The human immune system: a biological antivirus. Heuristic Algorithms
Good time of day, dear habr-community!
This is my first post on Habré, so I beg you, do not judge too harshly.
I suppose you all saw numerous commercials about vulnerable immunity, and everyone remembers school lessons that told about phagocytes that devour bacteria. However, the body's immune system is a complex mechanism designed to protect the owner from any danger. And the dangers can be very different. I would like to try to talk about how the immune system detects these dangers, how it fights with them, and how all this can be regulated and used.
What is immunity and what it eat
')
Actually, the primary task of the immune system is to determine what is dangerous and what is not. The problem is that it is not always obvious. Our body has many open ports: it must absorb food, air, water, remove waste. In addition, we are bad enough admins and every now and then create new vulnerabilities, for example, when you cut or even bruise! And through each such open port there is a huge amount of traffic, sometimes just unnecessary, and sometimes dangerous.
The immune system is an antivirus that scans everything that has come (and at the same time the whole body) and removes viruses, as well as bacteria, fungi and everything else. Sometimes she does not cope with the task, and the person falls ill. Sometimes there is a bug in the immune system itself, and then the person suffers from immunodeficiency (not acquired, but one of the many congenital). And sometimes a false positive occurs, and then either an allergy can develop (if the immune system responds to unauthorized traffic) or an autoimmune disease like lupus (if elements of the body were taken for the virus).
What are the ways the immune system will detect viruses? The simplest, oddly enough, is to use one of the long-developed heuristic algorithms. It is much more difficult to use the base - no one will write it, you have to generate it yourself!
Heuristic algorithms - innate immunity
There are three main congenital mechanisms for detecting infection: the detection of a foreign one, the fixation of a hazard, or the absence of a special marker. In fact, in pure form, none of them is found, and the immune system uses all three to eradicate the enemy.
foreign
This theory was put forward in 1989 by the British immunologist Charles Janeway. It is about the fact that the evolution of the immune system has led to the ability to recognize some of the characteristic molecular features that are often found among pathogens, but absent in the normal body.
This hypothesis was experimentally confirmed in 1997, when a protein called toll-like receptor 4 (TLR4) was discovered. Mice that did not have this protein did not respond to endotoxins of gram-negative bacteria, but at the same time were very vulnerable to a number of infections.
As it turned out later, toll-like receptors are a whole family of sensitive sensors that recognize various elements of microbes. For example, TLR4 is able to recognize lipopolysaccharides, elements of the cell wall of some bacteria; TLR5 is flaggelin, from which bacterial (and only bacterial) flagella are made, and TLR7 is generally located inside the cell and responds to single-stranded RNA molecules characteristic of viruses.
In addition to the TLR family, a number of proteins are responsible for recognizing extraneous intruders. For example, mannose-binding lectin recognizes mannose sugar molecules on the surface of the pathogen, dektin-1 responds to fungi, and RIG-1, like TLR7, is inside the cell and responds to viral RNA.
danger
It all looks just fine, but American scientist Polly Matzinger posed a completely logical question: “Lactation in women begins in adulthood, and milk proteins are foreign to the immune system. So why doesn't the immune system react to them? ”As a response, a new theory was proposed - the theory of danger.
The cells in our bodies die constantly, much more often than the files in the / tmp folder are deleted. However, normally the body does not bother. Normally dying cells cease to exist by apoptosis - a complex, almost samurai cell suicide ceremony. In this case, the cell membrane, which has a consistency close to the consistency of the oil film, disintegrates, forming peculiar bags for the corpses in which the former contents of the cell are enclosed. On the other hand, in the event of injury, whether it is cut, bruised, frostbite, or an acid burn, the cells burst (this is called necrosis), throwing its contents into the bloodstream. According to Polly's theory, it is this appearance of cellular proteins in the blood that should trigger an immune response.
In addition to the necrosis factor, there are other danger signals. In 2003, it was discovered that cells under stress emit uric acid crystals into the extracellular space, which also stimulates the immune response. Other examples of this kind include fragments of the extracellular matrix, heat shock proteins, and so on. That is why a scratch / burn is accompanied by redness, pain and swelling (albeit small), even if there is no infection - the immune system loads the processor, filtering traffic, as they received an anonymous message about the threat of a virus attack.
no marker
In 1992, it was shown that the long-known cells called natural killers (not to be confused with T-killers), who are responsible for fighting tumors, need constant restraint in order not to start attacking everything around them. The mechanism of this suppression is the molecules of the major histocompatibility complex (MHC I). Normally, these molecules are on the surface of any cell in the body, but in tumors, the production of these molecules can be stopped. Also, the synthesis of MHC I can be blocked by some viruses (for example, adenovirus or cytomegalovirus). In all these cases, the killer cell attaches to special receptors on the surface of the victim cell and, not finding the MHC molecules, injects poison into the victim, leading to apoptosis - cell death.
Either way, the immune system can recognize most pathogens. However, this recognition in most cases is not too fast and not very effective. To improve sensitivity and performance, the immune system can create its own anti-virus database using T-and B-lymphocytes. I will try to tell about it in the following part if it seems to someone interesting.
Thanks for attention!
Ps The authorship of this article (as well as possible follow- ups ) belongs to Ivan Stetsenko aka stetzen , who now has an account on Habré (thanks, markmariner !)
UPDATE: thanks for the karma, moved to Biotechnology.
