General characteristics of cytokines. Cytokines are the most numerous, most important and functionally universal group of humoral factors of the immune system, equally important for the implementation of innate and adaptive immunity. Cytokines are involved in many processes; they cannot be called factors related exclusively to the immune system, since they play an important role in hematopoiesis, tissue homeostasis, and intersystem signaling.
Cytokines can be defined as protein or polypeptide factors lacking antigen specificity, produced predominantly by activated cells of the hematopoietic and immune systems, and mediating intercellular interactions in hematopoiesis, inflammation, immune processes, and intersystem communications.
Cytokines differ in structure, biological activity, and other properties. However, along with differences, cytokines have common properties characteristic of this class of bioregulatory molecules:
- · Cytokines are, as a rule, glycosylated polypeptides of medium molecular weight (less than 30 kD).
- Cytokines are produced by cells of the immune system and other cells (for example, endothelium, fibroblasts, etc.) in response to an activating stimulus (pathogen-associated molecular structures, antigens, cytokines, etc.) and participate in innate and adaptive immunity reactions, regulating their strength and duration . Some cytokines are synthesized constitutively.
- · The secretion of cytokines is a short process. Cytokines are not stored as preformed molecules, and their synthesis always begins with gene transcription. Cells produce cytokines at low concentrations (picograms per milliliter).
- In most cases, cytokines are produced and act on target cells that are in close proximity (short-range action). The main site of action of cytokines is the intercellular synapse.
- · The redundancy of the cytokine system is manifested in the fact that each cell type is able to produce several cytokines, and each cytokine can be secreted by different cells.
- All cytokines are characterized by pleiotropy, or polyfunctionality of action. Thus, the manifestation of signs of inflammation is due to the influence of IL-1, TNFb, IL-6, IL-8. Duplication of functions ensures the reliability of the cytokine system.
- · The action of cytokines on target cells is mediated by highly specific, high-affinity membrane receptors, which are transmembrane glycoproteins, usually consisting of more than one subunit. The extracellular part of the receptors is responsible for cytokine binding. There are receptors that eliminate excess cytokines in the pathological focus. These are the so-called decoy receptors. Soluble receptors are the extracellular domain of a membrane receptor separated by an enzyme. Soluble receptors are able to neutralize cytokines, participate in their transport to the focus of inflammation and in excretion from the body.
- · Cytokines work on the principle of a network. They can act in concert. Many of the functions originally attributed to a single cytokine appear to be due to the concerted action of several cytokines (synergism of action). Examples of the synergistic interaction of cytokines are the stimulation of inflammatory reactions (IL-1, IL-6 and TNFa), as well as the synthesis of IgE (IL-4, IL-5 and IL-13).
Classification of cytokines. There are several classifications of cytokines based on different principles. The traditional classification reflects the history of the study of cytokines. The idea that cytokines play the role of factors mediating the functional activity of cells of the immune system arose after the discovery of the heterogeneity of the lymphocyte population and the understanding of the fact that only some of them - B-lymphocytes - are responsible for the formation of antibodies. Trying to find out whether the humoral products of T cells play a role in the implementation of their functions, they began to study the biological activity of factors contained in the culture medium of T lymphocytes (especially activated ones). The solution of this problem, as well as the question that soon arose about the humoral products of monocytes/macrophages, led to the discovery of cytokines. Initially, they were called lymphokines and monokines, depending on which cells produced them - T-lymphocytes or monocytes. It soon became clear that it was impossible to clearly distinguish between lymphokines and monokines, and the general term "cytokines" was introduced. In 1979, at a symposium on lymphokines in Interlaken (Switzerland), the rules for identifying factors of this group were established, which were given the group name "interleukins" (IL). At the same time, the first two members of this group of molecules, IL-1 and IL-2, received their names. Since then, all new cytokines (except chemokines -- see below) have received the designation IL and a sequence number.
Traditionally, in accordance with biological effects, it is customary to distinguish the following groups of cytokines:
- · Interleukins (IL-1-IL-33) - secretory regulatory proteins of the immune system, providing mediator interactions in the immune system and its connection with other body systems. Interleukins are divided according to their functional activity into pro- and anti-inflammatory cytokines, growth factors of lymphocytes, regulatory cytokines, etc.
- Interferons (IFN) - cytokines involved in antiviral protection, with a pronounced immunoregulatory effect (IFN type 1 - IFN b, c, d, k, ?, f; groups of IFN-like cytokines - IL-28A, IL-28B and IL-29 IFN type 2 - IFNg).
- · Tumor necrosis factors (TNF) - cytokines with cytotoxic and regulatory actions: TNF-a and lymphotoxins (LT).
- Hematopoietic cell growth factors - stem cell growth factor (Kit-ligand), IL-3, IL-7, IL-11, erythropoietin, trobopoietin, granulocyte-macrophage colony-stimulating factor - GM-CSF, granulocytic CSF - G-CSF, macrophage KSF - M-CSF).
- · Chemokines - С, СС, СХС (IL-8), СХ3С - regulators of chemotaxis of various cell types.
- Non-lymphoid cell growth factors - regulators of growth, differentiation and functional activity of cells of various tissue affiliations (fibroblast growth factor - FGF, endothelial cell growth factor, epidermal growth factor - epidermal EGF) and transforming growth factors (TGFv, TGFb).
The concept of "cytokines" is quite difficult to distinguish from the concept of "growth factors". A more accurate understanding of the concept of "interleukin" (actually coinciding with the concept of "cytokine") was facilitated by the introduction by the Nomenclature Committee of the International Union of Immunological Societies in 1992 of criteria governing the assignment of new interleukins of the next number: this requires molecular cloning, sequencing and expression of the interleukin gene, certifying the uniqueness of its nucleotide sequence, as well as the production of neutralizing monoclonal antibodies. To establish differences between interleukins and similar factors, data on the production of this molecule by cells of the immune system (leukocytes) and evidence of its role in the regulation of immune processes are important. Thus, the mandatory participation of interleukins in the functioning of the immune system is emphasized. If we consider that all cytokines discovered after 1979 (except chemokines) are called interleukins and, therefore, these concepts are actually identical, then we can assume that such growth factors as epidermal, fibroblast, platelet are not cytokines, but from transforming growth factors (TGF) on the basis of functional involvement in the immune system, only TGF can be classified as a cytokine. However, this issue is not strictly regulated in international scientific documents.
There is no clear structural classification of cytokines. Nevertheless, according to the features of their secondary structure, several groups are distinguished:
- · Molecules with a predominance of b-helix strands. They contain 4 6-helix domains (2 pairs of 6-helices located at an angle to each other). There are short and long (according to the length of b-helices) variants. The first group includes most hematopoietin cytokines -- IL-2, IL-3, IL-4, IL-5, IL-7, IL-9, IL-13, IL-21, IL-27, IFNr and M-CSF ; to the second - IL-6, IL-10, IL-11 and GM-CSF.
- · Molecules with a predominance of β-sheet structures. These include cytokines of the tumor necrosis factor family and lymphotoxins (“v-trefoil”), the IL-1 family (v-sandwich), the TGF family (cytokine node).
- · Short b / b-chain (b-layer with adjacent b-helices) - chemokines.
- Mixed mosaic structures, eg IL-12.
In recent years, in connection with the identification of a large number of new cytokines, sometimes related to the previously described ones, and forming single groups with them, a classification based on the belonging of cytokines to structural and functional families has become widely used.
