Neutrophils immunology. Cellular factors of innate immunity

Neutrophils (polymorphonuclear leukocytes, PMNs)

These are mobile phagocytes with a segmented nucleus. Neutrophils are identified either by nuclear structure or by the CD66 surface antigen.

The main role in the effector functions of neutrophils is played by the components of the granules. Neutrophil granules are classified into primary, secondary, tertiary and secretory vesicles. Differences between classes of granules can be determined after analysis of marker proteins. About 300 different proteins are stored in neutrophil granules, which can be released into the cell environment or remain attached to the neutrophil membrane.

Secretory vesicles
It is believed that secretory vesicles form only in mature segmented neutrophils when they enter the bloodstream. Secretory vesicles by origin endosomes, and represent a pool of receptors included in the plasma membrane after the fusion of the secretory vesicle membrane with the neutrophil membrane. There are many receptors in the membrane of secretory vesicles - β2-integrins, Cr1, formyl peptide receptors (fpr), CD14, CD16, as well as metalloproteinase enzymes and alkaline phosphatase. The cavity of secretory vesicles contains albumin and heparin-binding protein (HBP). The marker enzyme of the vesicles is alkaline phosphatase.

Secondary and tertiary granules
Peroxidase-negative granules of neutrophils can be divided into secondary and tertiary, which differ in protein content and secretory properties. Secondary granules contain more antibacterial compounds than tertiary ones. Tertiary granules are more easily exocytotic than secondary granules. Tertiary granules - reserve of matrix-degrading enzymes and membrane receptors necessary for extravasation and diapedesis of the neutrophil. On the contrary, secondary granules are mainly involved in the antibacterial actions of neutrophils through mobilization into phagosomes or secretion into the external environment. Their arsenal of antibacterial peptides includes lactoferrin, NGAL, lysozyme and hCAP18, LL-37. Marker protein of tertiary granules - enzyme gelatinase, secondary - lactoferrin.

Primary granules
Primary granules contain acid hydrolases, including acid phosphatase and antibacterial proteins; their membrane is devoid of receptors. In humans, antibacterial proteins are represented by neutrophil peptides - α-defensins and serine proteases with antibacterial activity. During the maturation of neutrophils in the bone marrow, azurophilic granules are the first to form at the stage of myeloblasts; defensins (cationic proteins) in azurophilic granules are synthesized at the second stage of neutrophil differentiation - the stage of promyelocyte formation.

The marker protein of these granules is the enzyme myeloperoxidase.

Monocytes/macrophages

Monocytes are phagocytes that circulate in the blood. When monocytes migrate into tissues, they become macrophages. Monocytes have characteristic shape kidney-shaped nuclei. They can be identified morphologically or by CD14, a cell surface marker. Unlike PMNs, they do not contain granules, but have numerous lysosomes, the content of which is similar to that of neutrophil granules. Specialized types of macrophages can be found in many organs, including the lungs, kidneys, brain, and liver.

Macrophages perform many functions. Like scavengers, they remove worn-out cells, immune complexes from the body. Macrophages present a foreign antigen for recognition by lymphocytes; in this respect, macrophages are similar to dendritic cells. Macrophages are able to secrete a surprising variety of powerful chemical signals called monokines, which are vital to the immune response. nonspecific immunity: the response of phagocytes to infection.

Neutrophils and monocytes circulating in the blood respond to danger signals (SOS) generated at the site of infection. SOS signals include N-formyl methionine released by bacteria; peptides formed during blood coagulation, soluble peptides - products of activation of the complement system and cytokines secreted by tissue macrophages that collided with bacteria in tissues. Some of the SOS signals stimulate the expression of cell adhesion molecules on endothelial cells near the site of infection, such as ICAM-1 and selectins. Adhesion molecules bind to complementary structures on the surface of phagocytic cells. As a consequence, neutrophils and monocytes adhere to the endothelium. Vasodilators released at the site of infection by mast cells promote diapedesis of adhering phagocytes through the endothelial barrier and their migration to the site of infection. Movement in tissues along the concentration gradient of SOS molecules. In parallel, SOS signals activate phagocytes, which leads to an increase in both the absorption of pathogens and and intracellular destruction of invasive organisms.

Initiation of phagocytosis in nonspecific immunity

The phagocyte cell has receptors on its membrane that help them bind to the pathogen-antigen and absorb it. The most important receptors include the following structures.

