Classes and types of immunoglobulins. Immunoglobulins

Immunoglobulins are divided into five classes according to their structure, antigenic and immunobiological properties: IgM, IgG, IgA, IgE, IgD.

Immunoglobulin class G. The G isotype makes up the bulk of serum Ig. It accounts for 70-80% of all serum Ig, while 50% is found in tissue fluid. The average content of IgG in the blood serum of a healthy adult is 12 g/l. The half-life of IgG is 21 days.

IgG is a monomer that has 2 antigen-binding centers (it can simultaneously bind 2 antigen molecules, therefore, its valency is 2), a molecular weight of about 160 kDa, and a sedimentation constant of 7S. There are subtypes Gl, G2, G3 and G4. Synthesized by mature B-lymphocytes and plasma cells. It is well defined in blood serum at the peak of the primary and secondary immune response.

Has high affinity. IgGl and IgG3 bind complement, and G3 is more active than Gl. IgG4, like IgE, has cytophilicity (tropism, or affinity, for mast cells and basophils) and is involved in the development of a type I allergic reaction. In immunodiagnostic reactions, IgG can manifest itself as an incomplete antibody.

Easily passes through the placental barrier and provides humoral immunity to the newborn in the first 3-4 months of life. It can also be secreted into the secret of mucous membranes, including milk by diffusion.

IgG provides neutralization, opsonization and labeling of the antigen, triggers complement-mediated cytolysis and antibody-dependent cell-mediated cytotoxicity.

Immunoglobulin class M. The largest molecule of all Ig. This is a pentamer that has 10 antigen-binding centers, i.e. its valency is 10. Its molecular weight is about 900 kDa, the sedimentation constant is 19S. There are subtypes Ml and M2. The heavy chains of the IgM molecule, unlike other isotypes, are built from 5 domains. The half-life of IgM is 5 days.

It accounts for about 5-10% of all serum Ig. The average content of IgM in the blood serum of a healthy adult is about 1 g/l. This level in humans is reached by the age of 2-4 years.

IgM is phylogenetically the most ancient immunoglobulin. Synthesized by precursors and mature B-lymphocytes. It is formed at the beginning of the primary immune response, it is also the first to be synthesized in the body of a newborn - it is determined already at the 20th week of intrauterine development.

It has high avidity and is the most effective complement activator in the classical pathway. Participates in the formation of serum and secretory humoral immunity. Being a polymeric molecule containing a J-chain, it can form a secretory form and be secreted into the secretion of mucous membranes, including milk. Most of the normal antibodies and isoagglutinins are IgM.

Does not pass through the placenta. The detection of specific isotype M antibodies in the blood serum of a newborn indicates a former intrauterine infection or placental defect.

IgM provides neutralization, opsonization and labeling of the antigen, triggers complement-mediated cytolysis and antibody-dependent cell-mediated cytotoxicity.

Immunoglobulin class A. Exists in serum and secretory forms. About 60% of all IgA is found in mucosal secretions.

Serum IgA: It accounts for about 10-15% of all serum Ig. The blood serum of a healthy adult contains about 2.5 g / l of IgA, the maximum is reached by the age of 10. The half-life of IgA is 6 days.

IgA is a monomer, has 2 antigen-binding centers (i.e., 2-valent), a molecular weight of about 170 kDa, and a sedimentation constant of 7S. There are subtypes A1 and A2. Synthesized by mature B-lymphocytes and plasma cells. It is well defined in blood serum at the peak of the primary and secondary immune response.

Has high affinity. May be an incomplete antibody. Does not bind complement. Does not pass through the placental barrier.

IgA provides neutralization, opsonization and labeling of the antigen, triggers antibody-dependent cell-mediated cytotoxicity.

Secretory IgA: Unlike serum, secretory sIgA exists in polymeric form as a di- or trimer (4- or 6-valent) and contains J- and S-peptides. Molecular weight 350 kDa and above, sedimentation constant 13S and above.

It is synthesized by mature B-lymphocytes and their descendants - plasma cells of the corresponding specialization only within the mucous membranes and is released into their secrets. The volume of production can reach 5 g per day. The slgA pool is considered the most numerous in the body - its number exceeds the total content of IgM and IgG. It is not found in blood serum.

The secretory form of IgA is the main factor in the specific humoral local immunity of the mucous membranes of the gastrointestinal tract, genitourinary system and respiratory tract. Due to the S-chain, it is resistant to proteases. slgA does not activate complement but effectively binds to antigens and neutralizes them. It prevents the adhesion of microbes on epithelial cells and the generalization of infection within the mucous membranes.

