What is humoral immunity, symptoms of weakening, methods of recovery. Humoral immunity - description, factors

After all, this phrase has to be heard quite often, especially within the walls of a medical facility. In this article, we will take a closer look at what humoral immunity is.

Disputes about how our immune system works began to arise back in the 19th century between such great scientists as Ilya Mechnikov and Paul Erlich. But, before delving into the classification of immunity and its differences among themselves, let's remember what human immunity is.

What is human immunity?

If a person's immunity decreases, then this is the cause of various diseases, ailments, inflammatory and infectious processes in the body.

Immunity is regulated in the human body at two levels - cellular and molecular. It is thanks to the increase in the body's defenses that the existence and life of a multicellular organism, that is, a person, became possible. Prior to this, only single-celled individuals functioned.

The mechanism of the emergence of immunity

After we realized that without immunity, a person would constantly get sick and, as a result, could not exist in this world, since his cells were constantly eaten by infections and bacteria. Now, back to the scientists - Mechnikov and Erlich, whom we talked about above.

There was a dispute between these two scientists about how the human immune system works (the dispute dragged on for several years). Mechnikov tried to prove that human immunity works exclusively at the cellular level. That is, all the body's defenses are manifested by the cells of the internal organs. The scientist Ehrlich made a scientific assumption that the body's defenses are manifested at the level of blood plasma.

As a result of numerous scientific studies and a huge number of days and years spent on experiments, a discovery was made:

Human immunity functions at the cellular and humoral levels.

For these studies, Ilya Mechnikov and Paul Ehrlich received the Nobil Prize.

Specific and non-specific immune response

The way our body reacts to pathogenic negative factors surrounding a person is called the immunity mechanism. What does this mean - let's take a closer look.

Today, specific and non-specific reactions of the body to environmental factors are classified.

A specific reaction is one that is directed to one particular pathogen. For example, a person once in childhood had chickenpox and after that he developed immunity to this disease.

This means that if a person has developed specific immunity, then he can be protected from negative factors throughout his life.

Nonspecific immunity is a universal protective function of the human body. If a person has nonspecific immunity, then his body immediately reacts to most viruses, infections, as well as foreign organisms that penetrate cells and internal organs.

A little about cellular immunity

To move on to the consideration of humoral immunity, let's first consider cellular immunity.

In our body, cells such as phagocytes are responsible for cellular immunity. Thanks to cellular immunity, we can be reliably protected from the penetration of various viruses and infections into the body.

Lymphocytes, which act as the body's defenses, are formed in the human bone marrow. After these cells are fully mature, they move from the bone marrow to the thymus or thymus. It is for this reason that in many sources you can find such a definition as T-lymphocytes.

T-lymphocytes - classification

Cellular immunity provides protection to the body through active T-lymphocytes. In turn, T-lymphocytes are divided into:

T-killers- that is, these are cells in the human body that are able to completely destroy and fight viruses and infections (antigens);
T-helpers- these are "smart" cells that are immediately activated in the body and begin to produce specific protective enzymes in response to the penetration of pathogenic microorganisms;
T-suppressors- they block the response of cellular immunity (of course, if there is such a need). T-suppressors are used in the fight against autoimmune diseases.

humoral immunity

Humoral immunity consists entirely of proteins that fill the human blood. These are cells such as interferons, C-reactive protein, an enzyme called lysozyme.

How does humoral immunity work?

The action of humoral immunity occurs through a large number of different substances that are aimed at inhibiting and destroying microbes, viruses and infectious processes.

All substances of humoral immunity are usually classified into specific and nonspecific.

Consider nonspecific factors of humoral immunity:

Blood serum (the infection enters the bloodstream - the activation of C-reactive protein begins - the infection is destroyed);
The secrets secreted by the glands - affect the growth and development of microbes, that is, they do not allow them to develop and multiply;
Lysozyme is an enzyme that is a kind of solvent for all pathogenic microorganisms.

Specific factors of humoral immunity are represented either by B-lymphocytes. These beneficial substances are produced by the internal organs of a person, in particular, the bone marrow, Peyer's patches, the spleen, and also the lymph nodes.

Most of the humoral immunity is formed during the development of the child in the womb and then transferred to the baby through breast milk. Some immune cells can be laid down during a person's life through vaccination.

Summary!

Immunity is the ability of our body to protect us (that is, internal organs and important vital systems) from the penetration of viruses, infections and other foreign objects.

Humoral immunity is built according to the type of constant formation in the human body of special antibodies that are necessary for an enhanced fight against infections and viruses that enter the body.

Humoral and cellular immunity are one common link, where one element cannot exist without the other.

To date, a wide range of types of human immune systems has been identified, among which it is necessary to distinguish cellular and humoral. The interaction of both types ensures the recognition and destruction of foreign microorganisms. The presented publication will help to consider the features and principles of operation of the extracellular defense system in more detail.

