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1. 1. What’s Cytokines?
Cytokines are a broad and loose category of small proteins, important in cell signaling. Cytokines
are crucial in controlling the growth and activity of other immune system cells and blood
cells.Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm.
Cytokines have been shown to be involved in autocrine, paracrine and endocrine signaling as
immunomodulating agents.When released, they signal the immune system to do its job.
2. What are the 5 Cytokines?
Interleukins
Interleukins (IL) are a type of cytokine first thought to be expressed by leukocytes alone but have
later been found to be produced by many other body cells. The primary function of interleukins is,
therefore, to modulate growth, differentiation, and activation during inflammatory and immune
responses. Interleukins consist of a large group of proteins that can elicit many reactions in cells
and tissues by binding to high-affinity receptors in cell surfaces. They have both paracrine and
autocrine function. Interleukins are also used in animal studies to investigate aspect related to
clinical medicine.
Interleukin-2 (IL-2) helps immune system cells grow and divide more quickly. A man-made version
of IL-2 is approved to treat advanced kidney cancer and metastatic melanoma. IL-2 can be used
as a single drug treatment for these cancers, or it can be combined with chemotherapy or with
other cytokines such as interferon-alfa.
Other interleukins, such as IL-7, IL-12, and IL-21, continue to be studied for use against cancer too,
both as adjuvants and as stand-alone agents.
Chemokines
Chemokines are a family of small cytokines or signaling proteins secreted by cells that induce
directional movement of leukocytes, as well as other cell types, including endothelial and
epithelial cells. chemokines are important for biological processes, including morphogenesis and

2. wound healing, as well as in the pathogenesis of diseases like cancers.
Chemokines have been classified into four main subfamilies: CXC, CC, CX3C and C. All of these
proteins exert their biological effects by interacting with G protein-linked transmembrane
receptors called chemokine receptors, that are selectively found on the surfaces of their target
cells.
Interferons
Interferons are a group of signaling proteins made and released by host cells in response to the
presence of several viruses. In a typical scenario, a virus-infected cell will release interferons
causing nearby cells to heighten their anti-viral defenses.
IFNs belong to the large class of proteins known as cytokines, molecules used for communication
between cells to trigger the protective defenses of the immune system that help eradicate
pathogens.
More than twenty distinct IFN genes and proteins have been identified in animals, including
humans. They are typically divided among three classes: Type I IFN, Type II IFN, and Type III IFN.
IFNs belonging to all three classes are important for fighting viral infections and for the regulation
of the immune system.
Lymphokines
Lymphokines are a subset of cytokines that are produced by a type of immune cell known as a
lymphocyte.They are protein mediators typically produced by T cells to direct the immune system
response by signaling between its cells. Lymphokines have many roles, including the attraction of
other immune cells, including macrophages and other lymphocytes, to an infected site and their
subsequent activation to prepare them to mount an immune response.
Important lymphokines secreted by the T helper cell include:
Interleukin 2，
Interleukin 3，
Interleukin 4，
Interleukin 5，
Interleukin 6，
Granulocyte-macrophage
colony-stimulating factor，Interferon-gamma
tumour necrosis factors
Tumor necrosis factor (TNF, cachexin, or cachectin; often called tumor necrosis factor alpha or
TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists
of various transmembrane proteins with a homologous TNF domain.
As an adipokine, TNF promotes insulin resistance, and is associated with obesity-induced type 2
diabetes.As a cytokine, TNF is used by the immune system for cell signaling. If macrophages
(certain white blood cells) detect an infection, they release TNF to alert other immune system
cells as part of an inflammatory response.

3. 3. Do cytokines reduce inflammation?
Cytokines are regulators of host responses to infection, immune responses, inflammation, and
trauma. Some cytokines act to make disease worse (proinflammatory), whereas others serve to
reduce inflammation and promote healing (anti-inflammatory).
Reference:
1.Janeway's Immunobiology. Garland Science. 2017. p. 107. ISBN 978-0-8153-4551-0.
2.Lackie J (2010). "Cytokines". A Dictionary of Biomedicine. Oxford University Press. ISBN
978-0-19-954935-1.
3. "Cytokine". Stedman's Medical Dictionary (28th ed.). Wolters Kluwer Health, Lippincott
Williams & Wilkins. 2006. ISBN 978-0-7817-6450-6.