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

In most cases, she does 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 and tissue systems and are capable of causing disease.

Organs of the immune system

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

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

Central bodies

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, predominantly yellowish, located inside the bone cavity. Bone marrow contains immature, or stem cells, which are capable of transforming 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 for which gave the organ its name. Basically, T cells of the immune system mature in the thymus, but the thymus gland is also able to provoke or maintain the production of antibodies against antigens.
• During the prenatal period of development, the liver also belongs to the central organs of the immune system..

It is interesting! The largest size of the thymus gland is observed in newborns; with age, the organ decreases and is replaced by adipose tissue.

Peripheral organs

Peripheral organs differ in that they contain already mature cells of the immune system, interacting with each other and with other cells and substances.

Peripheral organs are represented:

• 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 to get rid of old and damaged blood cells.
• The lymph nodes (LU) are small, bean-like structures that store the cells of the immune system. LU also produces lymph - a special transparent liquid, with the help of which immune cells are delivered to various parts of the body. As the body fights infection, LNs can grow in size and become painful.
• Clusters of lymphoid tissuecontaining immune cells and located under the mucous membranes of the digestive and genitourinary tract, as well as in the respiratory system.

Cells of the immune system

The main cells of the immune system are white blood cells, which circulate in the body through the 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 are introduced into the body.
• Phagocytesabsorbing foreign particles.

Various cells can be phagocytes; the most common type is neutrophils, which fight primarily against 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 are detected (that is, foreign particles that invade the body) are induced B-lymphocytesproducing antibodies(AT) - specialized proteins that block specific antigens.

Antibodies are able to recognize an antigen, but they cannot destroy it on their own - this function belongs to T-cells that perform several functions. T cellscan not only destroy foreign particles (for this there are special killer T-cells, 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; they also activate complement, a part of the immune system that helps destroy bacteria, viruses and other and foreign substances.

Recognition process

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

This process of recognizing a foreign substance is called antigen presentation. The formation of antibodies upon repeated 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 ingestion of the allergen into the body; clinically not expressed.
2. Formation of antibodies and their fixation on mast cells.
3. Sensitization - an increase in sensitivity to an allergen.
4. Re-entry of the allergen into the body.
5. The 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.

Introduction

Immunity is understood as a set of biological phenomena aimed at preserving the internal environment and protecting the body from infectious and other genetically alien agents. There are the following types of infectious immunity:

antibacterial

antitoxic

antiviral

antifungal

antiprotozoal

Infectious immunity can be sterile (there is no pathogen in the body) and non-sterile (pathogen in the body). Congenital immunity is present from birth, it can be specific and individual. Species immunity is the immunity of one species of animal or person to microorganisms that cause disease in other species. It is genetically determined in humans as a biological species. Species immunity is always active. Individual immunity is passive (placental immunity). Nonspecific protective factors are as follows: skin and mucous membranes, lymph nodes, lysozyme and other enzymes of the oral cavity and gastrointestinal tract, normal microflora, inflammation, phagocytic cells, natural killer cells, the complement system, interferons. Phagocytosis.

I. The concept of the immune system

The immune system is the collection of all lymphoid organs and clusters of lymphoid cells in the body. The lymphoid organs are subdivided into the central ones - the thymus, bone marrow, the bag of Fabricius (in birds) and its analog in animals - Peyer's patches; peripheral - spleen, lymph nodes, solitary follicles, blood and others. Its main component is lymphocytes. There are two main classes of lymphocytes: B-lymphocytes and T-lymphocytes. T-cells are involved in cellular immunity, regulation of B-cell activity, delayed-type hypersensitivity. There are the following subpopulations of T-lymphocytes: T-helpers (programmed to induce the multiplication and differentiation of other types of cells), suppressor T-cells, T-killers (secrete cytotoxic dymfokines). The main function of B-lymphocytes is that, in response to an antigen, they are able to multiply and differentiate into plasma cells that produce antibodies. B - lymphocytes are divided into two subpopulations: 15 B1 and B2. B - cells are long-lived B - lymphocytes, originated from mature B - cells as a result of antigen stimulation with the participation of T lymphocytes.

The immune response is a chain of sequential complex cooperative processes in the immune system in response to the action of an antigen in the body. There are primary and secondary immune responses, each of which consists of two phases: inductive and productive. Further, the immune response is possible in the form of one of three options: cellular, humoral and immunological tolerance. Antigens by origin: natural, artificial and synthetic; by chemical nature: proteins, carbohydrates (dextran), nucleic acids, conjugated antigens, polypeptides, lipids; by genetic relation: autoantigen, isoantigens, alloantigen, xenoantigens. Antibodies are proteins that are synthesized under the influence of an antigen.

II. Cells of the immune system

Immunocompetent cells are cells that make up the immune system. All of these cells originate from a single ancestral bone marrow stem cell. All cells are divided into 2 types: granulocytes (granular) and agranulocytes (non-granular).

Granulocytes include:

neutrophils

eosinophils

basophils

To agranulocytes:

macrophages

lymphocytes (B, T)

Neutrophilic granulocytes or neutrophils, segmented neutrophils, neutrophilic leukocytes - a subspecies of granulocytic leukocytes, called neutrophils because, when stained according to Romanovsky, they are intensely stained with both an acidic dye eosin and basic dyes, in contrast to eosinophils, stained only with eosin, and from basophils, stained only with basic dyes.

Mature neutrophils have a segmented nucleus, that is, they belong to polymorphonuclear leukocytes, or polymorphonuclear cells. They are classical phagocytes: they have adhesiveness, mobility, the ability to chemostaxis, as well as the ability to capture particles (for example, bacteria).

Mature segmented neutrophils are normally the main type of leukocytes circulating in human blood, accounting for 47% to 72% of the total number of blood leukocytes. Another 1-5% are normally young, functionally immature neutrophils, which have a rod-shaped solid nucleus and do not have nucleus segmentation characteristic of mature neutrophils - the so-called stab neutrophils.

