Dendritic Cells: What They Are, Characteristics And Functions In The Body
The immune system of living beings is the body’s natural defense against viral, bacterial and parasitic infections, which also protects against intrinsic events of the organism, 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 about the immune system, terms such as lymphocytes and other leukocytes come to mind, that is, the white blood cells circulating in the blood that signal, locate and eliminate agents that may cause us some type of harm.
Although lymphocytes are essential to understanding the immune response, they are by no means the only cell bodies involved in the eradication of pathogenic elements in our body. Today we come to tell you everything about dendritic cells, a very interesting cell type exclusive to mammals essential for the innate (nonspecific) and acquired immune response, at the same time. Do not miss it.
According to the National Cancer Institute (NIH), a dendritic cell is a type of specialized cell body found in tissues such as skin that stimulates immune responses by presenting an antigen on its surface to other specialized cells.
Before continuing, we must clarify the newly introduced term. For its part, an antigen can be defined as a substance that, when introduced into the body, induces an immune response, causing the formation of antibodies.
Antibodies or immunoglobulins are proteins circulating in the blood, whose function is to “signal” the antigen by adhering to it, so that other cell bodies such as macrophages interpret it as a threat and eliminate it.
It may seem strange to bring up such specific terms but, keeping the distance, the work of an antibody and a dendritic cell are not very different Anyway, let’s not get ahead of ourselves: it’s time to explore some of the most striking characteristics of this cell type.
Mature dendritic cells (mDC) have their own morphology, characterized by the presence of membranous extensions that can take the shape of stars, pseudopodia or veils Due to their antigen-presenting nature, these cell bodies contain multiple structures specialized in this very specific function, such as endosomes, lysosomes or Birbeck granules.
Endosomes are compartments within the cytoplasm that act as transporters of materials within animal and fungal cells. For their part, lysosomes act as destructive organelles, since they contain hydrolytic and proteolytic enzymes responsible for degrading cellular material, whether of external origin (heterophagy) or internal (autophagy). Birbeck granules, present in the dendritic cells of the epidermis, have a function yet to be discovered.
These characteristic cell bodies are present in lymphoid (lymphatic system) and non-lymphoid tissues, such as the skin, pharynx, upper part of the esophagus, vagina, anus and in the mucosal linings of the respiratory and intestinal systems. Its “tentacled” shape has a meaning, since the dendritic cells extend their protrusions between the 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 the capture of antigens.
Immature dendritic cells are those that have the typical stellate shape, while patrolling the peripheral areas of the body. The dendrites themselves (cytoplasmic processes that measure more than 10 μm and that protrude from the cell body) are in continuous movement in the cells, retracting and extending again, as if they were their own living being. Of course, the complex morphology of such a small element is impressive.
The function of dendritic cells
Dendritic cells were properly 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 an adaptive immune response is induced in the presence of possible pathogens. We explain this very complex process in the simplest way.
Dendritic cells patrol mammalian tissues, searching for and detecting potential pathogen antigens (viruses, bacteria and parasites) through the different receptors on its surface (PRR). Once the possible threat is identified, the immature DC becomes a mature dendritic cell (mDC), releasing different proinflammatory substances involved in the body’s innate response. In addition to this, they also have the ability to capture and degrade antigens, thanks to a process called phagocytosis.
Once the dendritic cell “has” the pathogen antigen in its domains, it migrates to the lymph nodes the place where T lymphocytes are stored. These lymphocytes “recognize” the antigen, and activate, proliferate and attack the initial dangerous substance, this being part of the adaptive immune response.
It is very interesting to know that, of the differentiated lymphocytes, some will be effectors and secreters of cytokines (inflammatory response), but others will remain as memory lymphocytes, that is, they will remember the pathogen’s antigen to respond more effectively to it on subsequent occasions. .
Immune tolerance
Beyond all these essential functions, it is worth noting that dendritic cells protect us from ourselves. When T lymphocytes first leave the thymus, dendritic cells control them destroying those carriers of antigens that could cause the immune system to attack itself.
Imagine that, for example, the antigen is part of a red blood cell. If this lymphocyte were to proliferate and generate copies of itself, the effect on the body could be disastrous.
Dendritic cells, in numbers
These cells are fascinating from both a histological and functional point of view, since They are capable of presenting an antigen to lymphocytes without them having had contact with the pathogen in any way They are considered the greatest activators of the adaptive immune system, since a single mDC is capable of stimulating, under experimental conditions, 100 to 3000 T lymphocytes.
In short: immature dendritic cells are those that have cytoplasmic protrusions (dendrites), with which they “search” almost all the tissues of the body for 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 They “warn” the lymphocytes agglutinated in the lymph nodes that they must act quickly and precisely Without a doubt, this is one of the most fascinating immune mechanisms that has been recorded in mammals.
Not everything remains in a theoretical framework, since the excellence of dendritic cells represents true promise in the medical field. For example, Tumor cells have been found to suppress DCs by emitting certain compounds, causing them to stimulate the production of suppressor T lymphocytes, leukocytes that suppress the activation of the immune system. Thus, the tumor can grow freely without the body acting against it.
As surprising as it may seem, it has been possible to expose dendritic cells to tumor antigens in laboratory conditions, in order to inject them into the patient with neoplasia to reactivate their immune response. It has not been functional in all cases but, of course, it is a promising mechanism. Should a broad spectrum of effectiveness be achieved in this methodology, We could be facing the first vaccine against some types of cancer Fascinating, right?
Summary
In this article we have presented very complex concepts, since explaining immune responses without resorting to overly specific terminology is, to say the least, a challenge. If we want you to keep an idea, this is the following: dendritic cells patrol our tissues and, when they observe a threat, they “hijack” their antigen and migrate to the place where the T lymphocytes are, warning them that they must act.
In addition to this, they also release different inflammatory substances on their own. Therefore, DCs are considered essential in both the innate and adaptive immune responses. Of course, spaces like this make us realize what a true work of engineering the human body is.
