Immunity is a combination of cellular and humoral means of protecting the body from infectious and tumor diseases. It is realized due to the existence of such cells as lymphocytes, plasmocytes and macrophages. What is it, it is necessary to understand in more detail. The value of these cells is really great for the body and ensuring its vital functions in an aggressive environment.
The origin of macrophages
A macrophage is a bone marrow cell that, after migration from the vascular bed under the action of cytokines, differentiated into a phagocyte. Strictly speaking, macrophages are phagocytes, that is, cells of active immunity that are able to capture antigens and present them on their membranes for plasmocytes. They are also able to phagocytose antigens, eliminating them from the body. A monocyte acts as a precursor of this phagocyte - a bone marrow cell circulating in the blood. It turns into a macrophage after it enters the intercellular space from the vascular bed. Here, under the action of cytokines, its typification occurs.
Macrophage species
Macrophages are a type of white blood cell that cannot be found in blood vessels. They are localized in the interalveolar spaces, in the spleen, among nerve fibers, in the lymph nodes and in the serous membranes. They are also represented in large numbers in the intercellular space of other tissues, where they protect them from antigens. Depending on the localization, some types of macrophages are isolated. Varieties of these cells allow you to track which antigens they have to phagocytize.
The first type of macrophage is a histiocyte. This is the most common type of phagocyte found in many tissues. This is a large cell up to 80 microns in size, which captures bacteria, viruses or foreign bodies and digests them.
The second type is macrophages of lymph nodes. In structure, they differ little from histiocytes and perform similar functions.
Resident Macrophages
The third type is resident macrophages. A special type of phagocyte, which acquire specific features depending on the location. Among the resident alveolar, Kupffer cells, macrophages of the spleen, dendritic cells are distinguished . Alveolar macrophages are located in the alveolar spaces, where bacteria and viruses capture, eliminating them from the internal environment of the body at its border with the air.
In the case of capture of a solid particle, which the enzyme systems cannot split, the macrophage gradually dies. After that, the foreign body again comes into contact with the external environment. New macrophages, like immune cells, are also trying to phagocytize it or form foci of fibrosis around it. This leads to chronic pulmonary diseases, especially among smokers and mining workers.
Kupffer and splenic macrophages
Kupffer cells are a specific type of resident macrophages located in the liver. Their task is to destroy blood cells that are present in the bloodstream for a long time and have lost their significance. The macrophage determines them by the absence of certain membrane antigens that are lost during the life of the cell. Most often, the Kupffer type destroys many white blood cells, tumor blood cells, and red blood cells.
Splenic macrophages, as well as Kupffer macrophages, also eliminate red blood cells and white blood cells from the bloodstream. However, located in the spleen. The macrophages of this organ also capture iron and, having accumulated a sufficient amount of it, migrate to the bone marrow, becoming a feeder cell for growing new red blood cells. This demonstrates an example of the transport function carried out by macrophages. What is it from the point of view of histology? Nothing but a feature of tissue differentiation under the action of cytokines.
Dendritic Resident Macrophages
Macrophage cells located on the border of the epithelium are called dendritic. Their name comes from the presence of many processes by which the cell captures a foreign body and is attached between the cytolemma of other epithelial cells. Dendritic macrophages are located on the border between the vessels and the external environment. In the skin, they are located proximal to the dermis, and in the intestinal and bronchial epithelium eccentrically from the basement membrane.
Structural Features of Macrophages
Considering macrophages (what it is, described above), it is necessary to highlight the key features of their structure. Firstly, they are highly dependent on location. Secondly, they are large. Thirdly, they have mobility and are able to migrate to areas of inflammation where an increased concentration of cytokines is noted. These structural features should be considered in more detail.
So, macrophages differentiate in place depending on the presence of specific cytokines, and therefore, after their transformation, they receive new receptors and functions. That is, their structure varies depending on localization. They also come from monocytes, the largest of the blood cells. Therefore, their sizes from 15 to 80 Ξm are embedded in them even before differentiation into resident macrophages (what it is, described above). After that, new macrophage resident cells can independently divide on the spot, already having their own set of affinity molecules for activating phagocytosis without the participation of cellular immunity.
The third feature of the structure is the ability to independently move towards cytokines. To move, they have knives, also necessary to simplify the formation of the cavity during phagocytosis of a foreign body. They are also able to change their shape, pushing into capillary fenestra. All this makes the macrophage a universal phagocyte, responsible for the direct elimination of foreign bodies of the internal environment of the body.