Humoral protective factors include: Nonspecific factors of body defense: definition of the concept, surface integument, humoral and cellular factors; the role of normal microflora

The macroorganism has mechanisms that prevent the penetration of pathogens of infectious diseases, the proliferation of microbes in tissues and the formation of pathogenicity factors by them. The main properties of the macroorganism that determine the occurrence, course and outcome of the infectious process are resistance and susceptibility.

Resistance– this is the body’s resistance to the effects of various damaging factors.

Susceptibility to infection is the ability of a macroorganism to respond to the introduction of microbes by developing various forms of the infectious process. There are specific and individual susceptibility. Species susceptibility is inherent in all individuals of a given species. Individual susceptibility is the predisposition of certain individuals to the occurrence of various forms of infectious process under the influence of microbes.

The resistance and susceptibility of a macroorganism to an infectious agent largely depend on nonspecific protective factors, which can be divided into several groups:

1. Physiological barriers:

Mechanical (epidermis and mucous membranes);

Chemical (secrets of the skin and mucous membranes);

Biological (normal microflora).

2. Cellular factors of nonspecific protection:

Phagocytes (macrophages, monocytes, dendritic cells, neutrophils);

NK cells (natural killer cells).

3. Humoral factors of nonspecific protection:

Complement system;

Substances with direct antimicrobial activity (lysozyme, alpha interferon, defensins);

Substances with indirect antimicrobial activity (lactoferrin, mannose-binding lectin - MSL, opsonins).

Physiological barriers

Epithelial tissue are a powerful mechanical barrier for microorganisms, due to the tight adherence of cells to each other and regular renewal, accompanied by the desquamation of old cells along with microorganisms adhered to them. The skin is a particularly strong barrier - the multi-layered epidermis is an almost insurmountable obstacle to microorganisms. Infection through the skin occurs mainly after a violation of its integrity. The movement of cilia of the respiratory epithelium and intestinal peristalsis also provide release from microorganisms. From the surface of the mucous membrane of the urinary tract, microorganisms are washed away with urine - if the outflow of urine is disrupted, infectious lesions of this organ system can develop. In the oral cavity, some microorganisms are washed off with saliva and swallowed. In the layer of epithelium of the mucous membranes of the respiratory tract and gastrointestinal tract, cells were found that are capable of endocytosing microorganisms from the intestinal mucus or respiratory tract and transferring them unchanged to the submucosal tissues. These cells are designated as M-cells of the mucous membranes (from microfold - microfolders). In the submucosal layers, M cells present microbes to dendritic cells and macrophages.

Towards chemical barriers include various secretions of the skin’s own glands (sweat and sebaceous), mucous membranes (hydrochloric acid of the stomach) and large exocrine glands (liver, pancreas). Sweat glands secrete large amounts of salts onto the surface of the skin, and sebaceous glands release fatty acids, which leads to an increase in osmotic pressure and a decrease in pH (both factors are unfavorable for the growth of most microorganisms). The parietal (lining) cells of the stomach produce hydrochloric acid, thereby sharply reducing the pH of the environment - most microorganisms die in the stomach. Bile and pancreatic juice contain enzymes and bile acids that inhibit the growth of microorganisms. Urine has an acidic environment, which also prevents the colonization of the epithelium of the urinary tract by microorganisms.

Representatives of normal microflora that inhabit various human biotopes also prevent the penetration of pathogenic microbes into the body, thereby biological barrier. They provide protection to the macroorganism through a number of mechanisms (competition with pathogenic microorganisms for adhesion area and nutrient substrate, acidification of the environment, production of bacteriocins, etc.), united by the term colonization resistance.

Humoral factors that provide resistance to the body include compliment, lysozyme, interferon, properdin, C-reactive protein, normal antibodies, and bactericidin.

Complement is a complex multifunctional system of blood serum proteins that is involved in reactions such as opsonization, stimulation of phagocytosis, cytolysis, neutralization of viruses, and induction of an immune response. There are 9 known fractions of complement, designated C 1 – C 9, which are in the inactive state in the blood serum. Activation of complement occurs under the influence of the antigen-antibody complex and begins with the addition of C 1 1 to this complex. This requires the presence of salts Ca and Mq. The bactericidal activity of complement manifests itself from the earliest stages of fetal life, however, during the newborn period, complement activity is the lowest compared to other age periods.

