, natural killer cells, antigen-specific cytotoxic T lymphocytes, and cytokines are released in response to antigen.
The immune system is historically divided into two parts - the humoral immunity system and the cellular immunity system. In the case of humoral immunity, protective functions are performed by molecules found in the blood plasma, but not by cellular elements. While in the case of cellular immunity, the protective function is associated specifically with the cells of the immune system. Lymphocytes of the CD4 differentiation cluster or T helper cells provide protection against various pathogens.
The cellular immune system performs protective functions in the following ways:
Cellular immunity is directed primarily against microorganisms that survive in phagocytes and against microorganisms that infect other cells. The cellular immune system is particularly effective against cells infected with viruses and is involved in protection against fungi, protozoa, intracellular bacteria and against tumor cells. The cellular immune system also plays an important role in tissue rejection.
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Types of immune responses: innate and adaptive. Comparison of humoral and cellular immunity
Cellular immunity
Cellular immunity
Subtitles
In the last video we discussed the immune system. In this video we will talk about the nonspecific or innate immune system. Let me write it down. Nonspecific immune system. And in connection with it, the so-called first-line barriers are identified. These include structures such as skin, gastric juice, acidity of skin fats. All of them are natural barriers that prevent penetration into the body. This is the first line of defense. Then comes the second line of defense, which is also non-specific. That is, the cells do not recognize what type of virus, protein or bacteria has attacked the body. They perceive him as a suspicious object. And they decide to capture or kill. An inflammatory reaction begins. An inflammatory response occurs, which I will make a separate video about after we discuss the entire immune system. The inflammatory response stimulates the movement of cells towards the infected area. We also have phagocytes. Phagocytes are the very cells that engulf suspicious objects. We already said in the last video that all phagocytes belong to white blood cells, or leukocytes. All of them belong to white blood cells. All. Phagocytes, as well as dendritic cells, macrophages and neutrophils, are all leukocytes. All of them. There are other types of leukocytes. A synonym for white blood cells is leukocytes. Leukocytes. They are non-specific. They do not allow suspicious bodies inside, and if these bodies do get inside, they capture them. They have receptors. If an organism with a double helix of DNA inside gets inside, they recognize it as a virus and destroy it. Regardless of what type of virus it is, and whether they have encountered it before or not. That's why they are non-specific. The nonspecific system exists in many species and types of organisms. And now an interesting fact about our immune system. The specific system is believed to be a newer form of adaptation. Let's talk about the specific human immune system. Let's consider another classification. Let me present it like this. Specific immune system. So, we humans have a specific immune system - or an adaptive immune system. You've probably already heard about it. We have resistance to certain bacteria and viruses. And therefore the system is adaptive. It adapts to certain organisms. We have already touched on the specific immune system when we talked about antigen-presenting molecules that are created by phagocytes; they play a major role here. Let's look at this in more detail, and I will try not to confuse you. Lymphocytes come into action, do not confuse them with leukocytes - since they also belong to leukocytes. I'll write it down. Lymphocytes play a key role in providing specific immunity. Providing specific immunity. Phagocytes are mostly nonspecific, but both of these subtypes are classified as white blood cells. Lymphocytes are another type of white blood cell or leukocyte. I need you to understand the terminology. White blood cells refer to a group of blood cells. Blood is made up of several components: red blood cells, which sort of settle at the bottom, then a white foamy substance in the middle, which consists of white blood cells, and the top layer will be the blood plasma, or the liquid part of it. All components perform different functions, although they interact with each other. That's where the name comes from. Lymphocytes can be divided into B lymphocytes, generally called B cells, and T lymphocytes. I’ll write down: B- and T-lymphocytes. B and T lymphocytes. The letters B and T come from the location of the cells. B lymphocytes were first isolated from the bursa of Fabricius. Therefore B. This is an organ in birds that is involved in the immune system. The letter B