Humoral factors of nonspecific defense of the body include: Nonspecific protective factors
humoral factors - complement system. Complement is a complex of 26 proteins in the blood serum. Each protein is designated as a fraction in Latin letters: C4, C2, C3, etc. Under normal conditions, the complement system is in an inactive state. When antigens enter, it is activated; the stimulating factor is the antigen-antibody complex. Any infectious inflammation begins with the activation of complement. The complement protein complex is integrated into the cell membrane of the microbe, which leads to cell lysis. Complement is also involved in anaphylaxis and phagocytosis, as it has chemotactic activity. Thus, complement is a component of many immunolytic reactions aimed at freeing the body from microbes and other foreign agents;
AIDS
The discovery of HIV was preceded by the work of R. Gallo and his colleagues, who isolated two human T-lymphotropic retroviruses using the T-lymphocyte cell culture they obtained. One of them, HTLV-I (humen T-lymphotropic virus type I), discovered in the late 70s, is the causative agent of a rare but malignant human T-leukemia. A second virus, designated HTLV-II, also causes T-cell leukemias and lymphomas.
After registering the first patients with acquired immunodeficiency syndrome (AIDS), a then unknown disease, in the United States in the early 80s, R. Gallo suggested that its causative agent was a retrovirus close to HTLV-I. Although this assumption was refuted a few years later, it played a large role in the discovery of the true causative agent of AIDS. In 1983, from a piece of tissue from an enlarged lymph node of a homosexual, Luc Montenier and a group of employees at the Pasteur Institute in Paris isolated a retrovirus in a culture of T-helper cells. Further studies showed that this virus was different from HTLV-I and HTLV-II - it reproduced only in T helper and effector cells, designated T4, and did not reproduce in T suppressor and killer cells, designated T8.
Thus, the introduction of T4 and T8 lymphocyte cultures into virological practice made it possible to isolate three obligate lymphotropic viruses, two of which caused the proliferation of T-lymphocytes, expressed in various forms of human leukemia, and one, the causative agent of AIDS, caused their destruction. The latter is called the human immunodeficiency virus - HIV.
Structure and chemical composition. HIV virions are spherical, 100-120 nm in diameter, and are similar in structure to other lentiviruses. The outer shell of virions is formed by a lipid bilayer with glycoprotein “spikes” located on it (Fig. 21.4). Each “spike” consists of two subunits (gp41 and gp!20). The first penetrates the lipid layer, the second is located outside. The lipid layer originates from the outer membrane of the host cell. The formation of both proteins (gp41 and gp!20) with a non-covalent bond between them occurs when the HIV outer shell protein (gp!60) is cut. Under the outer shell there is a cylindrical or cone-shaped core of the virion, formed by proteins (p!8 and p24). The core contains RNA, reverse transcriptase and internal proteins (p7 and p9).
Unlike other retroviruses, HIV has a complex genome due to the presence of a system of regulatory genes. Without knowledge of the basic mechanisms of their functioning, it is impossible to understand the unique properties of this virus, manifested in the various pathological changes that it causes in the human body.
The HIV genome contains 9 genes. Three structural genes gag, pol And env encode components of viral particles: gene gag- internal proteins of the virion, which are part of the core and capsid; gene pol- reverse transcriptase; gene env- type-specific proteins found in the outer shell (glycoproteins gp41 and gp!20). The large molecular weight of gp!20 is due to their high degree of glycosylation, which is one of the reasons for the antigenic variability of this virus.
Unlike all known retroviruses, HIV has a complex system of regulation of structural genes (Fig. 21.5). Among them, genes attract the most attention tat And rev. Gene product tat increases the rate of transcription of both structural and regulatory viral proteins tens of times. Gene product rev is also a transcription regulator. However, it controls the transcription of either regulatory or structural genes. As a result of this transcription switch, capsid proteins are synthesized instead of regulatory proteins, which increases the rate of virus reproduction. Thus, with the participation of the gene rev the transition from latent infection to its active clinical manifestation may be determined. Gene nef controls the cessation of HIV reproduction and its transition to a latent state, and the gene vif encodes a small protein that enhances the virion's ability to bud from one cell and infect another. However, this situation will become even more complicated when the mechanism of regulation of proviral DNA replication by gene products is finally elucidated vpr And vpu. At the same time, at both ends of the DNA of the provirus, integrated into the cellular genome, there are specific markers - long terminal repeats (LTRs), consisting of identical nucleotides, which are involved in the regulation of the expression of the genes considered. At the same time, there is a certain algorithm for the inclusion of genes during the process of viral reproduction in different phases of the disease.
Antigens. Core proteins and envelope glycoproteins (gp!60) have antigenic properties. The latter are characterized by a high level of antigenic variability, which is determined by the high rate of nucleotide substitutions in genes env And gag, hundreds of times higher than the corresponding figure for other viruses. During the genetic analysis of numerous HIV isolates, there was not a single one with a complete match of nucleotide sequences. Deeper differences were noted in HIV strains isolated from patients living in different geographic areas (geographical variants).
However, HIV variants have common antigenic epitopes. Intense antigenic variability of HIV occurs in the body of patients during infection and virus carriers. It allows the virus to “hide” from specific antibodies and cellular immunity factors, which leads to chronic infection.
The increased antigenic variability of HIV significantly limits the possibilities of creating a vaccine to prevent AIDS.
Currently, two types of pathogens are known - HIV-1 and HIV-2, which differ in antigenic, pathogenic and other properties. Initially, HIV-1 was isolated, which is the main causative agent of AIDS in Europe and America, and a few years later in Senegal, HIV-2 was isolated, which is distributed mainly in West and Central Africa, although isolated cases of the disease are also found in Europe.
