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Bacterial endotoxins. Endotoxins

Endotoxins endotoxins

complexes of lipopolysaccharides with proteins cell walls gram-negative bacteria, having properties poisons They have antigenic properties identical to somatic antigens of the whole cell (O-antigens). Unlike exotoxins thermostable. Isolated from all pathogenic gram-negative bacteria (Salmonella, Vibrio cholerae, Shigella etc.); on this basis in honey microbiol. are called enterotoxins. They are pyrogenic (cause an increase in body temperature) and toxic; the first property is determined by the lipopolysaccharide fraction of E., the second - by the protein fraction. Pyrogenicity and toxicity of E. are nonspecific and are believed to play only an auxiliary role in the pathogenesis of the causative agent of the disease.

(Source: “Microbiology: a dictionary of terms”, Firsov N.N., M: Drofa, 2006)

Endotoxins

toxic substances that enter the structure of bacteria (usually the cell wall) and are released from them after lysis of the bacteria. More often this name is used in relation to lipopolysaccharides of the cell wall of gram bacteria with m.m. 100 - 900 thousand, which form a complex macromolecular complex with proteins and lipids. Regardless of the species, E have a similar structure and chemical composition, have high and diverse activity. In experimental and wedge conditions, E causes fever, leukocytosis with a rapid transition to leukopenia, hypoglycemia, low blood pressure and shock, the Sanarelli-Schwartzmann phenomenon, tumor necrosis, increase the activity of nonspecific immune factors, have adjuvant and high antigenic activity. The toxic effect of E appears immediately after administration, is less pronounced than that of exotoxins, has little specificity, and is inextricably linked with antigenicity: loss of toxicity leads to loss of antigenicity. The mechanism of action of E. is associated with the activation of cell membrane phosphorylase and the subsequent release of arachidonic acid, as well as increased synthesis of prostaglandins, leukotrienes and thromboxanes. These inflammatory mediators promote the aggregation of leukocytes and platelets and affect vascular tone and permeability. Cm. Bacterial toxins.

(Source: Dictionary of Microbiology Terms)


See what “endotoxins” are in other dictionaries:

    Bacterial toxic substances, which are structural components of certain bacteria and are released only when the bacterial cell lysis (disintegrates). This distinguishes endotoxins from exotoxins, soluble compounds,... ... Wikipedia

    ENDOTOXINS- (from endo... and toxins), bacterial toxins, toxic substances formed inside microorganisms (especially gram-negative bacteria). Firmly bound to the cellular structure and released when cells disintegrate or are destroyed in... ... Ecological dictionary

    ENDOTOXINS- ENDOTOXINS, see Toxins. 3HflO0TA/lbMHT(endophthalmitis), according to Fuchs, inflammation of the iris and ciliary body, iridocyclitis, or less commonly iridochoroiditis, after perforating wounds of the eye (primary E.) or when infection penetrates through... ... Great Medical Encyclopedia

    endotoxins- Toxic substances tightly bound to the cellular structures of bacteria and released when cells disintegrate or are destroyed as a result of exposure to physical or chemical factors. See also Toxins. [English-Russian glossary... ... Technical Translator's Guide

    - (see endo...) poisons (toxins) released during the decay of microbes, their death cf. exotoxins). New dictionary of foreign words. by EdwART, 2009. endotoxins [see endo... + toxins] - bacterial poisons released during the decay of bacteria Large... ... Dictionary of foreign words of the Russian language

The discovery of bacterial toxins has played an exceptional role in understanding the mechanisms of development of infectious diseases. A surprisingly interesting page in the study of infectious diseases consists of studies devoted, in particular, to bacterial lipopolysaccharides (endotoxins), which, apparently, has not yet been fully completed.

R. Koch in 1884, at one of his lectures, discussing the mechanisms of cholera development, expressed the opinion that the nature of the detected pathological and anatomical changes in experimental animals with intraperitoneal administration of a culture of Vibrio cholerae suggests the role of bacterial poisons. This idea in itself was not revolutionary, since research into soluble toxins (such as diphtheria bacillus) was already being carried out at that time both in Berlin (Behring and Kitasato) and Paris (Roux and Yersin), but it directed Richard Pfeiffer, a student of R. Koch, to a more detailed study of the pathogenesis of cholera.