Neutrophils are capable of active amoeboid movement, extravasation (emigration outside the blood vessels), and chemotaxis (preferential movement towards sites of inflammation or tissue damage).

Neutrophils are capable of phagocytosis, and they are microphages, that is, they are able to absorb only relatively small foreign particles or cells. After phagocytosis of foreign particles, neutrophils usually die, releasing a large amount of biologically active substances that damage bacteria and fungi, enhance inflammation and chemotaxis of immune cells in the focus. Neutrophils contain large amounts of myeloperoxidase, an enzyme that is capable of oxidizing the chlorine anion to hypochlorite, a potent antibacterial agent. Myeloperoxidase as a heme-containing protein has a greenish color, which determines the greenish tint of the neutrophils themselves, the color of pus and some other secretions rich in neutrophils. Dead neutrophils, together with cellular debris from tissues destroyed by inflammation and pyogenic microorganisms that caused the inflammation, form a mass known as pus.

An increase in the proportion of neutrophils in the blood is called relative neutrophilia, or relative neutrophilic leukocytosis. An increase in the absolute number of neutrophils in the blood is called absolute neutrophilia. A decrease in the proportion of neutrophils in the blood is called relative neutropenia. A decrease in the absolute number of neutrophils in the blood is referred to as absolute neutropenia.

Neutrophils play a very important role in protecting the body from bacterial and fungal infections, and a comparatively smaller role in protecting against viral infections. Neutrophils practically do not play a role in antitumor or anthelmintic protection.

The neutrophil response (infiltration of the inflammation focus with neutrophils, an increase in the number of neutrophils in the blood, a shift of the leukocyte formula to the left with an increase in the proportion of "young" forms, indicating an increase in the production of neutrophils by the bone marrow) is the very first response to bacterial and many other infections. The neutrophilic response in acute inflammation and infections always precedes the more specific lymphocytic response. In chronic inflammation and infections, the role of neutrophils is insignificant and the lymphocytic response predominates (infiltration of the inflammatory focus with lymphocytes, absolute or relative lymphocytosis in the blood).

Eosinophilic granulocytes or eosinophils, segmented eosinophils, eosinophilic leukocytes - a subspecies of granulocytic blood leukocytes.

Eosinophils are so named because, when stained according to Romanovsky, they are intensely stained with an acidic dye eosin and are not stained with basic dyes, unlike basophils (stained only with basic dyes) and neutrophils (they absorb both types of dyes). Also, a distinctive feature of an eosinophil is a two-lobed nucleus (in a neutrophil it has 4-5 lobes, and in a basophil it is not segmented).

Eosinophils are capable of active amoeboid movement, extravasation (penetration beyond the walls of blood vessels) and chemotaxis (preferential movement towards the focus of inflammation or tissue damage).

Also, eosinophils are able to absorb and bind histamine and a number of other mediators of allergy and inflammation. They also have the ability to release these substances when needed, similar to basophils. That is, eosinophils are capable of playing both a pro-allergic and a protective anti-allergic role. The percentage of eosinophils in the blood increases in allergic conditions.

Eosinophils are less abundant than neutrophils. Most of the eosinophils do not remain in the blood for a long time and, getting into the tissues, remain there for a long time.

The normal level for humans is 120-350 eosinophils per microliter.

Basophilic granulocytes or basophils, segmented basophils, basophilic leukocytes - a subspecies of granulocytic leukocytes. They contain a basophilic S-shaped nucleus, which is often invisible due to the overlap of the cytoplasm with granules of histamine and other allergen mediators. Basophils are named so because, when stained according to Romanovsky, they intensively absorb the basic dye and do not stain with acidic eosin, in contrast to eosinophils, which are stained only with eosin, and from neutrophils, which absorb both dyes.

Basophils are very large granulocytes: they are larger than both neutrophils and eosinophils. Basophil granules contain large amounts of histamine, serotonin, leukotrienes, prostaglandins and other mediators of allergy and inflammation.

Basophils take an active part in the development of immediate allergic reactions (anaphylactic shock reactions). There is a misconception that basophils are the precursors of mast cells. Mast cells are very similar to basophils. Both cells are granulated and contain histamine and heparin. Both cells also release histamine when they bind to immunoglobulin E. This similarity has led many to assume that mast cells are the basophils in tissues. In addition, they share a common precursor in the bone marrow. Nevertheless, basophils leave the bone marrow already mature, while mast cells circulate in an immature form, only eventually entering the tissues. Thanks to the basophils, the poisons of insects or animals are immediately blocked in tissues and do not spread throughout the body. Basophils also regulate blood clotting with heparin. However, the initial statement is still correct: basophils are direct relatives and analogs of tissue mast cells, or mast cells. Like tissue mast cells, basophils carry immunoglobulin E on the surface and are capable of degranulation (release of granule contents into the external environment) or autolysis (dissolution, cell lysis) upon contact with an allergen antigen. During degranulation or lysis of the basophil, a large amount of histamine, serotonin, leukotrienes, prostaglandins and other biologically active substances are released. This is what determines the observed manifestations of allergy and inflammation when exposed to allergens.

Basophils are capable of extravasation (emigration outside the blood vessels), and they can live outside the bloodstream, becoming resident tissue mast cells (mast cells).

Basophils have the ability to chemotaxis and phagocytosis. In addition, in all likelihood, phagocytosis is neither the main nor natural (carried out in natural physiological conditions) activity for basophils. Their only function is instant degranulation, leading to increased blood flow, increased vascular permeability. an increase in the flow of fluid and other granulocytes. In other words, the main function of basophils is to mobilize the rest of the granulocytes to the inflammation focus.

Monocyte - large mature mononuclear leukocyte of agranulocyte group with a diameter of 18-20 microns with an eccentrically located polymorphic nucleus with a loose chromatin network and azurophilic granularity in the cytoplasm Like lymphocytes, monocytes have an unsegmented nucleus. Monocyte is the most active phagocyte of peripheral blood. The cell is oval in shape with a large bean-shaped nucleus rich in chromatin (which makes it possible to distinguish them from lymphocytes, which have a rounded dark nucleus) and a large amount of cytoplasm, which contains many lysosomes.