Another classification of cytokines is based on the structural features of their receptors. As you know, through the receptors and the action of cytokines is carried out. According to the structural features of the polypeptide chains, several groups of cytokine receptors are distinguished. The classification given is applied specifically to polypeptide chains. One receptor may include chains belonging to different families. The importance of this classification is due to the fact that different types of receptor polypeptide chains are characterized by a certain signaling apparatus, consisting of tyrosine kinases, adapter proteins, and transcription factors.
The most numerous type is cytokine hematopoietin receptors. Their extracellular domains are characterized by the presence of 4 cysteine residues and the presence of a sequence containing tryptophan and serine residues -- WSXWS. Fibronectin family domains containing 4 cysteine residues form the backbone of interferon receptors. A characteristic feature of the domains that form the extracellular portion of the TNFR family of receptors is their high content of cysteine residues ("cysteine-rich domains"). These domains contain 6 cysteine residues. The group of receptors whose extracellular domains belong to the immunoglobulin superfamily includes two groups - receptors for IL-1 and several receptors, the cytoplasmic part of which has tyrosine kinase activity. Tyrosine kinase activity is characteristic of the cytoplasmic part of almost all growth factors (EGF, PDGF, FGF, etc.). Finally, a special group is formed by rhodopsin-like chemokine receptors, penetrating the membrane 7-fold. However, not all receptor polypeptide chains fit this classification. Thus, neither b- nor b-chains of the IL-2 receptor belong to the families shown in Table 3 (the b-chain contains complement control domains). The main groups also do not include IL-12 receptors, the common β-chain of IL-3 receptors, IL-5, GMCSF, and some other receptor polypeptide chains.
Almost all cytokine receptors (except immunoglobulin-like ones with kinase activity) consist of several polypeptide chains. Often different receptors contain common chains. The most striking example is the r-chain, common for IL-2, IL-4, IL-7, IL-9, IL-15, IL-21 receptors, designated as r(s). Defects in this chain play an important role in the development of immunodeficiency pathology. The common β-chain is part of the GM-CSF, IL-3, and IL-5 receptors. Common chains have IL-7 and TSLP (b-chain), as well as IL-2 and IL-15, IL-4 and IL-13 (both in the b-chain).
As a rule, receptors are present on the surface of resting cells in a small amount and often in an incomplete subunit composition. Usually, in this state, the receptors provide an adequate response only when exposed to very high doses of cytokines. When cells are activated, the number of membrane cytokine receptors increases by orders of magnitude, moreover, these receptors are “understaffed” with polypeptide chains, as was shown above with the example of the receptor for IL-2. Under the influence of activation, the number of molecules of this receptor increases significantly and a b-chain appears in their composition, the gene of which is expressed during activation. Due to these changes, the lymphocyte acquires the ability to proliferate in response to the action of IL-2.
Mechanisms of action of cytokines
Intracellular signal transduction under the action of cytokines. The C-terminal cytoplasmic portion of some cytokine receptors (belonging to the immunoglobulin superfamily) includes a domain with tyrosine kinase activity. All these kinases belong to the category of proto-oncogenes; when the genetic environment changes, they become oncogenes, providing uncontrolled cell proliferation. These kinases have their own name. Thus, the kinase that is part of the M-CSF receptor is referred to as c-Fms; kinase SCF -- c-Kit; known hematopoietic factor kinase - Flt-3 (Fms-like thyrosine kinase 3). Receptors with their own kinase activity trigger signal transduction directly, since their kinase causes phosphorylation of both the receptor itself and molecules adjacent to it.
The most typical manifestation of activity is characteristic of receptors of the hematopoietic (cytokine) type, containing 4 6-helical domains. Molecules of tyrosine kinases of the Jak-kinase group (Janus-associated family kinases) adjoin the cytoplasmic part of these receptors. In the cytoplasmic part of the receptor chains, there are special sites for the binding of these kinases (proximal and distal boxes). A total of 5 Janus kinases are known - Jak1, Jak2, Jak3, Tyk1 and Tyk2. In various combinations, they cooperate with different cytokine receptors, having an affinity for specific polypeptide chains. Thus, the Jak3 kinase interacts with the r(c) chain; with defects in the gene encoding this kinase, a complex of disorders in the immune system develops similar to that observed with defects in the receptor polypeptide chain gene.
When the cytokine interacts with the receptor, a signal is generated that leads to the formation of transcription factors and the activation of genes that determine the cell's response to the action of the cytokine. Simultaneously, the cell takes up the complex of the cytokine with the receptor and cleaves it in endosomes. By itself, the internalization of this complex has nothing to do with signal transmission. It is necessary for the utilization of the cytokine, which prevents its accumulation at the site of activation of producer cells. The affinity of the receptor for the cytokine plays an important role in the regulation of these processes. Only at a sufficiently high degree of affinity (of the order of 10–10 M) is a signal generated and the cytokine–receptor complex is absorbed.
Signal induction begins with autocatalytic phosphorylation of receptor-bound Jak kinases triggered by conformational changes in the receptor that occur as a result of its interaction with a cytokine. Activated Jak kinases phosphorylate STAT (Signal transducers and activators of transcription) cytoplasmic factors present in the cytoplasm in an inactive monomeric form.
Phosphorylated monomers acquire affinity for each other and dimerize. STAT dimers migrate to the nucleus and act as transcription factors by binding to the promoter regions of target genes. Under the action of pro-inflammatory cytokines, the genes of adhesion molecules, the cytokines themselves, enzymes of oxidative metabolism, etc. are activated. Under the action of factors that cause cell proliferation, the induction of genes responsible for the passage of the cell cycle, etc. occurs.
The Jak/STAT-mediated cytokine signaling pathway is the main but not the only one. The receptor is associated not only with Jak kinases, but also with kinases of the Src family, as well as PI3K. Their activation triggers additional signaling pathways leading to the activation of AP-1 and other transcription factors. Activated transcription factors are involved not only in signal transduction from cytokines, but also in other signaling pathways.
There are signaling pathways involved in the control of the biological effects of cytokines. Such pathways are associated with the factors of the SOCS (Suppressors of cytokine signaling) group, which contains the SIC factor and 7 SOCS factors (SOCS-1 -- SOCS-7). The activation of these factors occurs upon activation of cytokine signaling pathways, which leads to the formation of a negative feedback loop. SOCS factors contain an SH2 domain involved in the implementation of one of the following processes:
- direct inhibition of Jak kinases by binding to them and inducing their dephosphorylation;
- competition with STAT factors for binding to the cytoplasmic part of cytokine receptors;
- Accelerating the degradation of signaling proteins along the ubiquitin pathway.
Switching off the SOCS genes leads to an imbalance of cytokines with a predominance of IFNg synthesis and accompanying lymphopenia and increased apoptosis.
Features of the functioning of the cytokine system. cytokine network.
It follows from the above that upon cell activation by foreign agents (PAMP carriers upon activation of myeloid cells and antigens upon activation of lymphocytes), both the synthesis of cytokines and the expression of their receptors are induced (or enhanced to a functionally significant level). This creates conditions for the local manifestation of the effects of cytokines. Indeed, if the same factor activates both cytokine-producing cells and target cells, optimal conditions are created for the local manifestation of the functions of these factors.
Typically, cytokines are bound, internalized, and cleaved by the target cell, with little or no diffusion from the secreted producer cells. Quite often, cytokines are transmembrane molecules (for example, IL-1b and TNFb) or are presented to target cells in the state associated with peptidoglycans of the extracellular matrix (IL-7 and a number of other cytokines), which also contributes to the local nature of their action.