comes from "bursa", but can also be associated with the human system, since these cells are produced in the bone marrow. It might be easier to remember that way. So they are produced in the bone marrow. They develop in the bone marrow, but historically the B came from the Bursa of Fabricius. It's easier to remember that way. B also stands for bone marrow, I repeat, from the English bone marrow, because these cells are formed there. T lymphocytes usually originate in the bone marrow and develop and mature in the thymus. Hence the letter T. In this video, we will only look at B-lymphocytes, so as not to drag on too much. B-lymphocytes are important - I don’t want to say that other cells are unimportant in our body. However, B lymphocytes participate in the so-called humoral immune response. Humoral immune response. What does humoral mean? Now I will explain to you. Let me just write it down. Humoral immune response. T cells are involved in the cellular response, but we'll talk more about that in other videos. Cellular response. There are several classes of T lymphocytes. There are T helper cells as well as cytotoxic T cells. I understand that this is difficult at first glance, so we will concentrate on this part first. We will then see that T helper cells play a role in enhancing the humoral immune response. What's the easiest way to differentiate between humoral and cellular immune responses? what happens when you become infected with an infection, that is, a virus? Let's say this is a cell of the body. Here's another one. When the virus enters the body, it simply circulates in its fluids. The humoral immune response is carried out in body fluids; this is the humoral environment of the body. And then suddenly viruses appeared. I'll take a different color. Little viruses circulate everywhere. Since they circulate in the fluid and do not sit inside cells, the humoral response is activated. Activation of humoral response. Likewise, if bacteria are circulating in fluids and have not yet had time to invade the body's cells, if they are circulating in body fluids, a humoral immune response is also suitable to combat them. But if they do get inside the cells, and now the cells are infected with viruses, and begin to reproduce them using cellular mechanisms, then more advanced weapons will be needed to combat the bacteria or viruses, since they are no longer circulating in the liquid. This cell may have to be killed, even if it is our own, but now it reproduces viruses. Or perhaps it is colonized by bacteria. In any case, you need to get rid of it. We'll talk more about how cellular immunity works. Subtitles by the Amara.org community
Lecture 8
Cellular immunity is cell-mediated immunity.
Cellular immunity is the body's main way of protecting itself from:
1) intracellular bacteria, viruses, fungi;
2) foreign cells and tissues altered by their own cells.
Cellular immunity is the basis of transplantation and antitumor immunity. Cellular immune reactions underlie type IV allergies and a number of autoimmune diseases.
Cellular immunity can be transferred to another organism using sensitized lymphocytes.
The main effectors of cellular immunity are T-cytotoxic lymphocytes. In addition to cytotoxic T-lymphocytes, NK cells and macrophages (K-cells) take part in the development and implementation of the cellular form of the body’s defense.
The protective effect of cellular immune reactions is manifested:
– in the cytotoxic effect of immunocompetent cells on target cells (in the killing of cells infected with a virus, foreign, tumor cells or transplant rejection);
– in intracellular digestion of bacteria (intracellular killing).
1. T-killers, NK cells, macrophages (K-cells) take part in the cytotoxic destruction of target cells (cells infected with a virus, tumor and allogeneic cells), which use the following mechanisms (Fig. 12-1.).
Rice. 12-1. Mechanisms of cytotoxic destruction of target cells in cellular immune reactions.
T lymphocytes (CD8 + cells) and NK cells (CD16 + cells) cause cytolysis of target cells through the production of perforins and fragmentins. The mechanism of cytolysis is shown in Fig. 12-5, 12-6.
Their recognition of target cells and foreign antigens is not associated with the presentation of antigenic peptides by MHC molecules. Unlike cytotoxic T lymphocytes, the development of cytotoxicity among NK cells does not require their proliferation and differentiation. NK cell activity does not increase during the secondary immune response; Among the NK cells, “immune memory” cells are not formed. The cytotoxic activity of NK cells is enhanced under the influence of IL-2, IFNa, IFNb, IL-12, IL-15. NK cells are able, without prior sensitization, to cause lysis of target cells at the first meeting (have a direct cytotoxic effect). The mechanism of the cytotoxic effect of NK cells on target cells is similar to that used by killer T cells. They, like T lymphocytes, produce perforins, fragmentins and carry membrane-bound Fas ligands.