What is humoral immunity?

humoral immunity - this is the protection of the human body from the regular entry into the internal environment of foreign pathogens of infections and diseases. Protection is carried out by means of proteins soluble in internal fluids, human blood - antigens (lysozyme, interferon, reactive protein).

The principle of operation is the regular formation of substances that contribute to the prevention and spread of viruses, bacteria, microbes, regardless of what kind of microorganism has entered the internal environment, dangerous or harmless.

The humoral link of immunity includes:

Blood serum - it contains C - a reactive protein, the activity of which is aimed at eliminating pathogenic microbes;
Secrets of the glands that prevent the development of foreign bodies;
Lysozyme - stimulates the dissolution of bacterial cell walls;
Mucin - a substance aimed at protecting the shell of the cellular element;
Properdin - responsible for blood clotting;
Cytokines are a combination of proteins secreted by tissue cells;
Interferons - perform signaling functions, announcing the appearance of foreign elements in the internal environment;
Complementary system - the total number of proteins that contribute to the neutralization of microbes. The system includes twenty proteins.

Mechanisms

The mechanism of humoral immunity is a process during which a protective reaction is formed, aimed at preventing the penetration of viral microorganisms into the human body. The state of health and vital activity of a person depends on how the process of protection proceeds.

The process of protecting the body consists of the following steps:

There is a formation of B - a lymphocyte, which is formed in the bone marrow, where the lymphoid tissue matures;
Next, the process of antigen exposure to plasma cells and memory cells is carried out;
Antibodies of extracellular immunity recognize foreign particles;
Antibodies of the acquired immune defense are formed.

The mechanisms of the immune system are divided into:

Specific - the action of which is aimed at the destruction of a specific infectious agent;

Non-specific — differ in the universal character of orientation. The mechanisms recognize and fight any foreign antibodies.

Specific Factors

Specific factors of humoral immunity are produced by B-lymphocytes, which are formed in the bone marrow, spleen, and lymph nodes within two weeks. Presented antigens react to the appearance of foreign particles in body fluids. Specific factors include antibodies and immunoglobulins (Ig E, Ig A, Ig M, Ig D). The action of lymphocytes in the human body is aimed at blocking foreign particles, after this process phagocytes come into action, which eliminate viral elements.

Stages of antibody formation:

Latent phase (inductive) - during the first days, the elements are produced in small quantities;
Productive phase - the formation of particles occurs within two weeks.

Non-specific factors

The list of nonspecific factors of humoral immunity is represented by the following substances:

Elements of tissue cells;
Blood serum and the protein elements contained in it, which stimulate the resistance of cells to pathogens;
Secrets of the internal glands - help to reduce the number of bacteria;
Lysozyme is a substance that has an antibacterial effect.

Indicators of humoral immunity

The action of humoral immunity is carried out by developing the elements necessary to protect the body. The general condition and viability of the human body depends on the amount of antibodies obtained and the correct functioning of them.

If it is necessary to determine the parameters of the extracellular immune system, it is required to conduct a comprehensive blood test, the results of which determine the total number of formed particles and possible violations of the immune system.

Cellular and humoral immunity

Favorable functioning of extracellular immunity is ensured only through interaction with cellular defenses. The functions of the immune systems differ, but there are similar characteristics. They have an effective effect on the internal system of the human body.

difference between humoral and cellular immunity lies in their object of influence. Cellular functions directly in the cells of the body, preventing the reproduction of foreign microorganisms, and humoral affects viruses and bacteria in the extracellular space. One immune defense system cannot exist without the other.

Of great importance in the life of every person is the viability of his internal environment. Strengthening the immune defense and will help protect the human body from pathogenic bacteria and viruses.

The immune system has an important protective function for the human body. It protects it from various harmful microorganisms, chemicals, as well as from its own affected cells. necessary to ensure the integrity and support of the body in a normal state throughout life. Without immunity, the body is susceptible to various viruses, bacteria, fungi. Immunity can only be realized with the help of the immune system, in which peripheral (lymph nodes, spleen, lymph tissue) and central organs (thymus and red bone marrow) play an important role.

What forms of immunity exist?

Non-specific form actively fights against all microorganisms, regardless of their origin. Immunity is provided by different glands, they secrete useful substances. For example, a highly acidic gastric environment leads to the fact that most microbes begin to die. Saliva contains the substance lysozyme, which has antibacterial properties. This form of immunity can also include the process of phagocytosis, in which white blood cells capture and digest microbes.
specific form actively fights specific harmful microbes. The implementation of a specific form occurs with the help of antibodies and.

What are the types of immunity?

natural immunity - this is what we get genetically or acquired after a person has been ill with a specific disease.

artificial immunity h a person receives after a vaccine, serum or immunoglobulin. What happens after vaccination? In the body are dead or completely weakened microbes, they develop immunity. Such vaccines include vaccination against diphtheria, tuberculosis, and other infections. Active immunity can be developed throughout life.

