Interleukins are proteins belonging to the group of cytokines. They participate in the process of communication between cells of the immune system. What are interleukins needed for? What characterizes them?

Interleukinsare mainly produced by leukocytes. It was long thought that only these cells had the ability to produce these proteins. However, it turned out that other cells, such as fibroblasts and fat cells, also have the ability to produce interleukins.

These proteins are involved in various immune and hematopoietic processes. It acts as signaling molecules. Cells of various types throughout the body can receive information transmitted by interleukins.

These compounds are described with numbers from 1 to 33. Currently, more than 48 interleukins have been discovered. The discrepancy between these numbers results from the fact that one number in the name can define several equal substances.

What does interleukin mean as cytokines?

Cytokines are proteins responsible for communication between cells. They form a sensitive system of connections known as the cytokine network. They participate, for example, in the development of conditions such as fever.

Cytokines have a very complex and broad activity. We can list the following most important features of proteins from this group, which also have interleukins:

  • pleiotropic - otherwise multidirectional action. This means that one cytokine can have a different effect depending on the cell it affects
  • redundancy - this means that different cytokines can have the same effect on a given group of cells
  • synergism - the action of two cytokines simultaneously has a stronger effect on cells than the activity of one
  • antagonism - cytokines of the opposite nature may mutually cancel each other's actions. The final effect is determined by the concentration difference
  • positive feedback - it means that one type of cytokines can stimulate the production of others
  • negative feedback - production of cytokines by one type of cell may block their production by other cells

Cytokines, also interleukins, can interact in three different ways:

  • autocrine - that is, the produced substance affects the cell that produces it
  • paracrine - it means that the substance affects the tissues innear the cell that produces it
  • endocrine - a substance produced by the cell enters the bloodstream and is transported to distant organs affected by

These features make cytokines create a very sensitive network of mutual dependencies. Interleukins are an essential part of it. The concentrations of these signaling substances control the immune response.

Cytokines affect the cell by binding to the appropriate membrane receptors. They are characterized by a very high sensitivity. Even a low concentration of signaling molecules causes excitation.

What is the role of interleukins?

Interleukins are cytokines responsible for the transmission of information between leukocytes. With their use, one group of leukocytes can influence another.

Leukocytes are cells that are the basic component of the immune system. Their task is to phagocytosis of microorganisms and dead cells. They are responsible for the formation of a specific response through the production of antibodies. They also have the ability to neutralize free radicals. The activity of leukocytes is controlled by interleukins.

Substances of the highest importance of this group:

  • Interleukin 1
  • Interleukin 2
  • Interleukin 3
  • Interleukin 4
  • Interleukin 6
  • Interleukin 7
  • Interleukin 8
  • Interleukin 10
  • Interleukin 12

Interleukins are involved in causing inflammation. The group of compounds known as interleukin 1 is of particular importance.

Interleukin 1

Interleukin 1 (IL 1) is the name that defines a whole group of cytokines that are key to the process of inflammation. It is produced in response to various types of antigens. The factors stimulating its production can be bacteria, viruses or fungi.

IL 1 acts as a universal factor stimulating the inflammatory response. It also has the ability to stimulate cells to produce other pro-inflammatory cytokines.

Interleukin 1 has potential as an anti-cancer drug. Intensive research into its use is still underway. The problem is the strong side effects associated with pyrogenic and post-inflammatory activity. Currently, high hopes are associated with interleukin 1 derivatives, which would have anti-cancer properties while limiting the harmful mechanisms.

There are 10 different compounds under the name interleukin 1. The most important are:

  • IL-1α
  • IL-1β
  • IL-1γ

Interleukin 2

Interleukin 2 (IL 2) is the most important excitatory cytokineincrease of T lymphocytes, especially those with cytotoxic properties. It means that IL 2 indirectly stimulates the process of programmed cell death (apoptosis) infected with viruses and neoplasms.

Stimulation of T cells increases the production of molecules that stimulate apoptosis on its surface.

Interleukin 2 has been considered in studies as an anti-cancer drug. However, strong side effects excluded this substance from potential therapeutic use.

Interleukin 3

Interleukin 3 (IL3) is a cytokine produced by T lymphocytes. Contrary to the previously mentioned, it does not significantly affect inflammatory processes. Its main task is to stimulate the process of haemopoiesis. This means that IL3 stimulates the production of various types of blood cells.

This cytokine is not active in he althy people. Its level rises during the inflammatory process. Its task is to increase the production of blood cells in response to an infection.

