Description and principle of operation of the human immune system. How the immune system works Functions of human immunity

The immune system serves as the main barrier to all kinds of infections: viral, fungal, bacterial. If there is a malfunction in its operation, then the likelihood of not only the penetration of infection increases, but also the development of such serious autoimmune diseases as multiple sclerosis.

The immune system consists of important parts, the so-called organs. They are significantly different from the usual ones: heart, liver, lungs. The organs of the immune system in most cases are areas of lymphoid tissue. These include lymph nodes, tonsils, spleen, bone marrow, .

The bone marrow is the central organ of the immune system and the most important hematopoietic organ. It is located in the largest ones, in the spine, and its main task is the production of leukocytes and red blood cells.

The thymus, or thymus gland, is an organ located behind the sternum. From the bone marrow, lymphoid cells enter the thymus, where they mature and multiply. It is most active in young people, but with age it becomes less productive and decreases in size.

The tonsils are located on both sides and are small collections of lymphoid tissue. They “do” what they do: produce lymphocytes.

The role of the spleen is very important in the functioning of the immune system: it filters and purifies the blood passing through it, removes defective or old blood cells, and produces new lymphocytes. This organ is located in the abdomen on the left side, next to the stomach.

A special role in the functioning of the immune system is played by the circulation system, consisting of lymphatic ducts and transporting lymphatic fluid. Lymph is a colorless liquid that circulates through the lymphatic vessels and contains a huge number of lymphocytes - the real “ordinaries” of the immune system that protect the body from many diseases.

When hostile bacteria enter the human body, on their way they encounter special “defender” cells - phagocytes. They can instantly recognize a foreign body and attach to it. Next, the process of destroying the hostile cell occurs, the side effect of which is swelling of the tissue at the site of pathogenic bacteria and an increase in temperature. It is the elevated temperature that is evidence of the well-coordinated functioning of the immune system.

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No. 1. What is immunity?

Human immunity is a state of immunity to various infectious and generally foreign organisms and substances to the human genetic code. The body's immunity is determined by the state of its immune system, which is represented by organs and cells.

No. 2. What organs are part of the immune system?

• Red bone marrow, spleen and thymus (or thymus) are the central organs of the immune system.
• Lymph nodes and lymphoid tissue in other organs (eg, tonsils, appendix) are peripheral organs of the immune system.

Tonsils and appendix - organs necessary for the immune system. The main task of the human immune system is to produce protective cells.

No. 4. Types of immunity

• Cellular immunity is represented by cells: T-killer cells, T-helper cells, macrophages, neutrophils, and so on.
• Humoral immunity is represented by antibodies and their source - B-lymphocytes.

This gradation is very important, since many drugs act on either one or the other type of immunity.

There is another gradation - according to the degree of specificity:

• nonspecific (or congenital) - for example, the work of neutrophils in any inflammatory reaction with the formation of purulent discharge;
• specific (acquired) - for example, the production of antibodies to the human papillomavirus or to the influenza virus.

The third classification is types of immunity associated with human medical activities:

• natural - resulting from a human illness, for example, immunity after chickenpox;
• artificial - resulting from vaccinations, that is, the introduction of a weakened microorganism into the human body, in response to this the body develops immunity.

No. 5. For example

To make it clearer, here’s an example: common juvenile warts (actually human papillomavirus type 3).

• The virus penetrates into microtrauma of the skin (scratches, abrasions) and gradually penetrates further into the deeper layers of the surface layer of the skin. It was not present in the human body before, so the human immune system does not yet know how to react to it.
• The virus integrates into the gene apparatus of skin cells, and they begin to grow incorrectly, taking on ugly forms.
• This is how a wart forms on the skin. But this process does not bypass the immune system. The first step is to turn on T-helpers. They begin to recognize the virus, remove information from it, but cannot destroy it themselves, since its size is very small, and the T-killer can only kill larger objects such as microbes.
• T-lymphocytes transmit information to B-lymphocytes, and they begin to produce antibodies that penetrate through the blood into skin cells, bind to virus particles and thus immobilize them, and then this entire complex (antigen-antibody) is eliminated from the body.
• T lymphocytes transmit information about infected cells to macrophages. They become active and begin to gradually devour the changed skin cells, destroying them. And in place of the destroyed ones, healthy skin cells gradually grow.

