What is immunity. Cellular and humoral immunity

Most modern people have heard about the existence of the body's immune system and that it prevents the emergence of all kinds of pathologies caused by external and internal factors. How this system works, and on what its protective functions depend, not everyone can answer. 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 nonspecific. Consider what the difference between them is.

The concept of immunity

Incredibly, even in the simplest 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 the most elementary form. In more highly organized organisms, the protective system has a multi-level organization. It performs the function of protecting all organs and parts of the body of an individual from penetrating into it various microbes and other foreign agents from the outside, and also to protect against internal elements that the immune system classifies as foreign, dangerous. To ensure that these functions for the protection of the body were carried out in full, nature "invented" for the higher beings immunity cellular and immunity humoral. They have specific differences, but act together, helping one another and complementing each other. Let's consider their features.

Immunity cellular

With the name of the given system of protection all is simple - cellular, means, it is somehow connected with cells of an organism. It involves an immune response without the involvement of antibodies and the complement system. The main "executors" for neutralizing 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 by direct contact with a foreign stimulus. Carrying out a comparison of cellular and humoral immunity, it should be noted that the former "specializes" on viruses, fungi, tumors of various etiologies, various microorganisms penetrated into the cell. He also neutralizes microbes that survived in phagocytes. The second prefers to deal with bacteria and other pathogenic agents located in the blood or lymphatic channels. The principles of their work differ slightly. Cellular immunity activates phagocytes, T-lymphocytes, NK cells( natural killers) and secretes cytokines. These are small peptide molecules, which, appearing on the membrane of cell A, interact with the receptors of cell B. So they transmit a signal of danger. It triggers response defense responses in neighboring cells.

Humoral immunity

As noted above, the main difference between cellular and humoral immunity is in the location of the objects of their action. Of course, the mechanisms by which protection from malicious agents is performed also has its own specific features. On the humoral immunity, in general, "work" B-lymphocytes. In adults, they are produced exclusively in the bone marrow, and in embryos additionally in the liver. Humoral, this type of defense was called from the word "humor", which in Latin means "bed".B-lymphocytes are able to produce antibodies that separate from the cell surface and move freely through the lymphatic or bloodstream. Activating B-lymphocytes( induce to action) are foreign agents or T-cells. This is the link between the principle of interaction between immunity of cellular and humoral immunity.

More about T-lymphocytes

These cells are a special kind of lymphocytes produced in the thymus. People are called the thymus gland, located in the chest just below the thyroid. The first letter of this important organ is used in the name of lymphocytes. In the bone marrow, progenitors of T-lymphocytes are produced. In the thymus, their final differentiation( formation) takes place, as a result of which they acquire cellular receptors and markers.

There are several types of T-lymphocytes:

• 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 "innate" killers, whose purpose is to destroy the cells of their own organism, in which the alien agent settled. These "killers" there are many variations. Each such cell "sees" the
  on only one type of pathogen. That is, T-killers, reacting, for example, to streptococcus, will ignore salmonella. They also "will not notice" an alien "pest" that has penetrated the human body, but while free circulating in its liquid media. The peculiarities of the action of T-killers make it clear why cellular immunity differs from humoral immunity, which works in a different way.
• γδ T-lymphocytes. They are formed very little, 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 specific case.

More about B-cells of

These cells were first detected in birds in their organ, which is written in Latin as Bursa fabricii. The first letter was added to the name of lymphocytes. They are born from stem cells located in the red bone marrow. From there they come immature. The final differentiation ends in the spleen and in the lymph nodes, where two types of cells are obtained:

• Plasmatic. These are B-lymphocytes, or plasmocytes, which are the main "factories" for the production of antibodies. For 1 second each plasma cell produces thousands of protein molecules( immunoglobulins), oriented to any one type of microbe. Therefore, the immune system is forced to differentiate many varieties of plasma B-lymphocytes in order to fight various pathogenic agents.
• Memory cells. These are small lymphocytes that live much longer than other forms. They "remember" the antigen against which they already protected the body. When re-infected with such an agent, they very quickly activate the immune response, producing a huge number of antibodies. There are also memory cells in T-lymphocytes. In this immunity, cellular and humoral immunity are similar. Moreover, these two types of protection against foreign aggressors act together, since B-lymphocytes of memory are activated with the participation of T-cells.

The ability to remember pathological agents formed the basis for vaccination, which creates acquired immunity in the body. This ability also acts after the person has suffered diseases that are resistant to immunity( chickenpox, scarlet fever, smallpox).