It was as a result of this work that “a toxic substance associated with the body by a microbial cell” was described. Pfeiffer was able to come to this conclusion as a result of a successfully composed, as they now say, “research design” and a broad hypothetical interpretation of the results obtained, since some other researchers also worked with a similar “toxic substance”, in particular, P. Panum, A. Cantani , H. Buchner.

It should be recognized that the discovery of any phenomenon or phenomenon is facilitated not only and not so much by the fact of its experimental or clinical reproduction, but by a hypothetical interpretation of the results that would fit into the generally accepted theory and would not violate the fundamental provisions. Pfeiffer had to look for a way out of what initially seemed like a hopeless situation. When attempting to replicate Pfeiffer's studies, no one was able to detect Vibrio cholerae in the abdominal cavity of experimental animals. Since the animals died, and the microbe was not detected in them, this contradicted the most important “Koch-Henle postulate” - the mandatory isolation of the pathogen. To find an explanation, it took Pfeiffer's great ingenuity to experimentally confirm and explain that the toxic substance in Vibrio cholerae is associated with the body by a microbial cell.

This was a daring and revolutionary idea, since it contradicted another fundamental idea of ​​the time, which initially explained the development of any infectious disease, namely, the vital activity of a microbe. Pfeiffer made the final point in confirming the connection of the described toxic substance with the microbial cell body by describing that the thermal destruction of Vibrio cholerae does not weaken its toxic potential. Thus, through a series of elegant experiments based on deep insight, Pfeiffer formulated the concept of endotoxin as a poison that is closely associated with the microbial cell, released only after its death, causing the development of pathological reactions.

Oddly enough, Pfeiffer in his early works avoided the term “endotoxin”, designating it as “primary cholera toxin”, allowing its use only in oral presentations, for example, at a lecture in Brussels in 1903. In the literature, the term “endotoxin” "was first used by J. Rehns in 1903, an employee of the Pasteur Institute, who previously worked at the Faculty of Medicine in Paris and at the Paul Ehrlich Institute in Frankfurt. Pfeiffer first used the term “endotoxin” in a printed work only in 1904. There is a certain irony in this fact: the term, proposed at the Institute of Infectious Diseases in Berlin, was first used in print by an employee of the Pasteur Institute. And this despite the fact that at the beginning of the twentieth century, the two leading centers for the study of infectious diseases - in Berlin and Paris - were in fierce scientific competition, excluding any official contacts and exchange of information, for which the priority in research was decisive.

Since the chemical structure of the biopolymer designated endotoxin remained unstudied for a long time, bacterial lysate obtained by heat treatment of a microbial cell culture was usually used for research purposes. The lack of possibility of standardization and comparison of the resulting drugs led to the fact that researchers, using bacterial lysates, described their various biological properties (in particular, “protective” and “damaging” effects), without even assuming that the active principle in all cases is the same the biopolymer is lipopolysaccharide (LPS).

Thus, in particular, already from the 90s of the 19th century (and up to the 40s of the 20th century), the American surgeon W. Coley with some success used microbial cell lysates for the conservative treatment of soft tissue sarcomas, and H. Buchner in Germany developed “new hygiene”, based on the introduction of bacterial lysates in order to increase the body’s resistance to infectious diseases.

It became possible to complete the study of the chemical structure of endotoxin and determine the optimal methods for its extraction only in the 50s, but this did not clarify the situation, but rather made this biopolymer even more mysterious. It remained completely unclear how endotoxins have such a surprisingly implausible spectrum of biological activity, including, on the one hand, participation in the development of infectious diseases, the induction of fever, disseminated intravascular coagulation syndrome and shock, and on the other hand, they are a powerful stimulator of the immune system, increasing the body’s resistance to infections that promote the resorption of certain types of sarcomas. Bringing together such diverse information about the biological activity of endotoxins into a single coherent concept turned out to be a very difficult task, requiring further research to clarify the molecular mechanisms of their action, which became possible only much later.

The main attention of researchers was concentrated on studying the role of endotoxins in the development of infectious diseases, which was greatly facilitated by the relative simplicity and accessibility of experimental studies. The spiral of these works ran parallel to achievements in the field of all fundamental sciences, and the original literature year after year, as if in a mirror, reflected the level of potential of the research being carried out. The intensity of the research was constantly increasing, since their effectiveness had direct applied significance, in particular, in the development of methods and methods for diagnosing, treating and preventing conditions in the development of which lipopolysaccharides play a leading role. The chronology of the main stages in the study of bacterial lipopolysaccharides is presented in the figure.

