Antigens classification properties their structure specificity. Types of antigens. Antibody classes IgM and IgA

Lecture outline:

1. Antigens: definition, structure, basic properties.

2. Antigens of microorganisms.

3. Antigens of humans and animals.

4. Antibodies: definition, main functions, structure.

5. Classes of immunoglobulins, their characteristics.

6. Dynamics of antibody formation.

Antigens (from Greek. anti- against, genos- create; term proposed in 1899 Deutsch) - substances of various origins that carry signs of genetic foreignness and, when introduced into the body, cause the development of specific immunological reactions.

Main functions of antigens:

Induce an immunological response (synthesis of antibodies and launch of cellular immunity reactions).

They specifically interact with the resulting antibodies (in vivo and in vitro).

Provide immunological memory- the body’s ability to respond to repeated introduction of an antigen with an immunological reaction characterized by greater strength and faster development.

Determine development immunological tolerance- lack of an immune response to a specific antigen while maintaining the ability to have an immune response to other antigens.

Structure of antigens:

Antigens consist of 2 parts:

1. High molecular weight carrier (schlepper)- a high-polymer protein that determines the antigenicity and immunogenicity of the antigen.

2. Determinant groups (epitopes)- surface structures of the antigen, complementary to the active center of antibodies or the T-lymphocyte receptor and determining the specificity of the antigen. One carrier may have several different epitopes, consisting of peptides or lipopolysaccharides and located in different parts of the antigen molecule. Their diversity is achieved due to a mosaic of amino acid or lipopolysaccharide residues located on the surface of the protein.

The number of determinant groups or epitopes determines antigen valency.

Antigen valency- the number of identical epitopes on an antigen molecule, equal to the number of antibody molecules that can attach to it.

Main properties of antigens:

1. Immunogenicity- the ability to induce immunity, immunity to infection (used to characterize infectious agents).

2. Antigenicity- the ability to induce the formation of specific antibodies (a particular variant of immunogenicity).

3. Specificity- a property by which antigens differ from each other and determines the ability to selectively react with specific antibodies or sensitized lymphocytes.

Immunogenicity, antigenicity and specificity depend on many factors.

Factors determining antigenicity:

- Foreignness (heterogeneity)- the genetically determined property of the antigens of some animal species to differ from the antigens of other animal species (the farther the animals are from each other phenotypically, the more antigenicity they have in relation to each other).

- Molecular weight must be at least 10,000 daltons; with increasing molecular weight, antigenicity increases.

- Chemical nature and chemical homogeneity: the most antigenic are proteins, their complexes with lipids (lipoproteins), with carbohydrates (glycoproteins), with nucleic acids (nucleoproteins), as well as complex polysaccharides (with a mass of more than 100,000 D), lipopolysaccharides; Nucleic acids and lipids themselves are non-immunogenic due to insufficient structural rigidity.

- Structure rigidity(in addition to a certain chemical nature, antigens must have a certain rigidity of structure, for example, denatured proteins do not have antigenicity).

- Solubility(insoluble proteins cannot be in the colloidal phase and do not cause the development of immune reactions).

Factors determining immunogenicity:

Properties of antigens.

Method of antigen administration (oral, intradermal, intramuscular).

Antigen dose.

Interval between administrations.

The state of an immunized macroorganism.

The rate of destruction of the antigen in the body and its removal from the body.

Immunogenicity and antigenicity may not be the same! For example, the dysentery bacillus is highly antigenic, but no pronounced immunity against dysentery is developed.

Factors that determine specificity:

Chemical nature of the antigenic determinant.

The structure of the antigenic determinant (type and sequence of amino acids in the primary polypeptide chain).

Spatial configuration of antigenic determinants.

Types of antigens by structure:

1. Haptens (defective antigens)- this is a pure determinant group (they have a small molecular weight, are not recognized by immunocompetent cells, have only specificity, i.e. they are not able to cause the formation of antibodies, but enter into a specific reaction with them):

- simple- interact with antibodies in the body, but are not able to react with them in vitro;

- complex- interact with antibodies in vivo and in vitro.

2. Complete (conjugated) antigens- are formed when a hapten binds to a high molecular weight carrier that is immunogenic.