Lysozyme is an enzyme from the group of glycosidases. Lysozyme was first described by Fleting in 1922. It is secreted constantly and is detected in all organs and tissues. In the body of animals, lysozyme is found in the blood, tear fluid, saliva, secretions of the mucous membranes of the nose, gastric and duodenal juice, milk, and amniotic fluid of fetuses. Leukocytes are especially rich in lysozyme. The ability of lysozyme to lyse microorganisms is extremely high. It does not lose this property even in a dilution of 1: 1,000,000. Initially, it was believed that lysozyme is active only against gram-positive microorganisms, but it has now been established that against gram-negative bacteria it acts cytolytically together with complement, penetrating through the cell wall damaged by it bacteria to objects of hydrolysis.

Properdin (from Latin perdere - to destroy) is a globulin-type blood serum protein with bactericidal properties. In the presence of compliment and magnesium ions, it exhibits a bactericidal effect against gram-positive and gram-negative microorganisms, and is also capable of inactivating influenza and herpes viruses, and is bactericidal against many pathogenic and opportunistic microorganisms. The level of properdin in the blood of animals reflects the state of their resistance and sensitivity to infectious diseases. A decrease in its content was revealed in irradiated animals, patients with tuberculosis, and with streptococcal infection.

C-reactive protein - like immunoglobulins, has the ability to initiate reactions of precipitation, agglutination, phagocytosis, and complement fixation. In addition, C-reactive protein increases the mobility of leukocytes, which suggests its participation in the formation of non-specific resistance of the body.

C-reactive protein is found in blood serum during acute inflammatory processes, and it can serve as an indicator of the activity of these processes. This protein is not detected in normal blood serum. It does not pass through the placenta.

Normal antibodies are almost always present in the blood serum and are constantly involved in nonspecific protection. They are formed in the body as a normal component of serum as a result of contact of the animal with a very large number of different environmental microorganisms or certain dietary proteins.

Bactericidin is an enzyme that, unlike lysozyme, acts on intracellular substances.

Humoral factors of nonspecific defense of the body include normal (natural) antibodies, lysozyme, properdin, beta-lysines (lysines), complement, interferon, viral inhibitors in the blood serum and a number of other substances that are constantly present in the body.

Antibodies (natural). In the blood of animals and humans, which have never been sick before and have not been immunized, substances are found that react with many antigens, but in low titers, not exceeding dilutions of 1:10 ... 1:40. These substances were called normal or natural antibodies. They are believed to arise as a result of natural immunization by various microorganisms.

Lysosomal enzyme is present in tears, saliva, nasal mucus, secretions of mucous membranes, blood serum and extracts of organs and tissues, in milk; There is a lot of lysozyme in the whites of chicken eggs. Lysozyme is resistant to heat (inactivated by boiling) and has the property of lysing living and killed mainly gram-positive microorganisms.

The method for determining lysozyme is based on the ability of the serum to act on a culture of Micrococcus lysodecticus grown on slant agar. A suspension of a daily culture is prepared according to an optical standard (10 units) in physiological solution. The test serum is successively diluted with physiological solution 10, 20, 40, 80 times, etc. An equal volume of microbial suspension is added to all test tubes. The test tubes are shaken and placed in a thermostat for 3 hours at 37 °C. The reaction is taken into account according to the degree of serum clearing. The lysozyme titer is the last dilution in which complete lysis of the microbial suspension occurs.

SECRETORY AND MUNOGLOBULINA A. Constantly present in the contents of the secretions of the mucous membranes, mammary and salivary glands, in the intestinal tract; has pronounced antimicrobial and antiviral properties.

Properdine (from Latin pro and perdere - prepare for destruction). Described in 1954 in the form of a polymer as a factor of nonspecific protection and cytolysin. Present in normal blood serum in amounts up to 25 mcg/ml. It is a whey protein (beta globulin) with a molecular weight

220,000. Properdin takes part in the destruction of microbial cells and neutralization of viruses. Properdin acts as part of the properdin system: properdin complement and divalent magnesium ions. Native properdin plays a significant role in nonspecific activation of complement (alternative activation pathway).