Chronology of the main stages in the study of bacterial lipopolysaccharides (according to Rietschel E. Th., Cavaillon J.-M., 2003).

Initially, it was believed that studies of bacterial LPS were narrowly focused only in relation to the clinic of infectious diseases, but their general pathological significance gradually became clear.

The leading areas of research in the second half of the twentieth century were:

1) study of the spectrum of biological activity of the purified LPS preparation and its individual components;

2) determination of patterns in the structural and functional activities of bacterial LPS;

3) study of the mechanism of action of LPS in vitro and in vivo;

4) determining the role of LPS in the pathogenesis of infectious diseases; and finally

5) development of treatment methods. Since the development of new pathogenetic therapy regimens depended on our knowledge and understanding of the mechanisms of action of LPS, this area was a priority in clinical research.

W.H. Welch in 1888 (cited by Atkins E., 1984) was one of the first to suggest that microbial agents cause the development of fever indirectly, promoting the release of “enzymes”, possibly from leukocytes, which already directly act on the central nervous system. Menkin W. in the 40s of the twentieth century formulated a hypothesis according to which the effect of endotoxin (LPS) on the body is mediated by mediators that are produced by the cells of the body. Already in the 50s, the capabilities of fundamental sciences made it possible to conduct large-scale research to study the role of various endogenous mediators in the implementation of the biological effects of endotoxins.

Of particular importance in proving the correctness of the hypothesis put forward was given to experimental work on the induction of fever. In one of the first fundamental studies performed by Bennett I.L. and Beeson P.B. in 1953, it was found that when laboratory animals were administered a crystalline extract of acute inflammatory exudate (“Menkin’s pyrexin”) and various microbial agents, a “leukocyte pyrogen” was detected in their blood. In systematically conducted studies, as in conditions of experimental endotoxemia , and in patients with various infectious diseases caused by gram-negative bacteria, the participation of such regulatory systems as renin-angiotensin-aldosterone, kallikrein-kinin, histamine and many other systems in the development of the body's response to LPS was established.

The 70-80s were marked by a detailed study of the molecular mechanisms of regulation of cellular functions of the body under the influence of endotoxins. A special place in these studies was occupied by studies of the role of prostaglandins, the increase in synthesis of which during experimental gram-negative infections was established in the works of R.A. Giannella (1973-1979). During these years, it was prostaglandins that played the leading role in the development of the inflammatory response induced by bacterial endotoxins. In 1976-1982 We conducted a series of clinical and experimental studies aimed at clarifying the importance of prostaglandins in the development of intoxication syndrome in acute intestinal infections.

In particular, it was found that enterobacteria endotoxins are capable of significantly enhancing the biosynthesis of prostaglandins from arachidonic acid (S.G. Pak, M.Kh. Turyanov, 1979), which, in turn, mediate the development of functional disorders in hemostasis, hemodynamics and others macroorganism systems. The logical conclusion of this series of works was the rationale for the early use of prostaglandin biosynthesis inhibitors in the treatment of patients with endotoxemia (S.G. Pak et al., 1988).

Later, cytokines were studied in equal detail, making it possible to establish a relationship between the level of some of them (primarily TNF-β and IL-1) with the development of infectious-toxic shock.

As our understanding of the mechanisms of action of bacterial LPS has expanded, attempts have been made repeatedly to use various classes of pharmacological drugs, the point of application of which was the “key links in the pathogenesis” of endotoxemia (Table 2).

Table 2

The main stages in studying the mechanisms of action of endotoxins and proposals for pathogenetic methods of treating endotoxemia

Infectious diseases and

pathogens

Chronic diseases

Viral hepatitis B, C (HBV infection, HCV infection)

Hepatocellular carcinoma, cryoglobulinemic membranoproliferative glomerulonephritis, cryoglobulinemia, autoimmune thyroiditis, acute disseminated encephalomyelitis

Group B Coxsasckie viruses

Diabetes mellitus

Rhinovirus infection

Chlamydial infection (Cl.pneumonia)