Rice. 12-5. Exocytosis of perforins by killer T cells and formation of a pore in the target cell membrane.
R and s 12-6. Pathways for inducing apoptosis of target cells by killer T cells.
Macrophages and K-cells cause cytolysis of target cells through the development of the ADCC reaction. The mechanism of cytotoxic action is shown in Fig. 12-7.
Rice. 12-7. Antibody-dependent cellular cytotoxicity.
2. Cellular immune responses are the body's main way of protecting itself from intracellular bacteria. Digestion of bacteria, for which the main “habitat” is macrophages, occurs as a result of activation of infected cells by factors (secretory IFN-g and membrane TNF-a), which are produced by antigen-stimulated inflammatory T cells. The mechanism of such a process is shown in Figure 12-8.
Rice. 12-8. The mechanism of activation of infected macrophages by T lymphocytes.
As a result of recognition of the immunogenic complex on infected macrophages, CD4 + inflammatory T cells are activated, express TNFa on their surface and increase the production of IFNg. The combined action of these cytokines leads to an oxygen explosion in macrophages and the active accumulation of substances with bactericidal activity in them. In addition, in activated macrophages, the expression of MHC class 2 molecules and the TNFa receptor is enhanced, which ensures additional involvement of naïve inflammatory T cells in the immune process.
Good day, dear readers.
Today I would like to raise a very important topic, which concerns the components of immunity. Cellular and humoral do not allow the development of infectious diseases, and suppress the growth of cancer cells in the human body. Human health depends on how well the protective processes proceed. There are two types: specific and nonspecific. Below you will find a description of the protective forces of the human body, as well as the difference between cellular and humoral immunity.
Basic concepts and definitions
Ilya Ilyich Mechnikov is the scientist who discovered phagocytosis and laid the foundation for the science of immunology. Cellular immunity does not involve humoral mechanisms - antibodies, and is carried out through lymphocytes and phagocytes. Thanks to this protection, tumor cells and infectious agents are destroyed in the human body. The main protagonist of cellular immunity is lymphocytes, the synthesis of which occurs in the bone marrow, after which they migrate to the thymus. It is because of their movement into the thymus that they were called T-lymphocytes. When some threat is detected in the body, these immunocompetent cells quickly leave their habitats (lymphoid organs) and rush to fight the enemy.
There are three types of T-lymphocytes, which play an important role in protecting the human body. The function of destroying antigens is played by T-killers. Helper T cells are the first to know that a foreign protein has entered the body and in response they secrete special enzymes that stimulate the formation and maturation of killer T cells and B cells. The third type of lymphocytes are T-suppressor cells, which, if necessary, suppress the immune response. With a lack of these cells, the risk of autoimmune diseases increases. The body's humoral and cellular defense systems are closely interconnected and do not function separately.
The essence of humoral immunity lies in the synthesis of specific antibodies in response to each antigen that enters the human body. It is a protein compound found in blood and other biological fluids.
Nonspecific humoral factors are:
- interferon (protection of cells from viruses);
- C-reactive protein, which triggers the complement system;
- lysozyme, which destroys the walls of a bacterial or viral cell, dissolving it.
Specific humoral components are represented by specific antibodies, interleukins and other compounds.
Immunity can be divided into innate and acquired. Congenital factors include:
- skin and mucous membranes;
- cellular factors - macrophages, neutrophils, eosinophils, dendritic cells, natural killer cells, basophils;
- humoral factors - interferons, complement system, antimicrobial peptides.
Acquired is formed during vaccination and during the transmission of infectious diseases.
Thus, the mechanisms of nonspecific and specific cellular and humoral immunity are closely related to each other, and the factors of one of them take an active part in the implementation of the other type. For example, leukocytes are involved in both humoral and cellular defense. Violation of one of the links will lead to a systemic failure of the entire protection system.