1. Fc receptors- if they bind to bacteria IgG antibodies, then there will be Fc fragments on the surface of the bacteria, which are recognized and bound by the Fc receptor on phagocytes. On the surface of one neutrophil there are about 150,000 of these receptors! Binding of bacteria coated with IgG initiates phagocytosis and activation of the metabolic activity of phagocytes (respiratory burst).

2. Complement receptors- phagocytes have receptors for the C3b component of complement. When complement is activated when interacting with bacterial surface structures, the latter is covered with a hydrophobic C3b fragment. Binding of the C3b receptor to C3b also leads to an increase in phagocytosis and stimulation of the respiratory burst.

3. Receptors are scavengers bind a wide range of polyanions on the bacterial surface, mediating bacterial phagocytosis.

4. Toll-like receptors- phagocytes have various Toll-like receptors that recognize a wide range of conserved structures on the surface of infectious agents. Binding of infectious agents through Toll-like receptors leads to phagocytosis and release of pro-inflammatory cytokines (IL-1, TNF-alpha and IL-6) by phagocytes.

Phagocytosis and nonspecific immunity

After attachment of the bacteria, the phagocyte membrane forms pseudopodia, which eventually surround the bacterium and engulf it, the bacterium being enclosed in the phagosome. Phagosomes fuse with secondary granules to form a phagolysosome.

Respiratory burst and intracellular killing in nonspecific immunity

During phagocytosis, phagocytic cells increase their intake of glucose and oxygen, a process called respiratory burst. The consequence of a respiratory explosion is the formation of reactive oxygen species that can kill bacteria in the phagolysosome. This process is called oxygen-dependent intracellular killing. In addition, as part of the phagolysosome, bacteria can be destroyed under d by the action of the contents already present in the granules. The complex of these reactions is called oxygen-independent intracellular killing.

1. In the process of phagocytosis, the mechanism of direct oxidation of glucose-6-phosphate in the pentose phosphate pathway is switched on with the formation of NADPH. The assembly of the supramolecular complex of the active NADPH oxidase molecule is carried out immediately. Activated NADPH oxidase uses oxygen to oxidize NADPH. As a result of the reaction, superoxide anion is formed. Under the action of superoxide dismutase, part of the superoxide anions is converted into singlet oxygen and H 2 O 2. Another part of the superoxide anions interacts with H 2 O 2 to form hydroxyl radicals and singlet oxygen. As a result of all these reactions, toxic oxygen compounds superoxide anion hydrogen peroxide, singlet oxygen and hydroxyl radicals (OH) are formed.

2. Oxygen dependent myeloperoxidase-dependent intracellular killing

Once the azurophilic granules fuse with the phagosome, myeloperoxidase is released into the phagolysosome. Myeloperoxidase catalyzes the formation of hypochlorite ion from H2O2 and chloride ion. Hypochlorite ion is a highly toxic compound, a powerful oxidizing agent. Some of the hypochlorite can spontaneously decompose to singlet oxygen. As a result of these reactions, toxic hypochlorite (OCl -) and singlet oxygen (1 O2) are formed.

3. Detoxification reactions (Table 3)

Neutrophils and macrophages have means of protection against the action of reactive oxygen species. These reactions include the dismutation of superoxide anion to hydrogen peroxide by superoxide dismutase and the conversion of hydrogen peroxide to water by catalase.

4. Oxygen-independent intracellular killing

Oxygen-independent mechanisms of intracellular killing

5. Nitric oxide-dependent killing in nonspecific immunity reactions

Binding of bacteria by macrophages, in particular through Toll-like receptors, leads to the production of TNF-alpha, which autocrine (stimulates the same cells that secreted it) induces the expression of the inducible NO synthase (iNOS) gene, as a result of which macrophages synthesize nitric oxide ( NO). If the cell is exposed to interferon gamma (IFN-gamma), nitric oxide synthesis is enhanced. The concentration of nitric oxide released by macrophages has a pronounced toxic effect on microorganisms in the immediate vicinity of macrophages.

