What is the Difference Between Cytokines and Interleukins

The main difference between cytokines and interleukins is that the cytokines are small proteins involved in cell signaling whereas the interleukins are a group of cytokines that regulate the immune and inflammatory responses. 

Cytokines and interleukins are two types of signaling molecules involved in mediating the responses of the immune system. Furthermore, cytokines can act as autocrine, paracrine or endocrine regulators while interleukins were first seen to be functional between leukocytes.

Key Areas Covered

1. What are Cytokines
     – Definition, Characteristics, Types
2. What are Interleukins
     – Definition, Characteristics, Types
3. What are the Similarities Between Cytokines and Interleukins
     – Outline of Common Features
4. What is the Difference Between Cytokines and Interleukins
     – Comparison of Key Differences

Key Terms

Cytokines, Immune System, Interleukins (IL), Signaling Molecules

What are Cytokines

Cytokines are small proteins secreted by the activated cells of the immune system in order to affect other cells. They can be either polypeptides or glycoproteins as well. The main function of cytokines is to regulate the nature, intensity, and the duration of the immune response by binding to the receptors on the target cells. Cytokines regulate hematopoiesis as well. Some of the characteristics of cytokines are as below.

• Pleiotropic molecules, a particular type of cytokine can exert different effects on different types of cells in the immune system,
• Redundant since different cytokines can exert the same effect on a particular type of immune cell,
• Bind to the receptors with a high affinity. Thereby, only a small concentration (picomolar) is sufficient for exerting the effect,
• Synergize with each other,
• Antagonize each other,
• One cytokine can induce the production of a second cytokine by its cascade effect,
• Induce the formation of cytokine receptors.
  

  Figure 1: Cytokine Evoked by Influenzavirus

They are named based on the function, cells of secretion, and the target. The type of action of a cytokine can be either autocrine, paracrine or endocrine:

• Autocrine cytokines bind to the receptors of the cell of secretion
• Paracrine cytokines bind to the receptors of the cells with close proximity to the cells of secretion
• Endocrine cytokines bind to the receptors of the cells in a distinct part of the body by travelling through the blood

Four Structural families of cytokines can be identified. They are hematopoietin family (IL-2, IL-4), interferon family (IFN-α, β, γ), chemokine family, and tumor necrosis family.

What are Interleukins

Interleukins (IL) are a group of cytokines first seen to be expressed by leukocytes. But, later it was found that they were produced by many immune system cells. They activate the proliferation, differentiation, maturation, migration, and adhesion of immune cells. They can exert pro- and anti-inflammatory functions as well. The action of interleukins can be either autocrine or paracrine.

Figure 2: IL-9 Function

Different types of interleukins can be found in the body and they are named as IL-1 to -40. The origin and the biological properties of some of the interleukins are listed below.

Biology of Interleukin

Similarities Between Cytokines and Interleukins

• Cytokines and interleukins are two types of signaling molecules in the immune system.
• They are small proteins, polypeptides or glycoproteins.
• Both regulate the nature, intensity, and duration of the immune response.
• Also, they bind to the receptors of the target cell with a high affinity.
• Both can be pleiotropic and redundant.

Difference Between Cytokines and Interleukins

Definition

Cytokines refer to a number of substances, such as interferon, interleukin, and growth factors, which are secreted by certain cells of the immune system and have an effect on other cells while interleukins refer to any of a class of proteins produced by leucocytes for regulating immune responses.

Correspondence

Cytokines are a large group of signaling molecules while interleukins are a subfamily of cytokines. This is a main difference between cytokines and interleukins. 

Action

Another difference between cytokines and interleukins is that the cytokines can have either autocrine, paracrine or endocrine action while interleukins have either autocrine or paracrine action.

Function

Yet another difference between cytokines and interleukins is their function. While cytokines regulate the nature, intensity, and duration of the immune response, interleukins induce the proliferation, differentiation, maturation, migration, and adhesion of cells of the immune system.

Conclusion

Cytokines are small proteins molecules produced by the cells of the immune system. They involve in the cell signaling. Interleukins, interferons, chemokines, and tumor necrosis factors are the four types of cytokines. Interleukins are mainly involved in the proliferation, differentiation, and maturation of immune system cells. The main difference between cytokines and interleukins is their function.

Reference:

1. “What Are Cytokines.” What Are Proteases-Enzyme, Available Here
2. Justiz Vaillant AA, Qurie A. Interleukin. [Updated 2018 May 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2018 Jan-. Available Here
3. Elmslie, Robyn E., et al. “Interleukins: Biological Properties and Therapeutic Potential.” Journal of Veterinary Internal Medicine, vol. 5, no. 5, 1991, pp. 283–293., doi:10.1111/j.1939-1676.1991.tb03135.x. Available Here

Image Courtesy:

1. “CytokineStormMechanism” By GrrlScientist (CC BY 2.0) via flickr
2. “IL 9 functions.large” By Ritobrata Goswami and Mark H. Kaplan –  (CC BY-SA 4.0) via Commons Wikimedia