Cytokines – Types and functions

What are cytokines?

Cytokines are small-membrane-bound protein-based cell signalling molecules that function as chemical messengers. They aid cell-to-cell communication in immune responses and stimulate the movement of cells towards the site of infection and inflammation.

Cytokines transmit signals for cell survival, differentiation, proliferation and functional activity. They boost anti-cancer activity by sending signals to kill the abnormal cells and make the normal cells live longer.

The main function of cytokines is cell signalling, and apart from it, there are types of cytokines that specialise in certain functions.

Types of cytokines

Chemokines

Chemokines are small proteins that play a major role in controlling the growth and activity of immune system cells and blood cells. A chemokine signals the immune cells and directs them towards the target.

The other types of chemokines include interferons, interleukins, growth factors and tumour necrosis factor (TNF). Some are engineered in the laboratory to target and treat cancer cells, whereas some are used to prevent and manage the side effects of chemotherapy. These cells are injected under the skin, into a vein or a muscle.

Interleukins

Interleukins are cytokines that signal white blood cells. Interleukin 2 (IL 2) aids in the growth and development of immune cells. A laboratory-engineered version of IL 2 is used to treat metastatic melanoma and kidney cancer.

Interleukin 2 is mostly used as a single drug to treat cancers or combined with other therapies or cytokines like interferon-alpha and then used.

Some of the common side effects of IL 2 include chills, fever, fatigue, confusion and other flu symptoms. Other symptoms include vomiting, nausea and diarrhoea. In rare cases, people tend to develop low blood pressure, which can be treated with medication.

Some of the major side effects include chest pain, abnormal heartbeat and other cardiovascular diseases. So, if IL 2 is administered in high doses, it is recommended to do it in a hospital. Other interleukins that are commonly used for treatment include IL 7, IL 12 and IL 21.

Interferons

Interferons are also chemical messengers that help the body to resist cancer cells and viral infections. The common interferons are

Interferon alpha (INF-alpha)

Interferon beta (INF-beta)

Interferon gamma (INF-gamma)

Among the three interferons, only interferon-gamma is used to treat cancer and boosts immune cells’ ability to attack cancer cells.

Additionally, it also slows the growth of cancer cells. Interferon alpha is used to treat cancers like

• Chronic myelogenous leukaemia
• Hairy cell leukaemia
• Cutaneous T-cell lymphoma
• Follicular non-Hodgkin lymphoma
• Melanoma
• Kidney cancer
• Kaposi sarcoma

Side effects of interferons include

• Skin rashes
• Hair thinning
• Flu-like symptoms
• Loss of appetite
• Low white blood cell count

In most cases, the side effects do not last longer and stop after the treatment. However, fatigue can last longer.

Other cytokines

Other cytokines include tumour necrosis factor (TNF) and colony-stimulating factor (CSF). The CSF are myeloid haematopoietic progenitor cells. They are mature cells like macrophages and neutrophils.

It also plays a crucial role in alveolar macrophage functions like neutralising autoantibodies.

Thymic stromal lymphopoietin (TSL) is expressed by epithelial cells in the lungs, skin, intestine and thymus. It plays a key role in intestinal immune homeostasis.

Functions of cytokines

Cytokines are known for regulating inflammation in the body. If we have inflammation, it is common to think that we may be sick or have an allergy. But the truth is, it can be a sign that the body is fighting foreign cells or healing tissue damage.

Additionally, the body tends to release cytokine when they feel threatened. The cytokines carry information on how to handle threats and repair injuries.

Cell activation

Cytokines activate a cell and instruct them about where to find the target cells. For instance, cytokines can direct the immune cells to the site of infection and fight the invasion of foreign cells. They can lessen the process depending on the inflammation.

Cell differentiation

Cytokines can help with cell differentiation. It signals the immature cells to transform into specific cells whenever required. For example, the cytokines signal the immature white blood cells to transform into mature cells so that they can fight the infection.

Cell proliferation

Cytokines can signal the immune cells to proliferate to fight the invading cells. Cytokines can also be self-signal to increase cytokine production so that they can increase the inflammatory response of the body.

How do cytokines work?

Cytokines work by releasing cytokines or cytokine receptors. The cytokines will be the key, and the receptor will act as a lock. So, when cytokines enter the receptors, the cells receive a signal to carry out the immune response. The cells will act depending on the signal they receive.

Suppose an immune cell detects harmful substances like bacteria and viruses. They release a cytokine as a response to the invasion. The cytokines travel through the bloodstream or directly enter the tissue and remove the foreign cells.

The cell signalling of cytokines occurs through three signals.

• Autocrine signalling
• Paracrine signalling
• Endocrine signalling

Autocrine signalling occurs when the receptors bind to the same cells that released it. When cytokines bind to nearby cells, it is called paracrine signalling, whereas if they bind to cells that are far away, it is called endocrine signalling.

Diseases or conditions that involve cytokines

Cytokines are vital for the body and play an important role in the diseases and conditions that affects you. Cytokines fight the foreign cells to keep you infection-free. If the immune cells release too many cytokines in response to a treatment or infection, it is called cytokine-released syndrome (CRS).

The condition can be life-threatening without proper treatment. It is also called as cytokine storm. It can damage the tissues and lead to conditions and diseases like

• Autoimmune diseases
• Cancer
• Sepsis

If a person has an autoimmune disease, it can attack the healthy cells of the body. It can also affect the metabolism of the body and called as a metabolic disorder. The body’s inflammatory response can reduce the blood flow to major organs and lead to sepsis. Sepsis without treatment can be fatal, and it is a medical emergency.

Conclusion

Cytokines are essential as they invade foreign cells. They signal the cells when they identify a pathogen, and other cells fight the pathogen and help remove it from the body.

Cytokines should be produced in moderation, and too many leads to inflammation that can damage the internal organs. And a few can lead to frequent infection. If you have health conditions related to cytokines, medical care is crucial to handle them.