Lizins. Serum proteins that have the ability to lyse (dissolve) some bacteria and red blood cells. The blood serum of many animals contains beta-lysines, which cause lysis of Bacillus subcultures, as well as many pathogenic microbes.

L a c t o f e r r i n. Non-heme glycoprotein with iron-binding activity. Binds two ferric iron atoms to compete with microbes, resulting in microbial growth being inhibited. It is synthesized by polymorphonuclear leukocytes and grape-shaped cells of the glandular epithelium. It is a specific component of the secretion of glands - salivary, lacrimal, mammary, respiratory, digestive and genitourinary tracts. Lactoferrin is a local immunity factor that protects epithelial covers from microbes.

COMPLEMENT. A multicomponent system of proteins in blood serum and other body fluids that play an important role in maintaining immune homeostasis. It was first described by Buchner in 1889 under the name “alexin” - a thermolabile factor, in the presence of which microbial lysis occurs. The term “complement” was introduced by Ehrlich in 1895. Complement is very unstable. It was noted that specific antibodies in the presence of fresh blood serum are capable of causing hemolysis of red blood cells or lysis of a bacterial cell, but if the serum is heated at 56 °C for 30 minutes before the reaction, then lysis will not occur. It turned out that hemolysis (lysis) occurs within due to the presence of complement in fresh serum. The largest amount of complement is contained in guinea pig serum.

The complement system consists of at least nine different serum proteins, designated C1 to C9. C1, in turn, has three subunits - Clq, Clr, Cls. The activated form of complement is indicated by a dash above (c).

There are two ways of activation (self-assembly) of the complement system - classical and alternative, differing in trigger mechanisms.

In the classical activation pathway, the complement component C1 binds to immune complexes (antigen + antibody), which include sequentially the subcomponents (Clq, Clr, Cls), C4, C2 and C3. The C4, C2 and C3 complex ensures the fixation of the activated C5 complement component on the cell membrane, and then are activated through a series of reactions of C6 and C7, which contribute to the fixation of C8 and C9. As a result, damage to the cell wall or lysis of the bacterial cell occurs.

In an alternative pathway of complement activation, viruses, bacteria or exotoxins themselves serve as activators. The alternative activation pathway does not involve components C1, C4 and C2. Activation begins at the S3 stage, which includes a group of proteins: P (properdin), B (proactivator), proactivator convertase S3 and inhibitors j and H. In the reaction, Properdin stabilizes convertases S3 and C5, therefore this activation pathway is also called the properdin system. The reaction begins with the addition of factor B to S3, as a result of a series of sequential reactions, P (properdin) is inserted into the complex (S3 convertase), which acts as an enzyme on S3 and C5, and the complement activation cascade begins with C6, C7, C8 and C9, resulting in cell wall damage or cell lysis.

Thus, the complement system serves as an effective defense mechanism for the body, which is activated as a result of immune reactions or through direct contact with microbes or toxins. Let us note some biological functions of activated complement components: they participate in regulating the process of switching immunological reactions from cellular to humoral and vice versa; Cell-bound C4 promotes immune attachment; S3 and C4 enhance phagocytosis; C1 and C4, by binding to the surface of the virus, block the receptors responsible for the introduction of the virus into the cell; C3 and C5a are identical to anaphylactoxins, they affect neutrophil granulocytes, the latter secrete lysosomal enzymes that destroy foreign antigens, provide directed migration of macrophages, cause contraction of smooth muscles, and increase inflammation.

It has been established that macrophages synthesize C1, C2, C3, C4 and C5; hepatocytes - SZ, Co, C8; liver parenchyma cells - C3, C5 and C9.

I nterferon. Released in 1957 English virologists A. Isaacs and I. Linderman. Interferon was initially considered as an antiviral defense factor. Later it turned out that this is a group of protein substances whose function is to ensure the genetic homeostasis of the cell. In addition to viruses, bacteria, bacterial toxins, mitogens, etc. act as inducers of interferon formation. Depending on the cellular origin of interferon and the factors inducing its synthesis, a-interferon is distinguished, or leukocyte, which is produced by leukocytes treated with viruses and other agents; (3-interferon, or fibroblast, which is produced by fibroblasts treated with viruses or other agents. Both of these interferons are classified as type I. Immune interferon, or γ-interferon, is produced by lymphocytes and macrophages activated by non-viral inducers.

