Cytokines are low molecular weight proteins that are secreted by cells of the immune system and other cells to regulate immune responses. They act as signaling molecules between cells through specific high-affinity receptors. Cytokines control processes like activation, growth, and differentiation of immune cells. They are classified based on their cellular source (monokines, lymphokines) or functional roles (interleukins, interferons, tumor necrosis factors, colony-stimulating factors, chemokines, growth factors). Binding of cytokines to their receptors triggers intracellular signaling cascades that regulate gene expression. Dysregulation of cytokines can contribute to diseases like cytokine release syndrome. Key cytokines discovered at the National Cancer Institute, like interleukin-2, interleukin-

1. Cytokines

2. What are cytokines?
 Cytokines/ Immunocytokines (Greek.cyto=‘cell’ and
kines=‘movement’) are low molecular weight regulatory proteins
or glycoproteins secreted by white blood cells and various other
cells in the body in response to number of stimuli.
 The complex interactions among immune cells are mediated by
cytokines to denote their role in cell-to-cell communications.
 Cytokines control activation, proliferation, differentiation and
functions of the cells of immune system.

3. Properties of cytokines
1. Target specific and induced signal transduction
 Cytokines bind to the specific receptor on the
membrane of the target cell, triggering signal
transduction pathways that ultimately alter gene
expression in target cell.
2. High affinity of cytokines and its receptors
 Cytokines and their fully assembled to receptors
exhibit very high affinity for each other and
deliver intracellular signals.

4. 3. Mode of action:
 A particular cytokine may show:
✓Autocrine activity
✓Paracrine activity
✓Endocrine activity
 A particular receptor may bind to the receptor on the membrane of the same cell that secreted it,
secreted it, exerting autocrine action.
 It may bind to receptor on target cell in close proximity to producer cell, exerting paracrine action.
paracrine action.
 It may bind to target cells in distant parts of the body, exerting endocrine action.

5. 4. Attributes of cytokines
 Cytokines, exhibit the attributes of pleiotropy,
pleiotropy, redundancy, synergy, antagonism and
antagonism and cascade induction which permit
permit them to regulate cellular activity in a
coordinated interactive way.
✓The ability of cytokine to exert different types of
responses, often on different cell types is pleiotropy.

6. Classification according to source:
According to their source cytokines are classified into:
1. Monokines:
The cytokines released from mono nuclear phagocytes are monokines.
2. Lymphokines:
When cytokines are released from T lymphocytes they are called
lymphokines.

7. Classification according to function:
Cytokines are classified according to their functions into following categories:
1. Interleukins:
 The term Interleukin means the cytokines that are produced from one leukocyte
and act on another leukocyte.
 They promote the development and differentiation of T and B lymphocytes and
hematopoietic cells.
 31 kinds of Interleukins have been identified and they are denoted by IL-1~IL-31.

8. 2. Interferon:
 The first cytokines to be discovered were interferons.
 There designated by IFN.
 Interfere with infection and replication of viruses.
 Further divided into three subtypes : alpha, beta and gamma.
 IFN-alpha and IFN-beta are collectively called type 1 interferon. They are produced
produced by plasma cystoid dendritic cells and cells with viral infection.
 Interferon-gama referred to as type 2 interference they are principally secreted
secreted from activated T cells and NK cells.

9. 3. Tumor necrosis factor:
 TNF was originally identified as the substance that can cause the necrosis of
necrosis of the tumor in Vivo.
 TNF is further subdivided into TNF-alpha and TNF-beta.
 TNF-alpha is the most well known member of this class and sometimes
sometimes referred to when the term tumor necrosis factor is used.
 TNF-beta is also termed as lymphotoxin and is produced by activated T cells.
T cells.

10. 4. Colony stimulating factor
 Stimulates the differentiation and expansion of the bone marrow projenator cells.
cells.
 It is assayed by its ability to stimulate the formation of cell colonies in the culture.
culture.
 It includes GM-CSF, G-CSF, EPO, SCF, TPO and so on.
5. Chemokines:
 They constitute a protein family and their main function is to recruit monocyte,
monocyte, lymphocytes and neutrophils at the infection site.
 Based on the number and position of the cystine they are further classified into four
into four sub groups:CXC, CC, C and CX3C.

11. 6. Growth factor
 GF is able to stimulate cell growth.
 Includes TGF-B, EGF, VEGF, FGF, NGF and PDGF.
Cytokine receptors:
There are four types of cytokines receptors.
1. TYPE I RECEPTORS:
 The largest family of cytokine receptors is Type I receptor superfamily. It is characterized by
characterized by an extracellular region of structural homology approximately 200 amino
amino acids long.
 Receptors for cytokines such as IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-12, G-CSF and GM-CSF
GM-CSF belong to this family.