3. Half-haptens- these are inorganic radicals (J -, Cr -, Br -, N +) bound by protein molecules.

4. Proantigens- haptens that can attach to body proteins and sensitize them as autoantigens.

5. Tolerogens- antigens that can suppress immunological reactions with the development of a specific inability to respond to them.

Types of antigens according to the degree of foreignness:

1. Species antigens- antigens of a certain type of organism.

2. Group antigens (alloantigens)- antigens that cause intraspecific differences in individuals of the same species, dividing them into groups (serogroups in microorganisms, blood groups in humans).

3. Individual antigens (isoantigens)- antigens of a specific individual.

4. Heterogeneous (cross-reacting, xenoantigens) antigens- antigens common to organisms of different species that are far apart from each other:

- antigenic mimicry- long-term absence of an immunological reaction to antigens due to similarity with host antigens (microorganisms are not recognized as foreign);

- cross reactions- antibodies formed against the antigens of microorganisms come into contact with the host antigens and can cause an immunological process (for example: hemolytic streptococcus has cross-reacting antigens with the antigens of the myocardium and renal glomeruli; the measles virus has cross-reacting antigens to the myelin protein, therefore the immune reaction contributes to the demyelination of nerve fibers and the development multiple sclerosis).

Antigens of microorganisms depending on systematic position:

1. Species-specific- antigens of one type of microorganism.

2. Group-specific- antigens of one group within a species (divide microorganisms into serogroups).

3. Type-specific- antigens of one type (variant) within a species (divide microorganisms into serovars/serotypes).

Antigens are high-molecular substances of organic origin that, when introduced into the body, can cause the formation of specific proteins -. Antigens are able to combine only with those antibodies that arose under their influence. (So-called full antigens) also have antigenic properties. Antigens are widely used in the diagnosis of infectious diseases to determine the nature of antibodies. Antigens used for these purposes are called diagnosticums.

In addition to full-fledged antigens that can cause the formation of antibodies and react with them, there are also defective ones - haptens (most often lipoids) that react with the corresponding antibodies, but are not capable of causing their formation. Haptens are compounds that give antigens a certain specificity. Haptens are converted into full-fledged antigens when protein is added to them. Some inorganic compounds, including drugs (, iodine, etc.), when entering the body, can combine with its proteins and acquire antigenic properties. By the nature of the immunological reaction, antigens can be designated as agglutinogens, causing the formation of antibodies that cause the reaction (see); precipitinogens - antigens that cause the formation of antibodies involved in the reaction (see).

Antigens (from the Greek anti - against and gennao - create, produce) are chemical compounds that, when introduced into the human or animal body, cause the formation of antibodies. A wide range of natural high-molecular compounds, primarily proteins, polysaccharides (see Vi-antigen) and their complexes, have antigenic properties. In addition, antigens can be artificially synthesized polypeptides, as well as protein complexes with chemical compounds of a wide variety of structures. When such conjugated compounds are introduced into the body, antibodies are formed (see), which specifically react with a simple chemical group introduced into the protein, which, when introduced into the body without a carrier, does not cause the formation of antibodies. Due to their immunological passivity, such compounds are called incomplete antigens, or haptens.

At present, not everything is still known about the conditions for the antigenicity of a particular substance, however, there is no doubt that the degree of antigenicity of proteins is determined by certain features of their chemical structure, which include a relatively high molecular weight. Indeed, protamine and gelatin, which are relatively simple in composition and structure, are not antigens, and egg and serum albumins (molecular weight 40,000-70,000) are less immunogenic than gamma globulins (mol. weight 160,000) or hemocyanin (mol. weight 160,000) weight 300,000 or more). An indispensable condition for antigenicity is the difference in the structure of a given substance from any substances present in the recipient’s body. The body's own proteins are not antigens unless they have been subjected to chemical treatment that can change their structure. Due to genetic differences between individuals of the same species, proteins of the same type (for example, gamma globulins) may have certain differences in structure. In this regard, a protein from one animal of a given species can be an antigen for another animal of the same species. Such antigens are called isoantigens.