All immune reactions are carried out due to two mechanisms - humoral immunity (the formation of specific substances) and cellular immunity (the work of specific body cells).

Features of humoral immunity

This immune mechanism is characterized by the production of antibodies to foreign microbes, chemical components. B-lymphocytes have a major role in. With their help, foreign agents are recognized in the body. Then the active production of antibodies (immunoglobulins) to foreign structures begins.

The antibodies produced are specific, they can only actively interact with foreign organisms to which they have reacted.

Antibodies can be found in the blood, on cell surfaces, in breast milk, gastric secretions, and even in tears. Due to the total number of antibodies, the immune system is formed. This happens after a person has had a specific infectious disease or been vaccinated. With the help of antibodies, toxic substances that are in the body are neutralized. For example, if a specific virus enters the body, antibodies begin to block the receptors, so it is not absorbed by the body. Due to specific antibodies, a person tolerates a particular disease more easily or does not get sick at all.

The value of cellular immunity for the body

This type of immunity is produced with the help of phagocytes and T-lymphocytes. To make it easier to understand what is the difference between humoral and cellular immunity, it is necessary to understand its functions. If humoral is responsible for the destruction of bacterial diseases, then cellular immunity helps fight viruses, fungus and prevents tumors from developing.

There are 3 main classes of T-lymphocytes:

T-killers have contact with foreign cells or damaged own cells, in the process, lymphocytes begin to actively destroy them.
T-helpers begin the production of interferon, a cytokine that helps to activate the immune system.
T-suppressors keep all immune processes under control.

The development of cellular immunity occurs due to phagocytes (a type of leukocytes), they can be both in the blood and in tissues. The blood contains the most granulocytes (basophils, neutrophils, eosinophils) and monocytes. Tissue-type phagocytes are found in the tissues of the lungs, spleen, lymph nodes, endocrine system, and pancreas.

In order to ensure the immune defense of the body, the process of phagocytosis is necessary, in which the antigen is destroyed by phagocytes.

Thus, humoral and cellular immunity in the body closely interact with each other. One cannot exist without the other. They differ in their functionality. If the humoral fights bacteria most of all, then the cellular one actively fights fungus, cancer cells and various viruses. These two types of immunity are necessary for the full functioning of the immune system. To increase the protective function of the body, it is necessary to regularly take vitamins, play sports, and walk in the fresh air as much as possible. It is also important not to forget to rest, get enough sleep. In extreme cases, immunomodulatory drugs may be required. Remember that immunity is one of the factors of your health. If you do not constantly strengthen it, all viruses, infections, bacteria will constantly cling to you. It is especially important to take care of the formation of the child's immune system, this should be done immediately after birth.

FGOU VPO Moscow State Academy of Veterinary Medicine and Biotechnology named after V.I. K.I. Scriabin"

on the topic: "Humoral immunity"

Performed:

Moscow 2004

Introduction

ANTIGENS

antibodies, structure and function of immunoglobulins

THE SYSTEM OF COMPLEMENT COMPONENTS

alternate activation path

classic activation path

cytokines

interleukins

interferons

tumor necrosis factors

colony stimulating factors

other biologically active substances

acute phase proteins

normal (natural) antibodies

bacteriolysins

inhibitors of enzymatic activity of bacteria and viruses

properdin

other substances...

HUMORAL IMMUNE RESPONSE

List of used literature

Introduction

To humoral immune components include a wide variety of immunologically active molecules, from simple to very complex, which are produced by immunocompetent and other cells and are involved in protecting the body from foreign or its defective:

immunoglobulins,

cytokines,

complement system,

acute phase proteins

enzyme inhibitors that inhibit the enzymatic activity of bacteria,

virus inhibitors,

numerous low molecular weight substances that are mediators of immune reactions (histamine, serotonin, prostaglandins and others).

Of great importance for the effective protection of the body are also the saturation of tissues with oxygen, the pH of the environment, the presence of Ca 2+ and Mg 2+ and other ions, trace elements, vitamins, etc.

All these factors function interrelatedly with each other and with the cellular factors of the immune system. Thanks to this, the precise direction of immune processes is maintained and, ultimately, the genetic constancy of the internal environment of the body.

Antigens

BUT An antigen is a genetically alien substance (protein, polysaccharide, lipopolysaccharide, nucleoprotein) that, when introduced into the body or formed in the body, can cause a specific immune response and interact with antibodies and antigen-recognizing cells.

An antigen contains several distinct or repetitive epitopes. An epitope (antigenic determinant) is a distinctive part of an antigen molecule that determines the specificity of antibodies and effector T-lymphocytes in an immune response. The epitope is complementary to the active site of an antibody or T-cell receptor.

Antigenic properties are associated with the molecular weight, which should be at least tens of thousands. Hapten is an incomplete antigen in the form of a small chemical group. The hapten itself does not cause the formation of antibodies, but it can interact with antibodies. When a hapten combines with a large molecular protein or polysaccharide, this complex compound acquires the properties of a full-fledged antigen. This new complex substance is called the conjugated antigen.

