Dendritic cells: what they are, their characteristics and functions in the body

The immune system of living things is the body’s natural defense against viral, bacterial and parasitic infections, which also protects against intrinsic events in the body, such as the formation of cancer cells and other deleterious processes. This set of elements allows us to maintain homeostasis (healthy internal balance), based on the recognition and destruction of what is considered harmful.

In general, if we think of the immune system, we accept terms such as lymphocytes and other leukocytes, which are white blood cells circulating in the blood which point to, locate and eliminate the agents that can cause us harm. .

Although lymphocytes are essential for understanding the immune response, they are by no means the only cell bodies involved in eradicating pathogens from our bodies. Today we come to tell you all about dendritic cells, a very interesting cell type exclusive to mammals essential for the innate (non-specific) and acquired immune response at the same time. Don’t miss it.

    What are dendritic cells?

    According to the National Cancer Institute (NIH), a dendritic cell is a specialized cell body type found in tissues such as skin that stimulates immune responses, When presenting / displaying an antigen on its surface before other specialized cells.

    Before continuing, we need to clarify the newly introduced term. For its part, an antigen can be defined as a substance which, when introduced into the body, induces an immune response there, causing the formation of antibodies.

    Antibodies or immunoglobulins are proteins circulating in the blood, the function is to “point” the antigen by adhering to it, so that other cell bodies such as macrophages interpret it as a threat and eliminate it.

    It may be strange to shine a light on these specific terms, but in bridging the gap, the task of an antibody and a dendritic cell are not very different. Either way, let’s not go ahead – it’s time to explore some of the most striking features of this cell type.

    Characteristics of dendritic cells

    Mature dendritic cells (MDCs) have their own morphology, characterized by the presence of membranous extensions that may take the form of stars, pseudopodia or sails. Due to their antigen presenting nature, these cell bodies contain multiple structures specialized in this particular function, such as endosomes, lysosomes or Birbeck granules.

    Endosomes are compartments in the cytoplasm that act as carriers of materials in animal and fungal cells. For their part, lysosomes act as destructive organelles, because they contain hydrolytic and proteolytic enzymes responsible for the degradation of cellular material, either of external origin (heterophagy) or internal (autophagy). Birbeck’s granules, present in the dendritic cells of the epidermis, have a function yet to be discovered.

    These characteristic cell bodies are found in lymphoid (lymphatic system) and non-lymphoid tissues, such as the skin, pharynx, upper esophagus, vagina, anus and mucous membranes, respiratory and intestinal tract. Its “tentacle” shape makes sense, as dendritic cells extend their protrusions between tight cell junctions without altering the nature of the tissue.. As we will see below, this mechanism allows the cell to “cover” more space for antigen uptake.

    Immature dendritic cells are those that have the typical star shape, while patrolling peripheral areas of the body. The dendrites themselves (cytoplasmic processes measuring more than 10 microns and protruding from the body of the cell) are in constant motion within the cells, retracting and spreading again, as if they came from a living being. Of course, the complex morphology of such a small item is impressive.

      The function of dendritic cells

      Dendritic cells were correctly described in 1973 by RM Steinman, a Canadian immunologist, and his colleague ZA. Cohn. In Steinman’s own words, “DCs are the natural sentinels of the immune system” as they decide whether or not to induce an adaptive immune response to the presence of possible pathogens. We explain this very complex process in the simplest way.

      Dendritic cells patrol the tissues of mammals as they search for and detect possible pathogenic antigens. (Viruses, bacteria and parasites) through the various receptors on its surface (PRR). Once the potential threat is identified, the immature CD becomes a mature dendritic cell (CDM), releasing different pro-inflammatory substances involved in the body’s innate response. In addition to this, they also have the ability to capture and break down antigens, through a process called phagocytosis.

      Once the dendritic cell “has” the antigen of the pathogen in its domains, it migrates to the lymph nodes., Where the T lymphocytes are stored. These lymphocytes “recognize” the antigen and activate, proliferate and attack the initial dangerous substance, which is part of the adaptive immune response.

      It is very interesting to know that, among the differentiated lymphocytes, some will be effectors and secretors of cytokines (inflammatory response), but others will remain in the form of memory lymphocytes, that is, they will remember the pathogen antigen to respond more effectively to subsequent occasions.

        immune tolerance

        Beyond all these essential functions, it should be noted that dendritic cells protect us against ourselves. When the T cells first leave the scam, the dendritic cells control them., Destroy carriers of antigens that could cause the immune system to attack.

        Imagine, for example, that the antigen is part of a red blood cell. If this lymphocyte proliferates and makes copies of itself, the effect on the body could be disastrous.

        Dendritic cells, in numbers

        These cells are histologically and functionally fascinating are able to present antigen to lymphocytes without them having come into contact in any way with the pathogen. They are considered to be the main activators of the adaptive immune system, since a single CDM is capable of stimulating, under experimental conditions, 100 to 3000 T lymphocytes.

        In short: immature dendritic cells are those that have cytoplasmic protuberances (dendrites), with which they “search” for almost any tissue for body antigens to present to lymphocytes. Once they detect one, they make it their own and quickly leave the affected tissue, travel through the lymphatic system, and “Warn” lymphocytes agglutinated in lymph nodes to act quickly and precisely. It is without a doubt one of the most fascinating immune mechanisms recorded in mammals.

        Dendritic cells and immunotherapy

        Everything does not remain within a theoretical framework, because the excellence of dendritic cells is a real promise in the medical field. For example, tumor cells have been found to suppress DCs by emitting certain compounds, Trying them to stimulate the production of suppressor T lymphocytes, leukocytes that suppress the activation of the immune system. This allows the tumor to grow freely without the body taking action against it.

        Surprising as it may seem, it has been possible to expose dendritic cells to tumor antigens under laboratory conditions, in order to inject them into the neoplastic patient to reactivate his immune response. It has not been functional in all cases, but it is of course a promising mechanism. If a wide range of efficiency is achieved in this methodology, we might be facing the first vaccine against certain types of cancer. Fascinating, isn’t it?

        summary

        In this article we have presented some very complex concepts, so explaining immune responses without incurring in overly specific terminology is challenging to say the least. If we want you to stick to one idea, it’s this: Dendritic cells patrol our tissues and, when they see a threat, “kidnap” their antigen and migrate to the T cell site, warning those. who must act.

        In addition to that, they also release different inflammatory substances on their own. Therefore, DCs are considered essential for both the innate and adaptive immune response. Of course, spaces like this make us do the real engineering work that is the human body.

        Bibliographical references:

        • Alfaro, C., Oñate, C., Rodríguez, A., Pérez-Gràcia, JL, Fernández de Sanmamed, M., & Melero, I. (2013, December). Dendritic cells specialized in the presentation of exogenous antigens to cytotoxic T lymphocytes. In Annals of the Health System of Navarre (Vol. 36, No 3, pp. 519-537).
        • Dendritic cells, British Society for Immunology. Collected January 9 at https://www.immunology.org/es/public-information/bitesized-immunology/cells/c%C3%A9lulas-dendr%C3%ADticas
        • Definition of dendritic cell, NIH. Collected January 9 from https://www.cancer.gov/espanol/publicaciones/diccionario/def/celula-dendritica.
        • Functions and classification of dendritic cells, University of Cordoba. Collected January 9 at https://helvia.uco.es/xmlui/handle/10396/9467.
        • Vázquez, MB, Sureda, M. and Rebollo, J. (2012). Dendritic cells I: fundamental aspects of their biology and their functions. Immunology, 31 (1): p. 21-30.

        Leave a Comment