Interferon takes part in the regulation of various mechanisms of the immune response: it enhances the cytotoxic effect of sensitized lymphocytes and K-cells, has anti-proliferative and antitumor effects, etc. Interferon has tissue specificity, i.e. it is more active in the biological system in which it is produced, protects cells from viral infection only if it acts on them before contact with the virus.

The process of interaction of interferon with sensitive cells includes several stages: adsorption of interferon on cellular receptors; induction of an antiviral state; development of viral resistance (filling with interferon-induced RNA and proteins); pronounced resistance to viral infection. Consequently, interferon does not interact directly with the virus, but prevents the penetration of the virus and inhibits the synthesis of viral proteins on cellular ribosomes during the replication of viral nucleic acids. Interferon has also been shown to have radiation protective properties.

I n g i b i t o r y. Nonspecific antiviral substances of protein nature are present in normal native blood serum, secretions of the epithelium of the mucous membranes of the respiratory and digestive tracts, and in extracts of organs and tissues. They have the ability to suppress the activity of viruses in the blood and liquids outside the sensitive cell. Inhibitors are divided into thermolabile (lose their activity when blood serum is heated to 6O...62°C for 1 hour) and thermostable (withstand heating up to 100°C). Inhibitors have universal virus neutralizing and antihemagglutinating activity against many viruses.

Inhibitors of animal tissues, secretions and excreta have proven active against many viruses: for example, secretory inhibitors of the respiratory tract have antihemagglutinating and virus-neutralizing activity.

Bactericidal activity of blood serum (BAS). Fresh blood serum of humans and animals has pronounced bacteriostatic properties against a number of pathogens of infectious diseases. The main components that inhibit the growth and development of microorganisms are normal antibodies, lysozyme, properdin, complement, monokines, leukins and other substances. Therefore, BAS is an integrated expression of the antimicrobial properties of humoral nonspecific defense factors. BAS depends on the health of the animals, the conditions of their housing and feeding: with poor housing and feeding, the activity of the serum is significantly reduced.

In addition to phagocytes, the blood contains soluble nonspecific substances that have a detrimental effect on microorganisms. These include complement, properdin, β-lysines, x-lysines, erythrin, leukins, plakins, lysozyme, etc.

Complement (from the Latin complementum - addition) is a complex system of protein fractions of blood that has the ability to lyse microorganisms and other foreign cells, such as red blood cells. There are several components of complement: C 1, C 2, C 3, etc. Complement is destroyed at a temperature of 55 ° C for 30 minutes. This property is called thermolability. It is also destroyed by shaking, under the influence of UV rays, etc. In addition to blood serum, complement is found in various body fluids and in inflammatory exudate, but is absent in the anterior chamber of the eye and cerebrospinal fluid.

Properdin (from Latin properde - to prepare) is a group of components of normal blood serum that activates complement in the presence of magnesium ions. It is similar to enzymes and plays an important role in the body's resistance to infection. A decrease in the level of properdin in the blood serum indicates insufficient activity of immune processes.

β-lysines are thermostable (temperature-resistant) substances in human blood serum that have an antimicrobial effect, mainly against gram-positive bacteria. Destroyed at 63° C and under the influence of UV rays.

X-lysine is a heat-stable substance isolated from the blood of patients with high fever. It has the ability to lyse bacteria, mainly gram-negative ones, without the participation of complement. Withstands heating up to 70-100° C.

Erythrin is isolated from animal erythrocytes. It has a bacteriostatic effect on diphtheria pathogens and some other microorganisms.

Leukines are bactericidal substances isolated from leukocytes. Heat stable, destroyed at 75-80° C. Found in the blood in very small quantities.

Plakins are substances similar to leukins isolated from platelets.

Lysozyme is an enzyme that destroys the membrane of microbial cells. It is found in tears, saliva, and blood fluids. The rapid healing of wounds of the conjunctiva of the eye, mucous membranes of the oral cavity, and nose is largely due to the presence of lysozyme.

The constituent components of urine, prostatic fluid, and extracts of various tissues also have bactericidal properties. Normal serum contains small amounts of interferon.

