are vital for T cell activation as they provide the necessary second signal after the initial antigen recognition by T cell receptors (TCR). The interaction between costimulatory proteins on antigen-presenting cells (APCs) and receptors like CD28 on T cells leads to complete activation. This process not only promotes proliferation but also influences the differentiation of T cells into specific subtypes that tailor the immune response based on the nature of the pathogen.
• What role do costimulatory molecules play in maintaining self-tolerance within the immune system?
  • Costimulatory molecules help ensure that T cells are activated only in response to legitimate threats. When self-antigens are presented without adequate costimulation, T cells may become anergic or undergo apoptosis, thus preventing autoimmunity. This mechanism is crucial for self-tolerance as it prevents inappropriate activation of T cells against the body’s own tissues while still allowing a robust response against pathogens.
• Evaluate the implications of manipulating costimulatory pathways in cancer immunotherapy.
  • Manipulating costimulatory pathways in cancer immunotherapy presents opportunities for enhancing anti-tumor responses. For instance, agents that provide additional costimulatory signals can boost the effectiveness of existing therapies by promoting stronger activation and proliferation of tumor-specific T cells. Conversely, inhibiting certain costimulatory interactions could help dampen excessive immune responses or promote tolerance in cases where there is a risk of autoimmunity. Thus, understanding and targeting these pathways can lead to more effective and personalized cancer treatment strategies.

Related terms

Antigen-Presenting Cells (APCs): Cells that process and present antigens to T cells, playing a key role in initiating an adaptive immune response.

T Cell Receptors (TCR): Molecules on the surface of T cells that recognize specific antigens presented by APCs, triggering T cell activation.

Cytokines: Small proteins released by cells that mediate and regulate immunity, inflammation, and hematopoiesis, often produced in response to costimulatory signals.