In the United States, live adenovirus vaccine is successfully used to immunize military personnel.
Laboratory diagnostics. To detect viral antigen in the epithelial cells of the mucous membrane of the respiratory tract, immunofluorescent and immunoenzyme methods are used, and in feces, immunoelectron microscopy is used. Isolation of adenoviruses is carried out by infecting sensitive cell cultures, followed by identification of the virus in RNA, and then in the neutralization reaction and RTGA.
Serodiagnosis is carried out in the same reactions with paired sera of sick people.
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Culture media
Microbiological research is the isolation of pure cultures of microorganisms, cultivation and study of their properties. Cultures consisting of microorganisms of the same type are called pure. They are needed in the diagnosis of infectious diseases, to determine the species and type of microbes, in research work, to obtain waste products of microbes (toxins, antibiotics, vaccines, etc.).
For the cultivation of microorganisms (cultivation under artificial conditions in vitro), special substrates are required - nutrient media. On media, microorganisms carry out all life processes (eat, breathe, reproduce, etc.), which is why they are also called “culture media.”
Culture media
Culture media are the basis of microbiological work, and their quality often determines the results of the entire study. Environments must create optimal (best) conditions for the life of microbes.
Environment requirements
Environments must meet the following conditions:
1) be nutritious, i.e. contain in an easily digestible form all the substances necessary to meet nutritional and energy needs. They are sources of organogens and mineral (inorganic) substances, including trace elements. Mineral substances not only enter the cell structure and activate enzymes, but also determine the physicochemical properties of media (osmotic pressure, pH, etc.). When cultivating a number of microorganisms, growth factors are added to the media - vitamins, some amino acids that the cell cannot synthesize;
Attention! Microorganisms, like all living things, need plenty of water.
2) have an optimal concentration of hydrogen ions - pH, since only with an optimal reaction of the environment, affecting the permeability of the shell, can microorganisms absorb nutrients.
For most pathogenic bacteria, a slightly alkaline environment (pH 7.2-7.4) is optimal. The exception is Vibrio cholerae - its optimum is in the alkaline zone
(pH 8.5-9.0) and the causative agent of tuberculosis, which requires a slightly acidic reaction (pH 6.2-6.8).
To prevent acidic or alkaline products of their vital activity from changing the pH during the growth of microorganisms, the media must be buffered, i.e., contain substances that neutralize metabolic products;
3) be isotonic for the microbial cell, that is, the osmotic pressure in the medium must be the same as inside the cell. For most microorganisms, the optimal environment is a 0.5% sodium chloride solution;
4) be sterile, since foreign microbes interfere with the growth of the microbe under study, the determination of its properties and change the properties of the medium (composition, pH, etc.);
5) solid media must be moist and have an optimal consistency for microorganisms;
6) have a certain redox potential, i.e. the ratio of substances donating and accepting electrons, expressed by the RH2 index. This potential shows the saturation of the environment with oxygen. Some microorganisms require a high potential, while others require a low one. For example, anaerobes reproduce at RH2 no higher than 5, and aerobes at RH2 no lower than 10. The redox potential of most environments satisfies the requirements of aerobes and facultative anaerobes;
7) be as unified as possible, i.e. contain constant amounts of individual ingredients. Thus, media for the cultivation of most pathogenic bacteria should contain 0.8-1.2 g of amino nitrogen NH2, i.e., the total nitrogen of the amino groups of amino acids and lower polypeptides; 2.5-3.0 hl total nitrogen N; 0.5% chlorides in terms of sodium chloride; 1% peptone.
It is desirable that the media be transparent - it is more convenient to monitor the growth of crops, and it is easier to notice contamination of the environment with foreign microorganisms.
Classification of media
The need for nutrients and environmental properties varies among different types of microorganisms. This eliminates the possibility of creating a universal environment. In addition, the choice of a particular environment is influenced by the objectives of the study.
Currently, a huge number of environments have been proposed, the classification of which is based on the following characteristics.
1. Initial components. Based on the starting components, natural and synthetic media are distinguished. Natural media are prepared from animal products and
of plant origin. Currently, media have been developed in which valuable food products (meat, etc.) are replaced with non-food products: bone and fish meal, feed yeast, blood clots, etc. Despite the fact that the composition of nutrient media from natural products is very complex and varies depending from raw materials, these media are widely used.
Synthetic media are prepared from certain chemically pure organic and inorganic compounds, taken in precisely specified concentrations and dissolved in double-distilled water. An important advantage of these media is that their composition is constant (it is known how much and what substances they contain), so these media are easily reproducible.
2. Consistency (degree of density). Media are liquid, dense and semi-liquid. Solid and semi-liquid media are prepared from liquid substances, to which agar-agar or gelatin is usually added to obtain a medium of the desired consistency.
Agar-agar is a polysaccharide obtained from certain
varieties of seaweed. It is not a nutrient for microorganisms and serves only to compact the environment. In water, agar melts at 80-100°C and solidifies at 40-45°C.
Gelatin is an animal protein. Gelatin media melt at 25-30°C, so crops are usually grown on them at room temperature. The density of these media decreases at a pH below 6.0 and above 7.0, and they harden poorly. Some microorganisms use gelatin as a nutrient - as they grow, the medium liquefies.
In addition, clotted blood serum, coagulated eggs, potatoes, and media with silica gel are used as solid media.
3. Composition. Environments are divided into simple and complex. The first include meat peptone broth (MPB), meat peptone agar (MPA), Hottinger broth and agar, nutritious gelatin and peptone water. Complex media are prepared by adding to simple media blood, serum, carbohydrates and other substances necessary for the reproduction of a particular microorganism.
