Phagocytes are a unique group of cells in the human body. They are simultaneously part of the immune and circulatory systems, as well as connective tissue. Their main task is to protect the body from dead cells, infections and other pathogens. And for this they use a unique function unique to them.
General characteristics of phagocytes
The world learned about the existence of phagocytes at the end of the 19th century thanks to the biologist Ilya Mechnikov. A scientist, observing the flatworms and larvae of starfish, discovered an amazing property in them: without a mouth, they are able to absorb and dissolve various substances. During the observation, the biologist suggested that the whole "focus" - in special cells that are contained in experimental organisms. It turned out that these cells quickly move inside the larvae and absorb everything that enters the body. Moreover, as the researcher soon discovered, the cells discovered by him are able to absorb not only food. Mechnikov stuck a small wooden splinter in the body of a starfish larva and began to observe under the microscope the behavior of amazing cells. Soon they gathered around the splinter and began to devour it. These "gluttonous" cells are phagocytes. By the way, their name comes from Greek words, which are translated - "devour".
In further studies, it was found that phagocytes are produced by bone marrow and are contained in the body of all animals and humans. They concentrate in the blood and almost all tissues. In human bodies they are represented in several forms at once.
How phagocytes "work" in the human body
For humans, phagocytes are important in that they protect the body from bacteria, toxic substances and some viruses. Some of this group of cells are able to produce various bioactive substances, stimulate inflammatory reactions, and also activate the work of other agents of the immune system. In fact, phagocytes are the second line of defense of the body from pathogens that nevertheless penetrated the body through protective barriers. The process of absorption of substances hazardous to humans by phagocytic cells is called phagocytosis.
To make it easier to understand how phagocytes work in the human body, one should recall the amoeba, a representative of unicellular organisms known to most from the school curriculum. Like the amoeba, the phagocyte has the so-called false legs, with which it envelops its prey and absorbs it. By the way, scientists suggest that amoeba and phagocytes, in terms of evolution, are relatives.
When a pathogen enters the body, phagocytes catch the chemicals spreading from it and are sent to them. When a pathogen comes into contact with phagocyte receptors, phagocytosis occurs. After a hostile substance penetrates into the phagocytic cell, it uses oxidizing agents or nitric oxide to destroy the "enemy". The remains of the "eaten" pathogen, the phagocyte throws back to its surface, after which the "digested" substances penetrate the lymph and are excreted from the body.
True, in some cases, the phagocytes are helpless in front of the "enemy". This usually happens when the pathogen is in a place that phagocytes cannot reach. Also, some "enemies" can produce chemicals that prevent the phagocyte from approaching an uninvited guest. In addition, sometimes phagocytic cells may lose their “working capacity” due to disturbances in the immune system.
Types of Phagocytes
All phagocytes that are present in the human body are usually divided into two groups: the so-called unprofessional and professional.
Professional phagocytic cells are distinguished, so to speak, by a narrower specialization, that is, they destroy only a certain category of "enemies". Professional phagocytes are monocytes, macrophages, neutrophils, dendritic and mast cells. This group is considered especially important for protecting the body.
Mononuclear phagocytes, or monocytes, are a type of white blood cell (white blood cell). Of the total number of leukocytes, they make up from 3% to 8%. Their main task in the body is to protect the blood from pathogens. But the mere destruction of harmful microorganisms does not limit their role. If you explain in simple terms, then, in addition to everything, monocytes for the body are also a kind of informant that a pathogen has entered the bloodstream. That is, as soon as a monocyte detects a suspicious object in the blood, all other representatives of the immune system receive news of this and go, so to speak, into a state of full combat readiness. Monocytes enter the bloodstream from the bone marrow, which synthesizes them. These cells move quite quickly and remain in the vessels for only 24 to 48 hours, after which they penetrate into other tissues and turn into macrophages.
The concentration of monocytes in the blood varies depending on the age of the person. When their number is too high, this may be a sign:
- bacterial, viral, or fungal infections;
- Hodgkin's lymphomas;
- ulcerative colitis;
- the presence of a tumor;
- alcoholic liver damage;
- multiple myeloma;
- Crohn's disease.
An insufficient number of cells from this group may be associated with immune disorders - both congenital and acquired (for example, AIDS, bone marrow atrophy).
Macrophages are also mononuclear cells. Under normal conditions, when nothing threatens the body, they do not show any activity. But as soon as inflammation begins in the body, macrophages immediately move to its focus. There, these cells kill bacteria, as well as organic and inorganic particles that cause inflammation. By the way, the pus that forms at the site of inflammation is dead white blood cells, including macrophages.
Neutrophils, like monocytes, are representatives of a group of white blood cells. In the bloodstream, neutrophils account for between 50% and 75% of all white blood cells. The life expectancy of each cell from this group is about 5 days, then new ones replace the dead ones. Their main task is to prevent the development of infection.
When everything is normal in the body, these cells live in the blood. But as soon as they receive a signal of danger in any part of the body, they only need 30 minutes to get to the place of the problem. Once at the epicenter, they determine the pathogen and absorb it. Like macrophages, after completing their mission, neutrophils die and become part of pus.
Modern laboratory methods can accurately determine the number of neutrophils in the body. If the number of cells is below normal, a person can be suspected of diseases such as:
- anemia (malignant or hemolytic);
- severe bacterial or viral infection;
- infectious liver diseases;
- acromegaly (excessive production of growth hormone - growth hormone);
- autoimmune diseases (for example, rheumatoid arthritis), against the background of which leukocytes or bone marrow cells are damaged - in this case, the body produces protein antibodies to neutrophils;
- hypersplenism (enlarged spleen);
- Felty's syndrome;
- Chediak-Higashi syndrome;
- deficiency of vitamins of group B (mainly B12 and B9).
