Leukocytes are white nucleated blood cells. 1 mm³ of blood usually contains 4-9 thousand leukocytes, but in some diseases their number can increase markedly.
The main function of white blood cells is to protect the body from various foreign objects.
The lifespan of these cells varies, but on average they only live for a few days. The destruction of leukocytes occurs in the spleen.
Several types of leukocytes are known. They differ in structural features and functions performed.
Some of the leukocytes can capture and destroy various foreign particles. Leukocytes are capable of active amoeboid movement and can pass through the capillary wall and penetrate into tissues, where they absorb and digest foreign particles. Leukocytes also protect against degenerated cancer cells.
The ability of leukocytes to capture foreign particles was first discovered by the Russian scientist Ilya Ilyich Mechnikov (the creator of the phagocytic theory of immunity). II Mechnikov called the discovered phenomenon phagocytosis, and leukocytes capable of phagocytosis – phagocytes (“devourers”).
Phagocytosis is the absorption of solid food particles by the cell.
If a lot of foreign bodies have penetrated into the body, then phagocytes, absorbing them, greatly increase in size and eventually collapse. At the same time, substances are released that cause a local inflammatory reaction, which is accompanied by edema, fever and redness of the affected area. These substances also attract new leukocytes to the site of introduction of foreign bodies. The pus that forms in the tissues during inflammation is an accumulation of dead white blood cells.
Other leukocytes (lymphocytes) produce special proteins (antibodies) that recognize and bind (neutralize) foreign cells and the substances they produce harmful to the body (toxins). Alien particles lose their harmful abilities and the disease does not develop.
The formation of antibodies occurs with the participation of a special type of leukocytes that are found not only in the blood, but also in the lymph. Therefore, they are called lymphocytes.
T-lymphocytes are able to bind to antigens of foreign particles and cause their destruction. B-lymphocytes secrete chemicals – antibodies. Antibodies, when attached to antigens, accelerate their capture by phagocytes, or lead to chemical destruction or adhesion and deposition of antigens.
Antibodies usually work against the causative agent of one disease (for example, against the causative agent of measles). The presence in the blood of antibodies to the causative agent of a certain disease creates the body’s immunity to repeated diseases of this disease.
It is thanks to B-lymphocytes (memory cells in the immune response) that a person acquires immunity to past diseases (once they come into contact with a pathogenic agent (bacteria, virus, chemical compound), these cells remember the agent and adapt to its elimination). And it is thanks to them that the effect of vaccination (vaccinations) is possible.
If the formation of lymphocytes is impaired, a person loses protection against infection.