Main Difference – Cytokines vs Chemokines
Cytokines and chemokines are two immune-modulating agents, which are involved in the mediating and modulating of the responses of the immune system. Several types of cytokine superfamilies are identified: chemokines, ILs, INFs, CSFs, TNFs and TGFs. They only differ in the function they perform in the body. Chemokines produce a concentration gradient, guiding other leukocytes to the site of infection. The main difference between cytokines and chemokines is that cytokines are small protein substances which are secreted by cells in the body, affecting other cells whereas chemokines are one of the superfamilies of cytokines, containing chemotactic activity.
This article explores,
1. What are Cytokines
– Structure, Types, Function
2. What are Chemokines
– Structure, Types, Function
3. What is the difference between Cytokines and Chemokines
What are Cytokines
Cytokines are substances which are secreted by the cells of the immune system, affecting other cells. Interferon, interleukin and growth factors are cytokines. Cytokines can be either proteins, polypeptides or glycoproteins, and serve as signalling molecules, mediating and regulating the immunity, inflammation as well as hematopoiesis. Different types of cells in the body are involved in the secretion of cytokines. The naming of cytokines is done depending on the function performed in the body, cells of secretion or target of action. Cytokines exhibit a very high affinity to their receptors. Hence, cytokines can be maintained at picomolar concentrations.
A particular cytokine may be involved in autocrine activity, paracrine activity or endocrine activity. Autocrine activity is the binding of cytokines to receptors of cells, which secreted that particular cytokine. Paracrine activity is the binding of cytokine to the receptors of cells, which have a close proximity to the secreted cells. Endocrine activity is the traveling of cytokines through blood to a distinct part of the body, where it is secreted. The super family of cytokines include chemokines, interleukins (ILs), interferons (INFs), colony-stimulating factors (CSFs), transforming growth factors (TGFs) andtumor necrosis factors (TNFs). Though each cytokine type is structurally similar, they differ in their functions. Type 1 cytokines are involved in enhancing the cellular immune response, and type 2 cytokines are involved in the antibody response. Type 1 cytokines are TNFα and IFN-γ. Type 2 cytokines are IL-4, IL-10, IL-13 and TGF-β.
Figure 1: Cytokines in hematopoiesis
What are Chemokines
Chemotactic cytokines are called chemokines. Chemotactic cytokines are capable of inducing directed chemotaxis in the nearby responsive cells. Infected tissues are stimulated by pro-inflammatory cytokines, releasing chemotactic cytokines. Pro-inflammatory cytokines are IL-1 and TNFs. A gradient of chemokines is generated, which directs leukocytes into the infected tissue. Leukocytes move from endothelial cells to the basement membrane of the infected tissue. Chemokines are also involved in controlling cells like directing lymphocytes into lymph nodes during immune surveillance. These types of chemokines are called homeostatic chemokines. Some chemokines are involved in the promotion of angiogenesis. Other chemokines are involved in the metastasis and tumor growth. The direction of chemotaxis from low concentration to the high concentration of chemokines is shown in figure 2.
figure 2: Direction of chemotaxis
Four groups of chemokines are found based on the first two cytosine residues on the polypeptide chain. CC chemokines consist of two adjacent cytosine residues at the amino terminus. CXC chemokines consist of two cytosine residues at the N-terminus, which are separated by one amino acid. C chemokines consist of one cytosine in the N-terminus and the other cytosine downstream. CX3C chemokines consist of three amino acids between the two cytosine residues. Structures of the different groups of chemokines are shown in figure 3.
Figure 3: Chemokine types
Difference Between Cytokines and Chemokines
Relationship
Cytokines: Cytokines are immune-modulating agents which are made up from proteins.
Chemokines: Chemokines are a super family of cytokines which mediate chemotaxis.
Function
Cytokines: Cytokines are involved in both cellular and antibody-mediated immunity in the body.
Chemokines: Chemokines are involved in the guiding of cells in the immune system to the site of infection.
Types
Cytokines: Chemokines, ILs, INFs, CSFs, TNFs and TGFs are the types of cytokines in the body.
Chemokines: CC chemokines, CXC chemokines, C chemokines and CX3C chemokines are the structural types of chemokines in the body.
Conclusion
Cytokines and chemokines are involved in the mediating of the immune response in the body. Chemokines are one type of cytokines, involved in the chemotaxis by guiding other leukocytes into the site of infection. Other types of cytokines are interferons (INFs), interleukins (ILs), colony-stimulating factors (CSF), transforming growth factors (TGFs) and tumor necrosis factors (TNFs). The main difference between cytokines and chemokines is their functions during the mediation of immune response. All cytokines are structurally similar. They only differ in their functions during immunity. Cytokines are involved in the cellular immunity during inflammation by inducing non-specific immune responses against pathogens. Chemotaxis is also a type of cellular immunity, which guides phagocytic cells in the blood into the site of inflammation in order to destroy pathogens by phagocytosis. Cytokines are also involved in the antibody-mediated immunity by inducing T and B lymphocytes to produce specific antibodies to a particular pathogen.
Reference:
1. Borish, L. C., and J. W. Steinke. “2. Cytokines and chemokines.” The Journal of allergy and clinical immunology. U.S. National Library of Medicine, Feb. 2003. Web. 21 Apr. 2017.
2. What are Cytokines. N.p., n.d. Web. 21 Apr. 2017. <http://www.sinobiological.com/What-Is-Cytokine-Cytokine-Definition-a-5796.html>.
Image Courtesy:
1. “Hematopoietic growth factors” By User:Mikael Häggström and A. Rad – File:Hematopoiesis (human) diagram.png, by A. Rad. (CC BY-SA 3.0) via Commons Wikimedia
2. “Chemokine concentration chemotaxis” By Pen1234567. Derivative of image by Kohidai, L. – Own work. Based on File:Chtxphenomen1.png. (CC BY-SA 3.0) via Commons Wikimedia
3. “ChtxChemokineStruct” By Kohlasz21 (Kohidai, Laszlo) – Own work (CC BY-SA 3.0) via Commons Wikimedia
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