The entire process can take from several weeks to months or even years. Everything depends on the activity of both cellular and humoral immunity, on the activity of all its links. After all, if, for example, at least one link falls out over a certain period of time, then the entire chain collapses, and the virus multiplies unhindered, penetrating into more and more new cells, contributing to the appearance of new ugly warts.

No. 6. Good and bad immunity

Science does not yet know how certain autoimmune processes are triggered in the body. For example, when a person’s immune system, out of the blue, begins to perceive its own cells as foreign and begins to fight them.

• Good immunity is a state of complete immunity to various foreign agents. Outwardly, this is manifested by the absence of infectious diseases and good human health. Internally, this is manifested by the full functionality of all parts of the cellular and humoral components.
• Poor (weak) immunity is a state of susceptibility to infectious diseases. It manifests itself as a weak reaction of one or another link, loss of individual links, inoperability of certain cells. There can be quite a few reasons for its decline, and it must be treated by eliminating all possible causes.

No. 7. Does immunity depend on lifestyle?

An interesting fact: the connection between lifestyle and the body’s ability to resist disease has not been proven to date. However, experts believe that healthy lifestyle strategies most likely have a positive effect on immunity. For the first time in a million, let’s repeat the rules that make sense to follow:

• Quit smoking
• Eat a balanced diet rich in fruits and vegetables, with a predominance of whole grains over flour products, and low in saturated fat.
• Get rid of excess weight.
• Limit your alcohol intake.
• Finally, start getting enough sleep.
• Avoid causing infections: wash your hands, wash your fruits and vegetables, and cook your meat thoroughly.
• Keep your blood pressure under control and get regular checkups recommended for your age group or risk group for the disease (if you are included in one of them).

No. 8. Do vitamins and dietary supplements help the immune system?

If you eat normally, move a lot and get enough sleep, your body does not need vitamins and minerals. But if you are on a strict diet or your stomach and intestines do not absorb nutrients well, you need to take them in medicinal form. Here are a few nutrients to consider as dietary supplements:

• Vitamin A. Vitamin A deficiency in the body has been proven to be associated with reduced immune system function and an increased risk of infections.
• Vitamin B6. Vitamin B6 deficiency reduces the ability of lymphocytes to differentiate into T cells and B cells. Moderate doses of the vitamin help restore this ability.
• Vitamin D. Its role in the functioning of the immune system is undeniable. Vitamin D, produced in the body under the influence of sunlight, has long been known as an important factor in the fight against tuberculosis, in the prevention of cancer, multiple sclerosis, and seasonal flu. Experts recommend taking a vitamin D3 supplement (not D2 - this form is poorly absorbed). Fish oil, which contains, in addition to D, vitamin A and healthy Omega-3 fatty acids, is also useful.
• Zinc. This trace element is necessary for the normal functioning of T cells and other immune cells. The recommended daily dose of zinc is 15-25 mg, but no more. High doses have the opposite effect.

No. 9. Does stress affect the body's resistance?

No experiments have been conducted in this area - doctors believe that this is not ethical. Therefore, scientists have to be content with experiments on animals and some observations of the human world.

Thus, experimental mice infected with the herpes virus showed a decrease in T-cell activity under stress conditions. Reduced lymphocyte production was demonstrated by Indian macaque infants separated from their mother.

Scientists observed a decrease in T-cell activity in depressed patients, as well as in divorced men compared to married men.

A decrease in a number of immune indicators was demonstrated by residents of Florida who lost their housing after Hurricane Andrew, as well as hospital workers in Los Angeles after the earthquake.

Summary: it has been proven that stress weakens immunity. But it has not been proven that stressed people get sick more often than happy people.

No. 10. Do low temperatures lower immunity?

If you go for a walk in winter and are slightly cold, your immunity is unlikely to decrease. Today, science believes that colds, paradoxical as it may sound, are not associated with catching a cold.

