Costimulation

Definition

Costimulation is the process by which T cells require a second signal, in addition to the specific signal from antigen recognition, to become fully activated. This dual signal ensures that T cells respond appropriately to antigens, preventing unwanted activation and promoting a robust immune response. The importance of costimulation lies in its role in enhancing T cell activation, survival, and differentiation into various functional subsets.

5 Must Know Facts For Your Next Test

1. Costimulation typically involves interactions between CD28 on T cells and B7 molecules (CD80/CD86) on APCs, providing a crucial second signal for T cell activation.
2. Without adequate costimulation, T cells can enter a state of anergy, where they are functionally inactive despite recognizing an antigen.
3. Different subsets of T cells may require distinct costimulatory signals to properly differentiate and function, tailoring the immune response to specific pathogens.
4. Certain immunotherapies, like checkpoint inhibitors, target costimulatory pathways to enhance T cell activation against tumors.
5. Costimulation is not only vital for initial T cell activation but also plays a role in memory formation and long-term immunity.

Review Questions

• How does the interaction between CD28 on T cells and B7 molecules on APCs illustrate the concept of costimulation?
  • The interaction between CD28 on T cells and B7 molecules (CD80/CD86) on antigen presenting cells is a classic example of costimulation. This second signal is crucial for full T cell activation after the initial recognition of an antigen. Without this interaction, T cells may fail to proliferate or produce cytokines effectively, illustrating how costimulation is essential for a robust immune response.
• In what ways does costimulation influence the differentiation of T cell subsets during an immune response?
  • Costimulation impacts the differentiation of T cell subsets by providing specific signals that can lead to distinct outcomes depending on the type of APC and its costimulatory molecules. For example, signals from different costimulatory receptors can guide naive T cells toward becoming helper T cells (Th1 or Th2) or cytotoxic T lymphocytes (CTLs). This tailored differentiation helps ensure an effective immune response that is appropriate for the type of pathogen encountered.
• Evaluate the role of costimulation in developing immunotherapeutic strategies targeting cancer treatment.
  • In cancer treatment, costimulation plays a pivotal role in developing immunotherapeutic strategies such as checkpoint inhibitors. These therapies aim to enhance T cell activation by blocking inhibitory signals or augmenting positive costimulatory signals. By overcoming the mechanisms tumors use to evade immune detection—often through downregulating B7 molecules or other inhibitory pathways—these treatments can restore robust T cell responses against cancerous cells, making them a promising avenue for cancer immunotherapy.

Related terms

Antigen Presenting Cells (APCs): Cells that capture, process, and present antigens to T cells, providing the first necessary signal for T cell activation.

T Cell Receptor (TCR): A complex on the surface of T cells that recognizes specific antigens presented by MHC molecules on APCs.

Cytokines: Signaling molecules produced by immune cells that mediate and regulate immunity, inflammation, and hematopoiesis.