Security questions

1. What are humoral factors of nonspecific protection?

2. What humoral factors of nonspecific protection do you know?

Specific body defense factors (immunity)

The components listed above do not exhaust the entire arsenal of humoral protection factors. The main ones among them are specific antibodies - immunoglobulins, which are formed when foreign agents - antigens - are introduced into the body.

Antigens

Antigens are substances genetically foreign to the body (proteins, nucleoproteins, polysaccharides, etc.), to the introduction of which the body responds by developing specific immunological reactions. One of these reactions is the formation of antibodies.

Antigens have two main properties: 1) immunogenicity, i.e. the ability to induce the formation of antibodies and immune lymphocytes; 2) the ability to enter into a specific interaction with antibodies and immune (sensitized) lymphocytes, which manifests itself in the form of immunological reactions (neutralization, agglutination, lysis, etc.). Antigens that have both characteristics are called complete. These include foreign proteins, serums, cellular elements, toxins, bacteria, viruses.

Substances that do not cause immunological reactions, in particular the production of antibodies, but enter into a specific interaction with ready-made antibodies, are called haptens - defective antigens. Haptens acquire the properties of full-fledged antigens after combining with large-molecular substances - proteins, polysaccharides.

The conditions that determine the antigenic properties of various substances are: foreignness, macromolecularity, colloidal state, solubility. Antigenicity manifests itself when a substance enters the internal environment of the body, where it encounters cells of the immune system.

The specificity of antigens, their ability to combine only with the corresponding antibody, is a unique biological phenomenon. It underlies the mechanism for maintaining the constancy of the internal environment of the body. This constancy is ensured by the immune system, which recognizes and destroys genetically foreign substances (including microorganisms and their poisons) found in its internal environment. The human immune system is under constant immunological surveillance. It is able to recognize foreignness when cells differ by just one gene (cancer).

Specificity is a structural feature of substances by which antigens differ from each other. It is determined by the antigenic determinant, i.e., a small part of the antigen molecule, which combines with the antibody. The number of such sites (groupings) is different for different antigens and determines the number of antibody molecules with which the antigen can bind (valence).

The ability of antigens to combine only with those antibodies that arose in response to activation of the immune system by a given antigen (specificity) is used in practice: 1) diagnosis of infectious diseases (determination of specific antigens of a pathogen or specific antibodies in the patient’s blood serum); 2) prevention and treatment of patients with infectious diseases (creation of immunity to certain microbes or toxins, specific neutralization of poisons of pathogens of a number of diseases during immunotherapy).

The immune system clearly differentiates between “self” and “foreign” antigens, reacting only to the latter. However, reactions to the body's own antigens - autoantigens and the emergence of antibodies against them - autoantibodies are possible. Autoantigens become “barrier” antigens - cells, substances that during the life of an individual do not come into contact with the immune system (the lens of the eye, sperm, thyroid gland, etc.), but come into contact with it during various injuries, usually being absorbed into the blood. And since during the development of the body these antigens were not recognized as “self,” natural tolerance (specific immunological unresponsiveness) was not formed, i.e., cells of the immune system remained in the body capable of an immune response to these own antigens.

As a result of the appearance of autoantibodies, autoimmune diseases can develop as a consequence of: 1) the direct cytotoxic effect of autoantibodies on the cells of the corresponding organs (for example, Hashimoto's goiter - damage to the thyroid gland); 2) indirect action of autoantigen-autoantibody complexes, which are deposited in the affected organ and cause its damage (for example, systemic lupus erythematosus, rheumatoid arthritis).

Antigens of microorganisms. A microbial cell contains a large number of antigens that have different locations in the cell and different significance for the development of the infectious process. Different groups of microorganisms have different antigen compositions. In intestinal bacteria, O-, K-, and H-antigens have been well studied.

O-antigen is associated with the cell wall of the microbial cell. It was usually called “somatic”, since it was believed that this antigen is contained in the body (soma) of the cell. O-antigen of gram-negative bacteria is a complex lipopolysaccharide-protein complex (endotoxin). It is heat-stable and does not collapse when treated with alcohol and formaldehyde. Consists of a main core and side polysaccharide chains. The specificity of O-antigens depends on the structure and composition of these chains.