To prove this hypothesis, scientists immersed volunteers in cold water, exposed them to temperatures close to 0°C, and studied the inhabitants of research stations in Antarctica and the northern regions of Canada. The results were mixed.

On the one hand, Canadian researchers noticed an increase in the incidence of respiratory infections in skiers during long-term training in the cold. At the same time, it is unclear whether this was the result of low temperatures or other factors (great physical activity, dry air).

So dress comfortably, beware of hypothermia and frostbite, and don’t worry about your immunity: most likely it will not suffer from the cold.

No. 11. Bonus: Echinacea, Garlic, and Lemon Don't Help Your Immune System

The most common recommendation at the first sign of a cold or flu is to take a high dose of vitamin C. However, science has not proven that vitamin C helps our immunity in any way. Same thing with echinacea: it has not been shown to be beneficial in studies. There is no convincing data on the effectiveness of garlic. However, garlic has been proven to fight bacterial, viral and fungal infections in vitro. It is possible that garlic is not useless for colds, although it does not seem to act through the immune system.

The human immune system is one of the most important systems, thanks to it a person is protected from various types of viruses, infections, all kinds of diseases, and the negative influence of the environment. The functioning of the immune system is one of the most important for humans. Human immunity most directly affects the functioning of our circulatory system, which is a very important factor. Our immune system is designed in such a way that when the slightest threat to the body appears, it instantly reacts and tries to destroy it or remove it from the body. This whole process is called an immune reaction.

The list of elements hostile to humans is quite large, has a different nature of origin and a very diverse structure, and they are called antigens. To antigens of various plants, viruses, infections, fungal spores, mushrooms, household dust, various chemical elements and so on. In cases where the human immune system is weakened for some reason and the components are not working at full strength, antigens can contribute to the occurrence of quite serious diseases that directly threaten human health and life.

You need to understand that the immune system is a collection of many different human systems that are aimed at giving a timely and adequate immune response to any threat hanging over a person, and you need to clearly know. In general terms, the immune system is slightly inferior in structural complexity to the nervous system, but remotely it can be compared with the nervous system. Next, we'll look at how the immune system works, what exactly the immune system consists of, and what it affects.

Immune system organs

1. Bone marrow

The bone marrow is considered to be the main component of the immune system. The bone marrow is responsible for the production of red blood cells, platelets and white blood cells, which must replace dead cells, normalizing the condition of the blood. Bone marrow comes in two types: yellow and red, the total weight of which reaches three kilograms. Bone marrow is located in the largest bones of the human skeleton, namely the spine, pelvic, tibia, and so on.

1. Thymus

The thymus, or as it is also called the thymus gland, is an equally important organ in our immune system, which also belongs to the central organs of the human immune system. The thymus is inseparably connected with the bone marrow, since the thymus consists of those stem cells that come directly from the bone marrow. In the thymus gland, cells mature and differentiate, resulting in the formation of T-lymphocytes necessary for the body. The functions of T-lymphocytes include the timely response of cell immunity to foreign invasions. The thymus is located in the upper part of the chest, next to the throat, which is why in ancient times it was considered the habitat of the human soul.

1. Tonsils

One of the first and no less important barriers encountered on the path of viruses and infections are the tonsils, popularly called tonsils. The tonsils are located in the throat in front of the vocal cords. They are an effective barrier due to the fact that they consist of small lymph nodes that have a beneficial effect on the human body as a whole.

1. The spleen plays an important role in the functioning of the human immune system. It also belongs to the main organs of the immune system, the functions of which include cleaning the blood entering it from various foreign elements and microorganisms, as well as removing dead blood cells.

Human peripheral immune system

This system is a branched system of vessels and capillaries, which are located throughout the body, feeding human organs and tissues with the necessary components. The human lymphatic system constantly works together with the circulatory system, thanks to which all the necessary substances are distributed throughout the human body. Lymph is a colorless, almost transparent liquid that distributes the protective cells of our immune system - lymphocytes, which are extremely important for our body, since it is they who come into contact with various antigens.