In some pathological conditions, self-proteins, polysaccharides and their complexes, as a result of changes in the chemical structure, acquire the ability to autoimmunize. Such autoantigens are known for acquired hemolytic anemia, idiopathic thrombopenic purpura, periarteritis nodosa, erythematous lupus and other diseases.

Due to the complex chemical structure of natural proteins and polysaccharides, a significant number of antigenic determinants of various structures are located on the surface of their macromolecules. Antigenic heterogeneity of individual proteins and polysaccharides leads to the formation of a large set of antibodies of different specificities during immunization (see Immunity). If some proteins or polysaccharides of different origin have individual antigenic determinants that are similar in structure, then the resulting antibodies will cross-react with both antigens. Antigenic affinity, along with specific differences, has been established for similar proteins of different species (serum albumins, gamma globulins) or somatic 0-antigens of bacteria of the intestinal group. In some cases, the same antigenic determinants are found in substances of completely different origin, for example, group-specific A-antigens of human erythrocytes and capsular polysaccharides of pneumococcus type XIV. Serologically related cellular antigens of species distant from each other are called heterogeneous antigens. Examples of such antigens are Forsman antigens - substances that, when injected into rabbits, cause the formation of sheep hemolysins.

Natural antigens can occur in both corpuscular and soluble forms. Since the former are tested with immune serum in an agglutination reaction, they are called agglutinogens. Accordingly, soluble antigens analyzed in the precipitation reaction are sometimes called precipitinogens. In corpuscular antigens of bacterial origin, a distinction is made between antigens of the cell body itself and flagellar antigens, which represent proteins in their chemical structure. In the presence of structurally identical determinants, agglutinogens and precipitinogens can have the same serological specificity. Despite the serological relationship, the immunogenic activity of agglutinogens and precipitinogens differs: the formation of antibodies to agglutinogens usually occurs much more intensely.

Antigens are substances that carry signs of genetically foreign information and, when introduced into the body, cause the development of specific immunological reactions.

Antigenic substances are high-molecular compounds that have certain properties: foreignness, antigenicity, immunogenicity, specificity and a certain molecular weight. Antigens can be a variety of protein substances, as well as proteins combined with lipids and polysaccharides. Cells of animal and plant origin, as well as poisons of animal and plant origin, have antigenic properties. Viruses, bacteria, microscopic fungi, protozoa, exo- and endotoxins of microorganisms have antigenic properties. All antigenic substances have a number of common properties:

Antigenicity is the ability of an antigen to cause an immune response. The degree of the body's immune response to various antigens is not the same, i.e., an unequal amount of antibodies is produced for each antigen.

Specificity is a feature of the structure of substances by which antigens differ from each other. It is determined by the antigenic determinant, i.e., a small section of the antigen molecule that combines with the antibody produced against it.

Immunogenicity is the ability to create immunity. This concept refers mainly to microbial antigens that provide immunity to infectious diseases. An antigen, to be immunogenic, must be foreign and have a sufficiently large molecular weight. With increasing molecular weight, immunogenicity increases. Corpuscular antigens (bacteria, fungi, red blood cells) are more immunogenic than soluble ones. Among soluble antigens, high-molecular compounds have the greatest immunogenicity.

Antigens are divided into complete and inferior. Complete antigens cause the synthesis of antibodies in the body or sensitization of lymphocytes and react with them both in vivo and in vitro. Full-fledged antigens are characterized by strict specificity, i.e. they cause the body to produce only specific antibodies that react only with a given antigen.

Defective antigens (haptens) are complex carbohydrates, lipids and other substances that are not capable of causing the formation of antibodies in the body, but enter into a specific reaction with them. Adding a small amount of protein to haptens gives them the properties of a full-fledged antigen.

Autoantigens are antigens formed from proteins of one’s own tissues that have changed their physicochemical properties under the influence of various factors (bacterial toxins and enzymes, drugs, burns, frostbite, radiation). Such altered proteins become foreign to the body, and the body responds by producing antibodies, i.e., autoimmune diseases occur.

If we consider the antigenic properties of a microorganism, it can be noted that the antigenic composition is a fairly constant characteristic of any microorganism. In the antigen complex, the most common antigens are generic (common to representatives of a given genus), group-specific (inherent in a certain group), species-specific (inherent in all individuals of a given species), and strain-specific.