Neutrophil deficiency can also be caused by taking certain medications, such as antibiotics or diuretics. A decrease in leukocytes, including neutrophils, occurs in patients with cancer departments undergoing radiation or chemotherapy.
An alarming sign if the number of neutrophils in the body significantly exceeds the norm. This may indicate the following diseases:
- hemolytic anemia;
- inflammation or acute infection;
- general or local tissue necrosis (for example, myocardial infarction);
- acute bleeding;
- hyperactivity of the adrenal cortex;
- Cushing's syndrome (excessive production of the hormone cortisol).
Dendritic cells got their name because of the specific structure. They have many branched processes that resemble the crown of a tree (dendron). Cells from this group are found in large quantities in different tissues of the human body. Their main amount is concentrated in the cavities of organs, as well as in proximity to the external environment, that is, in the mucous membranes of the nose, stomach, and alveolar tissues of the lungs. After complete maturation, dendritic cells penetrate the lymphoid tissue (lymph nodes, tonsils, serous membrane, nasopharynx) and increase the activity of lymphocytes and macrophages.
Mast cells (mast cells)
The main task of mast cells is to activate inflammatory reactions in the body, because they are the signal for macrophages, neutrophils and other phagocytes, which should protect the body from the pathogen-aggressor. Any inflammation is a kind of command to action for all phagocytes present in the body. That is, labocytes increase the activity of different groups of phagocytic cells and perform irreplaceable functions on which the work of the entire immune system depends. But mast cells themselves are also not devoid of phagocytic activity. They usually specialize in gram-negative bacteria.
Non-professional phagocytes are devoid of directed action against a specific type of pathogen. Their phagocytic activity is not as pronounced as in professional cells. To this group belong fibroblasts, as well as cells of the inner lining of blood vessels and epithelium. They respond to any pathogen that has entered the body.
Phagocytes are an indispensable link in the immune system. Analyzing the main characteristics of different types of phagocytic cells, it can be decided that their main task is to protect against infection. But this is far from their only function. They “devour” (the process of phagocytosis) solid particles that are pathogenic in the human body, purify the blood, support the health of internal organs and perform many more useful functions.
1. Protection against foreign bodies
To understand how phagocytes perform this function, it is enough to remember what happens when a splinter pierces the body. If it is not immediately removed, the place around the foreign body becomes inflamed and suppurates, and after a while the pus breaks out together with a splinter. Pus, as we already know, is dead phagocytes, which thus created a fence for dirt and a foreign body from healthy body tissue.
2. Protection against tumors
Nowadays, scientists already know for sure that almost every minute failures occur in different parts of the human body, as a result of which cells begin to divide incorrectly and degenerate into malignant. If this process is not stopped, cancerous tumors form. But if the body is healthy and the immune system is working correctly, phagocytes immediately look for degenerated cells and destroy them, thus preventing cancer.
3. Maintenance of apoptosis
On average, an adult's body is about 100 trillion cells. Some can live no more than 1-2 days, others - and for several years. But in any case, 70 billion cells die every day. Where do they go? They are "eaten" by macrophages. When any cell dies, certain substances emanate from it, which attract phagocytes. So they destroy the old cells and thereby make room for new ones. This process is called apoptosis.
4. Protection against disease
Phagocytic formations can prevent diseases that are not associated with infection, tumor, or other causes that may be of interest to phagocytes. Take for example atherosclerosis. The activity of macrophages helps to slow down the development of this disease. When cholesterol penetrates the inner lining of blood vessels, macrophages "eat up" particles of fat and instead foam cells form. But phagocytic cells are not able to completely destroy lipids, so cholesterol plaques continue to form on the walls of blood vessels, although in some cases they are somewhat slower.
5. Maintaining the health of the immune system
Phagocytic cells have the ability to stimulate the activity of each other, as well as other agents of the immune system. In addition, phagocytes secrete specific substances that affect the bone marrow, and it produces even more cells of the immune system.
6. Promote tissue repair
Phagocytes can not only “devour”, they also take part in the formation of tissues. So, if serious damage appears on any part of the body, phagocytes contribute to the formation of scar cells (fibroblasts). As a result, a patch in the form of a scar appears at the site of damage. This process occurs not only with external damage to the skin. Fibroblasts are indispensable for scarring the gastrointestinal tract ulcer and healing of the myocardium in the post-infarction period.
Are phagocytes always useful?
The mechanism of action on pathogens in phagocytes has been worked out for thousands of years of evolution. But even this does not make them absolutely safe and beneficial for the human body. And in many ways the blame is not so much the phagocytes themselves as the conditions of modern human life. Bad ecology, chronic stresses often lead to the fact that malfunctions appear in the principles of the work of phagocytes. Take at least autoimmune diseases. This group of diseases is caused by the fact that due to a malfunction, the immune system perceives the cells of its own body as pathogens. As a result, phagocytes “pounce” on the tissues of the kidneys, joints, different parts of the heart, and the body begins to age several times faster.
In the human body there is a huge number of cells of a specific action - phagocytes. They interact with each other and other cells, so it is very important that this process proceeds correctly. Any imbalance of this interaction entails health problems. The best help for the proper functioning of phagocytes is to maintain a healthy lifestyle, proper nutrition and maintaining immunity in the norm.
Specialty: doctor pediatrician, infectious disease specialist, allergist-immunologist.
Total experience: 7 years.
Education: 2010, Siberian State Medical University, pediatric, pediatrics.
Experience as an infectious disease specialist for more than 3 years.
He has a patent on the subject "A method for predicting a high risk of the formation of a chronic pathology of the adeno-tonsillar system in frequently ill children." As well as the author of publications in the journals of the Higher Attestation Commission.