Cytokines: what are they, what types are there and what functions do they have?

You've probably heard of cytokines.. But what exactly are they? What are they for? Who makes them? What biological sense do they have?

We could say that basically cytokines are like the messengers of our body, which are used to transmit messages between our cells when they need to perform a specific function.

• Related article: "The 20 types of proteins and their functions in the body"

What are cytokines?

Cytokines (also called cytokines) are proteins that cells make 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, who they send messages to, what their functions may be in the body 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 low molecular weight proteins act through complex interactions between different types of cells..

These proteins are part of the immune system and their operation is as follows: imagine a small molecule, which is produced by a cell that receives a stimulus.

this molecule travels to its receptor (located in another cell) to give a signal or message (These receptors are found on cell membranes.) This second cell will give a response, and from there an intracellular signal transduction cascade begins. This cascade will trigger a specific biological response.

• You may be interested in: "Main cell types of the human body"

Cytokine characteristics

cytokines They are very different and very complex molecules, although they share a series of characteristics which we will see in detail below.

Being part of the immune system, are produced mainly by macrophages, which are essential molecules in the innate immune system. Let us remember that the innate immune system is the one that implies that cells recognize pathogens in a generic way and attack them.

If we talk about the specific immune system, helper T cells are in charge of producing cytokines. The specific immune system is one that, as its name indicates, has specificity; that is, cells specifically attack specific pathogen receptors.

Cytokine production is relatively brief (transient) and is dependent on the duration of the stimulus (ie, the pathogen in the case of macrophages and T cells).

Other of its characteristics are the following:

• They have pleiotropy; that is, they trigger multiple effects after acting on different cells.
• They are redundant, that is, different cytokines can produce the same effect.
• They can be synergistic; that is, they cause an effect that is potentiated between them.
• They can be antagonistic; that is, they can block each other.
• Cytokines have different affinity to their specific receptor.

classifications

There are several classifications of cytokines, since these are very complex molecules., with different origins and different functions. Here we show you different classifications:

1. Based on cytokine interactions

Basically, the interactions occur between lymphoid cells (immune system cells), inflammatory, and hematopoietic cells (blood cells).

But these interactions can be of different types, and based on these types, we obtain a classification of cytokines:

1. 1. autocrine cytokines

Are those cytokines that act on the same cell that produces them.

1. 2. paracrine cytokines

They are those cytokines that act in the region adjacent to the site of secretion.

1. 3. endocrine cytokines

Are those cytokines that act in regions distant from where they are secreted. These cytokines travel through the blood and their function is to act on different tissues.

2. According to the functions of cytokines

Cytokines, being such diverse and complex molecules, can perform very widely varied functions. Here we will classify them into the most essential:

2. 1. pro-inflammatory function

They are proinflammatory cytokines; act on the innate immune response, nonspecific or inflammation.

2. 2. Developmental function, cell maturation, and/or cytotoxicity

They act at different moments of the cell cycle to model the development, maturation and/or death of cells.

2. 3. Producing functions of different immunoglobulins

They are the proteins that protect us from infections.

2. 4. hematopoietic functions

Are those cytokines involved in the development and maturation of blood cells (red blood cells, white blood cells and platelets essentially).

cytokine receptors

As we have already seen, cytokines must interact with a receptor on a cell to trigger a response.

There is a wide variety of cytokine receptors. These receptors are the ones that will determine the response that will be triggered by the effector cell. This variety of receptors It is grouped into the five so-called families of cytokine receptors..

1. Immunoglobulin superfamily

They are the receptors of the well-known antibodies, which are the essential molecules that the body creates to specifically attack pathogens.

2. Class I family of cytokine receptors

This family of receptors constitutes the receptors for hematopoietins, that is, for blood cells.

3. Class II family of cytokine receptors

This family of receptors make up interferon receptors. 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 named because are able to attract and direct other cells of the immune system to repair tissues.

Subgroups

Of all these "superfamilies" mentioned, there are various subgroups of each. That is, for example, there are many TNF receptors that are named TNF-ɑ and TNF-ᵦ, various types of receptors from the class I family, class II, etc.

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 one of the most important cytokines. These types of cytokines are mainly produced by lymphocytes and macrophages, but they can also be produced by endothelial cells, fat cells, endothelial cells, muscle cells, etc

Its fundamental action consists of regulating inflammation through various mechanisms. They are generally 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 them proinflammatory proteins.

As you can see, the organism is a complex system where many needs are orchestrated and measured by cytokines so that the body can function properly through a mechanism of stimulus-response.

Bibliographic references:

• Feduchi Canosa, Elena (2014). Biochemistry. Essential concepts. Editorial Médica Panamericana S.A.; second edition.
• Nelson, David L. Cox, MICHAEL M. (authors), Cuchillo Foix, Claudi M. (Translator). (2018). Principles of biochemistry. Lehninger Publisher; seventh edition.
• Tortora, Gerard J., Derrickson, Bryan (2018). Principles of anatomy and physiology. Editorial Médica Panamericana S.A.; fortnight edition.