Normally, if cytokines are contained in the blood serum, then in concentrations insufficient for the manifestation of their biological effects. Next, using the example of inflammation, we will consider situations in which cytokines have a systemic effect. However, these cases are always a manifestation of pathology, sometimes very serious. Apparently, the local nature of the action of cytokines is of fundamental importance for the normal functioning of the body. This is evidenced by the high rate of their excretion through the kidneys. Typically, the cytokine excretion curve consists of two components - fast and slow. T1 / 2 of the fast component for IL-1b is 1.9 minutes, for IL-2 - 5 minutes (T1 / 2 of the slow component is 30-120 minutes). The short-range property distinguishes cytokines from hormones - long-range factors (therefore, the statement "cytokines are hormones of the immune system" is fundamentally wrong).
The cytokine system is characterized by redundancy. This means that almost any function performed by a particular cytokine is duplicated by other cytokines. That is why the shutdown of an individual cytokine, for example, due to a mutation of its gene, does not cause fatal consequences for the body. Indeed, mutation of the gene for a particular cytokine almost never leads to the development of immunodeficiency.
For example, IL-2 is known as a T cell growth factor; artificial removal (by genetic knockout) of the gene encoding it does not reveal a significant violation of T-cell proliferation, however, changes caused by a deficiency of regulatory T-cells are recorded. This is due to the fact that T cell proliferation in the absence of IL-2 is provided by IL-15, IL-7, IL-4, as well as combinations of several cytokines (IL-1c, IL-6, IL-12, TNFb). Similarly, a defect in the IL4 gene does not lead to significant disturbances in the B-cell system and immunoglobulin isotype switching, since IL-13 exhibits similar effects. At the same time, some cytokines do not have functional analogues. The best-known example of an essential cytokine is IL-7, whose lymphopoietic action, at least at certain stages of T-lymphopoiesis, is unique, and therefore defects in the genes of IL-7 itself or its receptor lead to the development of severe combined immune deficiency (SCID).
In addition to redundancy, another regularity is manifested in the cytokine system: cytokines are pleiotropic (act on various targets) and polyfunctional (cause various effects). Thus, the number of target cells for IL-1c and TNFb is difficult to count. Equally diverse are the effects they cause, which are involved in the formation of complex reactions: inflammation, some stages of hematopoiesis, neurotropic and other reactions.
Another important feature inherent in the cytokine system is the relationship and interaction of cytokines. On the one hand, this interaction consists in the fact that some cytokines, acting against the background of inductors or independently, cause or enhance (less often suppress) the production of other cytokines. The most striking examples of enhancing action are the activity of pro-inflammatory cytokines IL-1b and TNFb, which enhance their own production and the formation of other pro-inflammatory cytokines (IL-6, IL-8, other chemokines). IL-12 and IL-18 are IFNg inducers. TGFβ and IL-10, on the contrary, suppress the production of various cytokines. IL-6 exhibits inhibitory activity against pro-inflammatory cytokines, while IFNg and IL-4 mutually inhibit the production of each other and cytokines of the corresponding (Th1 and Th2) groups. The interaction between cytokines is also manifested at the functional level: some cytokines enhance or suppress the action of other cytokines. Synergism (eg, within a group of pro-inflammatory cytokines) and cytokine antagonism (eg, between Th1 and Th2 cytokines) have been described.
Summarizing the data obtained, we can conclude that none of the cytokines exists and does not show its activity in isolation - at all levels, cytokines are influenced by other members of this class of molecules. The result of such diverse interaction can sometimes be unexpected. Thus, when high doses of IL-2 are used for therapeutic purposes, life-threatening side effects occur, some of which (for example, shock similar to toxic, without bacteremia) can be removed by antibodies directed not against IL-2, but against TNFb.
The presence of multiple cross-interactions in the cytokine system was the reason for the creation of the concept of "cytokine network", which quite clearly reflects the essence of the phenomenon.
The cytokine network is characterized by the following properties:
- inducibility of cytokine synthesis and expression of their receptors;
- locality of action due to the coordinated expression of cytokines and their receptors under the influence of the same inducer;
- redundancy due to overlapping action spectra of different cytokines;
- · interconnections and interactions, manifested at the level of synthesis and implementation of cytokine functions.
Cytokine regulation of target cell functions is carried out using autocrine, paracrine or endocrine mechanisms. Some cytokines (IL-1, IL-6, TNFb, etc.) are able to participate in the implementation of all of the above mechanisms.
The response of a cell to the influence of a cytokine depends on several factors:
- on the type of cells and their initial functional activity;
- from the local concentration of the cytokine;
- from the presence of other mediator molecules.
Thus, producer cells, cytokines, and their specific receptors on target cells form a single mediator network. It is a set of regulatory peptides, and not individual cytokines, that determine the final response of the cell. Currently, the cytokine system is considered as a universal system of regulation at the level of the whole organism, which ensures the development of protective reactions (for example, during infection).
In recent years, there has been an idea of a cytokine system that combines:
- 1) producer cells;
- 2) soluble cytokines and their antagonists;
- 3) target cells and their receptors.
Violations of various components of the cytokine system lead to the development of numerous pathological processes, and therefore the detection of defects in this regulatory system is important for the correct diagnosis and the appointment of adequate therapy.
The main components of the cytokine system.
Cytokine producing cells
I. The main group of cells producing cytokines in the adaptive immune response are lymphocytes. Resting cells do not secrete cytokines. Upon recognition of the antigen and with the participation of receptor interactions (CD28-CD80/86 for T-lymphocytes and CD40-CD40L for B-lymphocytes), cell activation occurs, leading to transcription of cytokine genes, translation, and secretion of glycosylated peptides into the extracellular space.
CD4 T-helpers are represented by subpopulations: Th0, Th1, Th2, Th17, Tfh, which differ from each other in the spectrum of secreted cytokines in response to various antigens.
Th0 produce a wide range of cytokines at very low concentrations.
The direction of Th0 differentiation determines the development of two forms of the immune response with a predominance of humoral or cellular mechanisms.
The nature of the antigen, its concentration, localization in the cell, the type of antigen-presenting cells and a certain set of cytokines regulate the direction of Th0 differentiation.
Dendritic cells, after antigen capture and processing, present antigenic peptides to Th0 cells and produce cytokines that regulate the direction of their differentiation into effector cells. IL-12 induces the synthesis of IFNg by T-lymphocytes and ]ChGK. IFNy provides differentiation of Th1, which begin to secrete cytokines (IL-2, IFNy, IL-3, TNFa, lymphotoxins), which regulate the development of reactions to intracellular pathogens (delayed-type hypersensitivity (DTH) and various types of cellular cytotoxicity).
IL-4 ensures the differentiation of Th0 into Th2. Activated Th2 produce cytokines (IL-4, IL-5, IL-6, IL-13, etc.), which determine the proliferation of B-lymphocytes, their further differentiation into plasma cells and the development of antibody responses, mainly to extracellular pathogens.
IFNg negatively regulates the function of Th2 cells and, conversely, IL-4, IL-10, secreted by Th2, inhibit the function of Th1. The molecular mechanism of this regulation is associated with transcription factors. The expression of T-bet and STAT4, determined by IFNy, directs T-cell differentiation along the Th1 pathway and suppresses the development of Th2. IL-4 induces the expression of GATA-3 and STAT6, which, accordingly, ensures the conversion of naive Th0 into Th2 cells.
