Macrophages: What They Are, Characteristics And Functions
The immune system enables the life of anatomically complex living beings on the planet All animals are open systems, since we require the input of energy in the form of organic matter, oxygen in the air and an infinite number of nutrients to develop our metabolic functions.
For all these reasons, the digestive and respiratory systems are exposed to the outside, since they communicate directly with the environment through the nasal passages and the mouth, respectively.
These routes of entry of gases and matter are a free track for thousands of viruses, bacteria, protozoa and helminths, which establish themselves in the mucous membranes of the tracts and, sometimes, travel through the circulatory system and invade even the interior of the cells. . To avoid the certain death of the host in the event of a pathogenic infestation, the immune system acts with various biological barriers.
From the skin to lymphocytes, there are a series of mechanisms that prevent the proliferation of microorganisms in our body, in one way or another. The primary barriers (skin, mucous membranes, saliva, sweat and cough) prevent the entry of pathogens, but when these are established for any reason, a series of cell bodies belonging to the “innate immune system” come into action, working in a general and rapid against invasions. Macrophages are one of the most important cell bodies in this process, and here we tell you everything about them.
Macrophages are some cell bodies of an immune nature that derive from blood monocytes , which in turn are produced in the bone marrow by specialized precursors. It should be noted that, unlike other circulating elements, these cells have a quite marked polymorphism, since they are spherical, ovoid and polygonal in shape, with a total diameter of about 12-15 microns. They also have an ovoid and almost empty nucleus, with very little chromatin.
Originating from monocytes, macrophages leave the circulation to establish themselves and differentiate into different tissues. These cell bodies are found in virtually all areas of the body, and Its main function is to phagocytize and digest any biological agent that is interpreted as dangerous or foreign to the organism In addition, it should be noted that there are several types depending on their location:
Features
As you can see, macrophages kill pathogens, but also the body’s own cells that are useless or too old Below, we explore some of the general functionalities of macrophages and their most striking characteristics. Do not miss it.
1. Phagocytosis
As its name indicates (macro, large and phage, eat, “big eater”), the main function of macrophages is to phagocytose all foreign bodies that enter the body, such as bacteria and metabolic waste substances.
Neutrophils (the most abundant white blood cells in the circulatory system, representing 70% of the total) are the first to reach the source of infection, but their lifespan is very short, from a few hours to a couple of days at most. The presence of neutrophils as the first internal defense barrier stimulates macrophages, which will go to the site of action and they will begin by phagocytosing the dead neutrophils themselves.
Once they have encountered the pathogen, the macrophage surrounds it with a phagosome or endocytic vesicle, a vacuole formed around a particle assimilated by phagocytosis, which then fuses with a lysosome internalized in the phagocytic cell, giving rise to a “phagolysosome.” ”. Finally, various enzymes and toxic peroxides act on the microorganism enclosed in the phagolysosome and destroy it.
2. Activation of the immune system
The macrophage destroys the threat located in the specific tissue, but its function does not end there. The metabolic remains resulting from the digestion of the microorganism are exposed in specific parts of the cell membrane of the phagocyte, which allows the identification of the threat by T helper lymphocytes
We are not going to focus on complex immune cascades, since it is enough for us to know that the recognition and multiplication of lymphocytes promotes the circulation of immunoglobulins (or antibodies). These antibodies recognize antigens on the surface of living microorganisms and adhere to them, acting as clear threat signalers. Thus, the rest of the macrophages know who to attack accurately and other cell bodies get started to stop the infective event.
The immune system is supposed to be divided into two aspects: “innate” and “acquired.” Macrophages are part of the innate mechanisms, but as you can see, the acquired immune system could not exist without them This makes us draw two very clear conclusions:
3. Tissue repair
Beyond the ingestion of foreign compounds, macrophages also play an essential role in wound healing and tissue regeneration.
When an injury occurs, platelets are among the first circulating structures to reach the open area, since their function is to induce coagulation as quickly as possible, in order to maintain internal homeostasis.
Attracted by platelet growth factors monocytes come through the bloodstream to the wound, with the help of the walls of fine vessels and capillaries.
These mature rapidly into macrophages, whose function is keep at bay any bacteria or pathogen that tries to enter through the bleeding opening to the environment They are also responsible for getting rid of dead tissue (through the release of proteases), which “makes room” for rapid and effective tissue regeneration.
Macrophages and cancer: a double-edged sword
As it could not be otherwise, we must dedicate a few last lines to the role of these immune cells in the development of malignant neoplasms, since cancer is one of the most serious health problems worldwide today.
Unfortunately, the information is discordant in this area, and much less positive than one might expect. According to studies such as “Macrophage diversity enhances tumor progression and metastasis”, published in the journal Cell, macrophages can promote and accelerate the growth and metastasis of cancer cells , contrary to what one might expect. The inflammatory events that they cause in the initial stages promote cell mutation to malignant strains, but in addition, they also stimulate the migration and proliferation of already cancerous cells, even inhibiting antitumor mechanisms.
We go even further, since the high number of macrophages in a tumor is positively correlated with a worse prognosis in many types of cancer, such as breast, cervical, brain or prostate cancer. Although not all the mechanisms that promote this very problematic symbiosis are yet understood, this reality undoubtedly puts into perspective that, Sometimes the human body kills itself without the help of exogenous factors
Summary
As we have seen, macrophages are essential cells for both innate and acquired immune responses, as well as for tissue repair and maintenance of hemostasis, among many other things. Furthermore, its study and characterization could help us better understand why malignant tumors arise, since there seems to be a clear relationship between macrophages and cancer cells.
The future of cancer therapy is promising, since the current intention is to use these macrophages as true “Trojan horses.” Due to their relationship with tumor cells, they could serve as reservoirs for anticancer drugs, even as an object of study to develop targeted antitumor therapies.
