With pleasure burying ourselves in the warm sand on the beach, tearing flowers in the forest, wandering barefoot on the ground and lying on the grass, we hardly think about what a huge and hard work is being carried out at this time by the immune system of the skin. But after all, myriads of microorganisms, allergens, dirt particles, sharp grains of sand and a whole spectrum of a wide variety of chemical compounds are on the skin. Even a cosmetic cream, standing on the shelf in the bathroom, can be an explosive mixture of microbes and aggressive chemicals, increasing the already heavy load on the skin's protective systems. Yes, I have to admit that usually our skin shows amazing stability. And nevertheless, acne and acne can appear on the skin, despite daily washing and rubbing it with alcohol lotion, it can blush and become inflamed from the "hypoallergenic" cream, itch and flake for no apparent reason. At the heart of these unpleasant phenomena lie the same protective reactions that make the skin such a reliable barrier for microorganisms. Of course, we are all interested in ensuring that the skin's defense systems work well, that is, they would prevent external invasions, if possible without an inflammatory response and other visible manifestations of infection control. In other words, a good immune system is one that you can not think about.
The skin is called the largest immune organ. And this is not surprising, because it is easier to prevent an invasion than to fight on its territory. In the skin there are two systems of protection - specific and nonspecific. From the point of view of evolution, the nonspecific system is the oldest. She immediately reacts to any invasion and immediately starts the fight. The main cells of the nonspecific immune system of the skin in the epidermis are keratinocytes and Langerhans cells, in the dermal layer - macrophages. Macrophages not only destroy the enemy, but also coordinate the activity of all cells of the immune system. The macrophage knows how to recognize bacterial cells, because their shell is built of special polysaccharides, which are not found in animals. Once the macrophage is in contact with the bacterial wall polysaccharide (or a substance similar to the bacterial wall polysaccharide), it immediately activates and starts fighting against the border violator.
The specific immune system is different in that it must first recognize the alien, and then memorize it in order to subsequently find and destroy. This ability to remember violators sometimes leads to trouble. The fact is that the cells of the immune system do not remember the whole molecule, but only a small part of it (which plays the role of an identity card). Macrophages react to any stranger, and leukocytes (cells of specific immunity) remember each molecule individually. In this sense, macrophages are like guardians of the order, which is enough to have a passport. And the white blood cells remind the criminal investigation workers who need to check identity documents and make sure that they are not a criminal. The problem is that in the world of molecules, many substances that are different in their chemical nature have the same "identity cards". And when the immune system again and again unfolds the whole arsenal of armed struggle against imaginary offenders, an allergic reaction develops.
The most serious danger of penetration of intruders into the skin occurs when the skin is damaged. Therefore, the main alarm signal for protective skin systems are fragments of cell membranes that inevitably appear when the skin cells are destroyed irrespective of its cause. From the fragments of cell membranes, substances structurally related to steroid hormones are synthesized - prostaglandins. Prostaglandins control the local inflammatory response. Macrophages are attracted to the injury site, which absorb bacteria and other foreign substances, and also throw out signaling molecules that call for the help of other cells. Prostaglandins and substances thrown out by macrophages cause an expansion of the blood vessels of the dermis - the skin turns red. From the dilated blood vessels begins to leave the tissue fluid and white blood cells (leukocytes) - there is swelling and condensation of the skin. Biologically active substances, produced by all these cells, act on the nerve endings of the skin, causing pain and itching.
Every war is destructive, and the war that the immune system leads is no exception. Cells involved in the fight against the border violator, produce many toxic molecules that damage the skin. Some scientists compare leukocytes with nuclear reactors, both useful and dangerous. In leukocytes, a huge number of aggressive and toxic molecules are formed, which are necessary for the destruction of the microbial cell. These molecules are formed as a result of a chain-less-controlled reaction, which at any time can get out of control. Toxic substances produced by leukocytes can destroy them themselves and damage surrounding tissues.
If the resistance that the immune system gives to the offender is commensurate with the scale of the invasion, soon everything will return to normal. Blood vessels shrink, and their walls become less permeable, cells creep away and are carried away by a blood stream, biologically active substances are inactivated, and restoration works begin on the site of destruction.
Disharmony and discord in the activity of cells of the immune system leads to excessive skin damage, allergic reactions, chronic dermatitis. If the defensive reaction was insufficient, the inflammatory reaction is prolonged, and microorganisms can be encapsulated in the deep layers of the skin, periodically renewing attacks.
Normalization of the immune system with the help of cosmetics immunomodulatory action is one of the most interesting and promising directions in cosmetology.
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