Besides blood, these cells are always present in large quantities in the lymph nodes, alveolar walls and sinuses of the liver, spleen and bone marrow.

Monocytes are in the blood for 2-3 days, then they go out into the surrounding tissues, where, having reached maturity, they turn into tissue macrophages - histiocytes. Monocytes are also precursors of Langerhans cells, microglia cells, and other cells capable of processing and presenting antigen.

Monocytes have a pronounced phagocytic function. These are the largest cells of peripheral blood, they are macrophages, that is, they can absorb relatively large particles and cells or a large number of small particles and, as a rule, do not die after phagocytosis (death of monocytes is possible if the phagocytosed material has any cytotoxic properties for a monocyte). This is how they differ from microphages - neutrophils and eosinophils, which can absorb only relatively small particles and, as a rule, die after phagocytosis.

Monocytes are able to phagocytose microbes in an acidic environment when neutrophils are inactive. Phagocytizing microbes, dead leukocytes, damaged tissue cells, monocytes cleanse the site of inflammation and prepare it for regeneration. These cells form a delineating shaft around indestructible foreign bodies.

Activated monocytes and tissue macrophages:

participate in the regulation of hematopoiesis (hemopoiesis)

take part in the formation of a specific immune response of the body.

Monocytes, leaving the bloodstream, become macrophages, which, along with neutrophils, are the main "professional phagocytes". Macrophages, however, are significantly larger and live longer than neutrophils. The precursor cells of macrophages - monocytes, leaving the bone marrow, circulate in the blood for several days, and then migrate into the tissues and grow there. At this time, the content of lysosomes and mitochondria increases in them. Near the inflammatory focus, they can multiply by division.

Monocytes are able, having emigrated into tissues, to turn into resident tissue macrophages. Monocytes are also able, like other macrophages, to perform antigen processing and present antigens to T-lymphocytes for recognition and learning, that is, they are antigen-presenting cells of the immune system.

Macrophages are large cells that actively destroy bacteria. Macrophages in large quantities accumulate in the foci of inflammation. Compared to neutrophils, monocytes are more active against viruses than bacteria, and are not destroyed during a reaction with a foreign antigen, therefore, pus is not formed in the foci of inflammation caused by viruses. Monocytes also accumulate in foci of chronic inflammation.

Monocytes secrete soluble cytokines that affect the functioning of other parts of the immune system. The cytokines secreted by monocytes are called monokines.

Monocytes synthesize the individual components of the complement system. They recognize the antigen and convert it into an immunogenic form (antigen presentation).

Monocytes produce both factors that enhance blood coagulation (thromboxanes, thromboplastins) and factors that stimulate fibrinolysis (plasminogen activators). Unlike B- and T-lymphocytes, macrophages and monocytes are not capable of specific antigen recognition.

T lymphocytes, or T cells- lymphocytes that develop in mammals in the thymus from precursors - pretimocytes entering it from the red bone marrow. In the thymus, T-lymphocytes differentiate by acquiring T-cell receptors (TCR) and various co-receptors (surface markers). Plays an important role in the acquired immune response. They ensure the recognition and destruction of cells carrying foreign antigens, enhance the action of monocytes, NK cells, and also take part in the switching of immunoglobulin isotypes (at the beginning of the immune response, B cells synthesize IgM, later they switch to the production of IgG, IgE, IgA).

Types of T-lymphocytes:

T-cell receptors are the main surface protein complexes of T-lymphocytes, responsible for the recognition of processed antigens associated with the molecules of the main histocompatibility complex on the surface of antigen-presenting cells. The T cell receptor is linked to another polypeptide membrane complex, CD3. The functions of the CD3 complex include signaling to the cell, as well as stabilizing the T-cell receptor on the membrane surface. The T cell receptor can associate with other surface proteins, TCR coreceptors. Depending on the coreceptor and the functions performed, there are two main types of T cells.

T-helpers

T-helpers - T-lymphocytes, the main function of which is to enhance the adaptive immune response. Activate T-killers, B-lymphocytes, monocytes, NK-cells in direct contact, as well as humorally, releasing cytokines. The main feature of T-helpers is the presence of the CD4 corereceptor molecule on the cell surface. T-helpers recognize antigens when their T-cell receptor interacts with the antigen associated with the molecules of the major histocompatibility complex II class.

T-killers

Helper T-cells and Killer T-cells form a group of effector T-lymphocytes directly responsible for the immune response. At the same time, there is another group of cells, regulatory T-lymphocytes, whose function is to regulate the activity of effector T-lymphocytes. By modulating the strength and duration of the immune response through the regulation of the activity of T-effector cells, regulatory T-cells maintain tolerance to the body's own antigens and prevent the development of autoimmune diseases. There are several mechanisms of suppression: direct, with direct contact between cells, and distant, carried out at a distance, for example, through soluble cytokines.

γδ T-lymphocytes

γδ T lymphocytes are a small population of cells with a modified T cell receptor. Unlike most other T cells, the receptor of which is formed by two α and β subunits, the T cell receptor of γδ lymphocytes is formed by γ and δ subunits. These subunits do not interact with peptide antigens presented by MHC complexes. It is assumed that γδ T-lymphocytes are involved in the recognition of lipid antigens.

B-lymphocytes (B-cells, from bursa fabricii birds, where they were first discovered) is a functional type of lymphocytes that play an important role in providing humoral immunity. When exposed to antigen or stimulated by T cells, some B lymphocytes are transformed into plasma cells capable of producing antibodies. Other activated B lymphocytes are converted to memory B cells. In addition to producing antibodies, B cells perform many other functions: they act as antigen-presenting cells, produce cytokines and exosomes.

