Cytokines are glycoproteins or low molecular weight proteins produced during the initial phase of the immune response in order to mediate and regulate the amplitude and duration of immune and inflammatory responses.
They are produced by the activation of leukocytes and also by the activation of neural cells, fibroblasts and endothelial cells.
Therefore, they are the mediators of the immune system that allow it to communicate with each other, in a coordinated way, regulating cell differentiation and proliferation, activating or inhibiting the expression of certain genes.
There are different classes of cytokines and they have multiple biological functions. Some have similar functions and others antagonistic.
The same cytokine can also have a specific function on one type of cell and a completely different function on another.
Cytokines can be divided into several groups, depending on their activation context, the class of cells that produce them, etc .:
-Interleukins (iL) are mainly responsible for regulating the activation of cells of the immune system and for controlling the differentiation and proliferation of some cell subpopulations. Some have pro-inflammatory functions and others anti-inflammatory.
They increase vascular permeability, facilitating the migration of immune cells from the bloodstream into the tissue, promote the secretion of antibodies, and control the response of T lymphocytes.
-Tumor Necrosis Factors (TNF): these are important cytokines during the early stages of the inflammatory response. They are produced by a wide variety of cells and have a central role in viral infections, as well as in proliferation and cell death or apoptosis, such as TNF-alpha
-Interferons: α, β and γ interferons play an important role in the innate response to viruses or other pathogenic microorganisms. They are, therefore, secreted as danger signals: they promote antiviral activity and the activation of cells of a type of lymphocytes called natural killer, which are highly cytotoxic.
-Stimulating Factors or stem cells factor (SCF): these are growth factors, which increase the differentiation and proliferation of stem cells, to cells of the immune system.
-Chemokines: they stimulate the motility of the cells of the immune system, in this case the neutrophils, and direct them to the site of inflammation, through a phenomenon called chemotaxis. One of them is IL-8 (interleukin-8).
Cytokines are also, the basis of the immune response, they favor the production of immunoglobulins and are produced especially by macrophages or activated lymphocytes.
They are also involved in hematopoiesis, inflammation, healing, cell reproduction, growth and maintenance of cells of the Nervous System and energy metabolism. They also influence the control of tumor cells (cytokine TGF-β).
This includes the positive or negative regulation of various genes and their transcription factors that result in the production of other cytokines, overstimulation of cytokines can generate a dangerous syndrome called cytokine storm.
Furthermore, cytokines are pleiotropic, meaning that they act on many different cell types and a cell can express receptors for more than one cytokine.
More than a hundred genetically and structurally different peptides are recognized as cytokines. They are very powerful and work by binding to specific receptors on the cell surface.
They have a short life acting locally in an autocrine and paracrine way, only some cytokines are normally present in the blood that are capable of acting at a distance, such as endocrine hormones, this is the case of erythropoietin (EPO) and others.
During inflammation, macrophages and other cells present antigens to helper T lymphocytes (CD4).
In inflammation macrophages are stimulated to produce multiple molecules such as:
Nitric Oxide (NO), chemokines, leukotrienes, prostaglandins, platelet activating factor, complement and especially.
Monokines (cytokines produced by monocytes, macrophages and T lymphocytes), such as IL-4, IL-5, IL-6, IL-10 and IL-13, which activate B lymphocytes, in the presence of an antigen, and they differentiate into plasma cells to produce antibodies.
We must bear in mind that not all of them are pro-inflammatory, since in some cases, such as IL-4, they have an anti-inflammatory action and some participate in hemostasis, such as interleukin 3 (IL-3), among others.
-J. R. Tisoncik, M. J. Korth, C. P. Simmons, J. Farrar, T. R. Martin, and M. G. Katze, Into the Eye of the Cytokine Storm, Microbiol. Mol. Biol. Rev., vol. 76, no. 1, pp. 16–32, 2012.
-C. to Dinarello, Historical Review of Cytokines, Eur. J. Immunol., Vol. 37.Suppl 1, pp. S34 – S45, 2007.
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