12. 2. TYPE II RECEPTORS:
 The Type II family of related cytokine receptors can be considered part of
part of the immunoglobulin superfamily and contains receptors for all IFN
all IFN types as well as IL-10 and M-CSF
3. TYPE III RECEPTORS:
 TNF family cytokines bind to Type III cytokine receptors which all have
have multiple cysteine-rich repeats of about 40 amino acids in the
extracellular domain.

13. 4. TYPE IV:
 Receptors for IL-1a and B are representative of the Type IV cytokine
cytokine receptor family.
 Regardless of these subtypes, cytokine receptors have several common
common characteristics. They usually consist of two or more subunits,
subunits, and receptors for different cytokines may even share common
common subunits.

14. Cell Activation Mechanism
1) The binding of a cytokines to its appropriate sets of a
cascade that leads to induction or inhibition transcription
of a number of cytokine regulating genes.
2) This occurs via protein protein recognition events
leading to binding of diverse transcription factors to DNA.
3) Cytokines initiate intracellular signals through ligand
induced aggregation of receptor components.
4) Cytokine binding can cause hetero or homo-
dimerization of receptors or trimerization depend on
particular family.

15. Cytokine signaling
 The cytokine receptors lack the Immunotyrosine Activation Motifs
(ITAMS) characteristic of B- and t-cell receptors.
 In the absence of cytokine, the receptor subunits are associated only
loosely with one another in the plane of the membrane, and the
cytoplasmic region of each of the receptor subunits is associated
noncovalently with inactive tyrosine kinases named Janus Activated
Kinases (JAKs).

16. Continue….
1. Binding of cytokine causes dimerization of
receptors and activation of JAK kinases.
2. Activated JAK kinases phosphorylate
receptor sites and create docking sites for
STAT (signal transducers and activators of
transcription) molecules.
3. The phosphorylated stats dimerize and
translocate to the nucleus, where they
activate transcription of Specific genes.

17. Cytokines Antagonist
Number of proteins can inhibit cytokines activity by
1) Binding to receptor.
2) Binding to cytokine molecule.
IMPORTANCE: Viruses Have Developed Strategies to Exploit
Cytokine activity. Epstein-Barr virus (EBV), for example,
produces an IL-10–like molecule (viral IL-10 or vIL-10) that
binds to the IL-10 receptor. Just like host-derived IL-10, this
viral homologue suppresses TH1-type cell-mediated responses
that would otherwise be effective in fighting a viral infection.

18. Cytokine as a disease
A condition that may occur after treatment with some
types of immunotherapy, such as monoclonal
antibodies and CAR-T cells. Cytokine release
syndrome (CRS) is caused by a large, rapid release of
cytokines into the blood from immune cells affected
by the immunotherapy. Cytokines are immune
substances that have many different actions in the
body.

19. 1- Interlukin-2 (IL-2)
 Interleukin-2 (IL-2), the first cytokine found to have
therapeutic benefit, was discovered in 1976 by
Robert Gallo, M.D., and Francis Ruscetti, Ph.D.
 The team demonstrated that this cytokine could
dramatically stimulate the growth of T and natural
killer (NK) cells, which are integral to the human
immune response. This seminal work enabled
researchers to grow and study T cells in the
laboratory for the first time, changing the field of
immunology forever.

20. 2- Interlukin-7
 CCR research groups led by Crystal Mackall, M.D., and Ron Gress, M.D.,
characterized another cytokine, IL-7, as a master regulator of T-cell homeostasis
or equilibrium.
 In the first human clinical trial with IL-7, they found that the cytokine drives
regeneration of T cells that are critical to the immune system but become depleted
during chemotherapy.
 IL-7-based therapies also might restore immune function in other
immunocompromised individuals, such as those with HIV and the aged, and might
enhance the activity of vaccines and other cancer immunotherapies.

21. 3- Interlukin-15
 A third cytokine, IL-15, was co-discovered in CCR in 1994 by Thomas
Waldmann, M.D., and his team. Like IL-2, it triggers the production of
immune cells that attack and kill cancer cells. The results of the trial,
published in 2015, showed IL-15 dramatically increased growth and activity
of T and NK cells.
 Studies investigating the potential for IL-15 to enhance the effectiveness of
vaccines against viruses that cause cancer and autoimmune diseases are
underway.