In human and other mammalian embryos, B-lymphocytes are formed in the liver and bone marrow from stem cells, and in adult mammals, only in the bone marrow. Differentiation of B-lymphocytes takes place in several stages, each of which is characterized by the presence of certain protein markers and the degree of genetic rearrangement of immunoglobulin genes.

There are the following types of mature B-lymphocytes:

Actually B-cells (also called "naive" B-lymphocytes) - non-activated B-lymphocytes, not in contact with the antigen. They do not contain Goll's little bodies, scattered in cytoplasm and monoribosomes. They are multispecific and have a weak affinity for many antigens.

Memory B-cells are activated B-lymphocytes, which have again passed into the stage of small lymphocytes as a result of cooperation with T-cells. They are a long-lived clone of B-cells, provide a fast immune response and the production of a large amount of immunoglobulins when the same antigen is re-administered. Called memory cells, as they allow the immune system to "remember" the antigen for many years after its termination. Memory B cells provide long-term immunity.

Plasma cells are the last stage of differentiation of antigen-activated B cells. Unlike other B cells, they carry few membrane antibodies and are able to secrete soluble antibodies. They are large cells with an eccentrically located nucleus and a developed synthetic apparatus - the rough endoplasmic reticulum occupies almost the entire cytoplasm, and the Golgi apparatus is also developed. They are short-lived cells (2-3 days) and are quickly eliminated in the absence of the antigen that caused the immune response.

A characteristic feature of B cells is the presence of surface membrane-bound antibodies belonging to the IgM and IgD classes. In combination with other surface molecules, immunoglobulins form an antigen-recognizing receptive complex responsible for antigen recognition. Also on the surface of B-lymphocytes are MHC class II antigens, which are important for interaction with T-cells, and on some clones of B-lymphocytes there is a marker CD5, which is common with T-cells. Receptors for complement components C3b (Cr1, CD35) and C3d (Cr2, CD21) play a role in the activation of B cells. It should be noted that markers CD19, CD20 and CD22 are used to identify B lymphocytes. Fc receptors are also found on the surface of B-lymphocytes.

Natural killers - large granular lymphocytes with cytotoxicity against tumor cells and cells infected with viruses. NK cells are currently considered as a separate class of lymphocytes. NKs perform cytotoxic and cytokine-producing functions. NK are one of the most important components of innate cellular immunity. NK are formed as a result of the differentiation of lymphoblasts (common precursors of all lymphocytes). They do not have T-cell receptors, CD3 or surface immunoglobulins, but usually carry markers CD16 and CD56 on their surface in humans or NK1.1 / NK1.2 in some mouse strains. About 80% of NK carry CD8.

These cells were called natural killer cells because, according to early concepts, they did not require activation to destroy cells that did not carry markers of the type I major histocompatibility complex.

The main function of NK is to destroy body cells that do not carry MHC1 on their surface and thus are inaccessible for the action of the main component of antiviral immunity - killer T cells. A decrease in the amount of MHC1 on the cell surface may be due to the transformation of the cell into a cancerous one or the action of viruses such as papillomavirus and HIV.

Macrophages, neutrophils, eosinophils, basophils, and natural killer cells mediate an innate immune response that is nonspecific.

The organs of the immune system are the bone marrow, thymus, spleen, appendix, lymph nodes, lymphoid tissue, diffusely dispersed in the mucous membrane of the internal organs, and numerous lymphocytes that are found in the blood, lymph, organs and tissues. In the bone marrow and thymus, lymphocytes differentiate from stem cells. They belong to the central organs of the immune system. The rest of the organs are peripheral organs of the immune system, where lymphocytes are expelled from the central organs. The total weight of all organs that represent the immune system of an adult is no more than 1 kg. Central to the immune system are lymphocytes, white blood cells whose function was a mystery until the 1960s. Lymphocytes normally account for about a quarter of all leukocytes. The body of an adult contains 1 trillion lymphocytes with a total mass of about 1.5 kg. Lymphocytes are formed in the bone marrow. They are round small cells, only 7-9 microns in size. The main part of the cell is occupied by the nucleus, covered with a thin membrane of the cytoplasm. As mentioned above, lymphocytes are found in the blood, lymph, lymph nodes, and spleen. It is the lymphocytes that are the organizers of the immune response, or "immune response". One of the important organs of the immune system is the thymus gland, or thymus. It is a small organ located behind the breastbone. The thymus is small. It reaches its greatest value - about 25 g - during puberty, and by the age of 60 it significantly decreases and weighs only 6 g. The thymus is literally filled with lymphocytes that get here from the bone marrow. Such lymphocytes are called thymus-dependent, or T-lymphocytes. The task of T-lymphocytes is to recognize “foreign” in the body, to detect a gene reaction.

Another type of lymphocytes is also formed in the bone marrow, but then it enters not the thymus, but another organ. So far, this organ has not been found in humans and mammals. Found in birds, it is an accumulation of lymphoid tissue near the large intestine. By the name of the researcher who discovered this formation, it is called the bursa of Fabricius (from Lat. Bursa - "bag"). If you remove the Fabricius bursa in chickens, then they stop producing antibodies. This experience shows that another type of lymphocytes, which produces antibodies, are "taught immunological literacy" here. Such lymphocytes were called B lymphocytes (from the word "bursa"). Although a similar organ has not yet been found in humans, the name of the corresponding type of lymphocytes stuck - these are B-lymphocytes. T-lymphocytes and B-lymphocytes, as well as macrophages and granulocytes (neutrophils, eosinophils and basophils) are all the main cells of the immune system. In turn, several classes are distinguished among T-lymphocytes: T-killers, T-helpers, T-suppressors. T-killers (from English kill - "to kill") destroy cancer cells, T-helpers (from English help - "to help") help to produce antibodies - immuno-globulins, and T-suppressors (from English suppress - "to suppress "), On the contrary, suppress the production of antibodies when it is necessary to stop the immune response. In addition to lymphocytes, the body has large cells - macrophages, located in some tissues. They capture and digest foreign microorganisms. Leukocytes, in addition to invading foreign agents, also destroy malfunctioning, damaged cells that can degenerate into cancer. They produce antibodies that fight against specific bacteria and viruses. The circulating lymph removes toxins and waste products from tissues and blood and transports them to the kidneys, skin and lungs for subsequent removal from the body. The liver and kidneys have the ability to filter out toxins and waste products from the blood. For the functioning of the immune system to be normal, a certain ratio must be observed between all types of cells. Any violation of this ratio leads to pathology. This is the most general information about the organs of the immune system. You should consider them in more detail.