8. Neutrophils. Basophils. Eosinophils. macrophages

Macrophages (aka phagocytes) - "eaters" foreign bodies and the most ancient cells immune system. Macrophages are derived from monocytes (a type of white blood cell). They pass the first stages of development in the bone marrow, and then leave it in the form of monocytes (rounded cells) and circulate in the blood for a certain time. From the bloodstream, they enter all tissues and organs, where they change their rounded shape to another, with processes. It is in this form that they acquire mobility and are able to stick to any potentially foreign bodies. They recognize some foreign substances and signal them to T-lymphocytes, and those, in turn, to B-lymphocytes. Then B-lymphocytes begin to produce antibodies - immunoglobulins against the agent, which was "reported" by the phagocyte cell and T-lymphocyte. Sedentary macrophages can be found in almost all human tissues and organs, which provides an equivalent response of the immune system to any antigen that enters the body anywhere. Macrophages eliminate not only microorganisms and foreign chemical poisons that enter the body from outside, but also dead cells or toxins produced by their own body (endotoxins). Millions of macrophages surround them, absorb and dissolve them in order to remove them from the body. A decrease in the phagocytic activity of blood cells contributes to the development of a chronic inflammatory process and the emergence of aggression against the body's own tissues (the appearance of autoimmune processes). With the inhibition of phagocytosis, dysfunction of the destruction and excretion of immune complexes from the body is also observed.

Leukocyte formula - percentage various kinds leukocytes (counted in stained blood smears). The study of the leukocyte formula has great importance in the diagnosis of most hematological, infectious, inflammatory diseases, as well as to assess the severity of the condition and the effectiveness of the therapy. Changes in the leukocyte formula occur in a number of diseases, but sometimes they are nonspecific.

The leukocyte formula has age-specific features (in children, especially during the neonatal period, the ratio of cells differs sharply from adults).

Leukocytes (WBC - White Blood Cells, white blood cells)

Blood leukocytes are represented by granulocytes, in the cytoplasm of which granularity is detected when stained (neutrophilic, eosinophilic and basophilic leukocytes), and agranulocytes, the cytoplasm of which does not contain granularity (lymphocytes and monocytes). About 60% of the total number of granulocytes is located in the bone marrow, making up the bone marrow reserve, 40% - in other tissues, and only less than 1% - in peripheral blood.

Different types of leukocytes perform different functions, so determining the ratio different types leukocytes, the content of young forms, the identification of pathological cellular forms carries valuable diagnostic information.

Options for changing (shifting) the leukocyte formula:

• Shift of the leukocyte formula to the left - an increase in the number of immature (stab) neutrophils in the peripheral blood, the appearance of metamyelocytes (young), myelocytes;
• Shift of the leukocyte formula to the right - a decrease in the normal number of stab neutrophils and an increase in the number of segmented neutrophils with hypersegmented nuclei (megaloblastic anemia, kidney and liver diseases, condition after blood transfusion).

Neutrophilic leukocytes (neutrophils)

The most numerous type of white blood cells, they make up 45-70% of all leukocytes. Depending on the degree of maturity and shape of the nucleus in the peripheral blood, stab (younger) and segmented (mature) neutrophils are isolated. Younger cells of the neutrophilic series - young (metamyelocytes), myelocytes, promyelocytes - appear in the peripheral blood in case of pathology and are evidence of stimulation of the formation of cells of this type. The duration of circulation of neutrophils in the blood is on average about 6.5 hours, then they migrate to the tissues.

They participate in the destruction of infectious agents that have entered the body, closely interacting with macrophages (monocytes), T- and B-lymphocytes. Neutrophils secrete substances that have bactericidal effects, promote tissue regeneration, removing damaged cells from them and secreting substances that stimulate regeneration. Their main function is protection against infections by chemotaxis (directed movement to stimulating agents) and phagocytosis (absorption and digestion) of foreign microorganisms.

An increase in the number of neutrophils (neutrophilia, neutrophilia, neutrocytosis), as a rule, is combined with an increase in the total number of leukocytes in the blood. A sharp decrease in the number of neutrophils can lead to life threatening infectious complications. Agranulocytosis is a sharp decrease in the number of granulocytes in the peripheral blood up to their complete disappearance, leading to a decrease in the body's resistance to infection and the development of bacterial complications.