Immunoglobulin class E. Also called reagin. The content in the blood serum is extremely low - approximately 0.00025 g / l. Detection requires the use of special highly sensitive diagnostic methods. Molecular weight - about 190 kDa, sedimentation constant - about 8S, monomer. It accounts for about 0.002% of all circulating Ig. This level is reached by 10-15 years of age.

It is synthesized by mature B-lymphocytes and plasma cells mainly in the lymphoid tissue of the bronchopulmonary tree and the gastrointestinal tract.

Does not bind complement. Does not pass through the placental barrier. It has a pronounced cytophilicity - tropism for mast cells and basophils. Participates in the development of immediate type hypersensitivity - type I reaction.

Immunoglobulin class D. There is not much information about Ig of this isotype. Almost completely contained in the blood serum at a concentration of about 0.03 g / l (about 0.2% of the total number of circulating Ig). IgD has a molecular weight of 160 kDa and a sedimentation constant of 7S, a monomer.

Does not bind complement. Does not pass through the placental barrier. It is a receptor for precursors of B-lymphocytes.

54. Antigens: definition, basic properties. Bacterial antigens
cells.

Antigen - it is a biopolymer of an organic nature, genetically alien to a macroorganism, which, when it enters the latter, is recognized by its immune system and causes immune reactions aimed at eliminating it.

Antigens have a number of characteristic properties: antigenicity, specificity and immunogenicity.

Antigenicity. Antigenicity is understood as the potential ability of an antigen molecule to activate components of the immune system and specifically interact with immunity factors (antibodies, a clone of effector lymphocytes). In other words, the antigen should act as a specific stimulus in relation to immunocompetent cells. At the same time, the interaction of the immune system component does not occur with the entire molecule at the same time, but only with its small area, which is called the "antigenic determinant" or "epitope".

Foreignness is a prerequisite for the realization of antigenicity. According to this criterion, the system of acquired immunity differentiates potentially dangerous objects of the biological world, synthesized from an alien genetic matrix. The concept of "foreignness" is relative, since immunocompetent cells are not able to directly analyze the foreign genetic code. They perceive only indirect information, which, as in a mirror, is reflected in the molecular structure of matter.

Immunogenicity- the potential ability of an antigen to cause a specific protective reaction in relation to itself in the macroorganism. The degree of immunogenicity depends on a number of factors that can be combined into three groups: 1. Molecular features of the antigen; 2. Clearance of the antigen in the body; 3. Reactivity of the macroorganism.

To the first group of factors the nature, chemical composition, molecular weight, structure and some other characteristics are assigned.

Immunogenicity largely depends on the nature of the antigen. The optical isomerism of the amino acids that make up the protein molecule is also important. Of great importance is the size and molecular weight of the antigen. The degree of immunogenicity is also influenced by the spatial structure of the antigen. The steric stability of the antigen molecule also turned out to be significant. Another important condition for immunogenicity is the solubility of the antigen.

The second group of factors associated with the dynamics of antigen entry into the body and its excretion. Thus, the dependence of the immunogenicity of an antigen on the method of its administration is well known. The amount of incoming antigen affects the immune response: the more it is, the more pronounced the immune response.

The third group combines factors, which determine the dependence of immunogenicity on the state of the macroorganism. In this regard, hereditary factors come to the fore.

Specificity called the ability of an antigen to induce an immune response to a strictly defined epitope. This property is due to the peculiarities of the formation of the immune response - the complementarity of the receptor apparatus of immunocompetent cells to a specific antigenic determinant is necessary. Therefore, the specificity of an antigen is largely determined by the properties of its constituent epitopes. However, one should take into account the conditionality of the boundaries of epitopes, their structural diversity and the heterogeneity of clones of antigen-reactive lymphocyte specificity. As a result, the body always responds to antigenic irritation with a polyclonal immune response.

Bacterial cell antigens. In the structure of a bacterial cell, flagella, somatic, capsular and some other antigens are distinguished. Flagella, or H-antigens, localized in the locomotor apparatus of bacteria - their flagella. They are epitopes of the contractile protein flagellin. When heated, flagellin denatures and the H-antigen loses its specificity. Phenol does not act on this antigen.

Somatic, or O-antigen, associated with the bacterial cell wall. Its basis is LPS. The O-antigen exhibits thermostable properties - it is not destroyed by prolonged boiling. However, the somatic antigen is subject to the action of aldehydes (for example, formalin) and alcohols, which disrupt its structure.

