Our body is an amazing thing. He 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 leukocytes form in humans?
Human blood consists of uniform elements and plasma. White blood cells are one of these shaped elements along with red blood cells and platelets. They are colorless, have a core and can move independently. You can see them under the microscope only after preliminary painting. From the organs that enter the human immune system, where leukocytes form, they enter the bloodstream and body tissues. They can also freely pass from vessels to adjacent tissues.
White blood cells move as follows. Having fixed on the vessel wall, the leukocyte forms a pseudopodia (pseudopod), which pokes through this wall and clings to the tissue from the outside. Then it squeezes through the formed gap and actively moves among other cells of the body leading a "settled" lifestyle. Their movement resembles the movement of an amoeba (a microscopic unicellular organism from the category of protozoa).
The main functions of white blood cells
Despite the similarity of leukocytes with amoeba, they perform complex functions. Their main tasks are to protect the body from various viruses and bacteria, the destruction of malignant cells. White blood cells chase bacteria, envelop them and destroy them. This process is called phagocytosis, which is translated from Latin as "devouring something by cells." Destroying the virus is more difficult. With the disease, viruses settle inside the cells of the human body. Therefore, in order to reach them, leukocytes need to destroy cells with viruses. Leukocytes also destroy malignant cells.
Where are white blood cells formed and how much do they live?
When performing their functions, many white blood cells die, so the body constantly reproduces them. White blood cells are formed in organs that enter 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 plaques). These organs are located in different places of the body. Bone marrow is also the place where white blood cells, platelets, and red blood cells form. White blood cells are believed to 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. They are replaced by organs from the immune system, where leukocytes are formed, new cells come out and continue to destroy bacteria.
Along with this, among T-lymphocytes there are immunological memory cells that live for decades. I met a lymphocyte, for example, with such a monster as the Ebola virus - he will remember it for life. Upon repeated encounter with this virus, lymphocytes are converted into large lymphoblasts, which have the ability to multiply rapidly. Then they turn into killer lymphocytes (killer cells) that block access to the body of the familiar dangerous virus. This indicates the existing immunity to this disease.
How do white blood cells learn about the introduction of a virus into the body?
In the cells of every person there is an interferon system, which is part of innate immunity. When a virus is introduced into the body, interferon is produced - a protein substance that protects cells that have not yet been infected from viruses entering them. At the same time, interferon activates killer lymphocytes, which are one of the types of white blood cells. From the bone marrow, where white blood cells are formed, they are sent to infected cells and destroy them. However, some viruses and their fragments fall out of the destroyed cells. Viruses that have fallen are trying to penetrate into cells that have not yet been infected, but interferon protects these cells from their introduction. Viruses that are outside the cells are not viable and die quickly.
The fight against viruses with the interferon system
In the process of evolution, viruses have learned to suppress the interferon system, which is too dangerous for them. Influenza viruses have a strong inhibitory effect on it. The human immunodeficiency virus (HIV) inhibits this system even more . However, all records were broken by the Ebola virus, which practically blocks the interferon system, leaving the body almost defenseless against a huge number of viruses and bacteria. From the spleen, lymph nodes and other organs related to the immune system, where white blood cells are formed, all new cells come out. But, not receiving 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 rupture, and the person bleeds. Death usually occurs in the second week of illness.
And when does immunity occur?
If a person has been ill with one disease or another and recovered, then a stable acquired immunity is formed, which is provided by white blood cells 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 can hardly overcome this powerful barrier.
How do killer lymphocytes kill dangerous cells?
Before you kill a dangerous cell, you must find it. Killer lymphocytes tirelessly seek out these cells. They focus on the so-called histocompatibility antigens (tissue compatibility antigens) located on cell membranes. The fact is that if a virus enters a cell, then this cell condemns itself to death to save the body and, as it were, throws a “black flag” signaling the introduction of the virus into it. This “black flag” is information about the invading virus, which is located in the form of a group of molecules next to histocompatibility antigens. This information is "seen" by the lymphocyte killer. He gains this ability after training in the thymus gland. Control over learning outcomes is very tight. If a lymphocyte has not learned to distinguish a healthy cell from a sick one, it itself is inevitably subject to destruction. With this strict approach, only about 2% of killer lymphocytes survive, which subsequently exit the thymus gland to protect the body from dangerous cells. When the lymphocyte accurately determines that the cell is infected, it gives it a “lethal injection” and the cell dies.
Thus, white blood cells play a huge role in protecting the body from pathogenic agents and malignant cells. These are small tireless warriors of the body's main defenses - the interferon system and immunity. They are massively dying in the struggle, but from the spleen, lymph nodes, bone marrow, tonsils and other organs of the immune system where white blood cells are formed in humans, they are replaced by many newly formed cells, ready, like their predecessors, to sacrifice their lives in the name of salvation of the human body. White blood cells provide our survival in an environment filled with a huge number of various bacteria and viruses.