The state of immunity is associated mainly with the coordinated activity of three types of leukocytes: B-lymphocytes, T-lymphocytes and macrophages. Initially, the formation of them or their precursors (stem cells) occurs in the red bone marrow, then they migrate to the lymphoid organs. There is a kind of hierarchy of organs of the immune system. They are divided into primary (where lymphocytes are formed) and secondary (where they function). All these organs are connected with each other and with other tissues of the body with the help of blood lymphatic vessels, along which leukocytes move. The primary organs are the thymus (thymus gland) and bursa (in birds), as well as red bone marrow (possibly the appendix) in humans: hence the T- and B-lymphocytes, respectively. "Learning" is aimed at acquiring the ability to differentiate one's own from someone else's (to recognize antigens). To be recognized, the cells of the body synthesize special proteins. Secondary lymphoid organs include the spleen, lymph nodes, adenoids, tonsils, appendix, and peripheral lymphatic follicles. These organs, like the immune cells themselves, are scattered throughout the human body to protect the body from antigens. In the secondary lymphoid organs, the development of an immune response to the antigen occurs. An example is a sharp increase in lymph nodes near the affected organ in inflammatory diseases. The lymphoid organs at first glance seem to be a small body system, but it has been estimated that their total mass is more than 2.5 kg (which, for example, is more than the mass of the liver). In the bone marrow, cells of the immune system are formed from a progenitor stem cell (the ancestor of all blood cells). B-lymphocytes differentiate there. The transformation of a stem cell into a B-lymphocyte occurs in the bone marrow. The bone marrow is one of the main sites for antibody synthesis. For example, in an adult mouse, the bone marrow contains up to 80% of the cells that synthesize immunoglobulins. Intravenous administration of bone marrow cells can restore the immune system in lethally irradiated animals.

The thymus is located directly behind the sternum. It is formed earlier than other organs of the immune system (already at the 6th week of pregnancy), but by the age of 15 it undergoes a reverse development, in adults it is almost completely replaced by fatty tissue. Penetrating from the bone marrow into the thymus, the stem cell, under the influence of hormones, first turns into the so-called thymocyte (a cell that is the precursor of the T-lymphocyte), and then, penetrating into the spleen or lymph nodes, turns into a mature, immunologically active T-lymphocyte. Most of the T-lymphocytes become the so-called T-killers (killers). A smaller part performs a regulatory function: T-helpers (helpers) increase immunological reactivity, T-suppressors (suppressors), on the contrary, reduce it. Unlike B-lymphocytes, T-lymphocytes (mainly T-helpers), with the help of their receptors, are able to recognize not just someone else's, but also their altered, that is, a foreign antigen should be presented most often by macrophages in combination with the body's own proteins. In the thymus gland, along with the formation of T-lymphocytes, thymosin and thymopoietin are produced - hormones that ensure the differentiation of T-lymphocytes and play a role in cellular immune responses.

Lymph nodes are peripheral organs of the immune system, which are located along the lymphatic vessels. The main functions are the retention and prevention of the spread of antigens, which is carried out by T-lymphocytes and B-lymphocytes. They are a kind of filter for microorganisms carried by lymph. Microorganisms pass through the skin or mucous membranes, enter the lymphatic vessels. Through them, they enter the lymph nodes, where they are retained and destroyed. Lymph node functions:

1) barrier - they are the first to react to contact with a damaging agent;

2) filtration - they delay microbes, foreign particles, and tumor cells penetrating with the lymph flow;

3) immune - associated with the production of immunoglobulins and lymphocytes in the lymph nodes;

4) synthetic - the synthesis of a special leukocyte factor that stimulates the multiplication of blood cells;

5) metabolic - the lymph nodes take part in the metabolism of fats, proteins, carbohydrates and vitamins.

The spleen has a structure close to the structure of the thymus gland. In the spleen, hormone-like substances are formed that are involved in the regulation of the activity of macrophages. In addition, phagocytosis of damaged and old erythrocytes occurs here. Spleen functions:

1) synthetic - it is in the spleen that immunoglobulins of classes M and J are synthesized in response to the ingress of antigen into the blood or lymph. The spleen tissue contains T and B-lymphocytes;

2) filtration - in the spleen, substances foreign to the body, damaged blood cells, coloring compounds and foreign proteins are destroyed and processed.

This type of lymphoid tissue is located under the mucous membrane. This includes the appendix, lymphoid ring, intestinal lymphatic follicles, and adenoids. Accumulations of lymphoid tissue in the intestine - Peyer's patches. This lymphoid tissue is a barrier to the entry of microbes through the mucous membranes. Functions of lymphoid accumulations in the intestines and tonsils:

1) recognition - the total surface area of \u200b\u200bthe tonsils in children is very large (almost 200 cm 2). In this area, there is a constant interaction of antigens and cells of the immune system. It is from here that information about a foreign agent follows in the central organs of immunity: thymus and bone marrow;

2) protective - on the mucous membrane of the tonsils and Peyer's patches in the intestine, in the appendix there are T-lymphocytes and B-lymphocytes, lysozyme and other substances that provide protection.

Thanks to the excretory system, the body is cleansed of microbes, their waste products and toxins.

The set of microorganisms that inhabit the skin and mucous membranes of a healthy person is a normal microflora. These microbes have the ability to resist the defense mechanisms of the body itself, but they are not able to penetrate tissues. The normal intestinal microflora has a great influence on the intensity of the immune response in the digestive organs. Normal microflora suppresses the development of disease-causing. For example, in a woman, the normal microflora of the vagina is represented by lactic acid bacteria, which in the process of life create an acidic environment that prevents the development of pathogenic microflora.