Capsular, or K-antigens, located on the surface of the cell wall. They are found in bacteria that form a capsule. As a rule, K-antigens consist of acidic polysaccharides (uronic acids). At the same time, in the anthrax bacillus, this antigen is built from polypeptide chains. By sensitivity to heat, three types of K-antigen are distinguished: A, B, and L. The highest thermal stability is characteristic of type A, it does not denature even with prolonged boiling. Type B withstands short heating (about 1 hour) up to 60 "C. Type L is rapidly destroyed at this temperature. Therefore, partial removal of the K-antigen is possible by prolonged boiling of the bacterial culture.

On the surface of the causative agent of typhoid fever and other enterobacteria that are highly virulent, a special variant of the capsular antigen can be found. He got the name virulence antigen, or Vi antigen. The detection of this antigen or antibodies specific to it is of great diagnostic value.

Bacterial bacteria also have antigenic properties. protein toxins, enzymes and some other proteins that are secreted by bacteria into the environment (eg tuberculin). When interacting with specific antibodies, toxins, enzymes and other biologically active molecules of bacterial origin lose their activity. Tetanus, diphtheria and botulinum toxins are among the strong full-fledged antigens, so they are used to obtain toxoids for human vaccination.

In the antigenic composition of some bacteria, a group of antigens with highly pronounced immunogenicity is distinguished, whose biological activity plays a key role in the formation of the pathogenicity of the pathogen. The binding of such antigens by specific antibodies almost completely inactivates the virulent properties of the microorganism and provides immunity to it. The described antigens are called protective. For the first time, a protective antigen was found in the purulent discharge of a carbuncle caused by anthrax bacillus. This substance is a subunit of a protein toxin, which is responsible for the activation of other, actually virulent subunits - the so-called edematous and lethal factors.

55. Antibody formation: primary and secondary response.

The ability to form antibodies appears in the prenatal period in a 20-week embryo; after birth, own production of immunoglobulins begins, which increases until adulthood and decreases somewhat in old age. The dynamics of the formation of antibodies has a different character depending on the strength of the antigenic effect (antigen dose), the frequency of exposure to the antigen, the state of the organism and its immune system. During the initial and repeated introduction of the antigen, the dynamics of antibody formation is also different and proceeds in several stages. Allocate latent, logarithmic, stationary phase and the phase of decline.

In the latent phase the processing and presentation of the antigen to immunocompetent cells take place, the reproduction of a cell clone specialized in the production of antibodies to this antigen, the synthesis of antibodies begins. During this period, antibodies in the blood are not detected.

During the logarithmic phase synthesized antibodies are released from plasma cells and enter the lymph and blood.

In the stationary phase the number of antibodies reaches a maximum and stabilizes, then comes descent phase antibody levels. During the initial administration of the antigen (primary immune response), the latent phase is 3-5 days, the logarithmic phase is 7-15 days, the stationary phase is 15-30 days, and the decline phase is 1-6 months or more. A feature of the primary immune response is that initially IgM is synthesized, and then IgG.

In contrast to the primary immune response during the secondary administration of an antigen (secondary immune response), the latent period is shortened to several hours or 1-2 days, the logarithmic phase is characterized by a rapid increase and a significantly higher level of antibodies, which in subsequent phases is retained for a long time and slowly, sometimes in for several years, decreases. In the secondary immune response, in contrast to the primary, mainly IgG is synthesized.

Such a difference in the dynamics of antibody production during the primary and secondary immune responses is explained by the fact that after the initial administration of the antigen, a clone of lymphocytes is formed in the immune system, carrying the immunological memory of this antigen. After a second encounter with the same antigen, the clone of lymphocytes with immunological memory multiplies rapidly and intensively switches on the process of antibody genesis.

Very fast and vigorous antibody formation upon repeated encounter with an antigen is used for practical purposes when it is necessary to obtain high antibody titers in the production of diagnostic and therapeutic sera from immunized animals, as well as for emergency immunity during vaccination.

The structure of immunoglobulins

According to its chemical structure immunoglobulins are glycoproteins.

According to the physicochemical and antigenic properties, immunoglobulins are divided into classes: G, M, A, E D.

Immunoglobulin moleculeG built from 2 heavy (H-chains) and 2 light polypeptide chains (L-chains).

Each polypeptide chain consists of variable (V), stable (constant, C) and the so-called hinge parts.

