Most modern people have heard about the existence of the body’s immune system and that it prevents all kinds of pathologies caused by external and internal factors. Not everyone can answer how this system works and what its protective functions depend on. Many will be surprised to learn that we have not one, but two immunities - cellular and humoral. Immunity, in addition, can be active and passive, innate and acquired, specific and non-specific. Consider the difference between the two.
The concept of immunity
Incredibly, even in simple organisms, for example, pre-nuclear prokaryotes and eukaryotes, there is a protective system that allows them to avoid infection with viruses. To this end, they produce special enzymes and toxins. This is also a kind of immunity in its most elementary form. In more highly organized organisms, the defense system has a multilevel organization.
It performs the functions of protecting all organs and body parts of an individual from the penetration of various microbes and other foreign agents into it from outside, and also to protect against internal elements that the immune system classifies as foreign, dangerous. In order for these functions to protect the body to be carried out in full, nature “invented” cellular immunity and humoral immunity for higher beings. They have specific differences, but act together, helping one another and complementing each other. Consider their features.
Cellular immunity
Everything is simple with the name of this defense system - cellular, which means it is somehow connected with the cells of the body. It suggests an immune response without the participation of antibodies and the complement system. The main "performers" for the neutralization of foreign agents that have penetrated the body in cellular immunity are T-lymphocytes, which produce receptors that are fixed on cell membranes. They begin to act in direct contact with a foreign stimulus. Comparing cellular and humoral immunity, it should be noted that the former “specializes” in viruses, fungi, tumors of various etiologies, and various microorganisms that have penetrated the cell. It also neutralizes the microbes that survived in phagocytes. The second prefers to deal with bacteria and other pathogenic agents located in the blood or lymphatic channel. The principles of their work are slightly different. Cellular immunity activates phagocytes, T-lymphocytes, NK - cells (natural killers) and secrete cytokines. These are small peptide molecules that, once on the membrane of cell A, interact with the receptors of cell B. So they transmit a danger signal. It triggers defensive responses in neighboring cells.
Humoral immunity
As already noted above, the main difference between cellular and humoral immunities is the location of the objects of their influence. Of course, the mechanisms by which protection against malicious agents is carried out also have their own specific features. B-lymphocytes mainly “work” on humoral immunity. In adults, they are produced exclusively in the bone marrow, and in embryos additionally in the liver. Humoral this type of protection was called from the word "humor", which in Latin means "channel". B-lymphocytes are capable of producing antibodies that separate from the cell surface and move freely along the lymphatic or bloodstream. B-lymphocytes activate (induce action) foreign agents or T cells. This shows the connection and the principle of interaction between immunity, cellular and humoral immunity.
More on T-lymphocytes
These are cells that are a special type of lymphocyte produced in the thymus. In humans, the thymus gland is located in the chest just below the thyroid gland. The first letter of this important organ is used in the name of the lymphocytes. Precursors of T-lymphocytes are produced in the bone marrow. In the thymus, their final differentiation (formation) occurs, as a result of which they acquire cellular receptors and markers.
T-lymphocytes are of several types:
- T-helpers. The name is derived from the English word help, which means "help." "Helper" in English is an assistant. Such cells themselves do not destroy foreign agents, but activate the production of killer cells, monocytes, cytokines.
- T-killers. These are “born” killers whose purpose is to destroy the cells of their own body in which the alien agent has settled. These "killers" there are many variations. Each such cell "sees"
only on any one type of pathogen. That is, T-killers that respond, for example, to streptococcus, will ignore Salmonella. They also “will not notice” the alien “pest” that has penetrated the human body, but is still freely circulating in its liquid media. Features of the action of T-killers make it clear how cellular immunity differs from humoral, working in a different way. - γδ T-lymphocytes. They are formed very few, in comparison with other T-cells. They are configured to recognize lipid agents.
- T-suppressors. Their role is to provide an immune response of such duration and strength that are required in each case.
More About B Cells
These cells were first found in birds in their organ, which is written in Latin as Bursa fabricii. The first letter was added to the name of the lymphocytes. They are born from stem cells located in the red bone marrow. From there they go immature. The final differentiation ends in the spleen and in the lymph nodes, where two types of cells are obtained from them:
- Plasma. These are B-lymphocytes, or plasmocytes, which are the main "factories" for the production of antibodies. In 1 second, each plasmocyte produces thousands of protein molecules (immunoglobulins) targeted to any one type of microbe. Therefore, the immune system is forced to differentiate many varieties of plasma B-lymphocytes in order to deal with various pathogenic agents.
- Memory cells. These are small lymphocytes, living much longer than other forms. They "remember" the antigen against which the body has already been protected. When re-infected with such an agent, they very quickly activate the immune response, producing a huge amount of antibodies. Memory cells are also found in T-lymphocytes. In this immunity, cellular and humoral immunity are similar. Moreover, these two types of protection against foreign aggressors act together, since memory B-lymphocytes are activated with the participation of T cells.
The ability to remember pathological agents formed the basis of vaccination, which creates acquired immunity in the body. Also, this skill works after a person transfers diseases to which stable immunity is developed (chickenpox, scarlet fever, smallpox).
