Antigen-presenting cells

Definition

Antigen-presenting cells (APCs) are a specialized group of immune cells that play a crucial role in the adaptive immune response by capturing, processing, and presenting antigens to T cells. These cells, including dendritic cells, macrophages, and B cells, help initiate and shape the immune response by activating T lymphocytes, which are essential for recognizing and combating pathogens. APCs bridge the innate and adaptive immune systems, ensuring a coordinated and effective response to foreign invaders.

5 Must Know Facts For Your Next Test

1. Dendritic cells are considered the most effective type of APC due to their ability to capture antigens in peripheral tissues and migrate to lymph nodes for T cell activation.
2. APCs can present antigens via both MHC class I and MHC class II molecules, allowing them to activate different types of T cells: CD8+ cytotoxic T cells and CD4+ helper T cells respectively.
3. The process of antigen presentation requires two signals: recognition of the antigen-MHC complex by the T cell receptor and additional co-stimulatory signals provided by the APC.
4. APCs not only present antigens but also produce cytokines that influence the differentiation and proliferation of T cells, shaping the adaptive immune response.
5. The effectiveness of an APC in activating T cells can determine the strength and type of immune response generated, making them key players in fighting infections or diseases.

Review Questions

• How do antigen-presenting cells activate T cells during the immune response?
  • Antigen-presenting cells activate T cells through a two-signal process. First, they present processed antigens bound to MHC molecules on their surface, which is recognized by T cell receptors. The second signal comes from co-stimulatory molecules on the APC interacting with receptors on the T cell. This dual signaling is crucial for fully activating T cells, leading to an effective immune response.
• Discuss the differences between MHC class I and class II molecules in relation to antigen presentation by APCs.
  • MHC class I molecules present antigens derived from intracellular proteins and are recognized by CD8+ cytotoxic T cells, which kill infected or cancerous cells. In contrast, MHC class II molecules present antigens from extracellular sources and are recognized by CD4+ helper T cells, which assist other immune cells. This distinction is important because it helps tailor the immune response according to whether the pathogen is inside or outside of host cells.
• Evaluate the significance of antigen-presenting cells in the context of vaccine development and immunotherapy.
  • Antigen-presenting cells play a critical role in vaccine development and immunotherapy by determining how effectively an immune response is initiated. Vaccines aim to present specific antigens to APCs in a way that mimics natural infection, leading to strong activation of T cells. In immunotherapy, enhancing the function or number of APCs can improve responses against tumors or chronic infections, highlighting their importance in designing strategies for disease prevention and treatment.

Related terms

T cells: A type of white blood cell that plays a central role in cell-mediated immunity, recognizing and responding to specific antigens presented by APCs.

MHC molecules: Major histocompatibility complex (MHC) molecules are proteins on the surface of APCs that present processed antigens to T cells, allowing for their recognition.

Cytokines: Small proteins released by immune cells that facilitate communication between cells and help modulate the immune response, often produced in response to antigen presentation.