According to localization, antigens can be surface (K-antigens - cell wall antigens), somatic (O-antigens, localized in the inner layer of the cell wall, thermostable) and flagellar (H-antigens, present in all motile bacteria, thermolabile). Many of them are actively secreted by the cell into the environment. At the same time, there are hydrophobic antigens that are tightly bound to the cell wall.

In addition, pathogenic microorganisms are capable of releasing a number of exotoxins. Exotoxins have the properties of full-fledged antigens with pronounced heterogeneity within the genus and species. Spores of a bacterial cell also have antigenic properties: they contain an antigen common to the vegetative cell and spores.

Pathogenic microorganisms constantly fight the immune system by changing the structure of surface antigens. Changes most often occur as a result of point mutations, resulting in variants of existing antigens.

Antibodies

In the process of evolution, organisms have developed a set of protective adaptations to pathogenic microorganisms, including nonspecific mechanisms that prevent the penetration of pathogens, substances that nonspecifically damage them (lysozyme, complement), phagocytosis and other cellular reactions. At the same time, pathogenic microorganisms have also learned to overcome nonspecific barriers. Therefore, in the process of evolution, specific humoral protection factors appeared in the form of antibodies and the body’s ability to express a specific immune response.

Antibodies are proteins related to immunoglobulins, which are synthesized by lymphoid and plasma cells in response to the entry of an antigen into the body, which have the ability to specifically bind to it. Antibodies make up more than 30% of serum proteins and provide the specificity of humoral immunity due to the ability to bind only to the antigen that stimulated their synthesis.

Initially, antibodies were conventionally classified according to their functional properties into neutralizing, lysing and coagulating. Antitoxins, antienzymes and virus-neutralizing lysines were classified as neutralizing agents. Coagulating agents include agglutinins and precipitins; to lysing - hemolytic and complement-fixing antibodies. Taking into account the functional ability of antibodies, names were given to serological reactions: agglutination, hemolysis, lysis, precipitation, etc.

In accordance with the International Classification, serum proteins that carry the function of antibodies are called immunoglobulins (Ig). Depending on their physicochemical and biological properties, immunoglobulins are classified into the classes IgM, IgG, IgA, IgE, and IgD.

Immunoglobulins are proteins with a quaternary structure, i.e. their molecules are built from several polypeptide chains. The molecule of each class consists of four polypeptide chains - two heavy and two light, interconnected by disulfide bridges. Light chains are a common structure for all classes of immunoglobulins. Heavy chains have characteristic structural features inherent in a certain class or subclass.

Antibodies included in certain classes of immunoglobulins have different physical, chemical, biological and antigenic properties.

Immunoglobulins contain three types of antigenic determinants: isotypic (the same for each representative of a given species), allotypic (determinants that are different among representatives of a given species) and idiotypic (determinants that determine the individuality of a given immunoglobulin and are different for antibodies of the same class or subclass). All of these antigenic differences are determined using specific sera.

Synthesis and dynamics of antibody formation

Antibodies are produced by plasma cells of the spleen, lymph nodes, bone marrow, and Peyer's patches. Plasma cells (antibody producers) are derived from B cell precursors after they are exposed to an antigen. The mechanism of antibody synthesis is similar to the synthesis of any proteins and occurs on ribosomes. Light and heavy chains are synthesized separately, then combined on polyribosomes, and their final assembly occurs in the lamellar complex.

Dynamics of antibody formation. During the primary immune response, antibody formation is divided into two phases: inductive (latent) and productive. The inductive phase is the period from the moment of parenteral administration of the antigen until the appearance of antigen-reactive cells (duration no more than a day). During this phase, proliferation and differentiation of lymphoid cells occurs in the direction of IgM synthesis. Following the inductive phase, the productive phase of antibody formation begins. During this period, up to approximately 10...15 days, the level of antibodies increases sharply, while the number of cells synthesizing IgM decreases and the production of IgA increases.

The phenomenon of antigen-antibody interaction.

Knowledge of the mechanisms of interaction between antigens and antibodies reveals the essence of the diverse immunological processes and reactions that occur in the body under the influence of pathogenic and non-pathogenic factors.