The internal environment of our body is separated from the outside world by skin and mucous membranes. It is they who are the mechanical barrier. In the epithelial tissue (it is located in the skin and mucous membranes), the cells are very tightly connected with each other by intercellular contacts. This obstacle is not easy to overcome. The ciliated epithelium of the airways removes bacteria and dust particles by vibrating cilia. The skin contains sebaceous and sweat glands. Sweat contains lactic and fatty acids. They lower the pH of the skin, harden it. Hydrogen peroxide, ammonia, urea, bile pigments contained in sweat inhibit the reproduction of bacteria. The lacrimal, salivary, gastric, intestinal and other glands, whose secretions are secreted on the surface of the mucous membranes, intensively fight microbes. First, they just wash them off. Second, some of the fluids secreted by the internal glands have a pH that damages or destroys bacteria (such as gastric juice). Thirdly, salivary and lacrimal fluids contain the enzyme lysozyme, which directly destroys bacteria.

And now let's take a closer look at the cells that ensure the coordinated work of the immune system. Leukocytes are the direct executors of immune responses. Their purpose is to recognize foreign substances and microorganisms, to combat them, and also to record information about them.

There are the following types of leukocytes:

1) lymphocytes (T-killers, T-helpers, T-suppressors, B-lymphocytes);

2) neutrophils (stab and segmented);

3) eosinophils;

4) basophils.

Lymphocytes are key figures in immunological surveillance. In the bone marrow, the precursors of lymphocytes are divided into two large branches. One of them (in mammals) ends its development in the bone marrow, and in birds - in a specialized lymphoid organ - bursa (bursa). These are B-lymphocytes. After the B-lymphocytes leave the bone marrow, they circulate for a short time in the bloodstream, and then they are introduced into the peripheral organs. They seem to be in a hurry to fulfill their mission, since the lifespan of these lymphocytes is short - only 7-10 days. A variety of B-lymphocytes are formed already during intrauterine development, and each of them is directed against a specific antigen. Another part of the lymphocytes from the bone marrow migrates to the thymus, the central organ of the immune system. This branch is T-lymphocytes. After completion of development in the thymus, part of the mature T-lymphocytes continues to be in the medulla, and part leaves it. A significant part of T-lymphocytes becomes T-killers, a smaller part performs a regulatory function: T-helpers increase immunological reactivity, and T-suppressors, on the contrary, weaken it. Helpers are capable of recognizing an antigen and activating the corresponding B-lymphocyte (directly on contact or at a distance using special substances - lymphokines). The most famous lymphokine is interferon, which is used in medicine for the treatment of viral diseases (for example, influenza), but it is effective only at the initial stage of the onset of the disease.

Suppressors have the ability to turn off the immune response, which is very important: if the immune system is not suppressed after the antigen is neutralized, the components of the immune system will destroy the body's own healthy cells, which will lead to the development of autoimmune diseases. Killers are the main link in cellular immunity, as they recognize antigens and effectively target them. Killers act against cells that are affected by viral infections, as well as tumor, mutated, aging cells of the body.

Neutrophils, basophils, and eosinophils are all types of white blood cells. They got their names for the ability to perceive dyes in different ways. Eosinophils react mainly to acidic dyes (Congo red, eosin) and are pink-orange in blood smears; basophils are alkaline (hematoxylin, methyl blue), so they look blue-violet in smears; neutrophils perceive both those and others, therefore they are stained with a gray-violet color. The nuclei of mature neutrophils are segmented, that is, they have constrictions (therefore they are called segmented), the nuclei of immature cells are called stab. One of the names of neutrophils (microphagocytes) indicates their ability to phagocytose microorganisms, but in smaller quantities than macrophages do. Neutrophils protect against bacteria, fungi and protozoa from entering the body. These cells eliminate dead tissue cells, remove old red blood cells and cleanse the wound surface. When evaluating a detailed blood test, a sign of an inflammatory process is a shift in the leukocyte formula to the left with an increase in the number of neutrophils.

Macrophages (they are also phagocytes) - "devourers" of foreign bodies and the most ancient cells of the immune system. Macrophages come from monocytes (a type of white blood cell). The first stages of development they pass in the bone marrow, and then leave it in the form of monocytes (rounded cells) and circulate in the blood for a certain time. From the bloodstream, they enter all tissues and organs, where they change their rounded shape to another, with processes. It is in this form that they acquire mobility and are able to adhere to any potentially foreign bodies. They recognize some foreign substances and signal them to T-lymphocytes, and these, in turn, to B-lymphocytes. Then B-lymphocytes begin to produce antibodies - immunoglobulins against the agent that the phagocyte cell and T-lymphocyte "reported" about. Sedentary macrophages can be found in almost all tissues and organs of a person, which provides an equivalent response of the immune system to any antigen that has entered the body anywhere. Macrophages eliminate not only microorganisms and foreign chemical poisons that enter the body from the outside, but also dead cells or toxins produced by the body's own (endotoxins). Millions of macrophages surround them, absorb and dissolve to remove them from the body. A decrease in the phagocytic activity of blood cells contributes to the development of a chronic inflammatory process and the emergence of aggression against the body's own tissues (the emergence of autoimmune processes). With the suppression of phagocytosis, dysfunction of destruction and removal of immune complexes from the body is also observed.

