Antigen-Presenting Cells

Definition

Antigen-presenting cells (APCs) are a diverse group of immune cells that play a crucial role in the adaptive immune response by processing and presenting antigens to T lymphocytes, triggering their activation and initiation of an immune response. These cells are central to the link between the innate and adaptive immune systems.

5 Must Know Facts For Your Next Test

1. Antigen-presenting cells, such as dendritic cells, macrophages, and B lymphocytes, internalize and process antigens, then display them on their surface using major histocompatibility complex (MHC) molecules.
2. The presentation of antigens by APCs is a crucial step in activating T lymphocytes, which then orchestrate the adaptive immune response against the recognized threat.
3. Impaired or dysregulated antigen presentation by APCs can lead to autoimmune diseases, where the immune system mistakenly attacks the body's own tissues.
4. In the context of transplantation, differences in MHC molecules between the donor and recipient can trigger a strong immune response, leading to graft rejection.
5. Tumor cells can evade the immune system by downregulating the expression of MHC molecules, preventing effective antigen presentation to T cells.

Review Questions

• Explain the role of antigen-presenting cells in the adaptive immune response.
  • Antigen-presenting cells (APCs) play a central role in the adaptive immune response by processing and presenting foreign antigens to T lymphocytes. These cells internalize and degrade the antigens, then display the antigen-derived peptides on their surface using major histocompatibility complex (MHC) molecules. The presentation of these antigens to T cells triggers their activation, leading to the initiation of the adaptive immune response, which involves the targeted destruction of the recognized threat.
• Describe how the function of antigen-presenting cells is related to diseases associated with depressed or overactive immune responses.
  • Dysregulation of antigen presentation by APCs can contribute to the development of various immune-related diseases. In autoimmune disorders, APCs may mistakenly present self-antigens to T cells, leading to an inappropriate immune response against the body's own tissues. Conversely, in immunodeficiency conditions, impaired antigen presentation by APCs can result in a diminished adaptive immune response, leaving the individual vulnerable to infections. Additionally, in the context of transplantation, differences in MHC molecules between the donor and recipient can trigger a strong immune response mediated by APCs, leading to graft rejection. Lastly, tumor cells may evade the immune system by downregulating the expression of MHC molecules, preventing effective antigen presentation to T cells.
• Analyze the significance of antigen-presenting cells in the context of cancer immunology and the potential for immunotherapeutic approaches.
  • Antigen-presenting cells play a crucial role in cancer immunology and the development of immunotherapeutic strategies. Tumor cells often exhibit altered or reduced expression of MHC molecules, which impairs their ability to present tumor-associated antigens to T cells effectively. This enables cancer cells to evade detection and destruction by the immune system. However, by enhancing the function of APCs, either through the use of cancer vaccines or other immunotherapies, the presentation of tumor antigens to T cells can be improved. This can lead to the activation of a robust adaptive immune response against the cancer cells, potentially leading to their elimination. Understanding the role of APCs in this context is essential for the design and optimization of effective cancer immunotherapies that harness the power of the immune system to combat malignant diseases.

Related terms

Antigen: A molecule or substance that is recognized by the immune system as foreign or potentially harmful, triggering an immune response.

T Lymphocytes: A type of white blood cell that plays a central role in the adaptive immune response, recognizing and responding to specific antigens presented by antigen-presenting cells.

Major Histocompatibility Complex (MHC): A set of genes that encode proteins involved in the presentation of antigens to T cells, essential for the proper functioning of the adaptive immune system.