The reaction between antibody and antigen occurs in two stages:

Specific - direct connection of the active center of the antibody with the antigenic determinant.

Nonspecific – the second stage, when the immune complex, characterized by poor solubility, precipitates. This stage is possible in the presence of an electrolyte solution and visually manifests itself differently, depending on the physical state of the antigen. If the antigens are corpuscular, then the phenomenon of agglutination (sticking together of various particles and cells) occurs. The resulting conglomerates precipitate, while the cells do not change morphologically, losing mobility, they remain alive.

The concept of antigens

Antigens are called substances or bodies that bear the imprint of foreign genetic information, the same substances, that “foreign”, against which the immune system “works”. Any cells (tissues, organs) that are not the body’s own (not one’s own) are a complex of antigens for the immune system, even some of the body’s own tissues (the lens of the eye) are the so-called barrier tissues: normally they do not come into contact with the internal environment of the body.

Antigens have 2 properties:

antigenicity, or antigenic action - they are capable of inducing the development of an immune response;
specificity, or antigenic function - to interact with the products of the immune response induced by a similar antigen.

Chemical nature of antigens different. These may be proteins:

polypeptides;
nucleoproteins;
lipoproteins;
glycoproteins;
polysaccharides;
high density lipids;
nucleic acids.

Classification of antigens

Antigens divided into the following:

strong, which cause a pronounced immune response;
weak, when administered the intensity of the immune response is low.

Strong antigens usually have a protein structure.

Some (usually non-protein) antigens are not capable of inducing the development of an immune response (they do not have antigenicity), but can interact with the products of the immune response. They are called inferior antigens, or haptens. Many simple substances and drugs are haptens; when they enter the body, they can conjugate with proteins of the host body or other carriers and acquire the properties of full-fledged antigens.

In order for any substance to exhibit properties of the antigen, In addition to the main thing - alien™, it must have another number of characteristics:

macromolecularity (molecular weight more than 10 thousand daltons);
complexity of the structure;
rigidity of the structure;
solubility;
ability to transform into a colloidal state.

Molecule of any antigen consists of 2 functionally different parts:

Part 1 is the determinant group, which accounts for 2-3% of the surface of the antigen molecule. It determines the foreignness of the antigen, making it precisely this antigen, different from others;
The second part of the antigen molecule is called conductor; when separated from the determinant group, it does not exhibit an antigenic effect, but retains the ability to react with homologous antibodies, i.e., it turns into a hapten.

all other signs of agency are connected by the conductive part, except for foreignness.

Any microorganism (bacteria, fungi, viruses) represents

a complex of antigens.

By specificity microbial antigens are divided:

for cross-reacting (heteroantigens) - these are antigens that are common with antigens of human tissues and organs. They are present in many microorganisms and are considered an important virulence factor and a trigger for the development of autoimmune processes;
group-specific - common among microorganisms of the same genus or family;
species-specific - common to different strains of the same type of microorganisms;
variant-specific (type-specific) - found in individual strains within a microorganism species. Based on the presence of certain variant-specific antigens, microorganisms within a species are divided into variants based on antigenic structure - serovars.

By localization Bacterial antigens are divided into:

to cellular (associated with a cell);
extracellular (not associated with a cell). Main cell antigens:
somatic - O-antigen (glucido-lipoid-polypeptide complex);
flagellar - H-antigen (protein);
superficial - capsule - K-antigen, fi-antigen, Vi-antigen.

Extracellular antigens are products secreted by bacteria into the external environment, including antigens of exotoxins, enzymes of aggression and defense, etc.

Antibodies and their properties

Antibodies are called serum proteins formed in response to the action of an antigen. They belong to serum globulins and are therefore called immunoglobulins (Ig). Through them, the humoral type of immune response is realized. Antibodies have 2 properties:

specificity, i.e. the ability to interact with an antigen similar to the one that induced (caused) their formation;
heterogeneity in physical and chemical structure, specificity, genetic determination of formation (by origin).

All immunoglobulins are immune, that is, they are formed as a result of immunization and contact with antigens. Nevertheless by origin they share:

for normal (anamnestic) antibodies that are found in any body as a result of household immunization;
infectious antibodies that accumulate in the body during an infectious disease;
post-infectious antibodies, which are found in the body after an infectious disease;
post-vaccination antibodies that arise after artificial immunization.