Antibodies, structure and functions of immunoglobulins

BUT
antibodies are immunoglobulins produced by B-lymphocytes (plasma cells). Immunoglobulin monomers consist of two heavy (H-chains) and two light (L-chains) polypeptide chains linked by a disulfide bond. These chains have constant (C) and variable (V) regions. Papain cleaves immunoglobulin molecules into two identical antigen-binding fragments - Fab (Fragment antigen binding) and Fc (Fragment cristallizable). The active center of antibodies is the antigen-binding site of the Fab-fragment of immunoglobulin, formed by the hypervariable regions of the H- and L-chains; binds antigen epitopes. The active center has specific complementary sites to certain antigenic epitopes. The Fc fragment can bind complement, interact with cell membranes, and is involved in the transfer of IgG across the placenta.

Antibody domains are compact structures held together by a disulfide bond. So, in IgG, there are: V - domains of light (V L) and heavy (V H) chains of the antibody, located in the N-terminal part of the Fab fragment; C-domains of constant regions of light chains (C L); C domains of heavy chain constant regions (C H 1, C H 2, C H 3). The complement binding site is located in the C H 2 domain.

Monoclonal antibodies are homogeneous and highly specific. They are produced by a hybridoma - a population of hybrid cells obtained by fusion of an antibody-forming cell of a certain specificity with an "immortal" myeloma cell.

There are such properties of antibodies as:

affinity (affinity) - the affinity of antibodies to antigens;

Avidity is the strength of the antibody-antigen bond and the amount of antigen bound by the antibody.

Antibody molecules are distinguished by exceptional diversity, associated primarily with variable regions located in the N-terminal regions of the light and heavy chains of the immunoglobulin molecule. The rest of the sections are relatively unchanged. This makes it possible to isolate the variable and constant regions of the heavy and light chains in the immunoglobulin molecule. Separate parts of the variable regions (the so-called hypervariable regions) are particularly diverse. Depending on the structure of the constant and variable regions, immunoglobulins can be divided into isotypes, allotypes and idiotypes.

The isotype of antibodies (class, subclass of immunoglobulins - IgM, IgG1, IgG2, IgG3, IgG4, IgA1, IgA2, IgD, IgE) is determined by the C-domains of heavy chains. Isotypes reflect the diversity of immunoglobulins at the species level. When animals of one species are immunized with the blood serum of individuals of another species, antibodies are formed that recognize the isotype specificities of the immunoglobulin molecule. Each class of immunoglobulins has its own isotype specificity, against which specific antibodies can be obtained, for example, rabbit antibodies against mouse IgG.

Availability allotypes due to genetic diversity within a species and concerns structural features of the constant regions of immunoglobulin molecules in individuals or families. This diversity is of the same nature as the differences in people according to the blood groups of the ABO system.

The antibody idiotype is determined by the antigen-binding sites of the Fab fragments of the antibodies, ie the antigenic properties of the variable regions (V-regions). An idiotype consists of a set of idiotopes - antigenic determinants of the V-regions of an antibody. Idiotypes are regions of the variable portion of an immunoglobulin molecule that are themselves antigenic determinants. Antibodies obtained against such antigenic determinants (anti-idiotypic antibodies) are able to distinguish between antibodies of different specificity. Anti-idiotypic sera can detect the same variable region on different heavy chains and in different cells.

According to the type of heavy chain, 5 classes of immunoglobulins are distinguished: IgG, IgM, IgA, IgD, IgE. Antibodies belonging to different classes differ from each other in many respects in terms of half-life, distribution in the body, ability to fix complement and bind to the surface Fc receptors of immunocompetent cells. Since all classes of immunoglobulins contain the same heavy and light chains, as well as the same heavy and light chain variable domains, the above differences should be due to the constant regions of the heavy chains.

IgG - the main class of immunoglobulins found in blood serum (80% of all immunoglobulins) and tissue fluids. It has a monomeric structure. It is produced in large quantities during the secondary immune response. Antibodies of this class are able to activate the complement system and bind to receptors on neutrophils and macrophages. IgG is the main opsonizing immunoglobulin in phagocytosis. Since IgG is able to cross the placental barrier, it plays a major role in protecting against infections during the first weeks of life. The immunity of newborns is also enhanced due to the penetration of IgG into the blood through the intestinal mucosa after the entry of colostrum containing large amounts of this immunoglobulin. The content of IgG in the blood depends on antigenic stimulation: its level is extremely low in animals kept in sterile conditions. It rises rapidly when the animal is placed under normal conditions.