No less important for human immunity are the lymph nodes, which are located in a person’s armpits, groin area, and so on. Like the spleen, which cleanses our blood and is a natural filter, the lymph nodes are also filters, but they are no longer engaged in cleaning the blood, but directly the lymph. This procedure is extremely important, since lymph carries lymphocytes, which destroy various harmful microorganisms and bacteria. In addition, it is in the lymph nodes that there are deposits of phagocytes and lymphocytes, which are among the first to resist antigens, thus forming the reaction of the immune system.

Lymph takes an active part in eliminating any inflammatory processes and consequences of injuries, and thanks to lymphatic cells it provides decent resistance to all antigens.

Types of lymphocytes

However, it is worth noting that lymphocytes, in turn, come in several types, which we will talk about later.

1. B lymphocytes.

These cells, or B cells as they are also called, begin to be produced and accumulate directly in the bone marrow. It is thanks to them that antibodies of a specific nature are formed, which are aimed at fighting a single antigen. Therefore, a simple relationship is developed, the more antigens enter the human body, the more our immune system will produce the necessary antibodies to fight these antigens, thus giving a worthy immune response. However, it is necessary to know that B cells are activated only by those antigens that are in the blood and move freely throughout the body, and do not in any way affect those antigens that are already located in the cells.

1. T lymphocytes.

T lymphocytes originate directly in the thymus. However, T lymphocytes are also divided into two groups of cells called T helper cells and T suppressor cells. They are also extremely important for our immunity. The functions of T-helpers include control and coordination in the work of immune cells, and T-suppressors control how strong and long-lasting the immune response to a particular disease should be, and in the case of timely neutralization of antigens, stop the immune response in time and prevent excessive production of lymphocytes in organism.

1. Killer T cells

In addition to the above types of lymphocytes, there are also some T-killers. They work as follows: if certain cells have been affected by antigens, then killer T cells attach themselves to the affected cells in order to subsequently eliminate them.

A huge role is played by phagocytes, which directly attack and destroy hostile antigens. Separately, it is worth noting macrophages, which are called the “great destroyer”. It works as follows: upon noticing a damaged cell or hostile antigen, it envelops them, and then digests them and destroys the cell or antigen completely.

The human immune system works on the principle of recognizing its own and foreign cells. The immune system responds to any foreign invasion with an immune response. As mentioned earlier, there are two types of immune response, which depend on certain lymphocytes.

The principle of operation of humoral immunity is based on the creation of antibodies, which will subsequently circulate freely in a person’s blood, thus protecting him from all kinds of antigens. This reaction is called nothing less than humoral. In addition to the humoral immune response, there is also a cellular reaction that occurs in the human body with the help of T lymphocytes. These two immune reactions reliably guard our health, destroying all hostile bacteria and microorganisms that enter a person.

The aforementioned humoral response of the immune system eliminates hostile antigens most effectively through freely circulating antigens that travel through the blood. If lymphocytes encounter a hostile microorganism along their route, they instantly analyze the situation and recognize it as an enemy, then change and become cells that directly produce antibodies, and as a result destroy all hostile organisms on their way. The transformed cells, which are called upon to produce antibodies, are called plasma cells. The main habitat of such cells is in the bone marrow and spleen.

In fact, antibodies are protein formations that resemble the English letter Y in shape. Antibodies can be loosely compared to a kind of key that clings to hostile antigens. With its upper part, the antibody is attached to the body of the hostile protein, and with its lower part, which is a kind of bridge, it connects directly to the phagocyte. Thanks to this bridge, the phagocyte begins the process of destroying both the antigen itself and the antibody that is attached to it.

However, it is worth clearly understanding that on their own, B-lymphocytes alone cannot in any way provide a truly worthy immune response, which creates the need for additional help. It is T-lymphocytes that come to their aid, which contribute to the launch of the immune response. There are also situations when, upon contact with hostile antigens, B lymphocytes are not converted into plasma cells, but instead call on T lymphocytes to come to their aid in the fight against foreign proteins. And in such a situation, those T-lymphocytes that came to the aid of B-lymphocytes produce a specific chemical substance called lymphokine, and are a kind of catalyst for many immune cells of the human body.

Video

The immune system, consisting of special proteins, tissues and organs, daily protects humans from pathogenic microorganisms, and also prevents the influence of some special factors (for example, allergens).