K-antigens (capsular) are associated with the capsule and cell wall of the microbial cell. They are also called shell ones. K antigens are located more superficially than O antigens. They are mainly acidic polysaccharides. There are several types of K-antigens: A, B, L, etc. These antigens differ from each other in their resistance to temperature influences. A-antigen is the most stable, L - the least. Surface antigens also include Vi-antigen, which is found in typhoid fever pathogens and some other intestinal bacteria. It is destroyed at 60° C. The presence of the Vi antigen has been associated with the virulence of microorganisms.

H-antigens (flagellar) are localized in the flagella of bacteria. They are a special protein - flagellin. Destroyed when heated. When treated with formalin, they retain their properties (see Fig. 70).

Protective antigen (protective) (from Latin protectio - patronage, protection) is formed by pathogens in the patient’s body. The causative agents of anthrax, plague, and brucellosis are capable of forming a protective antigen. It is found in exudates of affected tissues.

Detection of antigens in pathological material is one of the methods for laboratory diagnosis of infectious diseases. Various immune reactions are used to detect antigen (see below).

As microorganisms develop, grow, and reproduce, their antigens may change. There is a loss of some antigenic components that are more superficially located. This phenomenon is called dissociation. An example of this is the “S” - “R” dissociation.

Security questions

1. What are antigens?

2. What are the main properties of antigens?

3. What microbial cell antigens do you know?

Antibodies

Antibodies are specific blood proteins - immunoglobulins, formed in response to the introduction of an antigen and capable of specifically reacting with it.

There are two types of proteins in human serum: albumins and globulins. Antibodies are associated primarily with globulins that are modified by antigen and called immunoglobulins (Ig). Globulins are heterogeneous. Based on the speed of movement in the gel when an electric current is passed through it, they are divided into three fractions: α, β, γ. Antibodies belong mainly to γ-globulins. This fraction of globulins has the highest speed of movement in an electric field.

Immunoglobulins are characterized by molecular weight, sedimentation rate during ultracentrifugation (centrifugation at very high speed), etc. Differences in these properties made it possible to divide immunoglobulins into 5 classes: IgG, IgM, IgA, IgE, IgD. They all play a role in developing immunity against infectious diseases.

Immunoglobulins G (IgG) make up about 75% of all human immunoglobulins. They are most active in the development of immunity. The only immunoglobulins penetrate the placenta, providing passive immunity to the fetus. They have a low molecular weight and sedimentation rate during ultracentrifugation.

Immunoglobulin M (IgM) is formed in the fetus and is the first to appear after infection or immunization. This class includes “normal” human antibodies, which are formed during his life, without visible manifestations of infection or during repeated household infections. They have a high molecular weight and sedimentation rate during ultracentrifugation.

Immunoglobulins A (IgA) have the ability to penetrate mucosal secretions (colostrum, saliva, bronchial contents, etc.). They play a role in protecting the mucous membranes of the respiratory and digestive tracts from microorganisms. In terms of molecular weight and sedimentation rate during ultracentrifugation, they are close to IgG.

Immunoglobulin E (IgE) or reagins are responsible for allergic reactions (see Chapter 13). Play a role in the development of local immunity.

Immunoglobulin D (IgD). Found in small quantities in blood serum. Not studied enough.

Structure of immunoglobulins. Molecules of immunoglobulins of all classes are constructed in the same way. The simplest structure of IgG molecules is two pairs of polypeptide chains connected by a disulfide bond (Fig. 31). Each pair consists of a light and a heavy chain, differing in molecular weight. Each chain has constant sections that are genetically predetermined, and variable sections that are formed under the influence of the antigen. These specific regions of the antibody are called active centers. They interact with the antigen that caused the formation of antibodies. The number of active centers in an antibody molecule determines the valency - the number of antigen molecules that the antibody can contact. IgG and IgA are bivalent, IgM are pentavalent.

Rice. 31. Schematic representation of immunoglobulins

Immunogenesis- antibody formation depends on the dose, frequency and method of antigen administration. There are two phases of the primary immune response to an antigen: inductive - from the moment of antigen administration until the appearance of antibody-forming cells (up to 20 hours) and productive, which begins by the end of the first day after antigen administration and is characterized by the appearance of antibodies in the blood serum. The amount of antibodies gradually increases (by the 4th day), reaching a maximum on the 7-10th day and decreases by the end of the first month.