IgM makes up about 6% of serum immunoglobulins. The molecule is formed by a complex of five linked monomeric subunits (pentamer). IgM synthesis begins before birth. These are the first antibodies produced by developing B-lymphocytes. In addition, they are the first to appear in a membrane-bound monomeric form on the surface of B-lymphocytes. It is believed that IgM in the phylogenesis of the immune response of vertebrates appeared earlier than IgG. Antibodies of this class are released into the blood during the early stages of the primary immune response. The binding of the antigen to IgM causes the attachment of the Clq component of the complement and its activation, which leads to the death of microorganisms. Antibodies of this class play a leading role in removing microorganisms from the bloodstream. If a high level of IgM is found in the blood of newborns, then this usually indicates intrauterine infection of the fetus. In mammals, birds and reptiles, IgM is a pentamer, in amphibians it is a hexamer, and in most bony fish it is a tetramer. At the same time, there were no significant differences in the amino acid composition of the constant regions of IgM light and heavy chains of different classes of vertebrates.

IgA exists in two forms: in the blood serum and in the secrets of the exocrine glands. Serum IgA is approximately 13% of the total content of immunoglobulins in the blood. Dimeric (predominant), as well as tri- and tetrameric forms are presented. IgA in the blood has the ability to bind and activate complement. Secretory IgA (slgA) is the main class of antibodies in the secretions of exocrine glands and on the surface of mucous membranes. It is represented by two monomeric subunits associated with a special glycoprotein - the secretory component. The latter is produced by cells of the glandular epithelium and ensures the binding and transport of IgA to the secretions of the exocrine glands. Secretory IgA blocks the attachment (adhesion) of microorganisms to the surface of the mucous membranes and its colonization by them. slgA may also play the role of an opsonin. High levels of secretory IgA in mother's milk protect the mucous membranes of the infant's digestive tract from intestinal infections. When comparing different secrets, it turned out that the maximum level of slgA was found in tears, and the highest concentrations of the secretory component were found in the lacrimal glands.

IgD is less than 1% of the total content of immunoglobulins in the blood serum. Antibodies of this class have a monomeric structure. They contain a large amount of carbohydrates (9-18%). This immunoglobulin is characterized by extremely high sensitivity to proteolysis and a short plasma half-life (about 2.8 days). The latter may be due to the large length of the hinge region of the molecule. Almost all IgD, together with IgM, is located on the surface of blood lymphocytes. It is believed that these antigen receptors can interact with each other, controlling the activation and suppression of lymphocytes. It is known that the sensitivity of IgD to proteolysis increases after binding to an antigen.

Plasma cells secreting IgD have been found in the tonsils. They are rarely found in the spleen, lymph nodes and lymphoid tissues of the intestine. Immunoglobulins of this class are the main membrane fraction on the surface of B-lymphocytes isolated from the blood of patients with leukemia. Based on these observations, it was hypothesized that IgD molecules are receptors on lymphocytes and may be involved in the induction of immunological tolerance.

IgE is present in the blood in trace amounts, accounting for only 0.002% of all immunoglobulins in the blood serum. Like IgG and IgD, it has a monomeric structure. It is produced mainly by plasma cells in the mucous membranes of the digestive tract and respiratory tract. The content of carbohydrates in the IgE molecule is 12%. When injected subcutaneously, this immunoglobulin lingers in the skin for a long time, binding to mast cells. Subsequent interaction of the antigen with such a sensitized mast cell leads to its degranulation with the release of vasoactive amines. The main physiological function of IgE is apparently the protection of the mucous membranes of the body by local activation of blood plasma factors and effector cells due to the induction of an acute inflammatory reaction. Pathogenic microbes capable of breaking through the line of defense formed by IgA will bind to specific IgE on the surface of mast cells, as a result of which the latter will receive a signal to release vasoactive amines and chemotactic factors, and this in turn will cause an influx of circulating IgG, complement, neutrophils. and eosinophils. It is possible that local production of IgE contributes to protection against helminths, since this immunoglobulin stimulates the cytotoxic effect of eosinophils and macrophages.

Complement system

Complement is a complex complex of proteins and glycoproteins (about 20), which, like the proteins involved in the processes of blood coagulation, fibrinolysis, form cascade systems of effective protection of the body from foreign cells. This system is characterized by a rapid, multiply enhanced response to the primary antigenic signal due to a cascade process. The product of one reaction serves as a catalyst for the next. The first data on the existence of the complement system were obtained at the end of the 19th century. when studying the mechanisms of protecting the body from bacteria penetrating into it and the destruction of foreign cells introduced into the blood. These studies have shown that the body responds to the penetration of microorganisms and foreign cells with the formation of antibodies capable of agglutinating these cells without causing their death. The addition of fresh serum to this mixture caused the death (cytolysis) of the immunized subjects. This observation was the impetus for intensive research aimed at elucidating the mechanisms of lysis of foreign cells.