In most cases, she performs a huge amount of work aimed at maintaining health and preventing the development of infection.

Photo 1. The immune system is a trap for harmful microbes. Source: Flickr (Heather Butler)

What is the immune system

The immune system is a special protective system of the body that prevents the effects of foreign agents (antigens). Through a series of steps called the immune response, it “attacks” all microorganisms and substances that invade organ systems and tissues and are capable of causing disease.

Immune system organs

The immune system is amazingly complex. It is able to recognize and remember millions of different antigens, promptly producing the necessary components to destroy the “enemy”.

She includes central and peripheral organs, as well as special cells, which are produced in them and are directly involved in human protection.

Central authorities

The central organs of the immune system are responsible for the maturation, growth and development of immunocompetent cells - lymphopoiesis.

Central authorities include:

• Bone marrow- spongy tissue of a predominantly yellowish hue, located inside the bone cavity. Bone marrow contains immature, or stem cells, which are capable of turning into any, including immunocompetent, cell of the body.
• Thymus(thymus). It is a small organ located in the upper part of the chest behind the sternum. In shape, this organ is somewhat reminiscent of thyme, or thyme, the Latin name of which gave the name to the organ. The thymus is primarily where T cells of the immune system mature, but the thymus gland is also capable of inducing or maintaining the production of antibodies against antigens.
• During the prenatal period, the central organs of the immune system also include the liver..

This is interesting! The largest size of the thymus gland is observed in newborns; With age, the organ shrinks and is replaced by fatty tissue.

Peripheral organs

Peripheral organs are distinguished by the fact that they contain mature cells of the immune system that interact with each other and other cells and substances.

Peripheral organs are represented by:

• Spleen. The largest lymphatic organ in the body, located under the ribs on the left side of the abdomen, above the stomach. The spleen contains predominantly white blood cells and also helps get rid of old and damaged blood cells.
• The lymph nodes(LN) are small, bean-shaped structures that house cells of the immune system. The lymph node also produces lymph, a special clear liquid through which immune cells are delivered to various parts of the body. As the body fights an infection, the lymph nodes may increase in size and become painful.
• Clusters of lymphoid tissue, containing immune cells and located under the mucous membranes of the digestive and genitourinary tract, as well as in the respiratory system.

Immune system cells

The main cells of the immune system are white blood cells, which circulate in the body through lymphatic and blood vessels.

The main types of leukocytes capable of an immune response are the following cells:

• Lymphocytes, which allow you to recognize, remember and destroy all antigens that invade the body.
• Phagocytes, absorbing foreign particles.

Phagocytes can be various cells; the most common type are neutrophils, which primarily fight bacterial infection.

Lymphocytes are located in the bone marrow and are represented by B cells; If lymphocytes are found in the thymus, they mature into T-lymphocytes. B and T cells have different functions:

• B lymphocytes try to detect foreign particles and send a signal to other cells when an infection is detected.
• T lymphocytes destroy pathogenic components identified by B cells.

How the immune system works

When antigens (that is, foreign particles that invade the body) are detected, they are induced B lymphocytes, producing antibodies(AT) are specialized proteins that block specific antigens.

Antibodies are able to recognize the antigen, but cannot destroy it on their own - this function belongs to T cells, which perform several functions. T cells can not only destroy foreign particles (for this there are special T-killers, or “killers”), but also participate in the transmission of the immune signal to other cells (for example, phagocytes).

Antibodies, in addition to identifying antigens, neutralize toxins produced by pathogenic organisms; also activate complement - part of the immune system that helps destroy bacteria, viruses and other and foreign substances.

Recognition process

After antibodies are formed, they remain in the human body. If the immune system encounters the same antigen in the future, infection may not develop: for example, after suffering from chickenpox, a person no longer gets sick from it.

This process of recognizing a foreign substance is called antigen presentation. The formation of antibodies during re-infection is no longer required: the destruction of the antigen by the immune system is carried out almost instantly.