Increase in the total number of neutrophils:

• Acute bacterial infections (abscesses, osteomyelitis, appendicitis, acute otitis media, pneumonia, acute pyelonephritis, salpingitis, meningitis, tonsillitis, acute cholecystitis, thrombophlebitis, sepsis, peritonitis, pleural empyema, scarlet fever, cholera, etc.);
• Inflammation or necrosis of tissues (myocardial infarction, extensive burns, gangrene, rapidly developing malignant tumor with disintegration, periarteritis nodosa, acute rheumatism, rheumatoid arthritis, pancreatitis, dermatitis, peritonitis);
• Condition after surgery;
• Myeloproliferative diseases (chronic myeloid leukemia, erythremia);
• Acute hemorrhages;
• Cushing's syndrome;
• taking corticosteroids;
• Endogenous intoxications (uremia, eclampsia, diabetic acidosis, gout);
• Exogenous intoxications (lead, snake venom, vaccines);
• The release of adrenaline during stressful situations, physical stress and emotional stress (may lead to a doubling of the number of neutrophils in the peripheral blood).

Increase in the number of immature neutrophils (left shift):

• Acute inflammatory processes (croupous pneumonia);
• Some infectious diseases (scarlet fever, erysipelas, diphtheria);
• Malignant tumors (cancer of the parenchyma of the kidney, breast and prostate glands) and metastasis to Bone marrow;
• Myeloproliferative diseases, especially chronic myeloid leukemia;
• Tuberculosis;
• myocardial infarction;
• bleeding;
• hemolytic crisis;
• Sepsis;
• intoxication;
• Physical overstrain;
• Acidosis and coma.

Decrease in the number of neutrophils (neutropenia):

• Bacterial infections (typhoid, paratyphoid, tularemia, brucellosis, subacute bacterial endocarditis, miliary tuberculosis);
• Viral infections (infectious hepatitis, influenza, measles, rubella, chicken pox);
• Malaria;
• Chronic inflammatory diseases(especially in the elderly and debilitated people);
• kidney failure;
• Severe forms of sepsis with the development of septic shock;
• Hemoblastoses (as a result of hyperplasia of tumor cells and reduction of normal hematopoiesis);
• Acute leukemia, aplastic anemia;
• Autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, chronic lymphocytic leukemia);
• Isoimmune agranulocytosis (in newborns, post-transfusion);
• Anaphylactic shock;
• Splenomegaly;
• Hereditary forms of neutropenia (cyclic neutropenia, familial benign chronic neutropenia, Kostmann's permanent hereditary neutropenia;)
• Ionizing radiation;
• Toxic agents (benzene, aniline, etc.);
• Deficiency of vitamin B12 and folic acid;
• Taking certain medications (pyrazolone derivatives, non-steroidal anti-inflammatory drugs, antibiotics, especially chloramphenicol, sulfa drugs, gold preparations);
• Reception anticancer drugs(cytostatics and immunosuppressants);
• Alimentary-toxic factors (eating spoiled overwintered cereals, etc.).

Eosinophils

After maturation in the bone marrow, eosinophils spend several hours (about 3-4 hours) in the circulating blood, and then migrate to tissues, where their lifespan is 8-12 days. A person is characterized by the accumulation of eosinophils in tissues in contact with the external environment - in the lungs, gastrointestinal tract, skin, urogenital tract. Their number in these tissues is 100-300 times higher than the content in the blood.

At allergic diseases eosinophils accumulate in the tissues involved in allergic reactions and neutralize the biologically active substances formed during these reactions, inhibit the secretion of histamine by mast cells and basophils, and have phagocytic and bactericidal activity.

Eosinophils are characterized by a daily rhythm of fluctuations in the blood, the highest rates are noted at night, the lowest - during the day. Eosinopenia (a decrease in the number of eosinophils in the blood) is often observed at the onset of inflammation. An increase in the number of eosinophils in the blood (eosinophilia) corresponds to the onset of recovery. However, a number infectious diseases with a high level of IgE are characterized by a high number of eosinophils in the blood after the end of the inflammatory process, which indicates incompleteness immune response with its allergic component. A decrease in the number of eosinophils in the active phase of the disease or in postoperative period often indicates a serious condition of the patient.

Reduction in the number of eosinophils and their absence (eosinopenia and aneosinophilia):

• The initial period of the infectious-toxic (inflammatory) process;
• Increased adrenocorticoid activity;
• Purulent-septic processes.