4. Purpose: a) basic (commonly used) media are used for cultivating most pathogenic microbes. These are the above-mentioned MP A, MPB, broth and Hottinger agar, peptone water;
b) special media are used to isolate and grow microorganisms that do not grow on simple media. For example, for the cultivation of streptococcus, sugar is added to the media, for pneumo- and meningococci - blood serum, for the causative agent of whooping cough - blood;
c) elective (selective) environments serve to isolate a certain type of microbes, the growth of which they favor, delaying or suppressing the growth of accompanying microorganisms. Thus, bile salts, suppressing the growth of E. coli, make the environment
selective for the causative agent of typhoid fever. Media become selective when certain antibiotics, salts are added to them, and pH changes.
Liquid elective media are called accumulation media. An example of such a medium is peptone water with a pH of 8.0. At this pH, Vibrio cholerae actively multiplies on it, and other microorganisms do not grow;
d) differential diagnostic media make it possible to distinguish (differentiate) one type of microbe from another by enzymatic activity, for example, Hiss media with carbohydrates and an indicator. With the growth of microorganisms that break down carbohydrates, the color of the medium changes;
e) preservative media are intended for primary seeding and transportation of the test material; they prevent the death of pathogenic microorganisms and suppress the development of saprophytes. An example of such a medium is a glycerol mixture used to collect stool in studies conducted to detect a range of intestinal bacteria.
Hepatitis (A,E)
The causative agent of hepatitis A (HAV-Hepatitis A virus) belongs to the picornavirus family, the genus of enteroviruses. Causes the most common viral hepatitis, which has several historical names (infectious, epidemic hepatitis, Botkin's disease, etc.). In our country, about 70% of cases of viral hepatitis are caused by the hepatitis A virus. The virus was first discovered by S. Feystone in 1979 in the feces of patients using immune electron microscopy.
Structure and chemical composition. In terms of morphology and structure, the hepatitis A virus is close to all enteroviruses (see 21.1.1.1). The RNA of the hepatitis A virus contains nucleotide sequences common to other enteroviruses.
The hepatitis A virus has one virus-specific antigen of a protein nature. HAV differs from enteroviruses in its higher resistance to physical and chemical factors. It is partially inactivated when heated to 60°C for 1 hour, at 100°C it is destroyed within 5 minutes, and is sensitive to the action of formalin and UV radiation.
Cultivation and reproduction. The hepatitis virus has a reduced ability to reproduce in cell cultures. However, it was possible to adapt it to continuous cell lines of humans and monkeys. Reproduction of the virus in cell culture is not accompanied by CPE. HAV is almost not detected in the culture fluid, since it is associated with cells in the cytoplasm of which it reproduces:
Pathogenesis of human diseases and immunity. HAV, like other enteroviruses, enters the gastrointestinal tract with food, where it reproduces in the epithelial cells of the mucous membrane of the small intestine and regional lymph nodes. The pathogen then enters the blood, in which it is detected at the end of the incubation period and in the first days of the disease.
Unlike other enteroviruses, the main target of the damaging effect of HAV are liver cells, in the cytoplasm of which its reproduction occurs. It is possible that hepatocytes are damaged by NK cells (natural killer cells), which in an activated state can interact with them, causing their destruction. Activation of NK cells also occurs as a result of their interaction with interferon induced by the virus. Damage to hepatocytes is accompanied by the development of jaundice and an increase in the level of transaminases in the blood serum. Next, the pathogen enters the intestinal lumen with bile and is excreted in feces, which contain a high concentration of the virus at the end of the incubation period and in the first days of the disease (before the development of jaundice). Hepatitis A usually ends in complete recovery, and deaths are rare.
After suffering a clinically pronounced or asymptomatic infection, lifelong humoral immunity is formed, associated with the synthesis of antiviral antibodies. Immunoglobulins of the IgM class disappear from the serum 3-4 months after the onset of the disease, while IgG persists for many years. The synthesis of secretory immunoglobulins SlgA has also been established.
Epidemiology. The source of infection is sick people, including those with a common asymptomatic form of infection. The hepatitis A virus circulates widely among the population. On the European continent, serum antibodies against HAV are found in 80% of the adult population over 40 years of age. In countries with low socioeconomic levels, infection occurs already in the first years of life. Hepatitis A often affects children.
The patient is most dangerous to others at the end of the incubation period and in the first days of the height of the disease (before the appearance of jaundice) due to the maximum release of the virus in feces. The main mechanism of transmission is fecal-oral - through food, water, household items, children's toys.
Laboratory diagnosis is carried out by identifying the virus in the patient’s feces using immunoelectron microscopy. Viral antigen in feces can also be detected using enzyme immunoassay and radioimmunoassay. The most widely used serodiagnosis of hepatitis is the detection, using the same methods, of IgM class antibodies in paired blood sera, which reach a high titer during the first 3-6 weeks.
Specific prevention. Vaccine prevention of hepatitis A is under development. Inactivated and live culture vaccines are being tested, the production of which is difficult due to the weak reproduction of the virus in cell cultures. The most promising is the development of a genetically engineered vaccine. For passive immunoprophylaxis of hepatitis A, immunoglobulin obtained from a mixture of donor sera is used.
The causative agent of hepatitis E has some similarities with caliciviruses. The size of the viral particle is 32-34 nm. The genetic material is represented by RNA. Transmission of the hepatitis E virus, like HAV, occurs through the enteral route. Serodiagnosis is carried out by determining antibodies to the E-virus antigen.
Mechanisms of formation of protective reactions
The body’s protection from everything foreign (microorganisms, foreign macromolecules, cells, tissues) is carried out with the help of nonspecific protective factors and specific protective factors - immune reactions.
Nonspecific protective factors arose in phylogenesis earlier than immune mechanisms and are the first to be included in the body’s defense against various antigenic stimuli; the degree of their activity does not depend on the immunogenic properties and the frequency of exposure to the pathogen.