The heavy chains of immunoglobulins of different classes are built from different polypeptides (gamma, mu, alpha, delta, epsilon peptides) and therefore are different antigens.

Light chains are represented by 2 types of polypeptides - kappa and lambda peptides.

The variable regions are much shorter than the constant regions. Each pair of light and heavy polypeptide chains in their C-parts, as well as heavy chains, are interconnected by disulfide bridges.

Neither heavy nor light chains possess the properties of antibodies (interaction with haptens). Upon hydrolysis with papain, the immunoglobulin G molecule decomposes into 3 fragments - 2 Fab fragments and F c fragment.

The latter is the residues of heavy chains, their constant parts. It does not have the property of an antibody (does not interact With antigen), but has an affinity for complement, is able to fix and activate it. In this regard, the fragment is designated as F c -fragment (complement fragment). The same F c -fragment ensures the passage of immunoglobulins G through the blood-brain or placental barriers.

The other two immunoglobulin G fragments are heavy and light chain residues with their variable portions. They are identical to each other and have the property of antibodies (interact with the antigen), in this regard, these fragments and referred to as F ab ,-(antibody fragment).

Since neither heavy nor light chains have the property of an antibody, but it is detected in the F a - fragments, it is obvious that it is the variable parts of the heavy and light chains that are responsible for the interaction with the antigen. They form a unique structure and spatial organization structure - the active site of the antibody. Each active center of any immunoglobulin corresponds to the determinant group of the corresponding antigen, like a “key to a lock.

The immunoglobulin G molecule has 2 active centers. Since the structure of the active centers of immunoglobulins of one

class, but different specificity is not the same, then these molecules (antibodies of the same class, but different specificity) are different antibodies. These differences are referred to as idiotypic immunoglobulin differences, or idiotypes.

Molecules of immunoglobulins of other classes built on the same principle as IgG, i.e. from monomers having 2 heavy and 2 light chains, but class M immunoglobulins are pentamers (built from 5 such monomers), and class A immunoglobulins are dimers or tetramers.

The number of monomers that make up the molecule of a particular class of immunoglobulin determines its molecular weight. The heaviest are IgM, the lightest are IgG, as a result of which they pass through the placenta.

It is also obvious that immunoglobulins of different classes have a different number of active centers: IgG has 2 of them, and IgM has 10. In this regard, they are able to bind a different number of antigen molecules, and the speed of this binding will be different.

The rate of binding of immunoglobulins to an antigen is their avidity.

The strength of this bond is denoted as affinity.

IgMs are high avid but low affinity, while IgGs are low avid but high affinity.

If only one active center functions in an antibody molecule, it can bind to only one antigenic determinant without the subsequent formation of a network structure of antigen-antibody complexes. Such antibodies are called incomplete. They do not give visible reactions to the eye, but they inhibit the reaction of the antigen with complete antibodies.

Incomplete antibodies play an important role in the development of Rh conflict, autoimmune diseases (collagenosis), etc. and are detected using the Coombs reaction (antiglobulin test).

Protective role of immunoglobulins of different classes also not the same.

Class E immunoglobulins (reagins) realize the development of allergic reactions of the immediate type (hypersensitivity of the immediate type - HNT). Allergens (antigens) entering the body are attached to the F ab fragments of reagins fixed in tissues (the F c fragment is associated with tissue basophil receptors), which leads to the release of biologically active substances that trigger the development of allergic reactions. In allergic reactions, tissue basophils are damaged by the antigen-antibody complex and release granules containing histamine and other biologically active substances.

Class A immunoglobulins can be:

serum (synthesized in the plasma cells of the spleen, lymph nodes, have a monomeric and dimeric molecular structure and make up 80% of the IgA contained in the serum);
secretory (synthesized in the lymphatic elements of the mucous membranes).

The latter are distinguished by the presence of a secretory component (beta-globulin), which attaches to the immunoglobulin molecule during its passage through the epithelial cells of the mucosa.

Secretory immunoglobulins play a significant role in local immunity, preventing the adhesion of microorganisms on mucous membranes, stimulate phagocytosis and activate complement, and can penetrate into saliva and colostrum.

Class M immunoglobulins

first synthesized in response to antigenic stimulation. They are able to bind a large number of antigens and play an important role in the formation of antibacterial and antitoxic immunity. Most of the serum antibodies are class G immunoglobulins, which account for up to 80% of all immunoglobulins. They are formed at the height of the primary and secondary immune response and determine the intensity of immunity against bacteria and viruses. In addition, they are able to penetrate the placental and blood-brain barrier.

class immunoglobulinsD

unlike immunoglobulins of other classes, they contain N-acetylgalactoseamine and are unable to fix complement. The level of IgD is increased in multiple myeloma and chronic inflammatory processes.