In recent years, a distinct subpopulation of T helper cells (Th17) producing IL-17 has been described. Members of the IL-17 family can be expressed by activated memory cells (CD4CD45RO), y5T cells, NKT cells, neutrophils, monocytes under the influence of IL-23, IL-6, TGFβ produced by macrophages and dendritic cells. The main differentiation factor in humans is ROR-C, in mice it is ROR-gl. The cardinal role of IL-17 in the development of chronic inflammation and autoimmune pathology has been shown.
In addition, T lymphocytes in the thymus can differentiate into natural regulatory cells (Treg) expressing the CD4+ CD25+ surface markers and the FOXP3 transcription factor. These cells are able to suppress the immune response mediated by Th1 and Th2 cells through direct intercellular contact and synthesis of TGFβ and IL-10.
T-cytotoxic cells (CD8+), natural killers - weak producers of cytokines, such as interferons, TNF-a and lymphotoxins.
Excessive activation of one of the Th subpopulations can determine the development of one of the variants of the immune response. Chronic imbalance of Th activation can lead to the formation of immunopathological conditions associated with manifestations of allergies, autoimmune pathology, chronic inflammatory processes, etc.
II. In the innate immune system, the main producers of cytokines are myeloid cells. Using Toll-like receptors (TLRs), they recognize similar molecular structures of various pathogens, the so-called pathogen-associated molecular patterns (PAMPs), e.g. CpG repeats, etc. As a result of this interaction with TLR, an intracellular signal transduction cascade is launched, leading to the expression of genes of two main groups of cytokines: pro-inflammatory and IFN type 1. These cytokines are mainly (IL-1, -6, -8, -12 , TNFa, GM-CSF, IFN, chemokines, etc.) induce the development of inflammation and are involved in protecting the body from bacterial and viral infections.
III. Cells that are not part of the immune system (cells of the connective tissue, epithelium, endothelium) constitutively secrete autocrine growth factors (GGF, EGF, TGFr, etc.). and cytokines supporting the proliferation of hematopoietic cells.
Excessive expression of cytokines is unsafe for the body and can lead to the development of an excessive inflammatory reaction, an acute phase response. Various inhibitors are involved in the regulation of the production of pro-inflammatory cytokines. Thus, a number of substances have been described that nonspecifically bind the cytokine IL-1 and prevent the manifestation of its biological action (a2-macroglobulin, C3-component of complement, uromodulin). Specific inhibitors of IL-1 can be soluble decoy receptors, antibodies, and the IL-1 receptor antagonist (IL-1RA). With the development of inflammation, there is an increase in the expression of the IL-1RA gene. But even normally, this antagonist is present in the blood at a high concentration (up to 1 ng / ml or more), blocking the action of endogenous IL-1.
target cells
The action of cytokines on target cells is mediated through specific receptors that bind cytokines with very high affinity, and individual cytokines can use common receptor subunits. Each cytokine binds to its specific receptor.
Cytokine receptors are transmembrane proteins and are divided into 5 main types. The most common is the so-called hematopoietic type of receptors, which have two extracellular domains, one of which contains a common sequence of amino acid residues of two tryptophan and serine repeats separated by any amino acid (WSXWS motif). The second type of receptor may have two extracellular domains with a large number of conserved cysteines. These are IL-10 and IFN family receptors. The third type is represented by cytokine receptors belonging to the TNF group. The fourth type of cytokine receptor belongs to the superfamily of immunoglobulin receptors, which have extracellular domains similar in structure to those of immunoglobulin molecules. The fifth type of receptors that bind molecules of the chemokine family is represented by transmembrane proteins that cross the cell membrane in 7 places. Cytokine receptors can exist in a soluble form, retaining the ability to bind ligands.
Cytokines are able to influence the proliferation, differentiation, functional activity, and apoptosis of target cells. The manifestation of the biological activity of cytokines in target cells depends on the participation of various intracellular systems in signal transmission from the receptor, which is associated with the characteristics of the target cells. The signal for apoptosis is carried out, among other things, with the help of a specific region of the TNF receptor family, the so-called “death” domain. Differential and activating signals are transmitted via intracellular Jak-STAT proteins, signal transducers and transcription activators. G-proteins are involved in signal transduction from chemokines, which leads to increased cell migration and adhesion.
The last component, cytokines and their antagonists, have been described above.
METHODS FOR THE DETERMINATION OF CYTOKINES
S.V. Sennikov, A.N. Silkov
The review is devoted to the main methods for studying cytokines currently used. The possibilities and purpose of the methods are briefly characterized. The advantages and disadvantages of various approaches to the analysis of cytokine gene expression at the level of nucleic acids and at the level of protein production are presented. (Cytokines and inflammation. 2005. V. 4, No. 1. S. 22-27.)
Keywords: review, cytokines, methods of determination.
Introduction
Cytokines are regulatory proteins that form a universal network of mediators, characteristic of both the immune system and cells of other organs and tissues. Under the control of this class of regulatory proteins, all cellular events occur: proliferation, differentiation, apoptosis, and specialized functional activity of cells. The effects of each cytokine on cells are characterized by pleiotropy, the spectrum of effects of different mediators overlaps, and, in general, the final functional state of the cell depends on the influence of several cytokines acting synergistically. Thus, the cytokine system is a universal, polymorphic regulatory network of mediators designed to control the processes of proliferation, differentiation, apoptosis, and the functional activity of cellular elements in the hematopoietic, immune, and other homeostatic systems of the body.
Little time has passed since the description of the first cytokines. However, their study led to the allocation of an extensive section of knowledge - cytokinology, which is an integral part of various fields of knowledge and, first of all, immunology, which gave a powerful impetus to the study of these mediators. Cytokinology permeates all clinical disciplines, ranging from the etiology and pathogenesis of diseases to the prevention and treatment of various pathological conditions. Therefore, researchers and clinicians need to navigate the diversity of regulatory molecules and have a clear understanding of the role of each of the cytokines in the processes under study.
Methods for the determination of cytokines over 20 years of their intensive study have undergone a very rapid evolution and today represent a whole area of scientific knowledge. At the beginning of the work, researchers in cytokinology are faced with the question of choosing a method. And here the researcher must know exactly what information he needs to obtain in order to achieve his goal. Currently, hundreds of different methods for assessing the cytokine system have been developed, which provide diverse information about this system. Cytokines can be assessed in various biological media by their specific biological activity. They can be quantified using a variety of immunoassay methods using poly- and monoclonal antibodies. In addition to studying the secretory forms of cytokines, one can study their intracellular content and production in tissues by flow cytometry, Western blotting, and in situ immunohistochemistry. Very important information can be obtained by studying cytokine mRNA expression, mRNA stability, the presence of cytokine mRNA isoforms, and natural antisense nucleotide sequences. The study of allelic variants of cytokine genes can provide important information about the genetically programmed high or low production of a particular mediator. Each method has its own advantages and disadvantages, its own resolution and accuracy of determination. Ignorance and misunderstanding of these nuances by the researcher can lead him to false conclusions.