Immune protective factors act strictly specifically (only anti-A antibodies or anti-A cells are produced against antigen-A), and unlike non-specific protective factors, the strength of the immune reaction is regulated by the antigen, its type (protein, polysaccharide), quantity and frequency impact.
Nonspecific body defense factors include:
1. Protective factors of the skin and mucous membranes.
The skin and mucous membranes form the first barrier to protect the body from infections and other harmful influences.
2.Inflammatory reactions.
3. Humoral substances in serum and tissue fluid (humoral protective factors).
4. Cells with phagocytic and cytotoxic properties (cellular protection factors),
Specific protective factors or immune defense mechanisms include:
1. Humoral immunity.
2. Cellular immunity.
1. The protective properties of the skin and mucous membranes are due to:
a) mechanical barrier function of the skin and mucous membranes. Normal, intact skin and mucous membranes are impermeable to microorganisms;
b) the presence of fatty acids on the skin surface, lubricating and disinfecting the skin surface;
c) the acidic reaction of secretions released onto the surface of the skin and mucous membranes, the content of lysozyme, properdin and other enzymatic systems in the secretions that have a bactericidal effect on microorganisms. Sweat and sebaceous glands open onto the skin, the secretions of which have an acidic pH.
The secretions of the stomach and intestines contain digestive enzymes that inhibit the development of microorganisms. The acidic reaction of gastric juice is not suitable for the development of most microorganisms.
Saliva, tears and other secretions normally have properties that prevent the development of microorganisms.
Inflammatory reactions.
The inflammatory response is a normal reaction of the body. The development of the inflammatory reaction leads to the attraction of phagocytic cells and lymphocytes to the site of inflammation, activation of tissue macrophages and the release of biologically active compounds and substances with bactericidal and bacteriostatic properties from cells involved in inflammation.
The development of inflammation contributes to the localization of the pathological process, the elimination of factors that caused inflammation from the source of inflammation, and the restoration of the structural integrity of the tissue and organ. The process of acute inflammation is shown schematically in Fig. 3-1.
Rice. 3-1. Acute inflammation.
From left to right, the processes occurring in tissues and blood vessels are presented when tissues are damaged and inflammation develops in them. As a rule, tissue damage is accompanied by the development of infection (bacteria are indicated by black rods in the figure). A central role in the acute inflammatory process is played by tissue mast cells, macrophages and polymorphonuclear leukocytes coming from the blood. They are a source of biologically active substances, pro-inflammatory cytokines, lysosomal enzymes, all factors of inflammation: redness, heat, swelling, pain. When acute inflammation transitions to chronic, the main role in maintaining inflammation passes to macrophages and T-lymphocytes.
Humoral protective factors.
Nonspecific humoral protective factors include: lysozyme, complement, properdin, B-lysines, interferon.
Lysozyme. Lysozyme was discovered by P. L. Lashchenko. In 1909, he first discovered that egg white contains a special substance that can have a bactericidal effect on certain types of bacteria. Later it was found that this action is due to a special enzyme, which in 1922 was named lysozyme by Fleming.
Lysozyme is a muramidase enzyme. By its nature, lysozyme is a protein consisting of 130-150 amino acid residues. The enzyme exhibits optimal activity at pH = 5.0-7.0 and temperature +60C°
Lysozyme is found in many human secretions (tears, saliva, milk, intestinal mucus), skeletal muscles, spinal cord and brain, amniotic membranes and fetal fluids. In blood plasma its concentration is 8.5±1.4 µg/l. The bulk of lysozyme in the body is synthesized by tissue macrophages and neutrophils. A decrease in serum lysozyme titer is observed in severe infectious diseases, pneumonia, etc.
Lysozyme has the following biological effects:
1) increases phagocytosis of neutrophils and macrophages (lysozyme, changing the surface properties of microbes, makes them easily accessible to phagocytosis);
2) stimulates the synthesis of antibodies;
3) removal of lysozyme from the blood leads to a decrease in the serum levels of complement, properdin, and B-lysines;
4) enhances the lytic effect of hydrolytic enzymes on bacteria.
Complement. The complement system was discovered in 1899 by J. Bordet. Complement is a complex of blood serum proteins consisting of more than 20 components. The main components of complement are designated by the letter C and have numbers from 1 to 9: C1, C2, C3, C4, C5, C6, C7.C8.C9. (Table 3-2.).
Table 3-2. Characteristics of proteins of the human complement system.
| Designation | Carbohydrate content, % | Molecular weight, kD | Number of circuits | P.I. | Content in serum, mg/l | |
| Clq | 8,5 | 10-10,6 | 6,80 | |||
| С1r 2 | 9,4 | 11,50 | ||||
| C1s | 7,1 | 16,90 | ||||
| C2 | + | 5,50 | 8,90 | |||
| C4 | 6,9 | 6,40 | 8,30 | |||
| NW | 1,5 | 5,70 | 9,70 | |||
| C5 | 1,6 | 4,10 | 13,70 | |||
| C6 | 10,80 | |||||
| C7 | 5,60 | 19,20 | ||||
| C8 | 6,50 | 16,00 | ||||
| C9 | 7,8 | 4,70 | 9,60 | |||
| Factor D | - | 7,0; 7,4 | ||||
| Factor B | + | 5,7; 6,6 | ||||
| Properdin R | + | >9,5 | ||||
| Factor H | + | |||||
| Factor I | 10,7 | |||||
| S-protein, Vitronectin | + | 1(2) . | 3,90 | |||
| ClInh | 2,70 | |||||
| C4dp | 3,5 | 540, 590 | 6-8 | |||
| DAF | ||||||
| C8bp | ||||||
| CR1 | + | |||||
| CR2 | + | |||||
| CR3 | + | |||||
| C3a | - | 70* | ||||
| C4a | - | 22* | ||||
| C5a | 4,9* | |||||
| Carboxy-peptidase M (in-activator of anaphyl toxins) | ||||||
| Clq-I | ||||||
| M-Clq-I | 1-2 | |||||
| Protectin (CD 59) | + | 1,8-20 |
* - under conditions of full activation
Complement components are produced in the liver, bone marrow, and spleen. The main complement producing cells are macrophages. The C1 component is produced by intestinal epithelial cells.