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Isotypes

So far, features common to all immunoglobulin molecules have been described, such as the four chain construct and structural domains. In its opposition to aggressive foreign substances, the body has developed a number of mechanisms, each of which is based on some particular property or function of the immunoglobulin molecule.

Thus, when a specific antibody molecule binds to a specific antigen or pathogen, several different effector mechanisms come into play. These mechanisms are mediated by different classes (isotopes) of immunoglobulins, each of which can interact with the same epitope, but each can trigger a different reaction.

These differences are the result of structural variations in the heavy chains, which have created domains that determine the diversity of functions. A general overview of the properties of immunoglobulin classes is presented in Table. 4.2 and 4.3 and in fig. 4.7.

Table 4.2. The most important properties of immunoglobulin isotypes

Property	Isotype
Property	IgG	IgA	IgM	IgD	IgE
Molecular mass	150000	160000 for monomer	900000	180000	200000
Additional protein components	-	J and S	J	-	-
Approximate serum concentration, mg / ml	12	1,8	1	0,00-0,04	0,00002
Share of all Ig, %	80	13	6	0,2	0,002
Location	Approximately equal outside and inside the vessels	Inside the vessels and in secret	Mainly within vessels	on the surface of the lymphocyte	On mast cells, basophils, nasal secretions and saliva
Half-life, days	23	5,5	5,0	2,8	2,0
Passage through the placenta	+ +	-	-	-	-
Having a secret	-	+ +	-	-	-
Presence in milk	+		From zero to trace	-	-
Complement activation	+	-	+ + +	-	-
Binding to Fc receptors on macrophages, NK and PMN cells	+ +
Relative agglutination capacity	+	+ +	+ + +	-	-
Antiviral activity	+ + +	+ + +	+	-	-
Antibacterial activity	+ + +	(with lysozyme)	+ + + (with complement)
Antitoxic activity	+ + +	-	-	-	+ +
Allergic activity	-	-	-	-	+ +

Table 4.3. Important differences among human IgG subclasses

Allotypes

Another form of variation in the structure of immunoglobulins are allotypes. These variations are based on genetic differences between individuals and depend on the existence of allelic forms (allotypes) of the same protein as a result of the presence of different forms of the same gene at a given locus. As a result, the heavy or light chain allotypes that make up any immunoglobulin may be present in some members of the species and absent in others. This situation differs sharply from situations with classes or subclasses of immunoglobulins that are present in all members of the species.

Rice. 4.7. Different types of immunoglobulin variations

Allotypic differences at known loci affect only one or two amino acids in a chain constant region. With rare exceptions, the presence of allotypic differences between two identical immunoglobulin molecules usually does not affect antigen binding, but is an important marker for Mendelian inheritance analysis.

Some known allotypic markers are grouped on the human IgG γ chain (called Gm for IgG markers), the κ chain (called Km), and the α chain (called Am).

Allotypic markers have been detected in immunoglobulins from several species, usually using antisera obtained by immunizing a member of a given species with antibodies from another member of the same species. As with other allelic systems, allotypes are inherited as dominant Mendelian traits. The genes encoding these markers are codominantly expressed, and thus an individual may be homozygous or heterozygous for that marker.

Idiotypes

As we have seen, the antigen-binding center of a specific antibody molecule consists of a unique combination of amino acids in the variable regions of the light and heavy chains. Since such a combination is not found in other antibody molecules, it must be immunogenic and capable of stimulating an immunological response against itself in an animal of the same species. This fact was indeed discovered by J. Oudin and G. Kunkel, who in the early 1960s showed that experimental immunization with certain antibodies or myeloma protein can produce antiserum that is specific only to the used antibody and to no other immunoglobulin of this species.

Such antisera contain populations of antibodies specific for several epitopes, called idiotopes. which are present in the variable region (heavy and light chain) of the antibodies used for immunization. The totality of all idiotopes on an introduced antibody molecule is called an idiotype. In some cases, anti-idiotypic sera prevent an antibody from binding to its antigen. In this case, the idiotypic determinant is considered to be located within or adjacent to the antigen-binding site itself.

Anti-idiotypic sera that do not block antibody binding to antigen are likely directed against variable determinants in a framework region outside the antigen-binding site (Figure 4.8).