Determination of the biological activity of cytokines
The history of the discovery and the first steps in the study of cytokines was closely associated with the cultivation of immunocompetent cells and cell lines. Then the regulatory effects (biological activity) of a number of soluble protein factors on the proliferative activity of lymphocytes, on the synthesis of immunoglobulins, and on the development of immune responses in in vitro models were shown. One of the first methods for determining the biological activity of mediators is the determination of the human lymphocyte migration factor and its inhibition factor. As the biological effects of cytokines were studied, various methods for assessing their biological activity also appeared. So, IL-1 was determined by assessing the proliferation of mouse thymocytes in vitro, IL-2 - by the ability to stimulate the proliferative activity of lymphoblasts, IL-3 - by the growth of hematopoietic colonies in vitro, IL-4 - by the comitogenic effect, by increasing the expression of Ia proteins , by inducing the formation of IgG1 and IgE, etc. . The list of these methods can be continued, it is constantly updated as new biological activities of soluble factors are discovered. Their main drawback is the non-standard methods, the impossibility of their unification. Further development of methods for determining the biological activity of cytokines led to the creation of a large number of cell lines sensitive to one or another cytokine, or multisensitive lines. Most of these cytokine-responsive cells can now be found on lists of commercially distributed cell lines. For example, for testing IL-1a and b, the D10S cell line is used, for IL-2 and IL-15, the CTLL-2 cell line is used, for IL-3, IL-4, IL-5, IL-9, IL-13, GM-CSF - cell line TF-1, for IL-6 - cell line B9, for IL-7 - cell line 2E8, for TNFa and TNFb - cell line L929, for IFNg - cell line WiDr, for IL-18 - cell line line KG-1.
However, such an approach to the study of immunoactive proteins, along with well-known advantages, such as measuring the real biological activity of mature and active proteins, high reproducibility under standardized conditions, has its drawbacks. These include, first of all, the sensitivity of cell lines not to one cytokine, but to several related cytokines, the biological effects of which overlap. In addition, the possibility of inducing the production of other cytokines by target cells, which can distort the test parameter (as a rule, these are proliferation, cytotoxicity, chemotaxis), cannot be ruled out. We do not yet know all the cytokines and not all of their effects, so we evaluate not the cytokine itself, but the total specific biological activity. Thus, the assessment of biological activity as the total activity of different mediators (insufficient specificity) is one of the disadvantages of this method. In addition, using cytokine-sensitive lines, it is not possible to detect non-activated molecules and bound proteins. This means that such methods do not reflect the real production for a number of cytokines. Another important disadvantage of using cell lines is the need for a cell culture laboratory. In addition, all procedures for growing cells and incubating them with the studied proteins and media require a lot of time. It should also be noted that long-term use of cell lines requires renewal or re-certification, since as a result of cultivation they can mutate and be modified, which can lead to a change in their sensitivity to mediators and a decrease in the accuracy of determining biological activity. However, this method is ideal for testing the specific biological activity of recombinant mediators.
Quantification of cytokines using antibodies
Cytokines produced by immunocompetent and other cell types are released into the intercellular space for paracrine and autocrine signaling interactions. By the concentration of these proteins in the blood serum or in a conditioned environment, one can judge the nature of the pathological process and the excess or deficiency of certain cell functions in a patient.
Methods for determining cytokines using specific antibodies are currently the most common detection systems for these proteins. These methods went through a whole series of modifications using different labels (radioisotope, fluorescent, electrochemiluminescent, enzymatic, etc.). If radioisotope methods have a number of disadvantages associated with the use of a radioactive label and the limited time of using labeled reagents (half-life), then enzyme immunoassay methods are the most widely used. They are based on the visualization of insoluble products of an enzymatic reaction that absorb light of a known wavelength in quantities equivalent to the concentration of the analyte. Antibodies coated on a solid polymer base are used to bind the substances to be measured, and for imaging, antibodies conjugated to enzymes, typically alkaline phosphatase or horseradish peroxidase.
The advantages of the method are obvious: it is a high accuracy of determination under standardized conditions for storing reagents and performing procedures, quantitative analysis, and reproducibility. The disadvantages include the limited range of determined concentrations, as a result of which all concentrations exceeding a certain threshold are considered equal to it. It should be noted that the time required to complete the method varies depending on the manufacturer's recommendations. However, in any case, we are talking about several hours required for incubation and washing of reagents. In addition, latent and bound forms of cytokines are determined, which in their concentration can significantly exceed free forms, mainly responsible for the biological activity of the mediator. Therefore, it is desirable to use this method together with methods for assessing the biological activity of the mediator.
Another modification of the immunoassay method, which has found wide application, is the electrochemiluminescent method (ECL) for the determination of proteins with antibodies labeled with ruthenium and biotin. This method has the following advantages compared to radioisotope and enzyme immunoassays: ease of implementation, short execution time of the technique, no washing procedures, small sample volume, large range of determined cytokine concentrations in serum and in a conditioned medium, high sensitivity of the method and its reproducibility. The considered method is acceptable for use both in scientific research and in clinical.
The following method for evaluating cytokines in biological media is based on flow fluorometry technology. It allows you to simultaneously evaluate up to a hundred proteins in a sample. Currently, commercial kits have been created for the determination of up to 17 cytokines. However, the advantages of this method also determine its disadvantages. Firstly, this is the laboriousness of selecting optimal conditions for the determination of several proteins, and secondly, the production of cytokines is cascaded with production peaks at different times. Therefore, the determination of a large number of proteins at the same time is not always informative.
The general requirement of immunoassay methods using the so-called. "sandwich", is a careful selection of a pair of antibodies, which allows you to determine either the free or bound form of the analyzed protein, which imposes limitations on this method, and which must always be taken into account when interpreting the obtained data. These methods determine the total production of cytokines by different cells, while at the same time, antigen-specific production of cytokines by immunocompetent cells can only be judged tentatively.
Currently, the ELISpot (Enzyme-Liked ImmunoSpot) system has been developed, which largely eliminates these shortcomings. The method allows semi-quantitative assessment of cytokine production at the level of individual cells. The high resolution of this method makes it possible to evaluate antigen-stimulated cytokine production, which is very important for assessing a specific immune response.
The next, widely used for scientific purposes, method is the intracellular determination of cytokines by flow cytometry. Its advantages are obvious. We can phenotypically characterize a population of cytokine-producing cells and/or determine the spectrum of cytokines produced by individual cells, and it is possible to characterize this production relatively. However, the described method is rather complicated and requires expensive equipment.
The next series of methods, which are used mainly for scientific purposes, are immunohistochemical methods using labeled monoclonal antibodies. The advantages are obvious - determining the production of cytokines directly in tissues (in situ), where various immunological reactions occur. However, the methods under consideration are very laborious and do not provide accurate quantitative data.
A. Interferons (IFN):
1. Natural IFN (1 generation):
2. Recombinant IFN (2nd generation):
a) short action:
IFN a2b: intron-A
IFN β: Avonex and others.
(pegylated IFN): peginterferon
B. Interferon inducers (interferonogens):
1. Synthetic- cycloferon, tiloron, dibazol and etc.
2. Natural- ridostin, etc.
V. Interleukins : recombinant interleukin-2 (roncoleukin, aldesleukin, proleukin, ) , recombinant interleukin 1-beta (betaleukin).
G. colony stimulating factors (molgramming, etc.)
Peptide preparations
Thymic peptide preparations .
Peptide compounds produced by the thymus gland stimulate the maturation of T-lymphocytes(thymopoietins).
With initially low levels, preparations of typical peptides increase the number of T-cells and their functional activity.
The founder of thymic preparations of the first generation in Russia was Taktivin, which is a complex of peptides extracted from the thymus of cattle. Thymic peptide complex preparations also include Timalin, Timoptin and others, and to those containing thymus extracts - Timimulin and Vilozen.
Preparations of peptides from bovine thymus thymalin, thystimulin administered intramuscularly and taktivin, timoptin- under the skin, mainly in case of insufficiency of cellular immunity:
With T-immunodeficiencies,
viral infections,
For the prevention of infections during radiation therapy and chemotherapy of tumors.
The clinical efficacy of first-generation thymic preparations is not in doubt, but they have one drawback: they are an undivided mixture of biologically active peptides that are rather difficult to standardize.