A secondary immune response develops when the antigen is reintroduced. At the same time, the inductive phase is much shorter - antibodies are produced faster and more intensely.

Security questions

1. What are antibodies?

2. What classes of immunoglobulins do you know?

Related information.

Humoral protection factors play a major role in maintaining a high level of the body's defenses. It is known that freshly obtained blood from farm animals has the ability to inhibit the growth (bacteriostatic ability) or cause death (bactericidal ability) of microorganisms. These properties of blood and its serum are due to the content of substances such as lysozyme, complement, properdin, interferon, bacteriolysins, monokines, leukines and some others (S.I. Plyashchenko, V.T. Sidorov, 1979; V.M. Mityushnikov, 1985; S.A. Pigalev, V.M.

Lysozyme (muramidase) is a universal protective enzyme that is found in tears, saliva, nasal mucus, secretions of mucous membranes, blood serum and extracts obtained from various organs and tissues (Z.V. Ermolyeva, 1965; W.J. Herbert 1974; V.E. Pigarevsky, 1978; S.A. Pigalev, V.M. The smallest amount of lysozyme is found in skeletal muscles and brain (O.V. Bukharin, N.V. Vasiliev, 1974). There is a lot of lysozyme in the protein of chicken eggs (I.A. Bolotnikov, 1982; A.A. Sokhin, E.F. Chermushenko, 1984). The titer of lysozyme in the blood of chickens has a reliable relationship with the titer of lysozyme in egg whites (V.M. Mityushnikov, T.A. Kozharinova, 1974; V.M. Mityushnikov, 1980). A high concentration of this enzyme is noted in organs that perform barrier functions: liver, spleen, lungs, as well as phagocytes. Lysozyme is resistant to heat (inactivated by boiling), has the property of lysing living and dead, mainly gram-positive microorganisms, which is explained by the different chemical structure of the surface of the bacterial cell. The antimicrobial effect of lysozyme is explained by its disruption of the mucopolysaccharide structure of the bacterial wall, as a result of which the cell is lysed (P.A. Emelyanenko, 1987; G.A. Grosheva, N.R. Esakova, 1996).

In addition to its bactericidal effect, lysozyme affects the level of properdin and the phagocytic activity of leukocytes, regulates the permeability of membranes and tissue barriers. This enzyme causes lysis, bacteriostasis, agglutination of bacteria, stimulates phagocytosis, proliferation of T- and B-lymphocytes, fibroblasts, and antibody formation. The main sources of lysozyme are neutrophils, monocytes and tissue macrophages (W.J. Herbert 1974; O.V. Bukharin, N.V. Vasiliev, 1974; Ya.E. Kolyakov, 1986; V.A. Medvedsky, 1998).

According to A.F. Mogilenko (1990), the content of lysozyme in blood serum is an important indicator characterizing the state of nonspecific reactivity and defenses of the body.

Fresh blood serum contains a multicomponent enzymatic complement system, which plays an important role in removing antigen from the body by activating the humoral immune system. The complement system includes 11 proteins that have different enzymatic activities and are designated by symbols from C1 to C9. The main function of complement is antigen lysis. There are two ways of activation (self-assembly) of the complement system - classical and alternative. In the first case, the main thing is the antigen-antibody complex, in the second (alternative) the first components of the classical pathway are not required for activation: C1, C2 and C4 (F. Bernet, 1971; I.A. Bolotnikov, 1982; Ya.E. Kolyakov, 1986; A. Royt, 1991; V.A.

The complement system is directly involved in nonspecific complementary lysis of target cells, especially those affected by viruses, chemotaxis and nonimmune phagocytosis, antibody-dependent complementary lysis, specific antibody-dependent phagocytosis, cytotoxicity of sensitized cells. Individual components of complement or their fragments play an important role in regulating the permeability and tone of blood vessels, affect the blood coagulation system, and take part in the release of histamine by cells (F. Bernet, 1971; S.A. Pigalev, V.M. Skorlyakov, 1989 ; A. Royt, 1991; P. Benhaim, T.K. Hunt, 1992;

Natural (normal antibodies) are found in small titers in the blood serum of healthy animals that have not undergone special immunization. The nature of these antibodies is not fully understood. It is believed that they arise as a result of cross-immunization or in response to the introduction into the body of a small amount of an infectious pathogen, which is not capable of causing an acute disease, but causes only a latent or subacute infection (W.J. Herbert, 1974; S.A. Pigalev, V.M. Skorlyakov, 1989). According to P.A. Emelianenko (1987), it is more appropriate to consider natural antibodies in the category of immunoglobulins, the synthesis of which occurs in response to antigenic irritation. The content of natural antibodies in the blood reflects the degree of maturity of the immunocompetent system of the animal body. A decrease in the titer of normal antibodies occurs in many pathological conditions. Together with complement, normal antibodies also provide bactericidal activity in the blood serum.