Rice. 4.8. Two anti-idiotypic antibodies to AT1. (A) An anti-idiotypic antibody directed against the antigen-binding site of AT1 prevents AT1 from binding to the antigen. (B) The anti-idiotypic antibody binds to the AT1 framework without preventing it from binding to the antigen.

Based on theoretical considerations, it can be visualized that an anti-idiotypic antibody that binds to an antigen-binding center complementary to that center in the idiotype resembles an epitope that is also complementary to the antigen-binding center of the idiotype. Thus, an anti-idiotype may represent an imprint or internal image of a conditional epitope. Indeed, there are examples of immunization of experimental animals using anti-idiotypic internal images as immunogens.

Such immunogens result in antibodies capable of reacting with an antigen bearing the epitope to which the original idiotype is directed. The appearance of such antibodies is induced without any contact of the immunized animal with the original (original) antigen itself.

In some cases, especially in inbred animals, anti-idiotypic antibodies react with several different antibodies that are directed against the same epitope and have similar idiotypes. These idiotypes are called common or cross-reactive, and the term usually defines a family of antibody molecules.

In contrast to this situation, serum that reacts with only one specific antibody molecule is defined as having a unique idiotype. The presence of idiotypic determinants in immunoglobulin molecules may play a role in the control and modulation of the immune response, as described in N. Jerne's network theory, although opinions on this matter are contradictory.

On fig. 4.9 different types of the variations noted among immunoglobulins are presented.

Rice. 4.9. Structures of the main classes of secreted antibodies. Light chains are shown in green and heavy chains in blue. Orange circles show glycosylation sites. Polymeric IgM and IgA contain a polypeptide called the J chain. The shown dimeric IgA molecule contains a secretory component (shown in red)

Differences between constant regions resulting from the involvement of different heavy and light chain constant region genes are referred to as isotypes. Differences associated with different alleles of the same constant region gene are called allotypes. Finally, within a particular isotype (eg IgG), features in the specific rearrangement of VH and VL genes are called idiotypes.

R. Koiko, D. Sunshine, E. Benjamini

In humans, immunoglobulins are located in the secrets that are produced by the mucous membrane, or rather its glands, in the blood serum and interstitial fluid. Thanks to this, a person is fully protected from diseases, which is also called humoral immunity.

The immune response to this condition is of two types:

specific;
non-specific.

Since many do not know what immunoglobulins are, it is worth remembering that they give a specific response to the body, as they find in it and then destroy foreign bacteria. The human body produces its own antibodies that resist harmful bacteria and viruses. However, they will fight only one pathogen.

As a result of this, acquired immunity is formed in the body, which can be of two types:

Active. It can occur due to antibodies that appeared in the body after an illness. It is also formed after a prophylactic vaccine is given, when weakened or destroyed bacteria, as well as their modified toxins, are introduced into the body.
Passive. This immunity occurs in a newborn baby who received it from his mother in utero or during breastfeeding. It can also appear after vaccination against a specific disease.

Immunity, which was formed only as a result of the introduction of serum into the body with immunoglobulin components, is also called artificial. Whereas the immunity that the baby received from the mother is called natural.

As mentioned above, immunoglobulin is the protection of the patient from various diseases, since it is endowed with several important properties:

determines foreign substances in human cells and organs (these include microorganisms or their components);
forms a new immunity by binding to the antigen;
destroys the emerging immune complexes;
after the transfer of diseases, this element remains in the body forever, which ensures that the person does not re-infect.

In addition, such substances can perform other functions. For example, in the human body there are antibodies that neutralize the "extra" immunoglobulins that were excessively formed. Because of these antibodies, rejection of transplanted organs can occur. That is why, those patients who underwent a transplant operation need to constantly take drugs that suppress the immune response.

It is worth knowing that some autoimmune diseases can produce defective immunoglobulins that attack the tissues of your body.

