Macrophages – division, functions, role in the body. Macrophages and immunity

Macrophages are phagocytic cells whose task is to conduct phagocytosis in the human body, i.e. the process of absorbing and destroying, among others, microorganisms, microorganisms, as well as damaged and dying cells. These are very important cells of the immune system and are classified as white blood cells. They perform many important functions in the human body. Check what is worth knowing about them.

Macrophages – characteristics

Macrophages are food cells that enable migration and phagocytosis, i.e. the absorption and digestion of foreign bodies. Macrophages can receive stimuli sent by lymphocyte products, bacterial metabolites or microorganisms. When an infection begins in our body, macrophages begin to move to this place, which is associated with the appearance of positive leukocyte chemotaxis. It is very important for directing the food cells to areas where inflammation is developing and staying there.

The place where macrophages are formed is the bone marrow. They come from monocytes and are a constituent of white blood cells. Macrophages are the first to protect our body against various pathogenic microorganisms and get rid of dead or cancerous cells. They support the production of compounds that affect the work of the entire immune system. They can be found in various forms and in different places of the human body.

Macrophages – division

Macrophages can be divided according to their functions:

1. resting macrophages – these are macrophages found in all tissues and organs that are at risk of the appearance of foreign bodies or other pathogens;
2. migratory macrophages – these are macrophages that migrate and appear in various places of the body as a response to the inflammation that occurs there. They can turn into migrating macrophages in place of infection under the influence of stimulation. As a result, they appear activated macrophages capable of phagocytosis.

Macrophages can also be classified according to their place of occurrence and the type of tissues in which they appear. According to this criterion, the following can be distinguished:

1. Browicz-Kupffer cellswhich are macrophages settled in the blood vessels of the liver;
2. alveolar macrophageswhich are among the cells of the immune system deposited in the lungs;
3. histiocyty, that is, connective tissue macrophages;
4. osteoklasty, that is, bone tissue macrophages;
5. microglia cells, which are classified as macrophages appearing in the central nervous system;
6. macrophages of lymphatic organs;
7. residual macrophages in the myocardium;
8. synoviocytes, i.e. macrophages residing in the synovial membranes;
9. serous cavity macrophages.

However, if we take into account the heterogeneity of macrophages and the tasks performed by them, two types of macrophages can be distinguished:

1. macrophages M1 – these are classically activated macrophages, which arise as a result of the action of substances related to the presence of bacteria in the human body. They are an intermediary in the immune response and anti-tumor reactions;
2. macrophages M2 – they play the most important role in wound healing processes and stimulate the production of helper lymphocytes. M2 macrophages have well-known immunosuppressive properties that help to suppress the defense reactions of the immune system cells. In addition, they can stimulate the healing of damage and soothe inflammation in the body.

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Macrophages – functions

The primary function of macrophages is to participate in the processes of innate and acquired immunity. They are needed to regulate the immune response. They possess specific surface antigens and produce many known proteolytic enzymes. They are necessary for tissue homeostasis and are consuming.

In addition, macrophages have properties that allow the degradation of dead cells and cell debris. They are also responsible for initiating antibacterial or antiviral responses. They also exhibit phagocytic properties that enable them to destroy microbes and cell breakdown products.

Macrophages in the circulatory system

All defense cells are produced in the bone marrow and continue to enter the blood as monocytes. Importantly, they stay in the circulatory system only for 48 hours. When they mature, they travel from blood to tissues through the endothelium of blood vessels and transform into tissue macrophages. When the human body is attacked by some pathogens, they quickly migrate to the site of infection, where they initiate the phagocytosis process.

Macrophages are responsible for the presentation of the antigen to T lymphocytes, which is important for the proper functioning of the entire immune system. They are the initiator of the inflammatory process and regulate its course. They destroy microbes and initiate tissue reconstruction. Importantly, they can be activated by a signal sent physiologically, i.e. by the body, and pathologically, i.e. caused by external factors. The most potent activator of feeding cells are cytokines, which are released by mast cells and T lymphocytes.