UPDATE2: continued from the author.
This is my first post on Habré, so I beg you, do not judge too harshly.
I suppose you all saw numerous commercials about vulnerable immunity, and everyone remembers school lessons that told about phagocytes that devour bacteria. However, the body's immune system is a complex mechanism designed to protect the owner from any danger. And the dangers can be very different. I would like to try to talk about how the immune system detects these dangers, how it fights with them, and how all this can be regulated and used.
What is immunity and what it eat
')
Actually, the primary task of the immune system is to determine what is dangerous and what is not. The problem is that it is not always obvious. Our body has many open ports: it must absorb food, air, water, remove waste. In addition, we are bad enough admins and every now and then create new vulnerabilities, for example, when you cut or even bruise! And through each such open port there is a huge amount of traffic, sometimes just unnecessary, and sometimes dangerous.
The immune system is an antivirus that scans everything that has come (and at the same time the whole body) and removes viruses, as well as bacteria, fungi and everything else. Sometimes she does not cope with the task, and the person falls ill. Sometimes there is a bug in the immune system itself, and then the person suffers from immunodeficiency (not acquired, but one of the many congenital). And sometimes a false positive occurs, and then either an allergy can develop (if the immune system responds to unauthorized traffic) or an autoimmune disease like lupus (if elements of the body were taken for the virus).
What are the ways the immune system will detect viruses? The simplest, oddly enough, is to use one of the long-developed heuristic algorithms. It is much more difficult to use the base - no one will write it, you have to generate it yourself!
Heuristic algorithms - innate immunity
There are three main congenital mechanisms for detecting infection: the detection of a foreign one, the fixation of a hazard, or the absence of a special marker. In fact, in pure form, none of them is found, and the immune system uses all three to eradicate the enemy.
foreign
This theory was put forward in 1989 by the British immunologist Charles Janeway. It is about the fact that the evolution of the immune system has led to the ability to recognize some of the characteristic molecular features that are often found among pathogens, but absent in the normal body.
This hypothesis was experimentally confirmed in 1997, when a protein called toll-like receptor 4 (TLR4) was discovered. Mice that did not have this protein did not respond to endotoxins of gram-negative bacteria, but at the same time were very vulnerable to a number of infections.
As it turned out later, toll-like receptors are a whole family of sensitive sensors that recognize various elements of microbes. For example, TLR4 is able to recognize lipopolysaccharides, elements of the cell wall of some bacteria; TLR5 is flaggelin, from which bacterial (and only bacterial) flagella are made, and TLR7 is generally located inside the cell and responds to single-stranded RNA molecules characteristic of viruses.
In addition to the TLR family, a number of proteins are responsible for recognizing extraneous intruders. For example, mannose-binding lectin recognizes mannose sugar molecules on the surface of the pathogen, dektin-1 responds to fungi, and RIG-1, like TLR7, is inside the cell and responds to viral RNA.
danger
It all looks just fine, but American scientist Polly Matzinger posed a completely logical question: “Lactation in women begins in adulthood, and milk proteins are foreign to the immune system. So why doesn't the immune system react to them? ”As a response, a new theory was proposed - the theory of danger.
The cells in our bodies die constantly, much more often than the files in the / tmp folder are deleted. However, normally the body does not bother. Normally dying cells cease to exist by apoptosis - a complex, almost samurai cell suicide ceremony. In this case, the cell membrane, which has a consistency close to the consistency of the oil film, disintegrates, forming peculiar bags for the corpses in which the former contents of the cell are enclosed. On the other hand, in the event of injury, whether it is cut, bruised, frostbite, or an acid burn, the cells burst (this is called necrosis), throwing its contents into the bloodstream. According to Polly's theory, it is this appearance of cellular proteins in the blood that should trigger an immune response.
In addition to the necrosis factor, there are other danger signals. In 2003, it was discovered that cells under stress emit uric acid crystals into the extracellular space, which also stimulates the immune response. Other examples of this kind include fragments of the extracellular matrix, heat shock proteins, and so on. That is why a scratch / burn is accompanied by redness, pain and swelling (albeit small), even if there is no infection - the immune system loads the processor, filtering traffic, as they received an anonymous message about the threat of a virus attack.
no marker
In 1992, it was shown that the long-known cells called natural killers (not to be confused with T-killers), who are responsible for fighting tumors, need constant restraint in order not to start attacking everything around them. The mechanism of this suppression is the molecules of the major histocompatibility complex (MHC I). Normally, these molecules are on the surface of any cell in the body, but in tumors, the production of these molecules can be stopped. Also, the synthesis of MHC I can be blocked by some viruses (for example, adenovirus or cytomegalovirus). In all these cases, the killer cell attaches to special receptors on the surface of the victim cell and, not finding the MHC molecules, injects poison into the victim, leading to apoptosis - cell death.
Either way, the immune system can recognize most pathogens. However, this recognition in most cases is not too fast and not very effective. To improve sensitivity and performance, the immune system can create its own anti-virus database using T-and B-lymphocytes. I will try to tell about it in the following part if it seems to someone interesting.
Thanks for attention!
Ps The authorship of this article (as well as possible follow- ups ) belongs to Ivan Stetsenko aka stetzen , who now has an account on Habré (thanks, markmariner !)
UPDATE: thanks for the karma, moved to Biotechnology.
UPDATE2: continued from the author.
Source: https://habr.com/ru/post/75414/
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