Basophils

The smallest population of leukocytes. Basophilic granulocytes of blood and tissues (the latter include mast cells) perform many functions: they support blood flow in small vessels, promote the growth of new capillaries, and ensure the migration of other leukocytes into tissues. They participate in delayed-type allergic and cellular inflammatory reactions in the skin and other tissues, causing hyperemia, exudate formation, and increased capillary permeability. Basophils during degranulation (destruction of granules) initiate the development of an anaphylactic hypersensitivity reaction immediate type. Contain biologically active substances (histamine; leukotrienes that cause smooth muscle spasm; “platelet activating factor”, etc.).

The lifespan of basophils is 8-12 days, the time of circulation in the peripheral blood (as in all granulocytes) is several hours.

An increase in the number of basophils (basophilia):

• Allergic reactions to food, drugs, the introduction of a foreign protein;
• Chronic myeloid leukemia, myelofibrosis, erythremia, lymphogranulomatosis;
• Hypofunction thyroid gland(hypothyroidism);
• Nephritis;
• Chronic ulcerative colitis;
• hemolytic anemia;
• Iron deficiency, after treatment of iron deficiency anemia;
• B 12 - deficiency anemia;
• After splenectomy;
• estrogen treatment;
• During ovulation, pregnancy, at the beginning of menstruation;
• Lungs' cancer;
• True polycythemia;
• Diabetes;
• Acute hepatitis with jaundice.

Monocytes

Monocytes are the largest cells among leukocytes (a system of phagocytic macrophages). Participate in the formation and regulation of the immune response. Monocytes make up 2-10% of all leukocytes, are capable of amoeboid movement, and exhibit pronounced phagocytic and bactericidal activity. Macrophages - monocytes are able to absorb up to 100 microbes, while neutrophils - only 20-30. In the focus of inflammation, macrophages phagocytize microbes, denatured protein, antigen-antibody complexes, as well as dead leukocytes, damaged cells of inflamed tissue, clearing the focus of inflammation and preparing it for regeneration. Secrete more than 100 biologically active substances. Stimulate the factor that causes tumor necrosis (cachexin), which has cytotoxic and cytostatic effects on tumor cells. Secreted interleukin I and cachexin act on the thermoregulatory centers of the hypothalamus, increasing body temperature. Macrophages are involved in the regulation of hematopoiesis, immune response, hemostasis, lipid and iron metabolism.

Monocytes are formed in the bone marrow from monoblasts. After leaving the bone marrow, they circulate in the blood from 36 to 104 hours, and then migrate to the tissues. In tissues, monocytes differentiate into organ- and tissue-specific macrophages. Tissues contain 25 times more monocytes than blood.

An increase in the number of monocytes in the blood (monocytosis):

• Viral infections ( Infectious mononucleosis);
• Fungal, protozoal infections (malaria, leishmaniasis);
• Recovery period after acute infections;
• Granulomatosis (tuberculosis, syphilis, brucellosis, sarcoidosis, ulcerative colitis);
• Collagenosis (systemic lupus erythematosus, rheumatoid arthritis, periarteritis nodosa);
• Blood diseases (acute monoblastic and myelomonoblastic leukemia, chronic monocytic, myelomonocytic and myeloid leukemia, lymphogranulomatosis);
• Subacute septic endocarditis;
• Enteritis;
• Sluggish sepsis.

Reducing the number of monocytes in the blood:

• Hypoplasia of hematopoiesis;
• childbirth;
• Operational interventions;
• shock states.

Lymphocytes

Lymphocytes are the main cellular elements of the immune system; are formed in the bone marrow, actively function in the lymphoid tissue. The main function of lymphocytes is to recognize a foreign antigen and participate in an adequate immunological response of the body.

Lymphocytes are a uniquely diverse population of cells originating from various precursors and united by a single morphology. By origin, lymphocytes are divided into two main subpopulations: T-lymphocytes and B-lymphocytes. There is also a group of lymphocytes called "neither T- nor B-", or "0-lymphocytes" (null lymphocytes). The cells that make up specified group, morphologically identical to lymphocytes, but differ in origin and functional features - immunological memory cells, killer cells, helpers, suppressors.

Different subpopulations of lymphocytes perform different functions:

• ensuring effective cellular immunity (including transplant rejection, destruction of tumor cells);
• the formation of a humoral response (the synthesis of antibodies to foreign proteins - immunoglobulins of different classes);
• regulation of the immune response and coordination of the work of the entire immune system as a whole (isolation of protein regulators - cytokines);
• providing immunological memory (the body's ability to accelerate and enhance the immune response upon re-encounter with a foreign agent).