Atherosclerosis

Mycobacterium paratuberculosis

Crohn's disease

Cytomegalovirus infection

Diabetes mellitus, endocardial fibroelastosis, chronic fatigue syndrome

Rubella

Diabetes mellitus, congenital rubella syndrome, progressive panencephalitis

Human papillomavirus types 16, 18

Cervical carcinoma

Epstein-Barr viral infection

Nasopharyngeal carcinoma, Burkitt's lymphoma, B-cell lymphoma, oral leukoplakia

Polyoma virus (JC virus)

Colon cancer

Herpesvirus type 8 (HHV-8)

Kaposi's sarcoma, Castleman's disease, primary lymphoma

Mumps viruses, measles, cytomegaloviruses, adenoviruses, enteroviruses

Endocardial fibroelastosis, schizophrenia, depressive and borderline states

Campylobacter jejuni, Chlamydia psittaci

Helicobacter pylori

Gastric ulcer, noncardiac adenocarcinoma of the stomach, non-Hodgkin B-cell lymphoma of the stomach, salivary glands, duodenum, small intestine, rectum

Tropheryma whippelii

Whipple's disease

Schistosomiasis

Bladder cancer

Although ongoing clinical and experimental studies have given some hope for the therapeutic effectiveness of these drugs for endotoxemia, none of them have become the drug of choice.

These studies can be considered as a continuation of the fascinating search for the “golden bullet” (according to Paul Ehrlich) and the creation of “miracle drugs,” as antibacterial drugs were called until recently, however, in fact, they serve as a reflection of the degree and depth of our ideas about the intricacies of pathogenetic mechanisms of development of infectious diseases.

And it should be recognized that the deeper we understand the mechanisms of development of infectious diseases, the clearer and more clearly we understand that there cannot be a universal cure. The “golden key” in solving the problem of increasing the effectiveness of our therapeutic and preventive measures for infectious diseases is a comprehensive study of the infectious process with mandatory consideration of the functioning of the natural defense systems of the macroorganism.

“Illness is a drama in two acts,

of which the first is played out in the gloomy silence of our tissues,

with the candles extinguished.

When pain or other unpleasant phenomena appear,

it’s almost always the second act.”

“Fever is the strongest mechanism

which nature created to subdue her enemies"

Sydenham, 17th century English physician

Dermatovenereology, National leadership, 2011, p.99-110

Intestinal endotoxin and inflammation

M.Yu. Yakovlev

The current level of scientific knowledge makes it possible to give inflammationI have the following definition: “Inflammation is an emergency mechanismimmune defense aimed at recognizing, destroyingand elimination of foreign and self-antigens, carryingadaptive and/or pathogenic in nature.” In other words,burning is always a destructive process, even when it is vital necessary.

An interdisciplinary definition formulated in III Congress of the Russian Society of Pathologists, based on the teachingsI.I. Mechnikov “On the role of intestinal factor in the mechanisms of stagnation”rhenia"; G. Selye’s concept “General Adaptation Syndrome” O first cause nonspecific factors; "Clonallyselection theory of immunity" by F. Burnet and "Endotoxin concepts of human physiology and pathology.”

These scientific theories stimulated clinical, molecularscientific and genetic studies that made it possible to systematizepreviously obtained data on the work of innate and adaptive immunity, their interaction with each other and infectiousagents. Knowledge about this aspect of the problem until recentlywere fragmentary and did not allow us to obtain clearconcepts about the mechanisms of regulation of the immune system by the intestinalendotoxin at the level of the whole organism and the participation of general“nonspecific” factors in the implementation and initiation of inflammationlations, since without the participation of the systemic factor it is impossible andits local manifestations.

Endotoxin - thermostable component of the outer part of the cell membrane of all gram-negative microorganisms, lipopolysaccharide(LPS), consisting of 3 parts: hydrophobic lipid A - glycolipid Re- chemotype identical to endotoksyns of all gram-negative microorganisms; hydrophilic core and polysaccharide, which are individual and allow you to believeinfect gram-negative microorganisms using serological research methods. The presence of a glycolipid in a molecule of LPS of different origin determines their commonalitybiological properties: pyrogenic and antitumor effectstov, the ability to activate cell differentiation myelocyticbone marrow growth and lipid peroxidation,stimulate antiviral and antibacterial immunity,

induce disseminated intravascular coagulation syndromes andmultiorganinsufficiency.