Other immunity factors

Each type of body defense against foreign agents has its own, say, performers who seek to destroy pathogenic formation or at least to prevent its penetration into the system. Let's repeat, that immunity on one of classifications happens:

1. Congenital.

2. Purchased. It is active( appears after vaccinations and some diseases) and passive( occurs as a result of the transfer of antibodies to the infant from the mother or the introduction of serum with the ready antibodies).

According to another classification, the immunity can be:

• Natural( includes 1 and 2 types of protection from the previous classification).
• Artificial( this is the same acquired immunity, which appeared after inoculations or some sera).

Congenital type of protection has the following factors:

• Mechanical( skin, mucous, lymph nodes).
• Chemical( sweat, secrets of the sebaceous glands, lactic acid).
• Self-cleaning( tears, peeling, sneezing and others).
• Anti-adhesive( mucin).
• Mobilizable( inflammation of the infected site, immune response).

The acquired type of protection has only cellular and humoral immunity factors. Let us consider them in more detail.

Humoral factors

The effect of this type of immunity is provided by the following factors:

• Compliment system. This term denotes a group of whey proteins, constantly present in the body of a healthy person. While there is no introduction of a foreign agent, the proteins are inactive. Once the pathogen penetrates into the inner environment, the compliment system is instantaneously activated. This happens on the basis of the "domino" principle - one protein that has detected, for example, a microbe, informs the other nearest, the next one, and so on. As a result, complement proteins break down, releasing substances that perforate membranes of foreign living systems, leasing their cells, initiating an inflammation reaction.
• Soluble receptors( needed for the destruction of pathogens).
• Antimicrobial peptides( lysozyme).
• Interferons. These are specific proteins that can protect a cell infected by one agent from hitting another. They produce interferon lymphocytes, T-leukocytes and fibroblasts.

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 simultaneously the cell that it has infected. Also in the immune system 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 engaged in the same thing as T-lymphocytes( killers), but they have their own characteristics.

Neutrophils are indivisible cells containing a large number of granules. They contain antibiotic proteins. Important properties of neutrophils - a short life and the ability to chemotaxis, that is, the movement to the site of the introduction of the microbe.

Macrophages are cells that can absorb and process rather large foreign particles. In addition, their role is to transfer information about the pathogenic agent to other protective systems and to stimulate their activity.

As you can see, types of immunity cellular and humoral, performing each of its functions, predetermined by nature, act together, thus ensuring maximum protection of the organism.

Mechanism of cellular immunity work

To understand how it works, you need to return to T cells. In the thymus, they pass, so-called, selection, that is, acquire receptors that are able to recognize this or that pathogenic agent. Without this, they will not be able to perform their protective functions.

The first stage is called β-selection. Its process is very complex and deserves a separate consideration. In our article, we note only that during β-selection, most T-lymphocytes acquire pre-TRK receptors. Those cells that can not form them die.

The second stage is called positive selection. T cells that have pre-TPA receptors are not yet capable of protecting against pathogenic agents, since they can not bind to molecules from the histocompatibility complex. To do this, they need to acquire other receptors - CD8 and CD4.During complex transformations, some cells get the opportunity to interact with the MHC proteins. The rest perish.

The third stage is called negative selection. During this process, cells that have passed through the second stage move to the thymus boundary, where some of them come into contact with their own antigens. Such cells also die. This prevents autoimmune diseases in humans.

The remaining T cells begin to work to protect the body. In the inactive state they are sent to the place of their vital activity. When foreign agent penetrates into the body, they react to it, recognize, activate and begin to share, forming the T helper, T-killers and other factors described above.

Principle of humoral immunity

If the microbe has successfully passed all the mechanical barriers of protection, it has not died from the action of chemical and antiadhesive factors, and has penetrated the body, humoral immunity factors are being taken for granted. T-cells "do not see" the agent while he is in a free state. But activated antigen presenting cells( macrophages and others) capture the pathogen and rush with it into the lymph nodes. The T-lymphocytes found there are able to recognize pathogens, since they have corresponding receptors for this. Once the "identification" has occurred, the 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 fighting the alien agent are somewhat different, but are aimed at the complete destruction of the pathogen.

In conclusion

We examined how the body is protected against various harmful agents. On the guard of our life are cellular and humoral immunities. Their general characteristics consist in such features:

• Have memory cells.
• Act against the same agents( bacteria, viruses, fungi).
• In its structure have receptors, through which the recognition of pathogens occurs.
• Before starting work on protection, a long stage of maturation takes place.

The main difference is that cellular immunity destroys only those agents that have penetrated into cells, and the humoral immunity can work at any distance from the lymphocytes, since the antibodies they produce to the cell membranes are not attached.