Assessment of species and their general characteristics
When a microbe enters the human body, it triggers complex immune processes, using specific and nonspecific mechanisms. In order for a disease to develop, the microorganism must pass through a number of barriers - the skin and mucous membranes, subepithelial tissue, regional lymph nodes and the bloodstream. If it does not die when it enters the blood, it will spread throughout the body and enter the internal organs, which will lead to the generalization of the infectious process.
The differences between cellular and humoral immunity are insignificant, since they occur simultaneously. It is believed that the cellular one protects the body from bacteria and viruses, and the humoral one protects the body from fungal flora.
What are there immune response mechanisms you can see in the table.
| Action level | Factors and mechanisms |
| Leather | Mechanical barrier. Peeling of the epithelium. Chemical protection: lactic acid, fatty acids, sweat, cationic peptides. Normal flora |
| Mucous | Mechanical cleansing: sneezing, flushing, peristalsis, mucociliary transport, coughing. Adhesion factors: secretory Ig A, mucin. Epithelial macrophages, migrating neutrophils. |
| Subepithelial tissue | Cells: macrophages, neutrophils, eosinophils, mast cells, lymphocytes, natural killer cells. Mobilization factors: immune response and inflammatory reaction |
| Lymph nodes | Resident factors: dendritic cells of lymph nodes, macrophages, humoral factors. Mobilization factors: immune response and inflammatory response |
| Blood | Cellular factors: macrophages, monocytes, neutrophils, dendritic factors along the blood flow. Humoral factors: lysozyme, complement, cytokines and lipid mediators. Mobilization factors: immune response and inflammatory reaction. |
| Internal organs | Same as subepithelial tissue |
The links of the physiological chains of immunity are shown in the diagram.
Methods for assessing the state of the immune system
To assess a person’s immune status, you will have to undergo a series of tests, and you may even have to do a biopsy and send the result for histology.
Let us briefly describe all the methods:
- general clinical trial;
- state of natural protection;
- humoral (determination of immunoglobulin content);
- cellular (determination of T-lymphocytes);
- additional tests include determination of C-reactive protein, complement components, and rheumatoid factors.
That's all I wanted to tell you about the protection of the human body and its two main components - humoral and cellular immunity. And the comparative characteristics showed that the differences between them are very conditional.
Immune system- a subsystem that exists in most animals and unites organs and tissues in which the formation and interaction of cells occurs, providing protection for the body from foreign substances coming from outside or formed in the body itself, through their recognition and involvement in specific reactions. The immune system is the material basis of the phenomenon.
Purpose
The ultimate goal of the immune system is to destroy (eliminate) a foreign agent, which may be a pathogen, a foreign body, a toxic substance, or a degenerated cell of the body itself. This achieves the so-called biological individuality of the organism. Specific molecules produced by foreign agents are called antigens. In the immune system of developed organisms, there are many ways to detect and remove antigens and their producers. This process is called an immune response. It is worth noting that after the antigen is eliminated, the immune response stops. All forms of immune response can be divided into acquired and innate reactions. The main difference between them is that acquired immunity is highly specific to a specific type of antigen. For example, people who have had chickenpox (measles, diphtheria) often develop lifelong immunity to these diseases.
What is the immune system
The IS is a complex of organs and cells capable of performing immunological functions. First of all, the immune response is carried out by leukocytes. Most of the IS cells come from hematopoietic tissues. In humans and animals, the development of these cells occurs in the bone marrow. They just need special conditions for development inside the thymus (thymus gland). Mature cells settle in lymphoid organs and at the border with the environment, near the skin or on mucous membranes. The body produces many thousands of varieties of immune cells, each of which is responsible for eliminating a specific type of antigen. The presence of a large number of varieties of immune cells is necessary in order to repel attacks by microorganisms that can mutate and change their antigenic composition. A significant portion of these cells complete their life cycle without taking part in the body’s defense. For example, not having encountered suitable antigens.