Interleukin 4

Interleukin 4 (IL 4) is important in the process of developing an allergic reaction. It is wide-ranging and stimulates many different cells of the immune system. It is produced by basophils, mast cells and Th2 lymphocytes.

Its presence stimulates the activity of macrophages and monocytes. IL 4 is involved in the formation of the inflammatory focus. Positive effect on the production of cytokines stimulating haemopoiesis. Therefore, the increase in the concentration of interleukin 4 stimulates hematopoietic processes.

Interleukin 6

Interleukin 6 (IL 6) is characterized by multidirectional action. It is produced by monocytes and macrophages. The factors stimulating its production are post-inflammatory cytokines, especially interleukin 1. IL 6 directly and strongly stimulates inflammatory processes.

The high concentration of this substance may, however, limit the development of inflammation. This is because interleukin 6 blocks the synthesis of inflammatory cytokines through a feedback inhibition mechanism.

IL 6 is a pyrogenic agent. This means that it stimulates an increase in body temperature during inflammation. Other functions of interleukin 6 include the activation of T cells and the stimulation of B-cell differentiation.

Interleukin 7

Interleukin 7 (IL 7) is involved in the body's response to HIV. It stimulates the differentiation of cytotoxic lymphocytes. These immune units stimulate apoptosis, or suicide, of cells infected with the virus.

Interleukin 8

Interleukin 8 (IL 8) is a cytokine that stimulates the migration of immune cells in the body. This means that it stimulatesthe movement and spread of T lymphocytes, neutrophils and monocytes. This action is defensive in nature. IL 8 stimulates the release of histamine by basophils. This process causes an allergic reaction.

Interleukin 10

Interleukin 10 (IL 10) is opposite to the previously described cytokines. Its main task is to block the inflammatory process. It is produced by B lymphocytes, macrophages, dendritic cells and Treg lymphocytes.

IL 10 is used to control inflammatory processes in the body. Some bacteria and viruses have the ability to stimulate the production of interleukin 10. Thus, they block the immune response of our body, thus increasing their survival.

Interleukin 12

Interleukin 12 (IL12) is an IL10 antagonist. This means that it blocks its anti-inflammatory activity. Its tasks include the activation of monocyte macrophages and NK cells. It stimulates the production of interferon.

The synthesis of interleukin 12 occurs under the influence of various types of pathogens.

Interleukins and autoimmune diseases

Interleukins are responsible for keeping the immune system active. However, in the case of autoimmune diseases, elevated levels of some of this group of cytokines have been observed. This indicates the participation of interleukins in the pathomechanism of these disorders.

Interleukin 18 plays a physiological role in generating responses to pathogens. However, it is capable of producing very strong inflammatory reactions. Disturbances in the activity of this cytokine are involved in the development of autoimmune diseases. Examples include type 1 diabetes, multiple sclerosis and psoriasis.

Another example may be interleukin 15. It performs a physiological function that protects against the development of diseases. Its activity can potentially be used in the treatment of cancer.

Excessive activity of interleukin15 is currently associated with the pathogenesis of autoimmune diseases. Disturbance of its expression is observed in such diseases as:

  • systemic lupus erythematosus
  • psoriasis
  • inflammatory bowel diseases
  • multiple sclerosis
  • rheumatoid arthritis

Research is ongoing on monoclonal antibodies blocking the activity of interleukin 15 that could be used in the treatment of these diseases.

Effect of interleukins on transplant rejection

Probably IL15 also participates in the mechanism of transplant rejection by the recipient's organism.

Previously mentionedinterleukin 10, on the other hand, has the opposite effect and can be used to block the immune response after transplantation.

Effect of interleukins on transplant rejection

Interleukins are involved in defense mechanisms against many diseases. Disorders of their activity significantly contribute to the development of autoimmune diseases. Modern science is still studying these processes.

Therapeutic potential is demonstrated by both substances that block and increase the activity of interleukins. The great challenge in finding new drugs is reducing side effects.

About the authorSara Janowska, MA in pharmacyPhD student of interdisciplinary doctoral studies in the field of pharmaceutical and biomedical sciences at the Medical University of Lublin and the Institute of Biotechnology in Białystok. A graduate of pharmaceutical studies at the Medical University of Lublin with a specialization in Plant Medicine. She obtained a master's degree defending a thesis in the field of pharmaceutical botany on the antioxidant properties of extracts obtained from twenty species of mosses. Currently, in his research work, he deals with the synthesis of new anti-cancer substances and the study of their properties on cancer cell lines. For two years she worked as a master of pharmacy in an open pharmacy.

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Immune system