Progress in the field of drugs of thymic origin went along the line of creating drugs of the II and III generations - synthetic analogues of natural thymus hormones or fragments of these hormones with biological activity.
Modern drug Imunofan - hexapeptide, a synthetic analogue of the active center of thymopoietin, is used for immunodeficiencies, tumors. The drug stimulates the formation of IL-2 by immunocompetent cells, increases the sensitivity of lymphoid cells to this lymphokine, reduces the production of TNF (tumor necrosis factor), has a regulatory effect on the production of immune mediators (inflammation) and immunoglobulins.
Bone marrow peptide preparations
Myelopid obtained from a culture of bone marrow cells of mammals (calves, pigs). The mechanism of action of the drug is associated with stimulation of the proliferation and functional activity of B- and T-cells.
In the body, the target of this drug are B-lymphocytes. In violation of immuno- or hematopoiesis, the introduction of myelopide leads to an increase in the overall mitotic activity of bone marrow cells and the direction of their differentiation towards mature B-lymphocytes.
Myelopid is used in the complex therapy of secondary immunodeficiency states with a predominant lesion of the humoral immunity, for the prevention of infectious complications after surgical interventions, injuries, osteomyelitis, nonspecific pulmonary diseases, chronic pyoderma. Side effects of the drug are dizziness, weakness, nausea, hyperemia and soreness at the injection site.
All drugs in this group are contraindicated in pregnant women, myelopid and imunofan are contraindicated in the presence of Rhesus conflict between mother and fetus.
Immunoglobulin preparations
Human immunoglobulins
a) Immunoglobulins for intramuscular injection
Non-specific: normal human immunoglobulin
Specific: immunoglobulin against human hepatitis B, human antistaphylococcal immunoglobulin, human tetanus immunoglobulin, human immunoglobulin against tick-borne encephalitis, human immunoglobulin against rabies virus, etc.
b) Immunoglobulins for intravenous administration
Non-specific: normal human immunoglobulin for intravenous administration (gabriglobin, immunovenin, intraglobin, humaglobin)
Specific: immunoglobulin against human hepatitis B (neohepatect), pentaglobin (contains antibacterial IgM, IgG, IgA), immunoglobulin against cytomegalovirus (cytotect), human immunoglobulin against tick-borne encephalitis, anti-rabies IG, etc.
c) Immunoglobulins for oral administration: immunoglobulin complex preparation (CIP) for enteral use in acute intestinal infections; anti-rotavirus immunoglobulin for oral administration.
Heterologous immunoglobulins:
anti-rabies immunoglobulin from horse serum, anti-gangrenous polyvalent horse serum, etc.
Preparations of non-specific immunoglobulins are used for primary and secondary immunodeficiencies, preparations of specific immunoglobulins - for relevant infections (for therapeutic or prophylactic purposes).
Cytokines and preparations based on them
The regulation of the developed immune response is carried out by cytokines - complex complex of endogenous immunoregulatory molecules, which are the basis for creating a large group of both natural and recombinant immunomodulatory drugs.
Interferons (IFN):
1. Natural IFN (1 generation):
Alphaferons: human leukocyte IFN, etc.
Betaferons: human fibroblastic IFN, etc.
2. Recombinant IFN (2nd generation):
a) short action:
IFN a2a: reaferon, viferon, etc.
IFN a2b: intron-A
IFN β: Avonex and others.
b) prolonged action(pegylated IFN): peginterferon (IFN a2b + Polyethylene glycol), etc.
The main direction of action of IFN drugs is T-lymphocytes (natural killers and cytotoxic T-lymphocytes).
Natural interferons are obtained in a culture of donor blood leukocyte cells (in a culture of lymphoblastoid and other cells) under the influence of an inducer virus.
Recombinant interferons are produced by a genetic engineering method - by cultivating bacterial strains containing in their genetic apparatus an integrated recombinant human interferon gene plasmid.
Interferons have antiviral, antitumor and immunomodulatory effects.
As antiviral agents, interferon preparations are most effective in the treatment of herpetic eye diseases (locally in the form of drops, subconjunctival), herpes simplex with localization on the skin, mucous membranes and genitals, herpes zoster (locally in the form of a hydrogel-based ointment), acute and chronic viral hepatitis B and C (parenterally, rectally in suppositories), in the treatment and prevention of influenza and SARS (intranasally in the form of drops). In HIV infection, recombinant interferon preparations normalize immunological parameters, reduce the severity of the disease in more than 50% of cases, cause a decrease in the level of viremia and the content of serum markers of the disease. In AIDS, combination therapy with azidothymidine is carried out.
The antitumor effect of interferon preparations is associated with an antiproliferative effect and stimulation of the activity of natural killers. IFN-alpha, IFN-alpha 2a, IFN-alpha-2b, IFN-alpha-n1, IFN-beta are used as antitumor agents.
IFN-beta-lb is used as an immunomodulator in multiple sclerosis.
Interferon preparations cause similar side effects. Characteristic - influenza-like syndrome; changes from the side of the central nervous system: dizziness, blurred vision, confusion, depression, insomnia, paresthesia, tremor. From the gastrointestinal tract: loss of appetite, nausea; on the part of the cardiovascular system, symptoms of heart failure are possible; from the urinary system - proteinuria; from the hemopoietic system - transient leukopenia. Rash, itching, alopecia, temporary impotence, nosebleeds may also occur.
Interferon inducers (interferonogens):
1. Synthetic - cycloferon, tiloron, poludan, etc.
2. Natural - ridostin, etc.
Interferon inductors are drugs that enhance the synthesis of endogenous interferon. These drugs have a number of advantages over recombinant interferons. They do not have antigenic activity. Stimulated synthesis of endogenous interferon does not cause hyperinterferonemia.
Tiloron(amiksin) refers to low molecular weight synthetic compounds, is an oral interferon inducer. It has a wide spectrum of antiviral activity against DNA and RNA viruses. As an antiviral and immunomodulatory agent, it is used for the prevention and treatment of influenza, SARS, hepatitis A, for the treatment of viral hepatitis, herpes simplex (including urogenital) and herpes zoster, in the complex therapy of chlamydial infections, neuroviral and infectious-allergic diseases, with secondary immunodeficiencies. The drug is well tolerated. Possible dyspepsia, short-term chills, increased overall tone, which does not require discontinuation of the drug.
Poludan is a biosynthetic polyribonucleotide complex of polyadenylic and polyuridylic acids (in equimolar ratios). The drug has a pronounced inhibitory effect on herpes simplex viruses. It is used in the form of eye drops and injections under the conjunctiva. The drug is prescribed for adults for the treatment of viral eye diseases: herpetic and adenovirus conjunctivitis, keratoconjunctivitis, keratitis and keratoiridocyclitis (keratouveitis), iridocyclitis, chorioretinitis, optic neuritis.
Side effects occur rarely and are manifested by the development of allergic reactions: itching and sensation of a foreign body in the eye.
Cycloferon- low molecular weight interferon inducer. It has antiviral, immunomodulatory and anti-inflammatory effects. Cycloferon is effective against tick-borne encephalitis, herpes, cytomegalovirus, HIV, etc. viruses. It has an antichlamydial effect. Effective in systemic connective tissue diseases. The radioprotective and anti-inflammatory effect of the drug was established.
Arbidol is prescribed orally for the prevention and treatment of influenza and other acute respiratory viral infections, as well as for herpetic diseases.
Interleukins:
recombinant IL-2 (aldesleukin, proleukin, roncoleukin ) , recombinant IL-1beta ( betaleykin).
