How many types of phagocytes are there in the human body?

The cells of any type of organism can absorb substances and particles in many different ways. For example, they can absorb them by diffusion through the cytoplasmic membrane or by active transport using carrier proteins.

For the absorption of large molecules, particles and even small cells, diffusion and transport through the membrane is not very suitable. To absorb this type of particles, the cells resort to the endocytosisa type of absorption in which the cell engulfs foreign substances with membrane projections until a vesicle is formed that remains inside the cell. It would be the opposite process to exocytosis.

Phagocytosis is one of the most important types of endocytosis, along with pinocytosis and receptor-mediated endocytosis. The key feature of phagocytosis is that the cytoplasmic membrane surrounds Solid particles while in pinocytosis a fluid is trapped in which there are particles in suspension.

human phagocytes

In the human body there are several cells that carry out phagocytosis, almost all of them related to response immunological. Phagocytes would be responsible for trapping and destroying potentially harmful particles, including bacteria, viruses and their remains, as well as the remains of their own cells after the apoptosis or programmed cell death

The different phagocytic cells are usually divided into two large groups based on the effectiveness of phagocytosis and the specialization of the cell in this function:

  1. professional phagocytes: neutrophils, monocytes, macrophages, dendritic cells and mast cells.
  2. non-professional phagocytes: epithelial cells, endothelial cells, fibroblasts, NK cells and large granulocyte lymphocytes.

1. Professional phagocytes

The so-called professional phagocytes are cells that are specialized for phagocytic function. They are all cells of the immune system.

neutrophils

Neutrophils, also called polymorphonuclear lymphocytes (PMN), are one of the most important types of phagocytes in the human immune system. It represents between 60 and 70% of the leukocytes present in the blood circulation.

The main function of neutrophils is the phagocytosis of foreign substances and bodies for their destruction. The phagocytosed particles remain inside a vesicle called a phagosome. The phagosome subsequently fuses with another vesicle, the lysosome, which releases lytic enzymes to degrade the phagocytosed particle.

The phagocytic activity of neutrophils is nonspecific, that is, it is part of the innate immune responseand acts mainly against bacteria and fungi.

monocytes and macrophages

Monocytes and macrophages are the same cell; macrophages are monocytes that leave the bloodstream and settle in the tissues where they undergo a maturation process that ends up differentiating them from circulating monocytes.

Monocytes and macrophages are also lymphocytes, like neutrophils, but unlike neutrophils they are not granulocytes. macrophages are the phagocytic cells par excellence in the human body and have a very important role in the immune system as antigen presenting cells.

When macrophages phagocytize a pathogen, in addition to destroying it, they process its components. Some parts, called antigens, are exposed on its cell membrane. The B lymphocytes are able to interact with antigens presented by macrophages and produce antibodies even without having had direct contact with the pathogen, which prepares the body for a faster specific immune response.

The collaboration between macrophages and B lymphocytes is one of the most important points of interaction between the nonspecific immune response and the specific immune response.

dendritic cells

Dendritic cells are, like macrophages, phagocytic antigen-presenting cells, but they are specialized to act on tissues that are in contact with the external environment such as the skin and mucous membranes.

In some tissues, dendritic cells reach a high degree of specialization until they differentiate from dendritic cells in other tissues. This is the case of the skin where the dendritic cells specialize and form those known as Langerhans cells.

One of the main characteristics of dendritic cells, and to which they owe their name, is the presence of dendrites, long projections of the cytoplasmic membrane that serve to detect and trap bacteria and other invading pathogens.

mast cells

Mast cells, or mast cells, are characteristic phagocytic lymphocytes in connective tissue. One of its main functions is the mediation of the inflammatory response and the allergic response, and for this they have high amounts of histamine and heparin stored in granules of their cytoplasm. In addition, they play a decisive role in tissue repair, in the formation of new blood vessels (angiogenesis) and in the line of defense of the blood-brain barrier that protects the central nervous system.

2. Non-professional phagocytes

The so-called non-professional phagocytes are cells that have phagocytic capacity but are not specialized in this function or it is not their main function. Nonprofessional phagocytes have a much more limited phagocytic capacity, mainly due to the absence of specific phagocytic receptors, such as opsins. Another characteristic that differentiates them from professional phagocytes is that they do not produce reactive oxygen species during phagocytosis.

Nonprofessional phagocytic cells include skin epithelial cells, blood vessel endothelial cells, connective tissue fibroblasts, NK cells, and large granulocyte lymphocytes present in blood, lymph, and lymph nodes.

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