In modern medicine, structures such as mast cells are often mentioned. This is a type of white blood cells that, in a mature state, is located in the connective tissues and is part of the immune system.
Of course, some people are interested in more information. What do these structures represent? What are their main functions? How does mast cell degranulation occur? The answers to these questions will be interesting.
general information
Mast cells are one type of granulocyte. For the first time, these structures were described in 1878 in the doctoral dissertation of Paul Erlise. At that time, scientists believed that these cells exist in order to provide nutrition to surrounding tissues (due to the presence of granules in the plasma). That is why they were called mastocytes (mast translated from German means "fatten"). Only later it was proved that cells are part of the immune system.
Mastocytes are similar in structure to basophilic granulocytes. By the way, they come from myeloid stem cells. But if basophils leave the bone marrow fully matured, then mast cells circulate in an immature form and mature only after they exit and implant into the tissue.
Mast cells are concentrated in places that are prone to injuries and infections. For example, there are many around nerves and blood vessels. Mast cells are located in large quantities in the skin, mucous membranes of the lungs, conjunctiva, tissues of the oral cavity and the rest of the digestive tract.
Mast cell structure information
As already mentioned, mast cells are a form of white blood cells, in particular granulocytes. Therefore, their structure is quite usual - a membrane, nucleus, cytoplasm, in which various organelles are enclosed.
On the surface of the membrane there are special recipes that react with E. immunoglobulins. Despite the fact that these cells are small, about 50-300 thousand receptors are located on the wall of each of them. In the cytoplasm of the mast cell there are granules in which biologically active substances accumulate, including proteases, heparin, histamine.
Mast cells: functions
What is the role of these structures in the life of the body? In fact, mast cells (mast cells) perform important functions. Structures are part of the immune system, therefore, provide an appropriate response to infection of tissues. In addition, mast cell degranulation occurs when an allergen enters the body.
Degranulation mechanism
Mast cells are structures that play an important role in the development of the inflammatory process and allergic reactions. The activation process of these structures is called degranulation.
As already mentioned, on the surface of mast cells there are highly specific receptors for immunoglobulins E, which are produced by other cells of the immune system and play the role of antigens. The binding of these proteins and receptors is inevitable - very soon human mast cells become literally stuck with molecules of immunoglobulins.
If the receptor on the mast cell membrane binds to two or more immunoglobulin E molecules (proteins are linked by cross-conjugation), this triggers the degranulation process. Human mast cells are activated, and then a complex of certain mediators is released into the intercellular space, which are normally contained inside the cell granules (hence the name "degranulation").
Causes of degranulation
As already mentioned, mast cells are structures that provide the development of inflammatory and allergic reactions. Degranulation processes can be triggered by various factors, including:
- penetration of allergens into the tissues (substances to which the human immune system is sensitive);
- physical damage to tissues and cells;
- mast cell contact with bacterial pathogens;
- penetration into the body of certain chemicals, including morphine.
Mast cell mediators
As already mentioned, human mast cells secrete a specific set of mediators during degranulation. There are a lot of these substances, and each chemical compound has unique properties. There are several groups of mediators.
- Preformed mediators that have already been synthesized by the cell and contained in cytoplasmic granules. This group includes serine proteases (in particular, chemistry, tryptase), proteoglycans (including heparin, which acts as an anticoagulant), adenosine triphosphate and some chondroitin sulfates. Mediators are also histamine and serotonin (often called the “hormone of happiness”).
- Some cells secrete lysosomal enzymes, including aryl sulfates.
- Eicosanoids, including prostaglandin, thromboxane, leukotriene, are also included in the list of active mediators.
- Some cells release a large number of cytokinins during degranulation, including interleukin, chemokines, fibroblast growth factor, etc.
These are biologically active substances that act in a certain way on the cells and tissues of the human body, triggering a cascade of reactions. For example, it is the action of mediators that causes the appearance of edema in the process of an allergic reaction.
Histamine and its features
Mast cells are important structures that respond to the penetration of potentially hazardous substances into tissues. And one of the important mediators secreted by mast cells is histamine.
This is a biogenic amine, which is called the mediator of immediate allergic reactions. Normally, he is in an inactive, connected state. The amount of free, active histamine increases against the background of various pathological processes, including burns, frostbite, urticaria, anaphylactic shock, hay fever and other allergic diseases. This mediator is distinguished by high activity and acts on various tissues and organs:
- causes a spasm of smooth muscles (including the muscle layer of the bronchi);
- provides expansion of capillaries and, accordingly, a decrease in blood pressure;
- increases the permeability of the capillary walls, leads to stagnation and thickening of the blood;
- causes swelling of the surrounding tissue;
- enhances the secretion of gastric juice by parietal cells ;
- acts on the adrenal medulla, stimulating the synthesis and secretion of adrenaline, which, in turn, leads to a narrowing of the arterioles and an increase in heart contractions.
Mast cell membrane stabilizers
Of course, in the process of degranulation, it is important for the body, as it helps the immune system to cope with various infections. Nevertheless, in some cases, the active release of mediators, including histamine, is dangerous (for example, with anaphylactic shock and other allergic reactions). It is in such cases that mast cell membrane stabilizers are used.
It has been proven that certain substances can block the release of histamine and other allergy mediators. Stabilizers block the conductivity of the channels of the cell membrane for chlorine ions, inhibit oxidative phosphorylation, and also prevent the entry of calcium ions into the cell, which are necessary for degranulation. To the list of such drugs include ketotifen, cromolyn sodium, as well as nedocromil sodium. Medicines containing these substances are used to relieve symptoms of an allergic reaction and normalize the functioning of the immune system.