Cytokine preparations of natural origin, containing a sufficiently large set of cytokines of inflammation and the first phase of the immune response, are characterized by a multifaceted effect on the human body. These drugs act on cells involved in inflammation, regeneration processes, and the immune response.
Aldesleukin- recombinant analogue of IL-2. It has an immunomodulatory and antitumor effect. Activates cellular immunity. Enhances the proliferation of T-lymphocytes and IL-2-dependent cell populations. Increases the cytotoxicity of lymphocytes and killer cells that recognize and destroy tumor cells. Enhances the production of interferon gamma, TNF, IL-1. Used for kidney cancer.
Betaleukin- recombinant human IL-1 beta. Stimulates leukopoiesis and immune defense. It is administered under the skin or intravenously in purulent processes with immunodeficiency, with leukopenia as a result of chemotherapy, with tumors.
Roncoleukin- a recombinant preparation of interleukin-2 - is administered intravenously for sepsis with immunodeficiency, as well as for kidney cancer.
Colony stimulating factors:
Molgramostim(Leikomax) is a recombinant preparation of human granulocyte-macrophage colony-stimulating factor. Stimulates leukopoiesis, has immunotropic activity. It enhances the proliferation and differentiation of precursors, increases the content of mature cells in the peripheral blood, the growth of granulocytes, monocytes, macrophages. Increases the functional activity of mature neutrophils, enhances phagocytosis and oxidative metabolism, providing mechanisms for phagocytosis, increases cytotoxicity against malignant cells.
Filgrastim(Neupogen) is a recombinant preparation of human granulocyte colony stimulating factor. Filgrastim regulates the production of neutrophils and their entry into the blood from the bone marrow.
Lenograstim- recombinant preparation of human granulocyte colony stimulating factor. It is a highly purified protein. It is an immunomodulator and a leukopoiesis stimulator.
Synthetic immunostimulants: levamisole, polyoxidonium isoprinosine, galavit.
Levamisole(decaris), an imidazole derivative, is used as an immunostimulant, as well as an antihelminthic agent for ascariasis. The immunostimulating properties of levamisole are associated with an increase in the activity of macrophages and T-lymphocytes.
Levamisole is prescribed orally for recurrent herpetic infections, chronic viral hepatitis, autoimmune diseases (rheumatoid arthritis, systemic lupus erythematosus, Crohn's disease). The drug is also used for tumors of the large intestine after surgical, radiation or drug therapy of tumors.
Isoprinosine- a drug containing inosine. Stimulates the activity of macrophages, the production of interleukins, the proliferation of T-lymphocytes.
Assign inside for viral infections, chronic infections of the respiratory and urinary tract, immunodeficiencies.
Polyoxidonium- synthetic water-soluble polymer compound. The drug has an immunostimulating and detoxifying effect, increases the body's immune resistance against local and generalized infections. Polyoxidonium activates all factors of natural resistance: cells of the monocyte-macrophage system, neutrophils and natural killers, increasing their functional activity at initially reduced levels.
Galavit is a derivative of phthalhydrazide. The peculiarity of this drug is the presence of not only immunomodulatory, but also pronounced anti-inflammatory properties.
Drugs of other pharmacological classes with immunostimulating activity
1. Adaptogens and herbal preparations (phytopreparations): preparations of echinacea (immunal), eleutherococcus, ginseng, rhodiola rosea, etc.
2. Vitamins: ascorbic acid (vitamin C), tocopherol acetate (vitamin E), retinol acetate (vitamin A) (see section "Vitamins").
Echinacea preparations have immunostimulatory and anti-inflammatory properties. When taken orally, these drugs increase the phagocytic activity of macrophages and neutrophils, stimulate the production of interleukin-1, the activity of T-helpers, and the differentiation of B-lymphocytes.
Echinacea preparations are used for immunodeficiencies and chronic inflammatory diseases. In particular, immunal administered orally in drops for the prevention and treatment of acute respiratory infections, as well as together with antibacterial agents for infections of the skin, respiratory and urinary tract.
General principles for the use of immunostimulants in patients with secondary immunodeficiencies
The most reasonable use of immunostimulants seems to be in immunodeficiencies, manifested by increased infectious morbidity. The main target of immunostimulating drugs is secondary immunodeficiencies, which are manifested by frequent recurrent, difficult-to-treat infectious and inflammatory diseases of all localizations and any etiology. At the heart of each chronic infectious and inflammatory process are changes in the immune system, which are one of the reasons for the persistence of this process.
Immunomodulators are prescribed in complex therapy simultaneously with antibiotics, antifungal, antiprotozoal or antiviral agents.
· When carrying out immunorehabilitation measures, in particular in case of incomplete recovery after an acute infectious disease, immunomodulators can be used as monotherapy.
· It is advisable to use immunomodulators against the background of immunological monitoring, which should be carried out regardless of the presence or absence of initial changes in the immune system.
Immunomodulators acting on the phagocytic link of immunity can be prescribed to patients with both identified and undiagnosed immune status disorders, i.e. the basis for their use is the clinical picture.
A decrease in any parameter of immunity, revealed during an immunodiagnostic study in a practically healthy person, not necessarily is the basis for the appointment of immunomodulatory therapy.
Control questions:
1. What are immunostimulants, what are the indications for immunotherapy, what types of immunodeficiency states are divided into?
2. Classification of immunomodulators according to the preferential selectivity of action?
3. Immunostimulants of microbial origin and their synthetic analogues, their pharmacological properties, indications for use, contraindications, side effects?
4. Endogenous immunostimulants and their synthetic analogues, their pharmacological properties, indications for use, contraindications, side effects?
5. Preparations of thymic peptides and bone marrow peptides, their pharmacological properties, indications for use, contraindications, side effects?
6. Immunoglobulin preparations and interferons (IFN), their pharmacological properties, indications for use, contraindications, side effects?
7. Preparations of interferon inducers (interferonogens), their pharmacological properties, indications for use, contraindications, side effects?
8. Preparations of interleukins and colony-stimulating factors, their pharmacological properties, indications for use, contraindications, side effects?
9. Synthetic immunostimulants, their pharmacological properties, indications for use, contraindications, side effects?
10. Drugs of other pharmacological classes with immunostimulatory activity and general principles for the use of immunostimulants in patients with secondary immunodeficiencies?