It should be borne in mind that leukocyte formula reflects the relative (percentage) content of leukocytes of various types, and an increase or decrease in the percentage of lymphocytes may not reflect true (absolute) lymphocytosis or lymphopenia, but be the result of a decrease or increase in the absolute number of leukocytes of other types (usually neutrophils).

An increase in the number of lymphocytes (lymphocytosis):

• Viral infection (infectious mononucleosis, acute viral hepatitis, cytomegalovirus infection, whooping cough, SARS, toxoplasmosis, herpes, rubella);
• Diseases lymphatic system(acute and chronic lymphocytic leukemia, Waldenström's macroglobulinemia);
• Tuberculosis;
• Syphilis;
• Brucellosis;
• Intoxication (tetrachloroethane, lead, arsenic).

Reducing the number of lymphocytes:

• Acute infections and diseases;
• The initial stage of the infectious-toxic process;
• Severe viral diseases;
• miliary tuberculosis;
• taking corticosteroids;
• Malignant neoplasms;
• Secondary immune deficiencies;
• kidney failure;
• Circulatory failure;
• Taking drugs with a cytostatic effect.

Phagocytes are the main group of cells in the innate immune system. They are of myeloid origin and are capable of phagocytosis (see section 2.1.3). According to morphology and function, they are divided into mononuclear cells (monocytes / macrophages) and neutrophils, which corresponds to the proposed by I.I.

Mechnikov's division into macro- and microphages. The role of phagocytes in the immune response is extremely diverse. They perform a number of key functions in innate and adaptive immunity. The activation of phagocytes occurs through many surface receptors. The leading role in the activation of phagocytes is played by the RECs of innate immunity (for example, TKA, IOB receptors, mannose receptors, scavenger receptors, complement receptors, and many others). The response develops rapidly and does not require cell proliferation and differentiation.

Activation usually occurs in two stages: priming and actual activation. The essence of priming is that pre-treatment of cells with a small amount of a stimulant (1st signal), the action of which does not cause direct activation, is accompanied by an increase in the response
and phagocytes to the second signal. As a result, activated phagocytes perform the following functions:

Chemotaxis;

Phagocytosis;

Formation of reactive oxygen species;

Synthesis of nitric oxide;

Synthesis and secretion of cytokines and other biologically active mediator molecules (arachidonic acid metabolites, complement components, blood coagulation factors, matrix proteins, enzymes, antimicrobial peptides, hormones, etc.);

bactericidal activity;

Processing and antigen presentation (professional APC - DC, mononuclear phagocytes).

The main types of cells involved in the development of inflammation - the body's universal defense response to damage - are neutrophils, monocytes, macrophages, as well as endothelial cells and fibroblasts. The first to migrate to the focus of inflammation are neutrophils (in the first hours, days), then macrophages (within several days) and the latest - lymphocytes. At acute inflammation neutrophils and activated T-helpers predominate, with chronic inflammation more macrophages, CTLs and B-lymphocytes. This periodicity of migration of leukocytes to the focus of inflammation is due to chemokines and adhesion molecules.

Chemokines are a group of low molecular weight cytokines with a molecular weight of 8-10 kDa, which induce the process of migration of leukocytes from the blood. More than 40 different chemokines have been identified so far. According to the chemical structure, namely, depending on the position of cysteine ​​residues in the molecule, four main groups of chemokines are distinguished (Tables 4-3).

The selective involvement of various populations of leukocytes in the formation of inflammatory foci is provided by the expression of various chemokine receptors. Th1 cells and monocytes express the chemokine receptor CCK5, which provides a response to the chemokine Ccc3. Th2 cells, eosinophils, and basophils express CVD required for response to CC1. It should be noted that both groups of cells express the CCK1 and CCK2 receptors, which determines the response to CCL2, CCL7, CCL8, and CCN3. It is known that CXCK1 and CXCK2 are expressed on neutrophils - receptors for IL-8, CXClL and CXCL2.

Inflammation-induced penetration of neutrophils from vessels into tissues is provided by a number of adhesive interactions between leukocytes and endothelial cells, as well as by the action of chemokines.

In table. 4-4 show some clinically relevant adhesion molecules and their ligands. There are two groups of adhesion molecules: selectins and integrins.