A number of components of the complement system are denoted by the symbol "C" and a number that corresponds to the chronology of their discovery. There are two ways to activate a component:

without antibodies - alternative

with the participation of antibodies - classic

Alternative way to activate the computerelement

The first pathway of complement activation, caused by foreign cells, is phylogenetically the oldest. A key role in the activation of complement in this way is played by C3, which is a glycoprotein consisting of two polypeptide chains. Under normal conditions, the internal thioether bond in C3 is slowly activated as a result of interaction with water and trace amounts of proteolytic enzymes in blood plasma, leading to the formation of C3b and C3a (C3 fragments). In the presence of Mg 2+ ions, C3b can form a complex with another component of the complement system, factor B; then the last factor is cleaved by one of the blood plasma enzymes - factor D. The resulting C3bBb complex is a C3-convertase - an enzyme that cleaves C3 into C3a and C3b.

Some microorganisms can activate C3Bb convertase with the formation of a large amount of C3 cleavage products by binding the enzyme to the carbohydrate regions of their surface membrane and thereby protecting it from the action of factor H. Then another protein properdin interacts with convertase, increasing the stability of its binding. Once C3 is cleaved by convertase, its internal thioether bond is activated and the reactive C3b derivative covalently binds to the membrane of the microorganism. One C3bBb active center allows a large number of C3b molecules to bind to the microorganism. There is also a mechanism that inhibits this process under normal conditions: in the presence of factors I and H, C3b is converted to C3bI, the latter being cleaved to the final inactive C3c and C3d peptides under the influence of proteolytic enzymes. The next activated component, C5, interacts with membrane-bound C3b, becomes a substrate for C3bBb and is cleaved to form a short C5a peptide, while the C5b fragment remains fixed on the membrane. Then C5b sequentially adds C6, C7 and C8 to form a complex that facilitates the orientation of molecules of the last C9 component on the membrane. This leads to the deployment of C9 molecules, their penetration into the bilipid layer and polymerization into a ring-shaped "membrane attack complex" (MAC). The C5b-C7 complex wedged into the membrane allows C8 to come into direct contact with the membrane, cause disorganization of its regular structures and, finally, lead to the formation of helical transmembrane channels. The emerging transmembrane channel is completely permeable to electrolytes and water. Due to the high colloid osmotic pressure inside the cell, Na + and water ions enter it, which leads to the lysis of a foreign cell or microorganism.

In addition to the ability to lyse cells with foreign information, complement also has other important functions:

a) due to the presence on the surface of phagocytic cells of receptors for C3b and C33, adhesion of microorganisms is facilitated;

b) small peptides C3a and C5a (“anaphylatoxins”) formed during complement activation:

stimulate the chemotaxis of neutrophils to the place of accumulation of objects of phagocytosis,

activate oxygen-dependent mechanisms of phagocytosis and cytotoxicity,

cause the release of inflammatory mediators from mast cells and basophils,

cause the expansion of blood capillaries and increase their permeability;

c) proteinases that appear during complement activation, despite their substrate specificity, are able to activate other blood enzyme systems: the coagulation system and the kinin formation system;

d) complement components, interacting with insoluble antigen-antibody complexes, reduce the degree of their aggregation.

Classical complement activation pathway

The classical pathway is initiated when an antibody bound to a microbe or other cell carrying foreign information binds and activates the first component of the Clq cascade. This molecule is multivalent in relation to antibody binding. It consists of a central collagen-like rod that branches into six peptide chains, each of which terminates in an antibody-binding subunit. According to electron microscopy, the entire molecule resembles a tulip. Its six petals are formed by the C-terminal globular regions of polypeptide chains, collagen-like regions are twisted in each subunit into a three-helix structure. Together, they form a stem-like structure due to the association in the region of the N-terminal region by disulfide bonds. The globular regions are responsible for interaction with antibodies, and the collagen-like region is responsible for binding to the other two C1 subunits. To combine three subunits into a single complex, Ca 2+ ions are needed. The complex is activated, acquires proteolytic properties and participates in the formation of binding sites for other components of the cascade. The process ends with the formation of MAC.

Antigen-specific antibodies can complement and enhance the ability of natural immune mechanisms to initiate acute inflammatory responses. A smaller part of the complement in the body is activated through an alternative pathway, which can be carried out in absence of antibodies. This nonspecific pathway of complement activation is important in the destruction of aging or damaged body cells by phagocytes, when the attack begins with nonspecific sorption of immunoglobulins and complement on the damaged cell membrane. However, the classical pathway of complement activation in mammals is prevalent.

Cytokines

Cytokines are proteins mainly of activated cells of the immune system that provide intercellular interactions. Cytokines include interferons (IFN), interleukins (IL), chemokines, tumor necrosis factors (TNF), colony stimulating factors (CSF), growth factors. Cytokines act according to the relay principle: the effect of a cytokine on a cell causes the formation of other cytokines by it (cytokine cascade).

The following mechanisms of action of cytokines are distinguished:

Intracrine mechanism - the action of cytokines inside the producer cell; binding of cytokines to specific intracellular receptors.

The autocrine mechanism is the action of a secreted cytokine on the secreting cell itself. For example, IL-1, -6, -18, TNFα are autocrine activating factors for monocytes/macrophages.