This entire unique spectrum of biological activity of endotoxins up torecently (until 1987-1988) were considered exclusively in the sep formatsis and other infectious diseases, in the pathogenesis of which it was assumedthe leading role of LPS of exogenous gram-negative bacteria. The participation of intestinal endotoxin in the pathogenesis of “non-infectious pathology”, and especially in the physiological processes of adaptation, has not been considered. It was assumed that in healthyBy definition, there should not be a toxin (endotoxin) in the body. Same to meThe author of this chapter was also involved in research, so far with the help of highly purified antibodies to Re -glycolipid in peripheral blood smears of practically healthy patientsLPS fixed on the surface was not detected polymorphonuclear leukocytes.

This made it possible to postulate a new biological phenomenon - a systemicendotoxemiaand suggest an important role for intestinal LPS in the regulationimmune activity and initiation of inflammation. First, new research methods were developed, a normative range was established (“physiological gical") indicators of endotoxin concentration in serum and amountLPS-positivepolymorphonuclear leukocytes in peripheral bloodconditionally healthy volunteers; then the fact of the participation of excess LPS in the pathogenesis of various diseases was established, subsequently called “endotoxinaggression"; and finally, innate immune receptors were identified Niteta - TLR 4, interacting with LPS and determining immune activity no system.Thus, one of the main elements was verifiedpreviously postulated systemic endotoxemia, the molecularmechanisms immunoregulatory action of intestinal LPS, realized, as well aspreviously assumed, with the direct participation of the hypothalamic-pituitary-adrenal system. Stress (physical, psycho-emotional, of a different etiology) causes additional discharge of portal blood “rich” in intestinal endotoxin through the portacaval anastomoses, bypassing the liver, into the general bloodstream. In a state of relative rest, i.e. in the absence of stressorsinfluences, more than 95% of portal blood enters the liver, where all the LPSeliminated by the fixed macrophage system. The liver is the most “needed”given" in endotoxins organ, because when they interact with TLR 4V macrophages induce the synthesis of the most important pro-inflammatory cytokines new, providing the basic physiological tone of the antitumor, antibacterial and antiviral immunity 1. LPS not consumed by the liver returns to the intestines with bile, but most likely without polysaccharide parts.Part of the endotoxin (less than 5%) enters the general blood with portal blood. hemocirculationand maintains everything in a state of physiological tone immunocompetentorgans (bone marrow, thymus, etc.) and cells ( antigen presenting, polymorphonuclear leukocytes, lymphocytes, etc.). Thus, systemicendotoxemia performs an extremely important function in ensuring the physiological tone of the immune system. In extraordinary situations(fright, fear, orgasm, physical activity), always accompanied by stress,The immunostimulating effect of endotoxemia increases as the concentration of intestinal LPS in the general bloodstream increases. Obviously, that's why physiological concentrations of endotoxins fluctuate over a very wide range (from close to zero to 1.0 EU/ml ) and have a steady tendency to increasewith age. In very rare cases, LPS cannot be detected in serum (or rather,its concentration is less than 0.0001 EU/ml ). For these patientsThis results in a significant decrease in the main indicators of immune status. However, there is also the phenomenon of endotoxin tolerance - the absence ofthorny pyrogenic reaction at sufficiently high (significantly exceedingupper limit of normal) endotoxin concentrations in the blood. For implementationbiological properties of endotoxin (in particular, for the interaction of LPS with TLR 4) high density lipoproteins (HDL) are required LPS-binding proteintheine (an acute phase protein synthesized by the liver) that transmits endotoxins CD receptor 14, and some other protein molecules and cofactors. Shortageone or more of the above factors, most of whichsynthesized in the liver, may cause immunodeficient conditions that most often occur when using anti-inflammatory drugs in patients with liver failure and patients with concentratedtion of LPS in the general bloodstream is below 0.0001 EU/ml.

1 NThis is probably why gnotobiont animals are practically defenseless against infectionmi and are much more likely to be susceptible to cancer. "Germ-free" animalsare deprived of the immunostimulating effect of intestinal LPS, since they do not have gram-negativemicroflora. (Note, author)

For a more holistic understanding of the material presented, we considered it advisablebriefly outline the fundamental principles of how the immune system workssystems and interactions of innate and adaptive immunity.