Antibodies (immunoglobulins) are always specific to the antigen that induced their formation. Nevertheless antimicrobial immunoglobulins by specificity are divided into the same groups as the corresponding microbial antigens:

group-specific;
species-specific;
optionspecific;
cross-reacting.

Currently, immunoglobulins produced by one clone of cells are quite often obtained using biotechnology and/or genetic engineering. They're called monoclonal antibodies. Their producers are hybridoma cells, which are the descendants obtained by crossing a B-lymphocyte (plasma cell) with a tumor cell. The ability to synthesize antibodies is inherited from the hybridoma plasma cell, and the ability to be cultivated outside the body for a long time is inherited from the tumor cell.

Besides specificity, one of the main properties of immunoglobulins is their heterogeneity, that is, the heterogeneity of the immunoglobulin population in terms of the genetic determination of their formation and physicochemical structure.

Antigens are substances of a colloidal structure foreign to the body, which, when introduced into its internal environment, are capable of causing a specific immunological response, manifested, in particular, in the formation of specific antibodies, the appearance of sensitized lymphocytes, or the emergence of a state of tolerance to this substance.

Table 12

Indicators of the main humoral factors of healthy people

Substances that are antigens must be foreign to the body, macromolecular, in a colloidal state, and enter the body parenterally, i.e. bypassing the gastrointestinal tract, in which the substance is usually broken down and its foreignness is lost. The foreignness of antigens should be understood as a certain degree of chemical difference between the antigen and the macromolecules of the organism into the internal environment of which it enters.

Simple elements (iron, copper, sulfur, etc.), simple and complex inorganic compounds (acids, salts, etc.), as well as simple organic molecules such as monosaccharides, disaccharides, amino acids are not antigens. The biosynthesis of these molecules ends with the construction of chemically similar molecules, regardless of whether it is carried out in an animal, plant or microbial cell, i.e. These substances do not have specificity; specificity manifests itself at a higher level of organization of biological macromolecules. Thus, amino acids connected in a polymer chain become antigenic if this chain includes more than 8 amino acids. The term “antigenicity” usually refers not only to the ability of a foreign substance to induce the formation of antibodies in the body, but also to enter into a specific bond with them.

Antigenic properties are associated with the molecular weight of the macromolecule - it must be at least 10 thousand daltons. The higher the molecular weight of a substance, the higher its antigenicity. However, it is incorrect to assume that high molecular weight is a mandatory property of an antigen. Thus, glucagon (pancreatic hormone, mm 3800) vasopressin - angiotensin (mm 1000) also have antigenic properties.

It is customary to distinguish between complete antigens, inferior antigens (haptens) and half-haptens. Full-fledged antigens are those that cause the formation of antibodies or sensitization of lymphocytes and are able to react with them both in the body and in laboratory reactions. Proteins, polysaccharides, high-molecular nucleic acids and complex compounds of these substances have the properties of full-fledged antigens.

Defective antigens, or haptens, by themselves are not capable of causing the formation of antibodies or sensitization of lymphocytes. This property appears only when full-fledged antigens (“conductors”) are added to them, and among the resulting antibodies or sensitized lymphocytes, some are specific to the “conductor”, and some are specific to the hapten, with which they can react both in vivo and in vitro .

Hemihaptens are relatively simple substances that, when entering the internal environment of an organism, can chemically combine with the proteins of this organism and give them the properties of antigens. These substances may also include some medications (iodine, bromine, antipyrine, etc.).

The antigen molecule consists of two unequal parts. The active (small part) with a molecular weight of about 350-1000 daltons is called an antigenic determinant (epitope) and determines antigenic specificity. Antigenic determinants are located in those places of the antigen molecule that are in the greatest connection with the microenvironment. In a protein molecule, for example, they can be located not only at the ends of the polypeptide chain, but also in other parts of it. Antigenic determinants contain at least three amino acids with a rigid structure (tyrosine, tryptophan, phenylalanine). The specificity of the antigen is also related to the order of alternation of amino acids of the polypeptide chain and the combination of their positions in relation to each other. For approximately every 5000 daltons of relative molecular weight of an antigen molecule, there is one antigenic determinant (epitope). The number of antigenic determinants in an antigen molecule determines its valency. The higher the relative molecular weight of the antigen molecule, the higher it is. Thus, diphtheria toxin has 8 valencies, hemocyanin has 231, etc.

