Dendritic Cells - Function & Importance
Dendritic cells are specialised immune cells that act as a bridge between the innate and adaptive immune system, playing a central role in defending the body against pathogens.
Things worth knowing about "Dendritic Cells"
Dendritic cells are specialised immune cells that act as a bridge between the innate and adaptive immune system, playing a central role in defending the body against pathogens.
What are Dendritic Cells?
Dendritic cells (DCs) are highly specialised cells of the immune system belonging to the group of antigen-presenting cells (APCs). They get their name from their characteristic tree-like (dendritic) projections, which increase their surface area and facilitate the uptake of foreign substances. They were first described in 1973 by immunologist Ralph Steinman, who was awarded the Nobel Prize in Physiology or Medicine in 2011 for this discovery.
Dendritic cells are found in virtually all tissues of the body, particularly at sites that are in contact with the outside world, such as the skin, intestinal and lung mucosa, as well as blood and lymphoid organs.
Types of Dendritic Cells
There are several subtypes of dendritic cells that differ in their origin, location, and function:
- Conventional (classical) dendritic cells (cDC): Specialised in antigen presentation and activation of T-lymphocytes. Two subsets, cDC1 and cDC2, perform distinct roles in the immune response.
- Plasmacytoid dendritic cells (pDC): This subgroup produces large amounts of type I interferons and plays an important role in antiviral defence.
- Monocyte-derived dendritic cells: These arise from monocytes during inflammatory reactions and amplify the immune response in inflammatory settings.
- Langerhans cells: A specialised type of dendritic cell found in the epidermis (outer skin layer), forming the first immunological barrier of the skin.
Function and Mechanism of Action
The central task of dendritic cells is to act as sentinels of the immune system by capturing foreign substances (antigens), processing them, and presenting them to T-lymphocytes. This process occurs in several steps:
- Antigen uptake: Immature dendritic cells patrol tissues and capture antigens through phagocytosis, macropinocytosis, or receptor-mediated endocytosis.
- Maturation and migration: After antigen uptake, the cells mature and migrate via lymphatic vessels to the nearest lymph nodes.
- Antigen presentation: In the lymph nodes, they present processed antigen fragments on specialised molecules (MHC class I and MHC class II) to helper T-cells and cytotoxic T-cells.
- Activation of the adaptive immune response: Through presentation and additional co-stimulatory signals, T-cells are activated, leading to a specific, long-lasting immune response.
In addition, dendritic cells play an important role in immunological tolerance by preventing the immune system from attacking the body's own structures (autoimmunity).
Clinical Relevance
Dendritic cells are highly relevant in numerous medical contexts:
- Infectious diseases: They coordinate the early defence against viruses, bacteria, and fungi, and direct the type of immune response mounted.
- Autoimmune diseases: Dysfunction of dendritic cells can contribute to the development of autoimmune conditions such as multiple sclerosis, type 1 diabetes, or rheumatoid arthritis.
- Allergies: Dendritic cells in mucosal tissues influence whether the immune system reacts excessively to harmless substances.
- Cancer research and immunotherapy: Dendritic cells are used in modern cancer immunotherapy. So-called dendritic cell vaccines (DC vaccines) are produced from the patient's own cells, loaded with tumour antigens to stimulate the immune system to fight tumour cells. A well-known example is Sipuleucel-T, approved for prostate cancer.
- Transplantation medicine: They are involved in rejection reactions after organ transplantation and are being intensively researched to promote tolerance to transplanted organs.
Dendritic Cells in Research
Research on dendritic cells has made considerable progress in recent decades. Current research focuses include:
- The development of new mRNA-based vaccines that selectively activate dendritic cells.
- The use of dendritic cells in the treatment of melanoma, leukaemia, and other cancers.
- The role of dendritic cells in HIV infection, as the virus can subvert the function of these cells.
References
- Steinman, R.M. & Cohn, Z.A. (1973): Identification of a novel cell type in peripheral lymphoid organs of mice. Journal of Experimental Medicine, 137(5), 1142-1162.
- Banchereau, J. & Steinman, R.M. (1998): Dendritic cells and the control of immunity. Nature, 392, 245-252.
- World Health Organization (WHO) - Innate Immunity and Vaccine Development. Available at: https://www.who.int
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