Paracrine mechanism - the action of cytokines on nearby cells and tissues. For example, IL-1, -6, -12, -18, TNFα produced by macrophages activate T-helpers (Th0), recognizing the antigen and MHC of the macrophage (Scheme of autocrine-paracrine regulation of the immune response).

The endocrine mechanism is the action of cytokines at a distance from the producing cells. For example, IL-1, -6 and TNFα, in addition to auto and paracrine effects, can have a distant immunoregulatory effect, a pyrogenic effect, induction of the production of acute phase proteins by hepatocytes, symptoms of intoxication, and multiorgan damage in toxic-septic conditions.

Interleukins

At present, the structure and functions of 16 interleukins have been isolated, studied, their serial numbers are in the order of receipt:

Interleukin-1. Produced by macrophages, as well as AGP cells. It triggers the immune response by activating T-helpers, plays a key role in the development of inflammation, stimulates myelopoiesis and the early stages of erythropoiesis (later it suppresses, being an antagonist of erythropoietin), is a mediator of the interaction between the immune and nervous systems. Inhibitors of IL-1 synthesis are prostaglandin E2, glucocorticoids.

Interleukin-2. Produce activated T-helpers. It is a growth and differentiation factor for T-lymphocytes and NK cells. Participates in the implementation of antitumor resistance. Inhibitors are glucocorticoids.

Interleukin-3. They produce activated T-helpers, such as Th1 and Th2, as well as B-lymphocytes, bone marrow stromal cells, brain astrocytes, keratinocytes. Growth factor for mast cells of the mucous membranes and enhances their release of histamine, a regulator of the early stages of hematopoiesis, suppresses the formation of NK cells under stress.

Interleukin-4. Stimulates the proliferation of B-lymphocytes activated by antibodies to IgM. It is produced by T-helpers of the Th2 type, on which it has a stimulating differentiation effect, affects the development of hematopoietic cells, macrophages, NK cells, basophils. Promotes the development of allergic reactions, has anti-inflammatory and antitumor effects.

Interleukin-6. It is produced by lymphocytes, monocytes/macrophages, fibroblasts, hepatocytes, keratinocytes, mesanglial, endotholial and hematopoietic cells. According to the spectrum of biological action, it is close to IL-1 and TNFα, participates in the development of inflammatory, immune reactions, and serves as a growth factor for plasma cells.

Interleukin-7. Produced by stromal cells of the bone marrow and thymus (fibroblasts, endothelial cells), macrophages. It is the main lymphopoietin. Promotes the survival of pre-T cells, causes antigen-dependent reproduction of T-lymphocytes outside the thymus. Deletion of the IL-7 gene in animals leads to the devastation of the thymus, the development of total lymphopenia and severe immunodeficiency.

Interleukin-8. They form macrophages, fibroblasts, hepatocytes, T-lymphocytes. The main target of IL-8 is neutrophils, on which it acts as a chemoattractant.

Interleukin-9. Produced by T-helper type Th2. Supports the proliferation of activated T-helpers, affects erythropoiesis, mast cell activity.

Interleukin-10. It is produced by T-helper type Th2, T-cytotoxic and monocytes. Suppresses the synthesis of cytokines by T-cells of the Th1 type, reduces the activity of macrophages and their production of inflammatory cytokines.

Interleukin-11. Formed by fibroblasts. Causes the proliferation of early hematopoietic precursors, prepares stem cells to perceive the action of IL-3, stimulates the immune response and the development of inflammation, promotes the differentiation of neutrophils, the production of acute phase proteins.

There is the ability of our body to protect itself from pathogens, chemical agents, as well as from our own diseased and substandard cells.

The biological meaning of immunity is to ensure the integrity and maintenance of the constancy of the composition of the body at the genetic and molecular level throughout its life.

Immunity is realized thanks to the immune system, in which central and peripheral organs are isolated. They produce immunocompetent cells. The central organs include the bone red marrow and the thymus gland (thymus). Peripheral organs are the spleen, lymph nodes, as well as lymphoid tissue located in some organs. Immune defense is complex. Let's see what forms, types and mechanisms of immunity exist.

Nonspecific immunity is directed against all microorganisms, regardless of their nature. It is carried out by various substances that secrete the glands of the skin, digestive and respiratory tract. For example, in the stomach, the environment is strongly acidic, due to which a number of microbes die. Saliva contains lysozyme, which has a strong antibacterial effect, etc. Nonspecific immunity also includes phagocytosis - the capture and digestion of microbial cells by leukocytes.
Specific immunity is directed against a specific type of microorganism. Specific immunity is carried out due to T-lymphocytes and antibodies. For each type of microbe, the body produces its own antibodies.

There are also two types of immunity, each of which, in turn, is divided into two more groups.