Anyone who wants to figure out what classes of immunoglobulins are should know that all immunoglobulins are divided into 5 classes - G, M, E, A and D, the differences of which are in structure and functional purpose:

Immunoglobulin G (IgG). This element can be attributed to the main class of immunoglobulins located in the blood serum. There are 4 subclasses of this substance, which can work separately from each other. What does immunoglobulin show? Such a component notifies about malfunctions in the body, which can be easily diagnosed using a blood test. The production of this component occurs a few days after the appearance of class M immunoglobulin and then remains in the human body for a long time, preventing re-infection and destroying harmful toxic elements. Due to its small size, this immunoglobulin freely penetrates the fetal membranes located in the body of the expectant mother and protects the child from the harmful effects of various infections. An indicator of the norm of this immunoglobulin G is its content, which is 75% of the total amount of antibodies in the body.
Immunoglobulin M (IgM). This type is the very first defender, which is produced immediately after dangerous bacteria enter it. Unlike IgG, class M immunoglobulins are larger, therefore, in the body of a pregnant woman, they will not be able to penetrate the membrane to the fetus - which is why they can only be detected in the blood stream. The norm of such antibodies should be no more than 10% of their total amount.
Immunoglobulin E (IgE). The components of this class are difficult to find in the blood. They appear only with the development of allergies, which forms a “help” for the body to respond to the allergen. Also, immunoglobulin is able to protect a person from certain infections. If the normal level of IgE is elevated, this will indicate the patient's tendency to allergies and atopy.
Immunoglobulin A (IgA). The main property of IgA is the protection of the mucosa from the effects of microbes and foreign substances. It is found in the secretions of tears and saliva, as well as on the mucous membrane of the genitourinary and respiratory systems. The concentration of IgA reaches no more than 20%.
Immunoglobulin D (IgD). The function of this substance has not yet been fully elucidated. This element is in the blood in a minimum amount - only 1%. IgD is mainly used in medicinal formulations sold in pharmacies.

These classes of immunoglobulins help to determine the presence of pathology in the body and prescribe timely treatment. That is why a blood test for the detection of antibodies is used to examine the state of immunity in order to assess the patient's health status and the severity of the disease.

As mentioned above, the main immunoglobulin responsible for the formation of an allergy in a patient is IgE. After the body begins to come into contact with the allergen, histamine, serotonin and other components will be released, which causes an active suppression of inflammation developing in the body.

The greatest number of such antibodies is located on the mucous membrane located in the gastrointestinal tract, respiratory tract and on the skin. The immunoglobulin norm in the blood serum is small - it is in the range of 30-240 mcg / l. At the same time, the highest indicators of the number of antibodies are observed at the end of spring (in May), and the lowest - in December.

IgE appears in the human blood in a minimal amount at 10-12 weeks in the womb. Then, after birth, the amount of the substance increases significantly and continues to grow until the age of 18. In old age, these indicators begin, on the contrary, to decrease.

A sharp decrease or increase in the concentration of IgE indicates some human diseases, for example:

bronchial asthma;
dermatitis;
helminthiasis;
eczema;
pollinosis.

Important: donating blood for the determination of immunoglobulin E is also recommended if you develop an allergy to drugs or products. In addition, this analysis helps to determine the presence of possible hereditary diseases in children whose relatives suffer from allergies.

It is worth noting: if the IgE result shown in adolescents and children is low, the causes of this phenomenon may be the development of tumors or hypogammaglobulinemia, which develops in the body even before birth.

The norm of immunoglobulin is:

in newborns and children up to 3 months - 0-2kU / l;
at 3-6 months, the indicators are 3-10 kU / l;
up to 12 months, the values vary between 8-20 kU / l;
up to 5 years, the indicator is - 10-50 kU / l;
in adolescents under 15 years old - 16-60 kU / l;
in adults - 20-100 kU / l.

As mentioned above, deviations from these parameters indicate serious violations in the body, so it is important to conduct a blood test in a timely manner to make sure of your own health.

Answer: Immunoglobulins:

Immunoglobulins are called proteins that are synthesized under the influence of an antigen and specifically react with it. During electrophoresis, they are localized in globulin fractions.

Immunoglobulins are composed of polypeptide chains. There are four structures in the immunoglobulin molecule:

Primary is the sequence of certain amino acids. It is built from nucleotide triplets, is genetically determined and determines the main subsequent structural features.

The secondary is determined by the conformation of the polypeptide chains.

Tertiary determines the nature of the location of individual sections of the chain that create a spatial picture.

Quaternary is characteristic of immunoglobulins. A biologically active complex arises from four polypeptide chains. Chains in pairs have the same structure.

Any immunoglobulin molecule has a Y-shape and consists of 2 heavy (H) and 2 light (L) chains linked by disulfide bridges. Each IG molecule has 2 identical antigen-binding Fab fragments (Fragment antigen binding) and one Fc fragment (Fragment cristalisable), with the help of which IGs bind complementary to the Fc receptors of the cell membrane.