Blood cells responsible for immunity
Lymphocytes
Lymphocytes are one of the main cells of the immune system from the group of leukocytes. They are responsible for acquired immunity, as they can recognize infectious agents inside or outside cells, in tissues or in the blood. During the development of lymphocytes, receptors for antigens - foreign molecules - appear on their surface. Receptors are like an “imprint” of a foreign molecule. In this case, one cell can contain receptors for only one type of antigen. At the stage of development, lymphocytes undergo selection: only those that are significant from the point of view of protecting the body, as well as those that do not pose a threat to the body’s own tissues, remain. In parallel with this process, lymphocytes are divided into groups capable of performing one or another protective function. There are different types of lymphocytes, for example: , and large granular lymphocyte (LGL). B lymphocytes counteract extracellular pathogens by forming specific molecules - antibodies that are able to bind antigens. T lymphocytes have many tasks. One of them is the regulation, using special proteins (cytokines), of the activation of B-lymphocytes for the formation of antibodies; as well as regulation of phagocyte activation for more efficient destruction of microorganisms. This task is performed by a group of T-helpers. Another task of T cells is to destroy virus-infected body cells. T-killers are responsible for this.
Phagocytes
Helper cells
Supporting cells include dendritic and mast cells, basophils, and platelets. Cells of various tissues of the body also participate in immune defense.
Complement
The complement system is one of the main systems of innate immunity. The function of this system is to distinguish “one’s own” from “not one’s.” This is achieved due to the presence of regulatory molecules on the body's cells that suppress the activation of complement. There are three pathways of complement activation: classical, lectin and alternative.
Opsonization
Lysis of target cells
Complement regulation
Three stages of acquired immune defense
Antigen recognition
All immune cells are capable of recognizing antigens and hostile microorganisms to some extent. But the specific recognition mechanism is entirely a function of lymphocytes. As noted above, the body produces many thousands of varieties of immune cells with different receptors. In this way, it is possible to recognize not only known antigens, but also those that are formed as a result of mutations of microorganisms. Each B cell synthesizes a surface receptor that can recognize a specific antigen. The basis of this receptor is the immunoglobulin (Ig) molecule. T cells do not recognize the antigen as such. Their receptors recognize only modified body molecules - antigen fragments embedded in the molecules of the major histocompatibility complex (MHC). Large granular lymphocytes (LGLs), like T cells, are capable of recognizing cell surface changes due to malignant mutations or viral infection. They also effectively recognize cells whose surface is devoid of or has lost a significant part of MHC.
Immune response
At the initial stage, the immune response occurs with the participation of innate immune mechanisms, but later lymphocytes begin to carry out a specific (acquired) response. To activate the immune response, a simple connection of an antigen or damaged MHC with the receptors of IS cells is not enough. This requires a rather complex chain of intercellular interaction. At the initial stage, the main participants in this interaction are antigen presenting cells (APCs). Dendritic cells, macrophages, B-lymphocytes and some other cells act as APCs. The essence of the processes occurring in the APC is to process the antigen and integrate its fragments into the MHC, that is, present it in a form understandable to T-helpers. APCs activate only a certain group of T-helpers that can resist a certain type of antigen. After activation, T-helper cells begin to actively divide and then secrete cytokines, with the help of which phagocytes and other leukocytes, including T-killer cells, are activated. Additional activation of some IS cells occurs when they come into contact with T helper cells. When activated, B cells multiply and become plasma cells, which begin to synthesize many receptor-like molecules. Such molecules are called antibodies. These molecules interact with the antigen that has activated the B cells. As a result of this, foreign bodies are neutralized, becoming more vulnerable to phagocytes, etc. Activation of T cells turns them into cytotoxic lymphocytes, which kill foreign and damaged cells. Thus, as a result of the immune response, small groups of inactive leukocytes are activated, multiply and turn into effector cells that are able, using certain mechanisms, to fight antigens and the causes of their appearance. During the immune response, suppressor mechanisms are activated that regulate immune processes in the body.