Natural immunity is inherited or acquired after illnesses. He, respectively, and is divided into congenital and acquired.
A person acquires artificial immunity after vaccination - the introduction of vaccines, sera and immunoglobulins. Vaccination contributes to the emergence of active artificial immunity, since either killed or weakened cultures of microbes enter the body, and the body then develops immunity on them. This is how vaccines against poliomyelitis, tuberculosis, diphtheria and some other infectious diseases work. Active immunity is produced for years or for life.

With the introduction of sera or immunoglobulins, ready-made antibodies enter the body, which circulate in the body and protect it for several months. Since the body receives ready-made antibodies, this type of artificial immunity is called passive.

And finally, there are two main mechanisms by which immune responses are carried out. This is humoral and cellular immunity. As the name suggests, humoral immunity is realized through the formation of certain substances, and cellular immunity is realized through the work of certain cells of the body.

humoral immunity

This mechanism of immunity is manifested in the formation of antibodies to antigens - foreign chemicals, as well as microbial cells. B-lymphocytes play a fundamental role in humoral immunity. It is they who recognize foreign structures in the body, and then produce antibodies on them - specific substances of a protein nature, which are also called immunoglobulins.

The antibodies that are produced are extremely specific, that is, they can only interact with those foreign particles that caused the formation of these antibodies.

Immunoglobulins (Ig) are found in the blood (serum), on the surface of immunocompetent cells (surface), as well as in the secrets of the gastrointestinal tract, lacrimal fluid, breast milk (secretory immunoglobulins).

In addition to being highly specific, antigens also have other biological characteristics. They have one or more active sites that interact with antigens. More often there are two or more. The strength of the connection between the active center of an antibody and an antigen depends on the spatial structure of the substances that bind (i.e., antibodies and antigen), as well as the number of active centers in one immunoglobulin. Several antibodies can bind to one antigen at once.

Immunoglobulins have their own classification using Latin letters. In accordance with it, immunoglobulins are divided into Ig G, Ig M, Ig A, Ig D and Ig E. They differ in structure and function. Some appear immediately after infection, while others appear later.

The antigen-antibody complex activates the complement system (protein substance), which contributes to the further absorption of microbial cells by phagocytes.

Due to antibodies, immunity is formed after infections, as well as after. They help to neutralize toxins that enter the body. In viruses, antibodies block receptors, preventing them from being absorbed by the cells of the body. Antibodies are involved in opsonization (“wetting microbes”), making antigens easier to swallow and digest macrophages.

Cellular immunity

As already mentioned, cellular immunity is carried out at the expense of immunocompetent cells. These are T-lymphocytes and phagocytes. And if the protection against bacteria of the body occurs mainly due to the humoral mechanism, then antiviral, antifungal, and antitumor protection - due to the cellular mechanisms of immunity.

T-lymphocytes are divided into three classes:
T-killers (directly contact with a foreign cell or damaged cells of their own body and destroy them)
T-helpers (produce cytokines and interferon, which then activate macrophages)
T-suppressors (control the strength of the immune response, its duration)

As you can see, cellular and humoral immunity are interconnected.

The second group of immunocompetent cells involved in cellular immune responses are phagocytes. In fact, these are different types of leukocytes that are found either in the blood (circulating phagocytes) or in tissues (tissue phagocytes). Granulocytes (neutrophils, basophils, eosinophils) and monocytes circulate in the blood. Tissue phagocytes are found in connective tissue, spleen, lymph nodes, lungs, endocrine cells of the pancreas, etc.

The process of destruction of the antigen by phagocytes is called phagocytosis. It is essential for the immune defense of the body.

Phagocytosis proceeds in stages:

Chemotaxis. Phagocytes are sent to the antigen. This can be facilitated by certain complement components, some leukotrienes, as well as products secreted by pathogenic microbes.
Adhesion (gluing) of phagocytes-macrophages to the vascular endothelium.
The passage of phagocytes through the wall and out of it
Opsonization. Antibodies envelop the surface of a foreign particle, they are helped by complement components. This facilitates the absorption of antigen by phagocytes. The phagocyte then attaches itself to the antigen.
Actually phagocytosis. The foreign particle is absorbed by the phagocyte: first, a phagosome is formed - a specific vacuole, which then connects to the lysosome, where the lysosomal enzymes that digest the antigen are located).
Activation of metabolic processes in the phagocyte, contributing to the implementation of phagocytosis.
destruction of the antigen.

The process of phagocytosis can be completed and incomplete. In the first case, the antigen is phagocytosed successfully and completely; in the second case, it is not. The incompleteness of phagocytosis is used by some pathogenic microorganisms for their own purposes (gonococci, Mycobacterium tuberculosis).

Find out how you can support your immune system.

Immunity is the most important process of our body, helping to maintain its integrity, protecting it from harmful microorganisms and foreign agents. Cellular and humoral are two mechanisms that, acting in harmony, complement each other and help maintain health and life. These mechanisms are quite complex, but our body as a whole is a very complex self-organizing system.