3. Cytokines: general properties, classification. Interleukins.
Cytokines are peptide mediators secreted by activated cells that regulate interactions, activate all links of the SI itself and affect various organs and tissues. General properties cytokines: 1. They are glycoproteins. 2. They affect the cell itself and its immediate environment. These are short-distance molecules.3. They work in low concentrations. 4. Cytokines have specific receptors corresponding to them on the cell surface. 5. The mechanism of action of cytokines is to transmit a signal after interacting with the receptor from the cell membrane to its genetic apparatus. In this case, the expression of cellular proteins changes with a change in the function of the cell (for example, other cytokines are released). Cytokines are divided into several main groups .one. Interleukins (IL)2. Interferons 3. Group of tumor necrosis factors (TNF) 4. Group of colony-stimulating factors (for example, granulocyte-macrophage colony-stimulating factor - GM-CSF) 5. Group of growth factors (endothelial growth factor, nerve growth factor, etc.) 6. Chemokines . Cytokines, secreted mainly by cells of the immune system, are called interleukins (IL) - factors of interleukocyte interaction. They are numbered in order (IL-1 - IL-31). They are secreted by leukocytes when stimulated by microbial products and other antigens. IL-1 is secreted by macrophages and dendritic cells, causes an increase in temperature, stimulates and activates stem cells, T-lymphocytes, neutrophils, and is involved in the development of inflammation. It exists in two forms - IL-1a and IL-1b. IL-2 is secreted by T-helpers (mainly type 1, Tx1) and stimulates the proliferation and differentiation of T- and B-lymphocytes, NK cells, monocytes. IL-3 is one of the main hematopoietic factors, stimulates the proliferation and differentiation of early precursors of hematopoiesis, macrophages, phagocytosis. IL-4 - growth factor of B-lymphocytes, stimulates their proliferation at an early stage of differentiation; secreted by T-lymphocytes of the 2nd type and basophils. IL-5 stimulates the maturation of eosinophils, basophils and the synthesis of immunoglobulins by B-lymphocytes, is produced by T-lymphocytes under the influence of antigens. IL-6 is a multi-action cytokine secreted by T-lymphocytes, macrophages and many cells outside the immune system, stimulates the maturation of B-lymphocytes into plasma cells, T-cell development and hematopoiesis, and activates inflammation. IL-7 is a lymphopoietic factor that activates the proliferation of lymphocyte precursors, stimulates the differentiation of T cells, is formed by stromal cells, as well as keratocytes, hepatocytes and other kidney cells. IL-8 is a regulator of neutrophil and T cell chemotaxis (chemokine); secreted by T-cells, monocytes, endothelium. It activates neutrophils, causes their directed migration, adhesion, release of enzymes and reactive oxygen species, stimulates T-lymphocyte chemotaxis, basophil degranulation, macrophage adhesion, angiogenesis. IL-10 - secreted by T-lymphocytes (helper type 2 Tx2 and regulatory T-helpers - Tr). Suppresses the release of pro-inflammatory cytokines (IL-1, IL-2, TNF, etc.) IL-11 - produced by stromal cells of the bone marrow, hematopoietic factor, acts similar to IL-3. IL-12 - source - monocytes-macrophages, dendritic cells causes the proliferation of activated T-lymphocytes and natural killers, enhances the action of IL-2. IL-13 - secreted by T-lymphocytes, activates B-cell differentiation. IL-18 - produced by monocytes and macrophages, dendritic cells, stimulates type 1 T-helpers and their production of interferon gamma, inhibits IgE synthesis.
Cytokines are a special type of protein that can be generated in the body by immune cells and cells from other organs. The main number of these cells can be generated by leukocytes.
With the help of cytokines, the body can transmit different information between its cells. Such a substance enters the cell surface and can contact other receptors, transmitting a signal.
These elements are formed and allocated quickly. Different fabrics can participate in their creation. Also, cytokines can have a certain effect on other cells. They can both enhance each other's action and reduce it.
Such a substance can manifest its activity even when its concentration in the body is small. Also, a cytokine can affect the formation of various pathologies in the body. With the help of them, doctors conduct various methods of examining a patient, in particular, in oncology and in infectious diseases.
Cytokine makes it possible to accurately diagnose cancer, and therefore is often used in oncology to make a residual diagnosis. Such a substance can independently develop and multiply in the body, while not affecting its work. With the help of these elements, any examination of the patient, including in oncology, is facilitated.
They play an important role in the body and have many functions. In general, the work of cytokines is to transmit information from cell to cell and ensure their smooth work. So, for example, they can:
- Regulate immune responses.
- Take part in autoimmune reactions.
- Regulate inflammation processes.
- Take part in allergic processes.
- Determine the lifespan of cells.
- Participate in the bloodstream.
- Coordinate the reactions of body systems when exposed to stimuli.
- Provide a level of toxic effects on the cell.
- Maintain homeostasis.
Doctors have found that cytokines are able to take part not only in the immune process. They are also involved in:
- The normal course of various functions.
- The process of fertilization.
- humoral immunity.
- recovery processes.
Classification of cytokines
Today, scientists know more than two hundred types of these elements. But new species are constantly being discovered. Therefore, in order to improve the process of understanding this system, doctors came up with a classification for them. This:
- Regulating inflammatory processes.
- Immunity-regulating cells.
- Regulating humoral immunity.
Also, cytokines classification predetermines the presence of certain subspecies in each class. For a more accurate acquaintance with them, you need to view the information on the network.
Inflammation and cytokines
When inflammation begins in the body, cytokines begin to be produced by it. They can affect nearby cells and transmit information between them. Also among the cytokines you can find those that prevent the development of inflammation. They can cause effects that are similar to the manifestation of chronic pathologies.
Pro-inflammatory cytokines
Lymphocytes and tissues can produce such bodies. Cytokines themselves and certain pathogens of infectious diseases can stimulate the production. With a large release of such bodies, local inflammation occurs. With the help of certain receptors, other cells can also be involved in the inflammatory process. All of them also begin to produce cytokines.
The main inflammatory cytokines are TNF-alpha and IL-1. They can stick to the walls of blood vessels, penetrate into the blood and then spread with it throughout the body. Such elements can synthesize cells that are produced by lymphocytes and affect inflammation, providing protection.
Also, TNF-alpha and IL-1 can stimulate the work of various systems and cause about 40 active other processes in the body. In this case, the effect of cytokines can be on all types of tissues and organs.
Cytokines anti-inflammatory
Anti-inflammatory can control the above cytokines. They can not only neutralize the effects of the former, but also synthesize proteins.
When an inflammation process occurs, the amount of these cytokines is an important point. The complexity of the course of the pathology, its duration and symptoms largely depend on the balance. It is with the help of anti-inflammatory cytokines that blood clotting improves, enzymes are produced and tissue scarring is formed.
Immunity and cytokines
In the immune system, each cell has its own important role to play. By means of certain reactions, cytokines can control the interaction of cells. They allow them to exchange important information.
The peculiarity of cytokines is that they have the ability to transmit complex signals between cells and suppress or activate most of the processes in the body. With the help of cytokines, the immune system interacts with others.
When the connection is broken, the cells die. This is how complex pathologies manifest themselves in the body. The outcome of the disease largely depends on whether cytokines in the process can establish a connection between cells and prevent the pathogen from entering the body.
When the protective reaction of the body was not enough to resist the pathology, then cytokines begin to activate other organs and systems that help the body fight infection.
When cytokines exert their influence on the central nervous system, all human reactions change, hormones and proteins are synthesized. But such changes are not always random. They are either required for protection, or switch the body to fight pathology.
Analyzes
Determining cytokines in the body requires complex testing at the molecular level. With the help of such a test, a specialist can identify polymorphic genes, predict the occurrence and course of a particular disease, develop a scheme for preventing diseases, and so on. All this is done purely on an individual basis.
A polymorphic gene can only be found in 10% of the world's population. In such people, one can note an increased activity of immunity during operations or infectious diseases, as well as other effects on tissues.
When testing in such individuals, kipper cells are often detected in the body. Which can cause suppuration after the above procedures or septic disorders. Also, increased activity of immunity in certain cases in life can interfere with a person.
There is no need to prepare specifically for the test. For analysis, you will need to take part of the mucosa from the mouth.
Pregnancy
Studies have shown that pregnant women today may have an increased tendency for the body to form blood clots. This can cause an abortion or infection of the fetus with an infection.
When a gene begins to mutate in the mother's body during gestation, this causes the death of the child in 100% of cases. In this case, to prevent the manifestation of this pathology, it will be necessary to pre-examine the father.
It is these tests that help predict the course of pregnancy and take measures if there are any possible manifestations of certain pathologies. If the risk of pathology is high, then the conception process may be postponed to another period, during which the father or mother of the unborn child must undergo complex treatment.
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