Inflammatory reaction
The auxiliary cells of the IS are responsible for the inflammatory process. The main goal of this process is to attract leukocytes to the site of infection. Basophils, mast cells and platelets are responsible for the inflammatory process. The process occurs under the influence of special substances - inflammatory mediators. The release of mediators occurs when basophils and mast cells are activated. These cells can also release a number of mediators that regulate the immune response. Mast cells are located near blood vessels. Basophils, on the contrary, circulate in the blood. Platelets are activated during the blood clotting process.
Neutralization
Cells responsible for immune defense can produce antibodies to various antigens. Neutralization is one of the simplest methods of immune response. In this case, antibody molecules simply bind to microorganisms and neutralize them. For example, antibodies to the outer proteins (envelope) of some rhinoviruses that cause colds prevent the virus from binding to the body's cells.
Phagocytosis
Refers to the type of immune reaction when there is an active capture and absorption of living foreign cells and non-living particles by special cells -. Phagocytes can act independently, absorbing foreign microorganisms and antibodies. But phagocytosis occurs more effectively in cases where phagocytes are activated by antibodies or T-lymphocytes.
Cytotoxic reactions
Cytotoxicity is primarily caused by certain types of T cells. After activation, they begin to produce special toxic substances that kill foreign and damaged cells of the body.
The body's defense system against foreign substances consists of humoral and cellular immunity. Humoral is aimed at releasing antibodies that are present in the blood plasma. The cellular response is manifested only due to the formed elements of the blood.
Theory
Scientists began to actively study immunity at the end of the 19th century. Then the humoral and phagocytic or cellular theory of immunity was formed. The development of immunology in general was influenced by the work of Louis Pasteur, who experimented with vaccination of animals. At the same time, Emil von Berning worked with him, who proved the formation of resistance to diphtheria and tetanus in people who received the blood of patients who had recovered from these diseases.
However, the scientific basis for immunity was given by Ilya Mechnikov, who is considered the creator of the phagocytic theory of immunity. He discovered phagocytes in the blood that absorb foreign objects. These are the main defenders of the body, the first to react to external stimuli.
Rice. 1. Ilya Mechnikov.
Cellular immunity is part of adaptive or acquired immunity. Leukocytes learn during their life by encountering various bacteria, viruses and other foreign objects, developing specific immune responses.
Cells
The main function of immunity is performed by special blood cells - leukocytes. They differ in appearance and functionality.
There are two functional groups:
- phagocytes;
- lymphocytes.
Phagocytes are large in size and motile. These include neutrophils, monocytes, macrophages. They constitute nonspecific immunity, i.e. respond to the action of any pathogen. On the surface, phagocytes have receptors that recognize foreign objects.
Rice. 2. Phagocytes.
Phagocytes absorb and digest not only bacteria and viruses, but also any particles - fragments of cellular structures, solid metabolic products, old cells, etc. Their number increases sharply at the site of infection. Overcrowded phagocytes rupture and die, and their particles are absorbed by new phagocytes. Pus is a large accumulation of dead phagocytes in one place.
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When an infection enters the blood, lymphocytes, which make up specific immunity, come to the aid of phagocytes. They are trained in the thymus gland. As a result, it enters the blood three types of specialized lymphocytes:
- T-helpers , recognizing the antigen and informing other lymphocytes about the penetration of foreign substances;
- Killer T cells or cytotoxic T-lymphocytes that destroy certain antigens through lysis - dissolution of microorganisms;
- T-suppressors , stopping the response if the action of the antigen ceases.
Rice. 3. Lymphocytes.
Separately, NK lymphocytes or natural killer cells are isolated. Their actions are similar to the functions of killer T cells, but are aimed not at external antigens, but at internal ones. They target any cells that differ from normal ones, such as cancer cells.
Natural killer cells secrete a protein called perforin, which creates pores in the cell membrane. Through the formed pores, enzymes secreted by NK lymphocytes - proteases - penetrate into the cell. They provoke lysis or apoptosis - cell self-destruction.
Most white blood cells are produced in the bone marrow. Unlike other blood cells, they have a nucleus and can extend beyond the bloodstream into the intercellular space. 4.5. Total ratings received: 71.