Innate immunity caused by the activity of several hundredrespiratory genes that ensure the synthesis of the corresponding number of receptors.They are the ones who participate in the fight against infection in the first 3-5 days (before the formationclones of lymphocytes and the development of a pool of specific antibodies) due to the activation of complement, the action of antimicrobial peptides and the activity of phagocytes. In addition, innate immunity “organizes” the work of adaptive, in particularity, due to the interaction of LPS with TLR 4 2 and education of the main pro-inflammatory cytokines that ensure the implementation of a specific immune response.Thus, the evolutionarily more ancient innate immune systemcontrols the “younger” adaptive one.

Adaptive immunity largely provided by a random processsomatic mutations of lymphocytes, as a result of which receptors appear,capable of recognizing any (even synthetic) antigen, including autoantigens, antibodies ( AT ) to which are constantly present in the general bloodstream.The number of such receptors under physiological conditions reaches astronomyical values. This principle of organizing adaptive immunity makes it possible to provide a reliable system of body defense against infections and potentiallyharmful mutations, on the one hand, and on the other hand, poses a great dangerautoimmune damage. It seems fundamentally important thatthat innate immunity is involved in the regulation of this process, the activity of which, in turn, is largely determined by the concentration of LPS in general bloodstream

Innate and adaptive immunity work in tandem, which can be illustrated by the example of phagocytes, which are also activated by the intestinalendotoxin. Largest population immunocompetent cellsis at the peak of the interaction between innate and adaptive immunity due topresence on its surfaceFc-receptors that are capable of accepting

all AT , which means interact specifically with a wide variety of antigenes, which allows us to characterize the neutrophil as a phagocyte multispecificactions, which was previously hidden under the term “ non-specificity».

Under physiological conditions, 5-7% of circulating leukocytes carrysurface of LPS, and approximately the same number of phagocyteswe bind endotoxinsin vitro. When interacting with LPS, phagocyticthe potential of neutrophils and their adhesive activity increase. They are leavingthe vascular bed, and then the body (as part of excreta: feces, urine, sweat, etc.), perform the protective function of “kamikaze border guards” in the stroma of organs andtissues in direct contact with the external environment.

Thus, systemic endotoxemia (EE) - regulatory mechanism tion of immune activity by intestinal LPS with direct study conditions of the hypothalamic-pituitary-adrenal system. Stress beingan attribute of life itself, on the one hand it provides injection into the general bloodstreamadditional portion of universal immunostimulant, and on the other - the fieldlyrates powerful pro-inflammatory the effect of its excess is increased synthesisglucocorticoids(Figure 8-1). This results in a very unstable state.called “balanced immune status”, which in conditions of sufficientexactly a long period of adaptation (prolonged stress) may bebroken. An increase in the concentration of intestinal LPS in the general circulation may exceed physiologically acceptable values ​​(they are purely individual and have age-related characteristics) and serve as the only reason for initiationlocal inflammatory reaction (or its exacerbation) and systemic syndromeinflammatory response, with greater or lesser severity always accompanying inflammation (increased body temperature, protein concentrationsacute phase, ESR;leukocytosis, etc.). Aadaptation of the body to constantly changing conditions of the external and internal environment is directly involved in the regulationimmune activity and initiation of inflammation, indirectly in increasingconcentrations of intestinal endotoxin in the general bloodstream. So stressmay be the only reason for the development of endotoxin aggression and, as the consequence is inflammation.

Rice. 8-1. Systemic endotoxemia - balanced immune status.

Rice. 8-2. Endotoxin aggression as a cause of inflammation.



Endotoxin aggression- pathological process caused by excesscom LPS of intestinal and/or other origin in the general bloodstream, havingits clinical and laboratory manifestations, is a “pre-disease” or unia universal general factor in the pathogenesis of diseases and syndromes, which is manifested by one or another nosological form of the disease due to theinstitutional and/or acquired predisposition 3. This station wagonThe significant effect of endotoxin aggression is realized in at least three ways:induction of autoimmune reactions (due to the characteristics of adaptive immunity), formation hyperergic immune background and self-aggressivenessleukocytes. The reasons for the development of endotoxin aggression are very diverse: the most common is stress, as well as any pathological processes leading to increased permeability of the intestinal barrier (food poisoning and acute intestinal infections, alcoholic excess and dysbacteriosis, unusually fat and spicy foods, acute viral infections, shock, etc.), portal hypertension and liver diseases, chronic and acute renal failure (since the kidneys serve as the main LPS-excreting organ).Most clearlymechanism pro-inflammatory actions in a very simplified form (Fig. 8-2)can be represented by the example of long-term stress ( psycho-emotional overload, depression, hyper- and hypothermia, extreme physical activity, etc.).