Allergic reactions

Allergies follow a similar mechanism; A simplified diagram of the development of the state is as follows:

1. Primary entry of the allergen into the body; It is not expressed clinically in any way.
2. Antibody formation and fixation on mast cells.
3. Sensitization - increased sensitivity to an allergen.
4. Re-entry of the allergen into the body.
5. Release of special substances (mediators) from mast cells with the development of a chain reaction. Subsequent produced substances affect organs and tissues, which is determined by the appearance of symptoms of the allergic process.

Hello everyone, Olga Ryshkova is with you. Did you know that even when we feel absolutely healthy, our body fights disease? We live in an environment with a huge number of microbes, we inhale billions of microorganisms and do not get sick because our immune system protects us.

The immune system never rests; its cells circulate throughout the body, looking not only for microbes, viruses and foreign substances, but also for damage in its own tissues. Everything foreign is an enemy, and the enemy must be destroyed.

Most people have a vague idea of ​​where the human immune system is located and how it works. Its foundation is the central organs. All immune cells come from there. This is the bone marrow inside the long bones and the thymus (thymus gland), which is located behind the sternum. The thymus is the largest in children, because their immune system is intensively developing.

In an adult it is significantly less (in an elderly person 6 g or less).

The spleen is also one of the central organs of the immune system; in an adult it weighs about 200 g.

There are also many small structures - lymph nodes, which are located almost everywhere. Some are so small that they can only be seen under a microscope. There is no area in the body where the immune system does not exercise its control.

The cells of the immune system, lymphocytes, circulate freely throughout the body using blood, tissue and lymph fluids and regularly meet in the lymph nodes, where they exchange information about the presence of foreign agents in the body. This is a conversation at the molecular level.

In fact, immunity is represented by heterogeneous cells; they are united by one goal - to instantly move from reconnaissance to attack.

The first level is local protection. When a microbe penetrates mucous or damaged skin, the cells become activated and release chemicals (chemokines) that attract other immune cells and increase vascular permeability to them. A huge number of immune cells accumulate in this area and a focus of inflammation is formed.

Phagos means to swallow; these are the cells that can “eat” the pathogen. The largest representatives of phagocytes are called macrophages; they are capable of absorbing and destroying thousands of microbes at the same time.

Smaller phagocytes include neutrophils; there are billions of them in our blood.

If for some reason a person produces few neutrophils, severe infections can develop against this background, and even with massive antibacterial or antifungal therapy, life is threatened. Neutrophils attack pathogens in large numbers in the first rows of protective cells and usually die along with them. The pus at the site of inflammation is dead neutrophils.

Antibodies then join the fight. The immune system is a self-learning structure; during evolution, it invented the antigen-antibody system. An antigen is a molecule on a foreign cell (bacteria, virus, or protein toxin) against which an antibody is formed. Against a specific antigen there is a specific antibody that can accurately recognize it, because it fits like a key to a lock. This is an accurate recognition system.

The bone marrow produces a group of lymphocytes called B lymphocytes. They appear immediately with ready-made antibodies on the surface, with a wide range of antibodies that can recognize a wide range of antigens. B lymphocytes travel throughout the body and when they encounter pathogens with antigen molecules on the surface, they bind to them and signal to the immune system that they have detected an enemy.

But B lymphocytes detect pathogens in the blood, and if they penetrate the cell, as viruses do, they become inaccessible to B lymphocytes. The work involves a group of lymphocytes called T-killers. Affected cells differ from normal ones in that there are small fragments of the viral protein on their surface. Through them, T-killers recognize cells with viruses and destroy them.

Killer cells receive their receptor, which recognizes the viral protein, in the thymus (thymus gland).

The diversity of receptors makes it possible to detect all kinds of microorganisms. After their discovery, mass cloning of B-lymphocytes and T-killers begins. At the same time, special substances pyrogens are formed, which raise body temperature, and the lymph nodes in which lymphocytes are cloned enlarge.

If a person has immunity to the pathogen, the body will cope without treatment. The principle of vaccination is based on this. Memory cells are responsible for the formation of immunity after vaccination or after an infectious disease. These are lymphocytes that have encountered antigens. They enter the lymph nodes or spleen and wait there for a second encounter with the same antigen.