Immunoglobulins (antibodies) are a protein molecule. They combine with a foreign substance and form an immune complex, circulate in the blood and are located on the surface of the mucous membranes. The main feature of antibodies is the ability to bind a strictly defined antigen. For example, with measles, the body begins to produce "measles" immunoglobulin, against influenza - "anti-influenza", etc. The following classes of immunoglobulins are distinguished: JgM, JgJ, JgA, JgD, JgE. JgM - this type of antibodies appears the very first upon contact with an antigen (microbe), an increase in their titer in the blood indicates an acute inflammatory process, JgM play an important protective role in the penetration of bacteria into the blood in the early stages of infection. JgJ - antibodies of this class appear some time after contact with the antigen has occurred. They are involved in the fight against microbes - they form complexes with antigens on the surface of the bacterial cell. Subsequently, other plasma proteins (the so-called complement) are attached to them, and the bacterial cell is lysed (its membrane is ruptured). In addition, JgJ has been implicated in some allergic reactions. They make up 80% of all human immunoglobulins, are the main protective factor in a child during the first weeks of life, since they have the ability to pass through the placental barrier into the fetal blood serum. When breastfed, antibodies from the mother's milk enter the newborn's bloodstream through the intestinal mucosa of the newborn.

JgA - produced by lymphocytes of the mucous membranes in response to the local action of a foreign agent, thus they protect the mucous membranes from microorganisms and allergens. JgA inhibits the adhesion of microorganisms to the cell surface and thus prevents the penetration of microbes into the internal environment of the body. This is what prevents the development of chronic local inflammation.

JgD is the least studied. Researchers speculate that it is involved in the body's autoimmune processes.

JgE - antibodies of this class interact with receptors that are located on mast cells and basophils. As a result, histamine and other allergy mediators are released, resulting in an allergic reaction. Upon repeated contact with an allergen, JgE interacts on the surface of blood cells, which leads to the development of an anaphylactic allergic reaction. In addition to allergy reactions, JgE is involved in providing antihelminthic immunity.

Lysozyme.Lysozyme is present in all body fluids: tears, saliva, blood serum. This substance is produced by blood cells. Lysozyme is an antibacterial enzyme that is able to dissolve the shell of a microbe and cause its death. When acting on bacteria, lysozyme needs to support another factor of natural immunity - the complement system.

Complement.It is a group of protein compounds involved in the chain of immune responses. Complement may be involved in killing bacteria, preparing them for absorption by macrophages. The complement system consists of nine complex biochemical compounds. By changing the concentration of any of them, one can judge the place of possible pathology in the immunity link.

Interferons.These substances provide antiviral immunity, increase the resistance of cells to the effects of viruses, thereby preventing their reproduction in cells. These substances are produced mainly by leukocytes and lymphocytes. The result of the action of interferons is the formation of a barrier of cells not infected with the virus around the focus of inflammation. Of all the above-described organs of immunity, only the thymus undergoes reverse development. This process usually begins after the age of 15, but sometimes the thymus gland does not undergo age-related involution. As a rule, this happens with a decrease in the activity of the adrenal cortex and a lack of hormones that are produced in it. Then pathological conditions develop: susceptibility to infections and intoxications, the development of tumor processes. Children may have thymomegaly - an enlarged thymus. Often this leads to protracted courses of colds and is accompanied by allergic reactions.

Content

Various factors affect human health, but one of the main ones is the immune system. It consists of many organs that perform the functions of protecting all other components from external, internal adverse factors, and resists diseases. It is important to maintain immunity in order to weaken the harmful effects from the outside.

What is the immune system

In medical dictionaries and textbooks, it is said that the immune system is a collection of organs, tissues, and cells that make up it. Together, they form a comprehensive defense of the body against diseases, and also destroy foreign elements that have already entered the body. Its properties are to prevent the penetration of infections in the form of bacteria, viruses, fungi.

Central and peripheral organs of the immune system

Having appeared as an assistant in the struggle for survival in multicellular organisms, the human immune system and its organs have become an important component of the entire body. They connect organs, tissues, protect the body from cells that are alien at the genetic level, substances coming from outside. In terms of its functioning parameters, the immune system is similar to the nervous one. The device is also similar - the immune system includes central, peripheral components that respond to different signals, including a large number of receptors with specific memory.

Central organs of the immune system

1. The red bone marrow is the central organ supporting the immune system. It is a soft spongy tissue located inside the bones of a tubular, flat type. Its main task is the production of leukocytes, erythrocytes, platelets, which form blood. It is noteworthy that children have more of this substance - all bones contain a red brain, and in adults - only the bones of the skull, sternum, ribs, small pelvis.
2. The thymus gland or thymus is located behind the sternum. It produces hormones that increase the number of T-receptors, the expression of B-lymphocytes. The size, activity of the gland depends on age - in adults it is smaller in size and value.
3. The spleen is the third organ that looks like a large lymph node. In addition to storing blood, filtering it, preserving cells, it is considered a receptacle for lymphocytes. Here, old defective blood cells are destroyed, antibodies, immunoglobulins are formed, macrophages are activated, and humoral immunity is maintained.

Peripheral organs of the human immune system

Lymph nodes, tonsils, appendix belong to the peripheral organs of the immune system of a healthy person:

• Lymph node is called an oval formation, consisting of soft tissues, the size of which does not exceed a centimeter. It contains a large number of lymphocytes. If the lymph nodes are palpable, visible to the naked eye, this indicates an inflammatory process.
• The tonsils are also small oval-shaped accumulations of lymphoid tissue that can be found in the pharynx of the mouth. Their function is to protect the upper respiratory tract, supply the body with the necessary cells, and form microflora in the mouth and palate. A type of lymphoid tissue is Peyer's patches, located in the intestine. Lymphocytes ripen in them, an immune response is formed.
• The appendix has long been considered a rudimentary congenital process that is not necessary for humans, but this turned out to be not the case. It is an important immunological component that includes a large amount of lymphoid tissue. The organ is involved in the production of lymphocytes, storage of useful microflora.
• Another component of the peripheral type is lymph or lymph fluid without color, containing many white blood cells.

Cells of the immune system

Leukocytes, lymphocytes are important components to ensure immunity:

How the immune system works

The complex structure of the human immune system and its organs work at the genetic level. Each cell has its own genetic status, which the organs analyze when entering the body. In the case of a mismatch in status, a protective mechanism for the production of antigens is activated, which are specific antibodies for each type of penetration. Antibodies bind to the pathology, eliminating it, the cells rush to the product, destroy it, while you can see the inflammation of the site, then pus is formed from the dead cells, which comes out with the bloodstream.