The terminal sections of the light and heavy chains of the IG molecule are quite diverse (variable), and certain regions of these chains are distinguished by a particularly pronounced diversity (hypervariability). The remaining parts of the IG molecule are relatively low (constant). Depending on the structure of the constant regions of heavy chains, IGs are divided into classes (5 classes) and subspecies (8 subspecies). It is these constant regions of heavy chains, which differ significantly in amino acid composition for different classes of IGs, that ultimately determine the special properties of each class of antibodies:

lgM activate the complement system;

IgE binds to specific receptors on the surface of mast cells and basophils, releasing allergy mediators from these cells;

IgA is secreted into various body fluids, providing secretory immunity;

IgD functions primarily as membrane receptors for antigen;

in IgG exhibits a variety of activities, including the ability to cross the placenta.

Classes of immunoglobulins.

Immunoglobulins G, IgG

Immunoglobulins G are monomers that include 4 subclasses (IgGl - 77%; IgG2 - 11%; IgG3 - 9%; IgG4 - 3%), which differ from each other in amino acid composition and antigenic properties. Their content in blood serum ranges from 8 to 16.8 mg/ml. the half-life is 20-28 days, and is synthesized during the day from 13 to 30 mg / kg. They account for 80% of the total IG content. They protect the body from infections. Antibodies of the IgGl and IgG4 subclasses specifically bind through Fc fragments to the pathogen (immune opsonization), and due to Fc fragments interact with the Fc receptors of phagocytes (macrophages, polymorphonuclear leukocytes), thereby contributing to the phagocytosis of the pathogen. IgG4 is involved in allergic reactions and is unable to fix complement.

Antibodies of the IgG class play a fundamental role in humoral immunity in infectious diseases, causing the death of the pathogen with the participation of complement and opsonizing phagocytic cells. They cross the placenta and form anti-infective immunity in newborns. They are able to neutralize bacterial exotoxins, bind complement, participate in the precipitation reaction.

Immunoglobulins M, IgM

Immunoglobulins M are the most "early" of all classes of IGs, including 2 subclasses: IgMl (65%) and IgM2 (35%). Their concentration in blood serum ranges from 0.5 to 1.9 g/l or 6% of the total IG content. 3-17 mg/kg is synthesized per day, and their half-life is 4-8 days. They do not cross the placenta. IgM appears in the fetus and is involved in anti-infective protection. They are able to agglutinate bacteria, neutralize viruses, and activate complement. IgM play an important role in the elimination of the pathogen from the bloodstream, in the activation of phagocytosis. A significant increase in the concentration of IgM in the blood is observed in a number of infections (malaria, trypanosomiasis) in both adults and newborns. This is an indicator of intrauterine infection of the causative agent of rubella, syphilis, toxoplasmosis, cytomegaly. IgM are antibodies that are formed early in the infection process. They are highly active in the reactions of agglutination, lysis and binding of endotoxins of Gram-negative bacteria.

Immunoglobulins A, IgA

Immunoglobulins A are secretory IGs that include 2 subclasses: IgAl (90%) and IgA2 (10%). The content of IgA in blood serum ranges from 1.4 to 4.2 g/l or 13% of the total amount of IG; daily synthesized from 3 to 50 mcg/kg. The half-life of antibodies is 4-5 days. IgA is found in milk, colostrum, saliva, lacrimal, bronchial and gastrointestinal secretions, bile, and urine. The composition of IgA includes a secretory component consisting of several polypeptides, which increases the resistance of IgA to the action of enzymes. This is the main type of IG involved in local immunity. They prevent bacteria from attaching to the mucosa, neutralize enterotoxin, activate phagocytosis and complement. IgA is not detected in newborns. In saliva, it appears in children at the age of 2 months, with the secretory component SC being the first to be detected. And only later the complete SigA molecule. Age 3 months Defined by many authors as a critical period; this period is especially important for the diagnosis of congenital or transient insufficiency of local immunity.

Immunoglobulins E, IgE

Immunoglobulins D, IgD

Immunoglobulins D are monomers; their content in the blood is 0.03-0.04 g/l or 1% of the total amount of IG; per day they are synthesized from 1 to 5 mg / kg, and the half-life ranges from 2-8 days. IgDs are involved in the development of local immunity, have antiviral activity, and in rare cases activate complement. Plasma cells secreting IgD are localized mainly in the tonsils and adenoid tissue. IgD are found on B cells and are absent on monocytes, neutrophils, and T lymphocytes. It is believed that IgDs are involved in the differentiation of B cells, contribute to the development of an anti-idiotypic response, and participate in autoimmune processes.