Our body is an amazing thing. It is able to produce all the substances necessary for life, cope with many viruses and bacteria, and finally provide us with a normal life.
Where do human leukocytes form?
Human blood consists of formed elements and plasma. Leukocytes are one of these formed elements along with erythrocytes and platelets. They are colorless, have a nucleus and can move independently. They can be seen under a microscope only after preliminary coloring. From the organs that are part of the human immune system, where leukocytes are formed, they enter the bloodstream and body tissues. They can also freely pass from vessels to adjacent tissues.
Leukocytes move in the following way. Having fixed on the wall of the vessel, the leukocyte forms a pseudopodia (pseudopodia), which it pushes through this wall and clings to the tissue from the outside. Then it squeezes through the resulting gap and actively moves among other cells of the body leading a "sedentary" lifestyle. Their movement resembles the movement of an amoeba (a microscopic unicellular organism from the category of protozoa).
Main functions of leukocytes
Despite the similaritiesleukocytes with amoebas, they perform the most complex functions. Their main task is to protect the body from various viruses and bacteria, the destruction of malignant cells. Leukocytes chase bacteria, envelop them and destroy them. This process is called phagocytosis, which in Latin means "devouring something by cells." Destroying the virus is more difficult. When sick, viruses settle inside the cells of the human body. Therefore, in order to get to them, leukocytes need to destroy cells with viruses. Leukocytes also destroy malignant cells.
Where are leukocytes formed and how long do they live?
When performing their functions, many leukocytes die, so the body constantly reproduces them. Leukocytes are formed in the organs that make up the human immune system: in the thymus gland (thymus), bone marrow, lymph nodes, tonsils, spleen, and in the lymphoid formations of the intestine (in Peyer's patches). These organs are located in different places in the body. The bone marrow is also a place where white blood cells, platelets, and red blood cells are formed. It is believed that leukocytes live for about 12 days. However, some of them die very quickly, which happens when they fight with a large number of aggressive bacteria. Dead white blood cells can be seen if pus appears, which is their accumulation. In place of them, new cells emerge from the organs related to the immune system, where white blood cells are formed, and continue to destroy bacteria.
Along with this, among the T-lymphocytes there are cellsimmunological memory that live for decades. A lymphocyte met, for example, with such a monster as the Ebola virus - he will remember it for the rest of his life. When re-encountered with this virus, lymphocytes are converted into large lymphoblasts, which have the ability to multiply rapidly. Then they turn into killer lymphocytes (killer cells), which block the familiar dangerous virus from entering the body. This indicates the existing immunity to this disease.
How do white blood cells know when a virus has invaded the body?
In the cells of each person there is an interferon system, which is part of innate immunity. When a virus enters the body, interferon is produced - a protein substance that protects cells that have not yet been infected from the penetration of viruses into them. At the same time, interferon activates killer lymphocytes, which are one of the types of leukocytes. From the bone marrow, where white blood cells are formed, they travel to infected cells and destroy them. At the same time, some viruses and their fragments fall out of the destroyed cells. The dropped viruses try to penetrate into cells that are not yet infected, but interferon protects these cells from their introduction. Viruses outside of cells are not viable and die quickly.
Fighting viruses against the interferon system
In the process of evolution, viruses have learned to suppress the interferon system, which is too dangerous for them. Strong suppressive effectinfluenza viruses have it. The human immunodeficiency virus (HIV) depresses this system even more. However, all records were broken by the Ebola virus, which practically blocks the interferon system, leaving the body practically defenseless against a huge number of viruses and bacteria. From the spleen, lymph nodes and other organs related to the immune system, where leukocytes are formed, more and more new cells come out. But, having not received a signal about the destruction of the virus, they are inactive. In this case, the human body begins to decompose alive, many toxic substances are formed, blood vessels are torn, and the person bleeds. Death usually occurs in the second week of illness.
When does immunity occur?
If a person has been ill with one or another disease and recovered, then he develops a stable acquired immunity, which is provided by leukocytes belonging to the groups of T-lymphocytes and B-lymphocytes. These white blood cells are formed in the bone marrow from progenitor cells. Acquired immunity develops after vaccination. These lymphocytes are well aware of the virus that has been in the body, so their killing effect is targeted. The virus is practically unable to overcome this powerful barrier.
How do killer lymphocytes kill dangerous cells?
Before you kill a dangerous cage, you need to find it. Killer lymphocytes tirelessly search for these cells. They are guided by the so-called histocompatibility antigens (compatibility antigenstissue) located on cell membranes. The fact is that if a virus enters the cell, then this cell dooms itself to death to save the body and, as it were, throws out a “black flag”, signaling the introduction of the virus into it. This "black flag" is information about the introduced virus, which, as a group of molecules, is located next to the histocompatibility antigens. The killer lymphocyte “sees” this information. He acquires this ability after training in the thymus gland. Control over learning outcomes is very tight. If a lymphocyte has not learned to distinguish a he althy cell from a diseased one, it will inevitably be destroyed. With such a strict approach, only about 2% of killer lymphocytes survive, which later exit the thymus gland to protect the body from dangerous cells. When the lymphocyte determines for sure that the cell is infected, it gives it a "lethal injection" and the cell dies.
Thus, leukocytes play a huge role in protecting the body from disease-causing agents and malignant cells. These are small tireless warriors of the body's main defenses - the interferon and immunity systems. They die en masse in the struggle, but from the spleen, lymph nodes, bone marrow, tonsils and other organs of the immune system, where leukocytes are formed in humans, they are replaced by many newly formed cells, ready, like their predecessors, to sacrifice their lives in the name of saving the human body. White blood cells ensure our survival in an environment filled with a huge number of different bacteria and viruses.