Check it out: Cytokines, or the communication system inside our body

Macrophages in the bone marrow

Macrophages are involved in all early stages of hematopoiesis of stem and progenitor cells. Macrophages settled in the bone marrow regulate the release of hematopoietic cells into the blood circulation. Conversely, when an inflammatory process develops in the body, they have the ability to renew.

Macrophages in the lymph nodes

Lymph node macrophages exist in three distinct subtypes. These are the macrophages of the subcapsular sinus, medullary macrophages and medullary macrophages. They have different functions in the human body. Their task is, among others immediate antigen capture, phagocytosis of lymph pathogens and support of plasma cell function. They are also responsible for absorbing virions that come from certain viruses. In this way, they prevent the spread of infection.

Macrophages in the spleen

Macrophages in the spleen can be found in its marginal zone and red pulp. Their task is mainly to destroy pathogenic microorganisms that can lead to the development of inflammation in the body. Macrophages, which are located in the marginal zone, are responsible for maintaining tolerance to apoptotic cells, and also prevent the spread of inflammation from too much. On the other hand, macrophages located in the red pulp are responsible for cleaning the blood of residual erythrocytes.

Macrophages – neoplasms of the blood system

Cancer cells are the source of numerous chemokines and growth factors. On the other hand, macrophages found in neoplasms produce cytokines, proteolytic enzymes and proteases, which are responsible for the regulation of the tumor development process, the emergence of possible metastases, and also have an immunosuppressive effect. If we are talking about malignant lymphomas, an increased number of M2 macrophages can be observed, and patients with chronic leukemia develop the so-called food-like cells that have properties that stimulate the activation of B lymphocytes.

Macrophages in the lungs

The macrophages in the lungs play important defense functions in the event of a viral infection. However, they can contribute to the so-called a cytokine storm that results from the excess of secreted pro-inflammatory cytokines during severe pulmonary infections. In addition, among pulmonary macrophages, one should distinguish interstitial macrophages and alveolar macrophages, the increased number of which is characteristic of chronic obstructive pulmonary disease, i.e. COPD.

Macrophages – importance for the immune system

Macrophages are the product of the largest cells among white blood cells, or monocytes. They are formed in the bone marrow and circulate in the bloodstream for about 20 hours. After this time, they penetrate the endothelium of blood vessels into tissues, where they are transformed into macrophages. The most important thing for our immunity is phagocytosis, which is the process of macrophages absorbing cells and getting rid of them from the body.

Due to the fact that macrophages get rid of pathogenic or damaged cells, such as cancer cells, our body can properly regenerate and tissues are rebuilt. The purpose of macrophages is:

1. absorb large microorganic particles such as fungi, bacteria or other microorganisms;
2. recognize cells characterized by apoptosis and eliminate dead tissue from the body;
3. take part in the breakdown of red blood cells in the spleen;
4. are responsible for the breakdown and presentation of antigens to lymphocytes;
5. the production of a wide variety of cytokines, including interleukins, interferons and leukotrienes;
6. They participate in the process of wound healing, which is important also for those caused after myocardial infarction, and additionally they minimize local inflammation.

In a well-functioning immune system the task of macrophages is not only to carry out the process of phagocytosiss. They are also responsible for regulating the inflammatory process from start to finish, that is, extinguishing it and removing neutrophils from the site of inflammation. Macrophages are a necessary element of processes that are very important for human health:

1. innate immunity processes – the properties of macrophages include the destruction of bacteria damaged by cancerous tissues and the stimulation of the production of pro-inflammatory cytokines;
2. Acquired immunity processes – these processes include the presentation of absorbed antigen to T lymphocytes and the secretion of interleukin 12, which stimulates the production of T lymphocytes and the production of antigen-specific antibodies.

The life span of macrophages ranges from several hours to even several months. The viability of macrophages depends on the type of immune response in which they are involved.