Other immunity factors
Each type of protection of an organism from foreign agents has its own, let us say, performers who seek to destroy the pathogenic formation or at least prevent its penetration into the system. We repeat that immunity according to one of the classifications is:
1. Congenital.
2. Acquired. It is active (appears after vaccination and some diseases) and passive (occurs as a result of transmission of antibodies to the infant from the mother or the introduction of serum with ready-made antibodies).
According to another classification, immunity is:
- Natural (includes 1 and 2 types of protection from the previous classification).
- Artificial (this is the same acquired immunity that appeared after vaccinations or some serums).
The innate type of protection has the following factors:
- Mechanical (skin, mucous membranes, lymph nodes).
- Chemical (sweat, secrets of the sebaceous glands, lactic acid).
- Self-cleaning (tears, peeling, sneezing and others).
- Release agents (mucin).
- Mobilized (inflammation of the infected area, immune response).
The acquired type of protection has only cellular and humoral immunity factors. Let's consider them in more detail.
Humoral factors
The action of this type of immunity is provided by the following factors:
- Compliment system. This term refers to a group of whey proteins that is constantly present in the body of a healthy person. While there is no introduction of a foreign agent, the proteins are inactive. As soon as the pathogen enters the internal environment, the compliment system is instantly activated. This happens on the principle of "dominoes" - one protein that detects, for example, a microbe, informs the other nearest one, the next one and so on. As a result, complement proteins break down, releasing substances that perforate the membranes of alien living systems, lease their cells, and initiate an inflammation reaction.
- Soluble receptors (needed to kill pathogens).
- Antimicrobial peptides (lysozyme).
- Interferons. These are specific proteins that can protect a cell infected by one agent from being defeated by another. Interferon lymphocytes, T-cells and fibroblasts are produced.
Cell factors
Please note that this term has a slightly different definition than cellular immunity, the main factors of which are T-lymphocytes. They destroy the pathogen and at the same time the cell that it infected. Also in the immune system there is the concept of cellular factors, which include neutrophils and macrophages. Their main role is to absorb the problem cell and digest it (eat). As you can see, they are doing the same thing as T-lymphocytes (killers), but at the same time they have their own characteristics.
Neutrophils are indivisible cells containing a large number of granules. They contain antibiotic proteins. Important properties of neutrophils are short life and ability to chemotaxis, that is, movement to the site of introduction of the microbe.
Macrophages are cells capable of absorbing and processing fairly large foreign particles. In addition, their role is to transfer information about the pathogenic agent to other protective systems and stimulate their activity.
As you can see, the types of immunity are cellular and humoral, each performing its own function, predetermined by nature, act together, thereby ensuring maximum protection of the body.
The mechanism of cellular immunity
To understand how it works, you need to return to T cells. In the thymus, they undergo the so-called selection, that is, acquire receptors capable of recognizing one or another pathogenic agent. Without this, they will not be able to fulfill their protective functions.
The first stage is called β-selection. Its process is very complex and deserves separate consideration. In our article, we only note that during β-selection, most T-lymphocytes acquire pre-TRK receptors. Those cells that cannot form them die.
The second stage is called positive selection. T cells with pre-TRK receptors are not yet able to protect against pathogenic agents, since they cannot bind to molecules from the histocompatibility complex. To do this, they need to acquire other receptors - CD8 and CD4. During complex transformations, part of the cells is able to interact with MHC proteins. The rest die.
The third stage is called negative selection. During this process, cells that have passed the second stage move to the border of the thymus, where some of them come into contact with their own antigens. Such cells also die. This prevents human autoimmune diseases.
The remaining T cells begin to protect the body. In an inactive state, they are sent to the place of their life. When a foreign agent penetrates into the body, they react to it, recognize, activate and begin to divide, forming the T-helpers, T-killers and other factors described above.
The principle of humoral immunity
If the microbe has successfully passed all the mechanical protection barriers, has not died from the action of chemical and anti-adhesive factors, and has penetrated into the body, humoral immunity factors are taken into account. T cells "do not see" the agent while it is in a free state. But activated antigen-presenting cells (macrophages and others) capture the pathogen and rush into the lymph nodes with it. The T-lymphocytes located there are able to recognize pathogens, since they have corresponding receptors for this. As soon as "recognition" has occurred, T-cells begin to produce "helpers", "killers" and activate B-lymphocytes. Those, in turn, begin to develop antibodies. All these actions once again confirm the close interaction of cellular and humoral immunities. Their mechanisms for combating a foreign agent are somewhat different, but are aimed at the complete destruction of the pathogen.
Finally
We examined how the body protects itself from various malicious agents. On the guard of our lives are cellular and humoral immunities. Their general characteristic is in such features:
- Have memory cells.
- They act against the same agents (bacteria, viruses, fungi).
- In their structure, they have receptors through which pathogens are recognized.
- Before you begin work on protection, go through a long stage of maturation.
The main difference is that cellular immunity destroys only those agents that have penetrated the cells, and the humoral one can work at any distance from lymphocytes, since the antibodies they produce to the cell membranes are not attached.