Allergy is one of the reactions of innate immunity, in which a healthy body destroys allergens. External allergens are food, chemical, medical products. Internal - own fabrics with modified properties. These can be dead tissues, tissues with the effects of bees, pollen. An allergic reaction develops sequentially - at the first exposure of the allergen to the body, antibodies accumulate without loss, and at subsequent ones, they react with symptoms of a rash, a tumor.

How to improve human immunity

To stimulate the work of the human immune system and its organs, you need to eat right, lead a healthy lifestyle with physical activity. It is necessary to include vegetables, fruits, teas in the diet, harden, regularly walk in the fresh air. In addition, nonspecific immunomodulators - drugs that can be purchased on prescription during epidemics - will help improve the functioning of humoral immunity.

Video: the immune system of the human body

Attention! The information presented in the article is for informational purposes only. The materials of the article do not call for self-treatment. Only a qualified doctor can diagnose and give recommendations for treatment, based on the individual characteristics of a particular patient.

T cells are actually acquired immunity that can protect against cytotoxic damaging effects on the body. Alien aggressor cells, entering the body, bring about "chaos", which externally manifests itself in the symptoms of diseases.

In the course of their activity in the body, aggressor cells damage everything they can, acting in their own interests. And the task of the immune system is to find and destroy all foreign elements.

The body's specific defense against biological aggression (foreign molecules, cells, toxins, bacteria, viruses, fungi, etc.) is carried out using two mechanisms:

• the production of specific antibodies in response to foreign antigens (potentially dangerous substances for the body);
• development of cellular factors of acquired immunity (T-cells).

When "aggressor cells" enter the human body, the immune system recognizes foreign and own modified macromolecules (antigens) and removes them from the body. Also, during the initial contact with new antigens, they are memorized, which contributes to their faster removal, in the event of a secondary entry into the body.

The memorization process (presentation) occurs due to the antigen-recognizing receptors of cells and the work of antigen-presenting molecules (MHC molecules - histocompatibility complexes).

What are T cells of the immune system and what functions do they perform?

The immune system functions as a function of work. These are cells of the immune system that are
a variety of leukocytes and contributing to the formation of acquired immunity. Among them are:

• B cells (recognizing the "aggressor" and producing antibodies to it);
• T cells (acting as a regulator of cellular immunity);
• NK cells (destroying foreign structures marked with antibodies).

However, in addition to regulating the immune response, T-lymphocytes are able to perform an effector function, destroying tumor, mutated and foreign cells, participate in the formation of immunological memory, recognize antigens, and induce immune responses.

For reference. An important feature of T cells is their ability to respond only to presented antigens. On one T-lymphocyte there is only one receptor for one specific antigen. This ensures that the T cells do not react to the body's own autoantigens.

The variety of functions of T-lymphocytes is due to the presence of subpopulations in them, represented by T-helpers, T-killers and T-suppressors.

A subpopulation of cells, their stage of differentiation (development), degree of maturity, etc. is determined using special clusters of differentiation, designated as CD. The most significant are CD3, CD4 and CD8:

• CD3 is found on all mature T-lymphocytes and promotes signal transmission from the receptor to the cytoplasm. It is an important marker of lymphocyte function.
• CD8 is a marker for cytotoxic T cells.
• CD4 is a marker of T-helpers and a receptor for HIV (human immunodeficiency virus)

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T-helpers

For reference. The function of helpers is carried out through the synthesis of cytokines (information molecules that regulate interactions between cells).

Depending on the cytokine produced, they are divided into:

• T-helper cells of the 1st class (produce interleukin-2 and interferon gamma, providing a humoral immune response to viruses, bacteria, tumors and transplants).
• T-helper cells of the 2nd class (secrete interleukins-4, -5, -10, -13 and are responsible for the formation of IgE, as well as the immune response directed to extracellular bacteria).

T-helpers of the 1st and 2nd type always interact antagonistically, that is, the increased activity of the first type inhibits the function of the second type and vice versa.

The work of helpers provides interaction between all cells of the immune system, determining which type of immune response will prevail (cellular or humoral).

Important. Disruption of the work of helper cells, namely the lack of their function, is observed in patients with acquired immunodeficiency. Helper T cells are the main target of HIV. As a result of their death, the body's immune response to stimulation of antigens is disturbed, which leads to the development of severe infections, the growth of oncological neoplasms and death.

These are the so-called T-effectors (cytotoxic cells) or killer cells. This name is due to their ability to destroy target cells. Carrying out lysis (lysis (from the Greek λύσις - separation) - the dissolution of cells and their systems) of targets carrying a foreign antigen or mutated autoantigen (transplants, tumor cells), they provide antitumor defense reactions, transplant and antiviral immunity, as well as autoimmune reactions.

Killer T cells use their own MHC molecules to recognize a foreign antigen. By binding to it on the cell surface, they produce perforin (a cytotoxic protein).

After lysis of the "aggressor" cells, T-killers remain viable and continue to circulate in the blood, destroying foreign antigens.

T-killers make up 25 percent of all T-lymphocytes.

For reference. In addition to providing normal immune responses, T-effectors can participate in antibody-dependent cellular cytotoxicity reactions, contributing to the development of type II hypersensitivity (cytotoxic).

This can be manifested by drug allergies and various autoimmune diseases (systemic connective tissue diseases, hemolytic anemia of an autoimmune nature, malignant myasthenia gravis, autoimmune thyroiditis, etc.).

A similar mechanism of action is possessed by some drugs that can trigger the processes of necrosis of tumor cells.

Important. Drugs with a cytotoxic effect are used in chemotherapy of oncological diseases.

For example, Chlorbutin belongs to such medicines. This agent is used to treat chronic lymphocytic leukemia, lymphogranulomatosis and ovarian cancer.