Complement components are presented in the form of: proenzymes (esterases, proteinases), protein molecules that do not have enzymatic activity, and as inhibitors of the complement system. Under normal conditions, complement components are in an inactive form. Factors that activate the complement system are antigen-antibody complexes, aggregated immunoglobulins, viruses, and bacteria.
Activation of the complement system leads to the activation of lytic enzymes of complement C5-C9, the so-called membrane attack complex (MAC), which, being embedded in the membrane of animal and microbial cells, forms a transmembrane pore, which leads to hyperhydration of the cell and its death. (Fig. 3-2, 3-3).
Rice. 3-2. Graphical model of complement activation.
Rice. 3-3. Structure of activated complement.
There are 3 ways to activate the complement system:
The first way is classical. (Fig. 3-4).
Rice. 3-4. The mechanism of the classical pathway of complement activation.
E – erythrocyte or other cell. A – antibody.
With this method, activation of the lytic enzymes MAC C5-C9 occurs through cascade activation of C1q, C1r, C1s, C4, C2, followed by the involvement of the central components C3-C5 in the process (Fig. 3-2, 3-4). The main activator of complement along the classical pathway is antigen-antibody complexes formed by immunoglobulins of classes G or M.
Second way - bypass, alternative (Fig. 3-6).
Rice. 3-6. The mechanism of the alternative pathway of complement activation.
This mechanism of complement activation is triggered by viruses, bacteria, aggregated immunoglobulins, and proteolytic enzymes.
With this method, the activation of the lytic enzymes MAC C5-C9 begins with the activation of the C3 component. The first three complement components C1, C4, C2 are not involved in this mechanism of complement activation, but factors B and D are additionally involved in the activation of S3.
Third way represents a nonspecific activation of the complement system by proteinases. Such activators can be: trypsin, plasmin, kallikrein, lysosomal proteases and bacterial enzymes. Activation of the complement system with this method can occur at any segment from C 1 to C5.
Activation of the complement system can cause the following biological effects:
1) lysis of microbial and somatic cells;
2) promoting graft rejection;
3) release of biologically active substances from cells;
4) increased phagocytosis;
5) aggregation of platelets, eosinophils;
6) increased leukotaxis, migration of neutrophils from the bone marrow and release of hydrolytic enzymes from them;
7) through the release of biologically active substances and increased vascular permeability, promoting the development of the inflammatory reaction;
8) promoting the induction of an immune response;
9) activation of the blood coagulation system.
Rice. 3-7. Diagram of the classical and alternative pathways of complement activation.
Congenital deficiency of complement components reduces the body's resistance to infectious and autoimmune diseases.
Properdin. In 1954 Pillimer was the first to discover a special type of protein in the blood that can activate complement. This protein is called properdin.
Properdin belongs to the class of gamma immunoglobulins, has m.m. 180,000 daltons. In the serum of healthy people it is in an inactive form. Properdin is activated after it combines with factor B on the cell surface.
Activated properdin promotes:
1) activation of complement;
2) release of histamine from cells;
3) production of chemotactic factors that attract phagocytes to the site of inflammation;
4) the process of blood coagulation;
5) formation of an inflammatory reaction.
Factor B. It is a blood protein of globulin nature.
Factor D. Proteinases having m.m. 23,000. In the blood they are represented by the active form.
Factors B and D are involved in the activation of complement via the alternative pathway.
B-lysines. Blood proteins of various molecular weights that have bactericidal properties. B-lysines exhibit a bactericidal effect both in the presence and absence of complement and antibodies.
Interferon. A complex of protein molecules that can prevent and suppress the development of a viral infection.
There are 3 types of interferon:
1) alpha interferon (leukocyte), produced by leukocytes, represented by 25 subtypes;
2) beta interferon (fibroblastic), produced by fibroblasts, represented by 2 subtypes;
3) gamma interferon (immune), produced mainly by lymphocytes. Interferon gamma is known as one type.
The formation of interferon occurs spontaneously, as well as under the influence of viruses.
All types and subtypes of interferons have a single mechanism of antiviral action. It appears to be as follows: interferon, by binding to specific receptors of uninfected cells, causes biochemical and genetic changes in them, leading to a decrease in the translation of m-RNA in cells and activation of latent endonucleases, which, turning into an active form, are capable of causing the degradation of m-RNA as a virus , and the cell itself. This causes the cells to become insensitive to viral infection, creating a barrier around the site of infection.
The body's resistance is understood as its resistance to various pathogenic influences (from the Latin resisteo - resistance). The body's resistance to adverse effects is determined by many factors, many barrier devices that prevent the negative effects of mechanical, physical, chemical and biological factors.
Cellular nonspecific protective factors
Cellular nonspecific protective factors include the protective function of the skin, mucous membranes, bone tissue, local inflammatory processes, the ability of the thermoregulation center to change body temperature, the ability of body cells to produce interferon, cells of the mononuclear phagocyte system.
The skin has barrier properties due to the multilayer epithelium and its derivatives (hair, feathers, hooves, horns), the presence of receptor formations, cells of the macrophage system, and secretions secreted by the glandular apparatus.