There are E-selectins (on endothelial cells), L-selectins (on leukocytes) and P-selectins (on platelets). Selectins bind to carbohydrate residues on the surface of leukocytes and endothelial cells and are involved in cell migration to the site of inflammation.

Integrins are the main molecules of intercellular adhesion. These are heterodimers consisting of a- and p-subunits connected by non-covalent bonds. Integrins penetrate the cell membrane and through the adapter molecules talin and vinculin bind to the cytoskeleton. Depending on the type of p-chain that is part of the molecule, three families of integrins are distinguished.

β-Integrins ensure the binding of cells to the extracellular matrix. p2-Integrins are involved in the adhesion of leukocytes to endothelial cells. Р3-Integrins determine the interaction of platelets and neutrophils. Deficiency of p2-integrin LPA-1 (C018 / SB11) leads to the development of a congenital defect of phagocytes - leukocyte adhesion deficiency syndrome (LAE-syndrome), accompanied by severe infectious diseases.

diseases of a bacterial and fungal nature, a decrease in the migration of phagocytes into tissues (see section 11.2.5).

The inflammation-induced process of penetration of leukocytes into tissues from the vascular bed is provided by a number of adhesive interactions and includes several stages (Fig. 4-20):

Rolling (rolling);

adhesion;

tissue penetration.

Consider the stages of penetration of leukocytes into tissues using the example of neutrophils. The first stage - rolling (rolling) of neutrophils on the surface of endothelial cells - occurs with the participation of selectins. Normally, vascular endothelial cells do not carry adhesion molecules. When activated in the focus of inflammation, cells begin to express E-selectins and receptors for selectins. The speed of neutrophils in the bloodstream slows down due to the interaction of E-selectin and the carbohydrate determinant Le\V1$-X associated with the neutrophil CD15 molecule.

L-selectins of neutrophils interact with sialomucin (SB34) located on the endothelium. Activated endothelial cells secrete IL-8, which induces a change in selectins on the surface of neutrophils and stimulates the expression of (52-integrins).

The second stage is adhesion - the formation of strong bonds between leukocytes and endothelial cells, carried out due to integrin interactions. P2-iptegrin ligands are molecules of the ICAM group.

The third stage - the migration of neutrophils between endothelial cells (transendothelial migration) is carried out under the action of chemokines.

The subsequent migration of neutrophils into tissues is based on chemotaxis. Chemoattractants for neutrophils exist in the focus of inflammation.

These include platelet activating factor (PAF), leukotriene B4, complement components (C5a), N-formyl-methionyl-peptides of bacteria, IL-8. Pro-inflammatory cytokines increase the level of expression of p2-integrins, ICAM-1, IL-8.

In the zone of inflammation, phagocytes begin to recognize opsonized pathogens. Most often, inactivated complement components \C3b and 1^0 molecules act as opsonins. Complement receptors are involved in the recognition of opsonized pathogens: CK1, CK3 (in macrophages CK4 plays an important role) and RcyK (SB64, SB32, SB16). These

interactions induce the absorption process.

Neutrophils and macrophages have a powerful potential to destroy pathogens. Oxygen-dependent and oxygen-independent mechanisms of bactericidal ™ of phagocytes are distinguished.

Resident macrophages remove apoptotic cells and endogenous body molecules modified as a result of a pathological process (the so-called endogenous ligands: for example, modified collagen, heat shock proteins, low-density lipids, etc.) using scavenger receptors. In this case, the activation of macrophages and the development

Infection

To11-like receptors

/f CP14 (γ receptor for lipopolysaccharide)

Receptor that recognizes mannose residues

(neutrophil chemotaxis factor)

(activates MK cells, promotes TNO differentiation into TM)

> Other mediators: prostaglandins, oxygen radicals, nitric oxide

no mechanisms of cytotoxicity occur. The ingestion of foreign cells and pathogens leads to the activation of macrophages.

The functional activity of macrophages is regulated by cytokines. Cytokines produced by Th1 and Th2 cells induce various reactions in the macrophage. IFN-γ stimulates the production of reactive oxygen species, pro-inflammatory cytokines, and MHC-H expression.

IL-4 and IL-13 inhibit these macrophage functions, but promote the formation of giant cells in granulomas, the production of growth factors, thereby stimulating the healing of tissue damage. These cytokines induce alternative macrophage activation (see Fig. 3-32, Fig. 3-33).

