What Is the Innate Immune System?

The innate immune system includes a series of cells and related mechanisms that can resist foreign infections in a non-specific manner. Cells of the innate immune system recognize and act on pathogens non-specifically. Unlike the acquired immune system, the innate immune system does not provide lasting protective immunity, but exists as a rapid anti-infective effect in all animals and plants.

Innate immune system

Chinese name: Innate immune system
Foreign name: The innate immune system

System includes: A series of cells and related mechanisms
Features: Antigen complex

In evolution, the innate immune system is an earlier body defense mechanism. It occupies a major position in plants, fungi, insects and more primitive multicellular organisms. (See other forms of the innate immune system.) The main functions of the innate immune system of vertebrates include:

Immune cells are recruited to areas of infection or inflammation by producing a variety of chemical factors including cytokine. Promote the elimination of dead cells or antibody-antigen complexes by activating the complement system.

Use differentiated white blood cells to identify and eliminate foreign substances found in organs, tissues, blood, and lymph. The acquired immune system is activated by the antigen presentation process.

Natural killer cells, mast cells, eosinophils, basophils, including macrophages and neutrophils Phagocytic cells, and dendritic cells. The role of these cells is to identify and eliminate pathogens that may cause infection. [2]

Innate immune system mast cells

(Mast cells)

Mast cells are actually innate immune cells found in connective tissue and mucous membranes. They are directly related to the role of defense against antigens and wound healing, and are also related to allergic reactions. [3] When mast cells are activated, they will rapidly release the characteristic particles (rich in histamine and heparin), as well as various humoral regulators, chemokines, and cytokines, to the outside of the cell. Histamine dilates blood vessels, causes a characteristic response to inflammation, and recruits granulocytes and macrophages. [3]

Innate immune system phagocytic cells

Phagocytic cells can use endocytosis to engulf antigen bodies or other particles. When in effect, the phagocytic cell membrane continues to stretch and curl locally until it completely envelops the extracellular pathogen, thereby transferring it into the cell. Invading pathogens are now contained in inclusion bodies, which then bind to lysosomes. [2] The lysosome contains a variety of enzymes and acidic substances, which can kill and digest pathogenic microorganisms or particles. Phagocytic cells usually "patrol" the body to search for antigens and are able to respond to cytokines, highly specialized molecular signals produced by other cells. Phagocytic cells mentioned in the immune system include macrophages, neutrophils and dendritic cells.

This phagocytosis is common during normal body development and metabolism. Whether it is the normal induced apoptosis of host cells (also called apoptosis) or the death of host cells caused by cell damage caused by bacteria or viruses, phagocytic cells will be responsible for eliminating these dead cells to ensure new healthy cells. Development and tissue repair.

Innate immune system macrophages

(Macrophages)

Macrophages are large white blood cells that exist in the vascular system and participate in circulation. They also have the ability to penetrate the capillary wall into the tissue space to chase invading antigens. Macrophages that migrate in tissues are different from those in the blood and are called monocytes. Macrophages, as the most efficient phagocytic cells, can engulf a considerable number of microorganisms or other cells. [2] The binding of bacterial substance molecules to receptors on the surface of macrophages will trigger the encapsulation and killing effects of macrophages on bacteria. This process works by producing a "(respiratory burst)" effect that triggers the release of reactive oxygen species (mostly NO). Antigens also stimulate macrophages to produce chemokines, causing them to summon more cells to the infection. [2]

Innate immune system neutrophils

(Neutrophils)

Because there are many granules in the cytoplasm, neutrophils, neutrophils, are called neutrophils, together with basophils, eosinophils, and granulocytes, also known as polymorphonuclear leukocytes ( polymorphnuclear cells (PMNs). Neutrophil granules contain a variety of toxins, which can kill or inhibit the growth of bacteria and fungi. Similar to macrophages, neutrophil attacks on antigens are triggered by "breathing bursts." Neutrophils are the largest number of phagocytes, usually accounting for 50% to 60% of total circulating white blood cells, and are usually the first lymphocytes to reach the infected area. [3] Normal adult bone marrow can produce more than 100 billion neutrophils per day, which is more than 10 times the output of acute infection. [3]

Innate immune system dendritic cells

(Dendritic cells, DC)

Dendritic cells are phagocytic cells that exist in tissues and come into contact with the external environment. They are usually found in the skin (commonly called Langerhans cells), the inside of the nasal mucosa, the lungs, the stomach, and the intestines. [1] Dendritic cells are named because they are similar to dendrites of nerve cells, but they are not related. Dendritic cells are an important place in the process of antigen presentation, so they are also the link between innate and [[[born's immune system]]].

Eosinophils and basophils

Eosinophils

After activation of eosinophils, the released histamine plays an important role in the process of removing parasites and plays an allergic reaction; [2] activated eosinophils will secrete a variety of toxin proteins and free radicals. Effectively kills bacteria and parasites, but also causes severe tissue damage in allergic reactions. Therefore, the activation process of the two is very complicated to prevent unnecessary tissue damage. [3]

Natural killer cells of the innate immune system

Natural killer cells, also called NK cells for short, mainly attack host cells that have been identified as infected, but also directly attack invading microorganisms. For example, NK cells attack and destroy tumor cells and virus-infected cells. This effect occurs through the so-called "missing-self effect," which means that host cells infected with the virus will show low levels of MHC I on the cell surface. [4] "Natural killing" means that it does not need to be activated when it kills cells that show "self-deficient response".

T Innate immune system T cells

T cells are cells that are between innate and acquired immunity. On the one hand, T cells are considered to be part of acquired immunity because they have a VDJ rearrangement effect when producing T cell receptors; at the same time, T cells are subject to pattern recognition by limiting TCR receptors or NK receptors. It is considered part of innate immunity. It may be related to the recognition of non-peptide antigens.