The human and mammalian body has a functional immune system designed to protect it from the influence of infectious factors. Many viruses, bacteria, fungi and protozoa come into daily contact with the human body, but do not cause the development of the disease, which is the merit of immunity and cells such as phagocytes. These are specific cells capable of devouring a microorganism or a foreign body, splitting it and stopping its contact with the internal environment of the body.
Essence of phagocytosis
The term phagocytosis refers to the complete absorption of a foreign solid body. It is carried out by a cell capable of digesting a phagocytosed organism. In unicellular biology, the term denotes a type of nutrition, but evolution has found another use for this process, putting it on guard against immunity. And if we consider the term from the point of view of immunology, then it means the absorption of a living organism or part of it in order to eliminate it from the internal environment of the organism. This reduces the likelihood of causing disease.
Some bacteria, such as Mycobacterium tuberculosis and leprosy, are able to live even inside the digestive vacuole of the macrophages that have swallowed it. This is an example of how phagocytes and phagocytosis areineffective against adapted microorganisms. Also, some viruses use phagocytosis to get into the cell and replicate. At the heart of preventing phagocytosis is the process of preventing the fusion of the phagosome with the macrophage digestive vacuole.
Immunocompetent human phagocytes
In the human immune system, phagocytes are cells that make primary contact with an antigen or neutralize it after opsonization with antibodies. The most common phagocytes are neutrophils, a common leukocyte in the blood. They have enzyme systems for the formation of a food vacuole and enzymes, with the help of which the lysis of a phagocytosed foreign body will be carried out.
Often, due to the huge amount of bacteria or residues from damaged cells of the body, mass death of neutrophils is also observed in places of inflammation. Macroscopically, this is manifested by the appearance of pus in inflamed tissues. Pus is a mixture of dead neutrophilic phagocytes, damaged cells, and eliminated microbes. All this mixture is called detritus.
Monocyte phagocytes
The second type of phagocytes is monocytes. They can carry out intravascular phagocytosis. This is such a process of absorption of foreign bodies and microorganisms that occurs in the blood even before primary differentiation into a tissue cell, into a dendrocyte or into a histiocyte. The monocyte, as a precursor of tissue macrophages, is capable of phagocytosis before differentiation. Alsophagocytes are all cells derived from monocytes and subsequent clones of cells from resident macrophages.
Phagocytes of humoral immunity
Immunocompetent phagocytes are cells capable of absorbing solid particles. They are foreign bodies and microorganisms. If the immune system has not previously been in contact with the antigen, then the foreign body will immediately interact with the macrophage. Being in the tissue, it will absorb the microorganism, digest it, recognize its antigens and present them on its membrane. In immunology, the subjects of initial contact are called antigen-presenting cells.
Antigen-presenting phagocytes are called macrophages that were able to cleave the antigen and determine its structure, which will be presented on their membrane MHC receptor. After presentation, T-lymphocytes will form humoral immunity associated with the synthesis of specific antibodies. Upon repeated contact with the same foreign body, other phagocytes will be involved. This means that if a specific antibody is attached to the antigen, then any neutrophil can carry out its phagocytosis.
If the strength of the enzyme systems of one phagocyte is not enough to split the foreign body, it uses reactive oxygen species. Through them, not only the infection itself is damaged, but also the surrounding tissues. This provokes the formation of a capsule around the body, which cannot be phagocytosed or broken down. The body adopts the tactics of "preserving" the foreign body in the connective tissue membrane, excluding itfurther contact with the internal environment of the body.
