You have probably heard of cytokines . But what exactly are they? What are they for? Who makes them? What biological meaning do they have?
We could say that basically cytokines are like the messengers of our body, serving to transmit messages between our cells when they need to do a specific function.
What are cytokines?
Cytokines (also called cytokines) are proteins that are generated by cells and act by sending signals between different types of cells , depending on what our body needs.
In this article we will talk about cytokines and their biochemistry, their properties, to whom they send messages, what their functions may be in the organism and finally what types exist.
What are they for?
As we have already mentioned, cytokines are proteins that cells make when they want to communicate with each other. These proteins, of low molecular weight, act through complex interactions between different types of cells .
These proteins are part of the immune system and its functioning is as follows: imagine a small molecule, which is produced by a cell that receives a stimulus.
This molecule travels to its receptor (found on another cell) to give a signal or message (these receptors are found on the cell membranes). This second cell will give a response, and from there an intracellular signal transduction cascade is initiated. This cascade will trigger a specific biological response.
Characteristics of cytokines
Cytokines are very different and complex molecules, although they share a number of characteristics that we will see below.
Being part of the immune system, are produced mostly by macrophages, which are essential molecules in the innate immune system . Remember that the innate immune system is the one that involves the cells recognizing pathogens in a generic way and attacking them.
If we speak of a specific immune system, the collaborating T cells are the ones in charge of producing cytokines. The specific immune system is that, as its name indicates, has specificity ; that is, the cells specifically attack specific receptors of pathogens.
The production of cytokines is relatively short (transient) and is subject to the duration of the stimulus (i.e. the pathogen in case of macrophages and T-cells).
Other characteristics are as follows:
- They have pleiotropy; that is, they trigger multiple effects after acting on different cells.
- They are redundant, i.e. different cytokines can produce the same effect.
- They can be synergistic; that is, they have a mutually reinforcing effect.
- They can be antagonistic; that is, they can block each other.
- Cytokines have varying affinity for their specific receptor.
There are several classifications of cytokines, as they are very complex molecules , with different origins and different functions. Here we show you different classifications:
1. According to the interactions of the cytokines
Basically, interactions occur between lymphoid cells (immune system cells), inflammatory cells, and hematopoietic cells (blood cells).
But these interactions can be of different types, and according to these types, we obtain a classification of the cytokines:
1. 1. Autocrine cytokines
They are those cytokines that act on the same cell that produces them .
1. 2. Paracrine cytokines
These are the cytokines that act in the region adjacent to the site of secretion.
1. 3. Endocrine cytokines
They are those cytokines that act in regions distant from where they have been secreted . These cytokines travel through the blood and their function is to act on different tissues.
2. According to the functions of the cytokines
As cytokines are such diverse and complex molecules, they can exercise a wide variety of functions . Here we will classify them into the most essential ones:
2. 1. Pro-inflammatory function
These are pro-inflammatory cytokines that act on the innate , non-specific immune response or inflammation.
2. 2. Developmental function, cell maturation, and/or cytotoxicity
They act at different times in the cell cycle to model the development, maturation and/or death of cells.
2. 3. Productive functions of different immunoglobulins
It’s the proteins that protect us from infection.
2. 4. Hematopoietic functions
These are the cytokines involved in the development and maturation of blood cells (red blood cells, white blood cells and platelets essentially).
As we have seen, cytokines must interact with a receptor on a cell to trigger a response.
There is a wide variety of cytokine receptors. It is these receptors that will determine the response that will trigger the effecting cell. This variety of receptors is grouped into five so-called families of cytokine receptors .
1. Immunoglobulin superfamily
They are the receptors of the known antibodies, which are the essential molecules that the body creates to attack pathogens in a specific way .
2. Class I family of cytokine receptors
This family of receptors constitutes the hematopoietic receptors, i.e. the blood cells.
3. Class II family of cytokine receptors
This family of receivers constitutes the interferon receivers . Let us remember that interferons are proteins that the body manufactures in response to pathogens (viruses, bacteria, parasites…).
4. TNF (tumor necrosis factor) receptor family
They are the molecules that mediate the processes of inflammation and cell death.
5. Chemokine receptor family
This last group of cytokine receptors are especially peculiar: they are so called because they are able to attract and direct other cells of the immune system to repair tissues .
Of all these “superfamilies” mentioned, there are several subgroups of each. That is, for example, there are many TNF receptors that are named TNF-ɑ and TNF-ᵦ, several types of Class I family receptors, Class II receptors, and so on.
Each superfamily, as we have already seen, is involved in specific molecular mechanisms.
The best known cytokines
Of all the cytokines that the body can produce, interleukins (IL) are among the most important cytokines . This type of cytokine is mainly produced by lymphocytes and macrophages, but can also be produced by endothelial cells, adipose cells, endothelial cells, muscle cells, etc.
Its fundamental action consists of regulating inflammation through various mechanisms . In general they are classified as pro-inflammatory and anti-inflammatory.
The other cytokines, also essential for the inflammatory response, are Tumor Necrosis Factor Alpha (TNF-α) and interferons. All of these are pro-inflammatory proteins .
You see, the body is a complex system where many needs are orchestrated and measured by cytokines so that the body can function properly through a stimulus-response mechanism.
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