A humoral factor of natural resistance is also properdin, or more precisely the properdin system (Ya.E. Kolyakov, 1986). The name properdin comes from the Latin. pro and perdere - to prepare for destruction. The properdin system plays an important role in the natural nonspecific resistance of the animal organism. Properdin is contained in fresh normal blood serum in amounts up to 25 mcg/ml. This is whey protein. weighing 220,000, which is bactericidal and can neutralize some viruses. According to Ya.E. Kolyakova, (1986); S.A. Pigaleva, V.M. Skorlyakova (1989); N.A. Radchuk, G.V. Dunaeva, N.M. Kolycheva, N.I. Smirnova (1991) bactericidal activity is manifested not by properdin itself, but by the properdin system, which consists of three components: 1) properdin - a serum protein, 2) magnesium ions, 3) complement. Thus, properdin does not act on its own, but together with other factors contained in the blood of animals, including complement.

Interferon is a group of protein substances produced by the cells of the body that prevent the reproduction of the virus. In addition to viruses, inducers of interferon formation are bacteria, bacterial toxins, mutagens, etc. Depending on the cellular origin and the factors inducing its synthesis, a-interferon is distinguished, or leukocyte, which is produced by leukocytes and B-interferon, or fibroblast, which is produced by fibroblasts. Both of these interferrons are classified as type 1 and are produced when leukocytes and fibroblasts are treated with viruses and other agents. Immune interferon, or y-interferon, which is produced by lymphocytes and macrophages activated by non-viral inducers (W.J. Herbert 1974; Z.V. Ermolyeva, 1965; S.A. Pigalev, V.M. Skorlyakov, 1989; N. A. Radchuk, G.V. Dunaev, 1991; P.S. Morahan, D. Stewart, 1993; , 1993).

In addition to the above listed humoral protective factors, beta-lysines, lactoferrin, inhibitors, C-reactive protein, etc. play an important role.

Beta-lysines are serum proteins that have the ability to lyse certain bacteria. They act on the cytoplasmic membrane of the microbial cell, damaging it, thereby causing lysis of the cell wall by enzymes (autolysins) located in the cytoplasmic membrane, activated and released when beta-lysins interact with the cytoplasmic membrane. Thus, beta lysines cause autolytic processes and microbial cell death.

Lactoferrin is a non-hymine glycoprotein with iron-binding activity. It binds two atoms of ferric iron, thereby competing with microbes and inhibiting their growth.

Inhibitors are nonspecific antiviral substances contained in saliva, blood serum, secretions of the epithelium of the respiratory and digestive tracts, extracts of various organs and tissues. They have the ability to suppress the activity of viruses outside the sensitive cell, when the virus is in the blood and liquids. Inhibitors are divided into two classes: thermolabile (lose activity when heated to 60-62 0C for an hour) and thermostable (withstand heating up to 100 0C) (O.V. Bukharin, N.V. Vasiliev, 1977; V.E. Pigarevsky, 1978 ; S.I. Plyashchenko, V.T. Bolotnikov, V.N. Belousova, N.A. .V. Dunaev, N.M. Kolychev, N.I.

C-reactive protein is found in acute inflammatory processes and diseases accompanied by tissue destruction, since it can serve as an indicator of the activity of these processes. This protein is not detected in normal serum. C-reactive protein has the ability to initiate reactions of precipitation, aglutination, phagocytosis, complement fixation, i.e. has functional features similar to immunoglobulins. In addition, this protein increases the mobility of leukocytes (W.J. Herbert 1974; S.S. Abramov, A.F. Mogilenko, A.I. Yatusevich, 1988; A. Royt, 1991).