3 The introduction of this term was preceded by many years of research in many domesticand foreign scientists, including the creation of methods available for clinical practice for determining integral indicators of LPS concentration and activity antiendotoxinimmunity, determination of normative indicators. That is why in this chapter we will limit ourselves to only the most important of them. (Note, author)

Stress-inducedpro-inflammatory the effect of endotoxins in determiningto a lesser extent is stopped by the opposite effect glucocorticoids. Forthe synthesis of these hormones uses cholesterol entering the cortexadrenal glands exclusively in combination with high-density lipoproteins (HDL), the affinity of which for LPS is much higher than for cholesterol. That is why an excess of endotoxins causes a deficiency of HDL, which partially blocks the synthesis glucocorticoids and leads to increased pro-inflammatoryeffect. As a result, it develops hypercholesterolemia and increases " atherogenic index", which for many years was mistakenly considered a manifestation of a violationlipid metabolism and the basis for the development of atherosclerosis. Currently there are fewwho have doubts about the inflammatory nature of atherosclerosis, in particular the role of “endothelial dysfunction” in its initiation (endothelial dysfunction, in turn, is induced by endotoxin aggression, which was predicted back in 1987). This concept is very convincingly confirmed by a decrease in the concentration of “atherogenic” fractions of lipoproteins (low and verylow density) with a decrease in the level of LPS content (<1,0 EU/ml) in blood serum.

Toxic substances synthesized by bacteria are chemically related to proteins (exotoxins) and LPS (endotoxins) - localized in the wall B!! and are released only after their destruction.

Endotoxins. These include lipopolysaccharides (LPS), which are found in the cell wall of gram-negative bacteria. Toxic properties are determined the entire LPS molecule , and not its individual parts: PS or lipid A. Endotoxins of enterobacteria (Escherichia, Shigella and Salmonella, Brucella, tularemia bacteria) have been well studied.

LPS (endotoxins), unlike exotoxins, are more resistant to elevated temperatures, less toxic and less specific. When injected into  experimental subjects F!! cause approximately the same reaction, regardless of which gr–B!! they are highlighted. With the INTRODUCTION OF LARGE DOSES, inhibition of phagocytosis, symptoms of toxicosis, weakness, shortness of breath, intestinal upset (diarrhea), decreased activity and ↓ body temperature are observed. When SMALL DOSES are administered, the opposite effect occurs: stimulation of phagocytosis, body temperature.

In HUMANS, the entry of endotoxins into the bloodstream leads to fever as a result of their action on blood cells (granulocytes, monocytes), from which endogenous pyrogens are released. Early leukopenia, which is replaced by secondary leukocytosis. Glycolysis increases and hypoglycemia may occur. Also developing hypotension(the amount of serotonin and kinins entering the blood) is disrupted blood supply organs and acidosis.

LPS activates the complement C3 fraction via an ALTERNATIVE PATHWAY  ↓ its content in the serum and the accumulation of biologically active fractions (C3a, C3b, C5a, etc.). Large amounts of endotoxin entering the blood lead to TOXIC-SEPTIC SHOCK.

LPS is a relatively weak immunogen. The blood serum of animals immunized with pure endotoxin does not have high antitoxic activity and is not able to completely neutralize its toxic properties.

Some bacteria simultaneously produce both protein toxins and endotoxins, for example E. coli, etc.

    pathogenicity enzymes and antigens

Pathogenicity enzymes - these are factors of aggression and protection of microorganisms. The ability to form exoenzymes largely determines the invasiveness of bacteria - the ability to penetrate mucous, connective tissue and other barriers. These include various lytic enzymes - hyaluronidase, collagenase, lecithinase, neuraminidase, coagulase, proteases. Their characteristics are given in more detail in the lecture on the physiology of microorganisms.

The most important pathogenicity factors are considered toxins , which can be divided into two large groups - exotoxins and endotoxins .

Exotoxins are produced into the external environment (host organism), usually of a protein nature, can exhibit enzymatic activity, and can be secreted by both gram-positive and gram-negative bacteria. They have very high toxicity, are thermally unstable, and often exhibit antimetabolite properties. Exotoxins are highly immunogenic and cause the formation of specific neutralizing antibodies -antitoxins. According to the mechanism of action and point of application, exotoxins differ - cytotoxins (enterotoxins and dermatonecrotoxins), membrane toxins (hemolysins, leukocidins), functional blockers (cholerogen), exfoliants and erythrogenins. Microbes capable of producing exotoxins are calledToxigenic.