Intact skin of healthy animals resists mechanical, physical, and chemical factors. It represents an insurmountable barrier to the penetration of most pathogenic microbes and prevents the penetration of pathogens not only mechanically. It has the ability to self-cleanse by constantly exfoliating the surface layer and secreting secretions from the sweat and sebaceous glands. In addition, the skin has bactericidal properties against many microorganisms from the sweat and sebaceous glands. In addition, the skin has bactericidal properties against many microorganisms. Its surface is an environment unfavorable for the development of viruses, bacteria, and fungi. This is explained by the acidic reaction created by the secretions of the sebaceous and sweat glands (pH - 4.6) on the surface of the skin. The lower the pH, the higher the bactericidal activity. Great importance is attached to skin saprophytes. The species composition of the permanent microflora consists of up to 90% epidermal staphylococci, some other bacteria and fungi. Saprophytes are capable of secreting substances that have a detrimental effect on pathogenic pathogens. By the species composition of the microflora one can judge the degree of resistance of the organism, the level of resistance.
The skin contains cells of the macrophage system (Langerhans cells) capable of transmitting information about antigens to T lymphocytes.
The barrier properties of the skin depend on the general condition of the body, determined by proper feeding, care of the integumentary tissues, the nature of its maintenance, and use. It is known that emaciated calves are more easily infected with microsporia and trichofetia.
The mucous membranes of the oral cavity, esophagus, gastrointestinal tract, respiratory and genitourinary tracts, covered with epithelium, represent a barrier, an obstacle to the penetration of various harmful factors. The intact mucous membrane represents a mechanical obstacle to some chemical and infectious foci. Due to the presence of cilia of the ciliated epithelium, foreign bodies and microorganisms that enter with the inhaled air are removed from the surface of the respiratory tract into the external environment.
When the mucous membranes are irritated by chemical compounds, foreign objects, or waste products of microorganisms, protective reactions occur in the form of sneezing, coughing, vomiting, and diarrhea, which helps remove harmful factors.
Damage to the oral mucosa is prevented by increased salivation, damage to the conjunctiva by copious discharge of tear fluid, damage to the nasal mucosa by serous exudate. The secretions of the glands of the mucous membranes have bactericidal properties due to the presence of lysozyme in them. Lysozyme is capable of lysing staphylo- and streptococci, salmonella, tuberculosis and many other microorganisms. Due to the presence of hydrochloric acid, gastric juice suppresses the proliferation of microflora. A protective role is played by microorganisms that populate the intestinal mucosa and genitourinary organs of healthy animals. Microorganisms take part in the processing of fiber (ciliates of the proventriculus of ruminants), the synthesis of protein and vitamins. The main representative of normal microflora in the large intestine is Escherichia coli. It ferments glucose, lactose, and creates unfavorable conditions for the development of putrefactive microflora. A decrease in the resistance of animals, especially in young animals, turns E. coli into a pathogenic pathogen. The protection of the mucous membranes is carried out by macrophages, preventing the penetration of foreign antigens. Secretory immunoglobulins, based on class A immunoglobulins, are concentrated on the surface of the mucous membranes.
Bone tissue performs various protective functions. One of them is the protection of central nervous formations from mechanical damage. The vertebrae protect the spinal cord from injury, and the bones of the skull protect the brain and integumentary structures. The ribs and breastbone perform a protective function in relation to the lungs and heart. Long tubular bones protect the main hematopoietic organ - the red bone marrow.
Local inflammatory processes, first of all, strive to prevent the spread and generalization of the pathological process. A protective barrier begins to form around the source of inflammation. Initially, it is caused by the accumulation of exudate - a liquid rich in proteins that adsorb toxic products. Subsequently, a demarcation shaft of connective tissue elements is formed at the border between healthy and damaged tissues.
The ability of the thermoregulation center to change body temperature is important for the fight against microorganisms. High body temperature stimulates metabolic processes, the functional activity of cells of the reticulomacrophage system, and leukocytes. Young forms of white blood cells appear - young and band neutrophils, rich in enzymes, which increases their phagocytic activity. Leukocytes begin to produce immunoglobulins and lysozyme in increased quantities.
Microorganisms at high temperatures lose resistance to antibiotics and other drugs, and this creates conditions for effective treatment. Natural resistance during moderate fevers increases due to endogenous pyrogens. They stimulate the immune, endocrine, and nervous systems, which determine the body’s stability. Currently, veterinary clinics use purified bacterial pyrogens, which stimulate the body’s natural resistance and reduce the resistance of pathogenic microflora to antibacterial drugs.
The central link of cellular protection factors is the system of mononuclear phagocytes. These cells include blood monocytes, connective tissue histiocytes, liver Kupffer cells, pulmonary, pleural and peritoneal macrophages, free and fixed macrophages, free and fixed macrophages of lymph nodes, spleen, red bone marrow, macrophages of the synovial membranes of joints, osteoclasts of bone tissue, microglial cells nervous system, epithelioid and giant cells of inflammatory foci, endothelial cells. Macrophages carry out bactericidal activity due to phagocytosis, and they are also capable of secreting a large number of biologically active substances that have cytotoxic properties against microorganisms and tumor cells.
Phagocytosis is the ability of certain cells of the body to absorb and digest foreign substances. Cells that resist pathogens, freeing the body from its own, genetically foreign cells, their fragments, and foreign bodies, were called I.I. Mechnikov (1829) phagocytes (from the Greek phaqos - devour, cytos - cell). All phagocytes are divided into microphages and macrophages. Microphages include neutrophils and eosinophils, macrophages include all cells of the mononuclear phagocyte system.