The remaining (inactive) part of the antigen molecule is believed to play the role of a carrier of the determinant and promotes the penetration of the antigen into the internal environment of the body, its pinocytosis or phagocytosis, the cellular reaction to the penetration of the antigen, the formation of mediators of intercellular interaction in the immune response (T lymphocytes have receptors for the carrier , B- to the antigenic determinant). Antigenic determinants of some antigens are obtained artificially. Their introduction into the body of animals without a carrier, contrary to expectation, leads to a low immune response. Currently, developments are underway to create synthetic carriers for synthetic antigenic determinants.

For the manifestation of antigenicity, the route of introduction of the antigen into the body and its dose are of great importance. For most antigens of bacteria and viruses, intradermal and subcutaneous administration is most effective. Both routes are much more effective than intramuscular or intravenous. The enteral route of entry for many antigens is ineffective. Overdose of slowly released antigens can cause immunological paralysis. The introduction of an antigen into the embryo leads to the emergence of tolerance after the birth of the animal. Depending on the route of entry, a predominant accumulation of the antigen is observed in one or another organ: with intravenous administration - in the spleen, bone marrow, liver; with subcutaneous treatment - in regional lymph nodes. Antigens enter the body's cell as a result of phago- or pinocytosis. The preservation of an antigen in the body depends, other things being equal, on the size and chemical structure of its molecules. Its longest stay in the body (several hundred days) is observed when the antigen is combined with a substance that has a long half-life. The antigen is released from the body, mainly in urine and (less) in feces.

Proteins and carbohydrates in the blood and internal organs are usually not antigenic for the organism in which they are synthesized, and at the same time antigenic for other individuals of the same species (isoantigens). This pattern does not apply to the so-called barrier organs, i.e. organs separated from the bloodstream by a special barrier (blood-brain, hematotesticular, etc.), the proteins of which do not normally enter the blood and are antigens for the body’s own. These organs include the brain, the lens of the eye, the parathyroid glands, and the testis.

Due to the complexity of their structure and chemical composition, various microbes contain various antigens: proteins (full antigens), carbohydrates, lipoid compounds (haptens) and their complexes.

According to the anatomical structures of the bacterial cell, there are H-antigens (flagellar, if the bacterium has them), K-antigens (surface, cell wall antigens - polysaccharides, lipopolysaccharides, proteins), O-antigens (somatic, intracellular - proteins, nucleoproteins, bacterial enzymes) , antigens excreted by bacteria into their environment (exotoxin proteins, capsule polysaccharides).

Among the numerous antigens of a microbial cell, there are those that are inherent only to a given type of microbe (type antigens), a given species (species antigens), as well as those common to a group (family) of microorganisms (group antigens). Such antigens are extracted from disintegrated microbes, animals are immunized with them and, accordingly, type, species, and group antisera are obtained. Such sera are used to identify unknown bacteria isolated from the patient’s body (or the environment), determining not only the species, but also the serotype within the species.

Thus, a bacterial cell (as well as microorganisms of other microbial kingdoms - viruses, protozoa, fungi) represent a complex complex of numerous antigens. When it enters the internal environment of the macroorganism, many of these antigens will form their own specific antibodies. Some antigens induce the formation of a barely noticeable amount of antibodies (titer), while others induce rapid and significant antibody formation. Accordingly, “weak” and “strong” antigens are distinguished.

Not all antigens of a bacterial cell are equally involved in the induction of immunity (immunity) to the re-entry of pathogenic microbes of the same species into the macroorganism. The ability of an antigen to induce immunity is called immunogenicity, and such an antigen is called an immunogen. It has also been established that certain antigens of certain microorganisms can cause the development of various types of hypersensitivity (allergies). Such antigens are called allergens.

Antigens of bacterial cells are obtained in two ways: preparatively - by isolating cellular structures after the disintegration of microbes (physical method) or by extracting antigenic fractions with chemicals (chemical method).