The human and mammalian organism has a functional immunity system designed to protect it from the influence of infectious factors. Many viruses, bacteria, fungi and protozoa daily come into contact with the human body, but do not cause the development of the disease, which is a merit of the immune system and cells such as phagocytes. These are specific cells that can devour a microorganism or foreign body, splitting it and stopping its contact with the internal environment of the body.
The essence of phagocytosis
The term phagocytosis means the absorption of a foreign solid in its entirety. It is carried out by a cell capable of digesting a phagocytosed organism. In unicellular biology, the term refers to the type of nutrition, but evolution has found another use for this process, putting it on guard of 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 body. This reduces the likelihood of causing a disease.
Some bacteria, for example, mycobacterium tuberculosis and leprosy, are able to live even inside the digestive vacuole of the macrophages that have absorbed it. This is an example of how phagocytes and phagocytosis are ineffective against adapted microorganisms. Also, some viruses use phagocytosis in order to enter the cell and replicate. The obstacle to phagocytosis is based on the process of preventing the fusion of the phagosome with a macrophage digestive vacuole.
Human immunocompetent 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, often found white blood cells in the blood. They have enzyme systems for the formation of a food vacuole and enzymes by which the phagocytized foreign body will be lysed.
Often, due to the huge number of bacteria or residues from damaged body cells in places of inflammation, a massive death of neutrophils is also observed. 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. This whole mixture is called detritus.
Monocytic 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 the primary differentiation into a tissue cell, into a dendrocyte or into a histiocyte. A monocyte, as a precursor to tissue macrophages, is capable of carrying out phagocytosis before differentiation. Also, phagocytes are all cells derived from monocytes, and subsequent cell clones from resident macrophages.
Phagocytes of humoral immunity
Immunocompetent phagocytes are cells that can absorb solid particles. Foreign bodies and microorganisms act in their quality. 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, subjects of primary contact are called antigen presenting cells.
Antigen-presenting phagocytes are called macrophages that were able to break down the antigen and determine its structure, which will be presented on their membrane MHC receptor. After the presentation, T-lymphocytes will form a 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 attaches to the antigen, then any neutrophil can carry out its phagocytosis.
If the strength of the enzyme systems of one phagocyte is not enough for the splitting of a foreign body, it uses active forms of oxygen. Through them, not only the infect itself is damaged, but also the surrounding tissues. This provokes the formation of a capsule around the body, which cannot be phagocytosed or cleaved. The body adopts the tactic of "preserving" a foreign body into the connective tissue membrane, excluding its further contact with the internal environment of the body.