An extremely important role in the activation of phagocytes and in the implementation of their oxygen-dependent bactericidal function is played by reactive oxygen species and nitric oxide, formed during an oxygen or respiratory explosion.

The basis of the respiratory burst is an increase in glucose consumption and its breakdown with the participation of NSAPH by the mechanism of hexose monophosphate shunt, which is accompanied by the accumulation of NSAPH. The interaction of NAOPH with an oxygen molecule with the participation of NAOPH oxidase leads to the formation of superoxide anion (O2-), from which, with the participation of hydrogen ions, hydroxyl radicals (OH), potentially toxic to bacteria, hydrogen peroxide (H2O2) and singlet oxygen are formed. This process begins spontaneously after the formation of the phagosome before fusion with the lysosome. The bactericidal effect is most pronounced in phagolysosomes. The formation of H2O2 occurs spontaneously and with the participation of superoxide dismutase. The enzyme myeloperoxidase ensures the formation of hypochloride from H202 with the participation of halogen ions. Nitric oxide (NO) is formed as a result of the breakdown of arginine to citrulline and is catalyzed by NO synthase (Fig. 4-22).

Nitric oxide (NO) is involved in many physiological and pathological processes both at the cellular and organismal levels, providing protective, regulatory and damaging effects.

The regulatory action of NO is manifested in the maintenance of vascular tone and permeability, the suppression of platelet adhesion, the modulation of cell adhesion, neurotransmission and bronchodilation, as well as the regulation of some functions of the kidneys and the immune system.

The protective effect of nitric oxide is understood as its antioxidant properties, i.e., protection against oxidative stress agents (hydrogen peroxide, alkyl hydroperoxides, superoxide anion radical, etc.), a decrease in leukocyte adhesion and an antitoxic effect, in particular, against TNF- a.

The damaging effect of nitric oxide is through the suppression of enzyme functions, the induction of lipid peroxidation processes.

oxidase

OH HOC1 01400" 8-nitrosothiols

Rice. 4-22. Scheme of the formation of bactericidal substances by phagocytes (reactive oxygen species and nitric oxide).

and damage to the DNA of the cell, increasing the sensitivity of the cell to the action of radiation, alkylating agents and toxic metals, as well as through the depletion of the antioxidant capacity of the cell. indirect

the cytotoxic effect of nitric oxide is due to changes in the cytokine balance and IL-12-mediated activation of NK cells and CTLs. By itself, nitric oxide is not a powerful cytotoxic agent, but it can increase the sensitivity of cells to the action of other cytotoxic substances. The most pronounced antibacterial activity is possessed by compounds formed during the interaction of reactive oxygen species and nitric oxide. As a result of the interaction of N0 with active forms oxygen and some other compounds, cytotoxic substances are formed, including peroxynitrite (ONY), 5-nitrosothiols (N5N0), nitrogen dioxide (LGO2), dinitrogen trioxide (JM203), dinitrogen tetroxide (I204), and iron dinitrosyl complexes (N11C).

The effects of nitric oxide are usually divided into basic and indirect. The main effects include reactions in which it directly interacts with specific biological molecules (for example, with guanylate cyclase, cytochrome P450, etc.).

Indirect effects of nitric oxide action are associated with reactive nitrogen forms formed during the interaction of NO with oxygen or with the superoxide anion radical.

Basic and side effects reactions with the direct participation of nitric oxide are determined by its local concentration. The main effects are likely at low concentrations of nitric oxide (less than 1 μM), while side effects, including the formation of radicals, become possible at higher concentrations (greater than 1 μM).

Nitric oxide in vyu is formed with the participation of IM0 synthase (NO5), which exists in mammals in three isoforms: nNO5 - neutral (type 1); 1N05 - inducible (type 2); eNO5-synthase - endothelial (3rd type).

In macrophages, 1N05 functions, the expression of which is stimulated by

some cytokines and products of microorganisms, often acting in synergy. NO-synthases of types] and 3 are also called cNO5 - selective (they exist in cells and can be activated by calcium influx, which subsequently binds to calmodulin). In the presence of 1008, nitric oxide is produced in large quantities and often has side effects such as lipid peroxidation and hydroxylation, the formation of nitrosamines and nitrotyrosine.

On fig. 4-23 show some types of receptors involved in phagocytosis and apoptosis.