The process of phagocytosis is complex, multi-level. It begins with the approach of the phagocyte to the pathogen, then the adhesion of the microorganism to the surface of the phagocytic cell is observed, then absorption with the formation of a phagosome, intracellular association of the phagosome with the lysosome and, finally, digestion of the object of phagocytosis by lysosomal enzymes. However, cells do not always interact in this way. Due to enzymatic deficiency of lysosomal proteases, phagocytosis may be incomplete (incomplete), i.e. Only three stages occur and microorganisms can remain in the phagocyte in a latent state. Under unfavorable conditions for the macroorganism, bacteria become capable of reproduction and, destroying the phagocytic cell, cause infection.
Humoral nonspecific protective factors
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 at a dilution of 1:1000000. Initially, it was believed that lysozyme was 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 bacterial cell wall damaged by it 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 nonspecific 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.
Nonspecific factors natural resistance protect the body from microbes at the first meeting with them. The same factors are also involved in the formation of acquired immunity.
Cell reactivity is the most persistent natural defense factor. In the absence of cells sensitive to a given microbe, toxin, or virus, the body is completely protected from them. For example, rats are insensitive to diphtheria toxin.
Skin and mucous membranes represent a mechanical barrier for most pathogenic microbes. In addition, the secretions of the sweat and sebaceous glands containing lactic and fatty acids have a detrimental effect on microbes. Clean skin has stronger bactericidal properties. The removal of microbes from the skin is facilitated by desquamation of the epithelium.
In the secretions of mucous membranes contains lysozyme, an enzyme that lyses the cell wall of bacteria, mainly gram-positive ones. Lysozyme is found in saliva, conjunctival secretions, as well as in the blood, macrophages, and intestinal mucus. Discovered for the first time by P.N. Lashchenkov in 1909 in the white of a chicken egg.
Epithelium of the mucous membranes of the respiratory tract is an obstacle to the penetration of pathogenic microbes into the body. Dust particles and droplets of liquid are thrown out with mucus secreted from the nose. Particles that enter here are removed from the bronchi and trachea by the movement of the cilia of the epithelium directed outward. This function of the ciliated epithelium is usually impaired in heavy smokers. The few dust particles and microbes that reach the pulmonary alveoli are captured by phagocytes and rendered harmless.
Secret of the digestive glands. Gastric juice has a detrimental effect on microbes supplied with water and food, due to the presence of hydrochloric acid and enzymes. Reduced acidity of gastric juice helps to weaken resistance to intestinal infections such as cholera, typhoid fever, and dysentery. Bile and enzymes from intestinal contents also have a bactericidal effect.
The lymph nodes. Microbes that penetrate the skin and mucous membranes are retained in the regional lymph nodes. Here they undergo phagocytosis. The lymph nodes also contain so-called normal (natural) killer lymphocytes (killer lymphocytes), which carry out the function of antitumor surveillance - the destruction of the body's own cells, changed due to mutations, as well as cells containing viruses. Unlike immune lymphocytes, which are formed as a result of an immune response, natural killer cells recognize foreign agents without prior contact with them.
Inflammation (vascular cell reaction) is one of the phylogenetically ancient protective reactions. In response to the penetration of microbes, a local inflammatory focus is formed as a result of complex changes in the microcirculation, blood system and connective tissue cells. The inflammatory response promotes the removal of microbes or delays their development and therefore plays a protective role. But in some cases, when the agent that caused the inflammation is re-entered, it can take on the character of a damaging reaction.
Humoral protective factors . Blood, lymph and other body fluids (lat. humor - liquid) contain substances with antimicrobial activity. Humoral factors of nonspecific protection include: complement, lysozyme, beta-lysines, leukins, antiviral inhibitors, normal antibodies, interferons.
Complement - the most important humoral protective factor of the blood, is a complex of proteins designated as C1, C2, C3, C4, C5, ... C9. Produced by liver cells, macrophages and neutrophils. In the body, complement is in an inactive state. When activated, proteins acquire the properties of enzymes.
Lysozyme produced by blood monocytes and tissue macrophages, has a lysing effect on bacteria, and is thermostable.
Beta-lysine secreted by platelets, has bactericidal properties, and is thermostable.
Normal antibodies contained in the blood, their occurrence is not associated with the disease, they have an antimicrobial effect and promote phagocytosis.
Interferon - a protein produced by cells in the body, as well as cell cultures. Interferon suppresses the development of the virus in the cell. The phenomenon of interference is that a cell infected with one virus produces a protein that suppresses the development of other viruses. Hence the name - interference (lat. inter - between + ferens - transferring). Interferon was discovered by A. Isaac and J. Lindenman in 1957.
The protective effect of interferon turned out to be nonspecific to the virus, since the same interferon protects cells from different viruses. But it has species specificity. Therefore, the interferon that is formed by human cells acts in the human body.
Subsequently, it was discovered that the synthesis of interferon in cells can be induced not only by live viruses, but also by killed viruses and bacteria. Some drugs can be interferon inducers.
Currently, several interferons are known. They not only prevent the virus from multiplying in the cell, but also inhibit the growth of tumors and have an immunomodulatory effect, that is, they normalize the immune system.
Interferons are divided into three classes: alpha interferon (leukocyte), beta interferon (fibroblastic), gamma interferon (immune).
Leukocyte α-interferon is produced in the body mainly by macrophages and B-lymphocytes. Donor alpha-interferon preparation is obtained in cultures of donor leukocytes exposed to an interferon inducer. Used as an antiviral agent.
Fibroblast beta interferon in the body is produced by fibroblasts and epithelial cells. The beta-interferon preparation is obtained in cultures of human diploid cells. Has antiviral and antitumor effects.
Immune gamma interferon in the body is produced mainly by T-lymphocytes stimulated by mitogens. The gamma-interferon drug is obtained in lymphoblast culture. It has an immunostimulating effect: it enhances phagocytosis and the activity of natural killer cells (NK cells).