Endotoxins are released only when bacteria die, are characteristic of gram-negative bacteria, and are complex chemical compounds of the cell wall (LPS) - for more details, see the lecture on the chemical composition of bacteria. Toxicity is determined by lipid A, the toxin is relatively heat stable; immunogenic and toxic properties are less pronounced than those of exotoxins.

The presence of capsules in bacteria complicates the initial stages of protective reactions - recognition and absorption (phagocytosis). A significant factor in invasiveness is the mobility of bacteria, which determines the penetration of microbes into cells and into intercellular spaces.

Pathogenicity factors are controlled:

- chromosome genes;

- plasmid genes;

- genes introduced by temperate phages.

    Biological microscope.

The size of microbes with a cellular structure is 0.2–20 microns and they are easily detected in an immersion microscope. Viruses are many times smaller. The diameter of the largest of them, for example the variola virus, is about 300 nm, and the smallest is 20–30 nm. Because of this, electron microscopes are used to identify viruses.

Microbiological studies use light and electron microscopes; methods of optical and electron microscopy.

Optical microscope. The most important optical part of a microscope is the objectives, which are divided into dry and immersion.

Dry lenses with a relatively large focal length and low magnification are used to study microorganisms that are large in size (more than 10–20 microns), immersion(Latin immersio - immersion) with a focal length - when studying smaller microbes.

By microscopy immersion lens x90 a prerequisite is that it be immersed in cedar, peach or vaseline oil, the refractive indices of which are close to the glass slide on which the preparations are made. In this case, the light beam incident on the preparation is not scattered and, without changing direction, enters the immersion lens. The resolution of an immersion microscope is within 0.2 microns, and the maximum object magnification reaches 1350.

When using an immersion objective, first center the optical part of the microscope. Then the condenser is raised to the level of the stage, the diaphragm is opened, a low magnification lens is installed, and the field of view is illuminated using a flat mirror. A drop of oil is applied to a slide with a colored preparation, into which, under the control of the eye, the lens is carefully immersed, then, lifting the tube, they look into the eyepiece and, first with a macro-screw, and then with a micro-screw, establish a clear image of the object. At the end of the work, remove the oil from the front lens of the lens with a napkin.

Dark field microscopy is carried out under lateral illumination and is usually used when studying bacterial motility or detecting pathogenic spirochetes, the diameter of which may be less than 0.2 μm. To obtain bright side illumination, a conventional condenser is replaced with a special paraboloid condenser, in which the central part of the lower lens is darkened and the side surface is mirrored. This condenser blocks the central part of the parallel beam of rays, forming a dark field of view. The edge rays pass through the annular slit, fall on the side mirror surface of the condenser, are reflected from it and are concentrated at its focus. If there are no particles in the path of the beam, it is refracted, falling on the side mirror surface, reflected from it and exits the condenser. When the beam encounters microbes on its path, the light is reflected from them and hits the lens - the cells glow brightly. Since side illumination requires a parallel beam of light, only a flat microscope mirror is used. Typically, darkfield examination is performed under a dry system. In this case, a small drop of material is placed on a glass slide and covered with a coverslip, preventing the formation of air bubbles.

Phase contrast and anoptral microscopy are based on the fact that the optical path length of light in any substance depends on the refractive index. This property is used to increase the contrast of the image of transparent objects, such as microbes, i.e., to study the details of their internal structure. Light waves passing through optically denser areas of an object lag behind in phase the light waves that do not pass through them. In this case, the intensity of the light does not change, but only the phase of the oscillation changes, which is not caught by the eye and the photographic plate. To increase the contrast of the image, phase oscillations using a special optical system are converted into amplitude ones that are well captured by the eye. Drugs in the light field of view become more contrasting - positive contrast; With negative phase contrast, a light object is visible against a dark background. A halo often appears around images.

Greater clarity of images of low-contrast living microbes (even some viruses) is achieved in an anoptral microscope. One of its most important parts is the objective lens, located near the “exit” pupil, on which a layer of soot or copper is applied, absorbing at least 10% of the light. Due to this, the background of the field of view acquires a brown color, microscopic objects have various shades - from white to golden brown.