Anatomy & Organs

Dendritic Cell – Structure, Function & Diseases

Dendritic cell

The dendritic cells are antigen-representing immune cells capable of T-cell activation. They trigger a specific immune response. Because of their guard position in the immune system , they have been discussed in the past as therapeutic agents for diseases such as cancer and multiple sclerosis .

What is the dendritic cell?

The dendritic cells are part of the immune system. Together with monocytes, B-lymphocytes and macrophages , they are among the antigen-presenting cells in the immune system. The group includes several types of immune cells that are distantly related. Based on shape and surface features, two main forms are differentiated: the myeloid and the plasmacytoid dendritic cells.

Sometimes the cell group is also subdivided into follicular dendritic reticulum cells, interdigitating dendritic reticulum cells and so-called Langerhans cells. The fact that they are included in a common group is due to their common tasks, which include in particular the activation of the T cells. Dendritic cells develop from monocytes, or progenitor stages of B and T cells.

Each dendritic cell recognizes and represents specific antigens. Because of their ability to activate T cells, the dendrites are the only immune cells that can trigger a primary immune response. This distinguishes them from other antigen representatives, which are only capable of uptake, multiplication and representation. Colloquially, dendritic cells are known as sentinels of the immune system.

Anatomy & Structure

Immature dendrites in peripheral tissue are star-shaped. They are equipped with more than ten µm long cytoplasmic processes, which can be used for radiation in all directions. Living dendritic cells keep their dendrites constantly moving and thus catch pathogens and antigens . Immature dendritic cells also contain endocytic vesicles made of stainable and lysosomal proteins .In this phenotypic form, the cells have few MHC proteins and no B7 molecules at all. During their migration into the secondary lymphatic organs, the dendritic cells change their anatomy. The dendrites of the cells become membrane protrusions and the cells are no longer capable of phagocytosis or antigen processing. Mature dendritic cells express MHC class II complexes loaded with peptides. They also absorb co-stimulating B7 molecules. The cells interact with T cell receptors via the peptide MHC elements. They bind to CD28 antigens on naïve T cells through the co-stimulating B7 molecules.

Function & Tasks

Dendritic cells are found in almost all peripheral tissues of the human body. In the context of defense against pathogens, the dendritic cells fulfill a guard function. They constantly control their environment. They take up extracellular components by phagocytosis. Phagocytic cells flow around the foreign bodies and carry the individual particles of the foreign bodies through the indentations and constrictions of their cell membrane into the cell.

Large vesicles, also known as phagosomes, form and coalesce with lysosomes to form phagolysosomes. In these phagolysosomes, the absorbed particles of the foreign bodies are broken down enzymatically. With phagocytosis, the dendritic cells process foreign bodies and then represent them in the form of peptides in their MHC complex on the surface. As soon as they come into contact with a foreign body, the dendritic cells migrate out of the affected tissue and embark on their journey to the nearest lymph node . In the lymph nodes they encounter 100 to 3000 T cells with which they interact.

Through direct contact with a T cell, the dendritic cells in the lymph nodes trigger a specific immune response that is precisely tailored to the antigen they present. As immunity mediators, dendritic cells have two main functions: as immature cells, they take up antigens and process them. They become mature cells and, after migrating into the lymphatic tissue, stimulate T and B cells. Thus, they have a controlling function in the cellular immune response. They also help protect against autoimmune reactions because they induce tolerance to so-called self-antigens.

Apoptotic cells are constantly accumulating in the organism and are a source of self-antigens. This makes maintaining immunological self-tolerance difficult. In this context, the dendritic cells are involved in the elimination of the self-reactive T cells.

Diseases

Dendritic cells are believed to play a role in autoimmune diseases as well as allergies and cancer. Cancer cells, for example, evade the body’s own defense mechanisms and have an immunosuppressive effect, so to speak. A reduced function of the dendritic cells is a possible cause in this context. In autoimmune diseases and allergies, on the other hand, the opposite mechanism is present: the dendritic cells overreact in both cases.In the past, these connections have made scientists think of dendritic cells as part of various therapeutic approaches. For example, when considering cancer vaccination, the use of dendritic cells was discussed. Specific and autologous antigen-presenting cells are supposed to trigger an immune reaction in which the activated T-lymphocytes attack the tumor cells. Immunotherapies have been used as secondary therapies for various cancers for years.

In connection with autoimmune diseases, a reduction in dendritic cells was discussed as a therapeutic option. Surprisingly, studies then showed that the intensity of autoimmune diseases even increases after a reduction in dendritic cells. It is not the reduction, but the proliferation of cells that could bring about an improvement in these diseases.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.