The production of interferon in the body plays a role in the recovery process of a patient with an infectious disease. With influenza, for example, interferon production increases in the first days of the disease, while the titer of specific antibodies reaches a maximum only by the 3rd week.
The ability of people to produce interferon is expressed to varying degrees. “Interferon status” (IFN-status) characterizes the state of the interferon system:
2) the ability of leukocytes obtained from the patient to produce interferon in response to the action of inducers.
Alpha, beta, and gamma interferons of natural origin are used in medical practice. Recombinant (genetically engineered) interferons have also been obtained: reaferon and others.
Effective in the treatment of many diseases is the use of inducers that promote the production of endogenous interferon in the body.
I.I. Mechnikov and his doctrine of immunity to infectious diseases. Phagocytic theory of immunity. Phagocytosis: phagocytic cells, stages of phagocytosis and their characteristics. Indicators for characterizing phagocytosis.
Phagocytosis - the process of active absorption by the cells of the body of microbes and other foreign particles (Greek phagos - devouring + kytos - cell), including the body’s own dead cells. I.I. Mechnikov - author phagocytic theory of immunity - showed that the phenomenon of phagocytosis is a manifestation of intracellular digestion, which in lower animals, for example, amoebas, is a method of nutrition, and in higher organisms phagocytosis is a defense mechanism. Phagocytes free the body from microbes and also destroy old cells of their own body.
According to Mechnikov, everything phagocytic cells are divided into macrophages and microphages. Microphages include polymorphonuclear blood granulocytes: neutrophils, basophils, eosinophils. Macrophages are blood monocytes (free macrophages) and macrophages of various body tissues (fixed) - liver, lungs, connective tissue.
Microphages and macrophages originate from a single precursor - a bone marrow stem cell. Blood granulocytes are mature, short-lived cells. Peripheral blood monocytes are immature cells and, leaving the bloodstream, enter the liver, spleen, lungs and other organs, where they mature into tissue macrophages.
Phagocytes perform a variety of functions. They absorb and destroy foreign agents: microbes, viruses, dying cells of the body itself, tissue breakdown products. Macrophages take part in the formation of the immune response, firstly, by presenting antigenic determinants (epitopes on their membrane and, secondly, by producing biologically active substances - interleukins, which are necessary for regulating the immune response.
IN process of phagocytosis differentiate several stages :
1) the approach and attachment of the phagocyte to the microbe - is carried out due to chemotaxis - the movement of the phagocyte in the direction of a foreign object. Movement is observed due to a decrease in the surface tension of the phagocyte cell membrane and the formation of pseudopodia. The attachment of phagocytes to the microbe occurs due to the presence of receptors on their surface,
2) absorption of the microbe (endocytosis). The cell membrane bends, an invagination is formed, and as a result, a phagosome is formed - a phagocytic vacuole. This process is cross-linked with the participation of complement and specific antibodies. For the phagocytosis of microbes with antiphagocytic activity, the participation of these factors is necessary;
3) intracellular inactivation of the microbe. The phagosome merges with the lysosome of the cell, a phagolysosome is formed, in which bactericidal substances and enzymes accumulate, as a result of which the death of the microbe occurs;
4) digestion of the microbe and other phagocytosed particles occurs in phagolysosomes.
Phagocytosis, which leads to microbe inactivation , that is, includes all four stages, is called completed. Incomplete phagocytosis does not lead to the death and digestion of microbes. Microbes captured by phagocytes survive and even multiply inside the cell (for example, gonococci).
In the presence of acquired immunity to a given microbe, opsonin antibodies specifically enhance phagocytosis. This type of phagocytosis is called immune. In relation to pathogenic bacteria with antiphagocytic activity, for example, staphylococci, phagocytosis is possible only after opsonization.
The function of macrophages is not limited to phagocytosis. Macrophages produce lysozyme, complement protein fractions, participate in the formation of the immune response: interact with T- and B-lymphocytes, produce interleukins that regulate the immune response. During the process of phagocytosis, particles and substances of the body itself, such as dying cells and tissue breakdown products, are completely digested by macrophages, that is, into amino acids, monosaccharides and other compounds. Foreign agents such as microbes and viruses cannot be completely destroyed by macrophage enzymes. The foreign part of the microbe (determinant group - epitope) remains undigested, is transmitted to T- and B-lymphocytes, and thus the formation of an immune response begins. Macrophages produce interleukins that regulate the immune response.
Humoral factors of nonspecific protection
The main humoral factors of nonspecific defense of the body include lysozyme, interferon, complement system, properdin, lysines, lactoferrin.
Lysozyme is a lysosomal enzyme and is found in tears, saliva, nasal mucus, secretions of mucous membranes, and blood serum. It has the property of lysing living and dead microorganisms.
Interferons are proteins that have antiviral, antitumor, and immunomodulatory effects. Interferon acts by regulating the synthesis of nucleic acids and proteins, activating the synthesis of enzymes and inhibitors that block the translation of viral and RNA.
Nonspecific humoral factors include the complement system (a complex protein complex that is constantly present in the blood and is an important factor in immunity). The complement system consists of 20 interacting protein components that can be activated without the participation of antibodies, forming a membrane attack complex with subsequent attack on the membrane of a foreign bacterial cell, leading to its destruction. The cytotoxic function of complement in this case is activated directly by the foreign invading microorganism.
Properdin takes part in the destruction of microbial cells, neutralization of viruses and plays a significant role in the nonspecific activation of complement.
Lysines are blood serum proteins that have the ability to lyse certain bacteria.
Lactoferrin is a local immunity factor that protects epithelial surfaces from microbes.
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