M.Prasad NaiduMSc Medical

Biochemistry,Ph.D.Research Scholar

CYTOKINESCYTOKINES Cytokines are small secreted proteins which mediate and Cytokines are small secreted proteins which mediate and regulate immunity, inflammation, and hematopoiesis. They are regulate immunity, inflammation, and hematopoiesis. They are produced in response to an immune stimulus. produced in response to an immune stimulus.

Cytokine is the general term for a large group of molecules Cytokine is the general term for a large group of molecules involved in signaling between cells during immune responses. involved in signaling between cells during immune responses. All cytokines are proteins, some with sugar molecules All cytokines are proteins, some with sugar molecules attached (glycoproteines). attached (glycoproteines).

They are synthesized and released by white blood cells and They are synthesized and released by white blood cells and tissue macrophages.tissue macrophages.

They are proteins, peptides or glycoproteins in nature.They are proteins, peptides or glycoproteins in nature.

Cytokines stimulate or suppress the functional activity of Cytokines stimulate or suppress the functional activity of lymphocytes, monocytes, neutrophils, fibroblast and lymphocytes, monocytes, neutrophils, fibroblast and endothelial cells.endothelial cells.

They modulate the function of other cell types. Long They modulate the function of other cell types. Long known to be involved in cellular immune response, these known to be involved in cellular immune response, these products have additional effects that play important roles products have additional effects that play important roles in both acute and chronic inflammation.in both acute and chronic inflammation.

200 different human cytokines was have been identified200 different human cytokines was have been identified

TERMS AND DEFINITIONSTERMS AND DEFINITIONS::

Cytokines generated by mononuclear phagocytes Cytokines generated by mononuclear phagocytes are often called ‘Monokines’ and those by activated are often called ‘Monokines’ and those by activated lymphocytes are reffered to as ‘Lymphokines’.lymphocytes are reffered to as ‘Lymphokines’.

Additionally, both monocytes and macrophages Additionally, both monocytes and macrophages produce cytokines such as CSF’s, which stimulate produce cytokines such as CSF’s, which stimulate the growth of immature leukocytes in the bone the growth of immature leukocytes in the bone marrow.marrow.

GENERAL PROPERTIES GENERAL PROPERTIES

Cytokines are produced during immune and inflammatory Cytokines are produced during immune and inflammatory responses and secretion of these mediators is transient and responses and secretion of these mediators is transient and closely regulated.closely regulated.

Cytokine effects are often redundant and these proteins can Cytokine effects are often redundant and these proteins can influence the synthesis or action of other cytokines.influence the synthesis or action of other cytokines.

Cytokines mediate their effects by binding to specific Cytokines mediate their effects by binding to specific receptors on target cells and the expression of cytokine receptors on target cells and the expression of cytokine receptors can be regulated by a variety of exogenous and receptors can be regulated by a variety of exogenous and endogenous signals.endogenous signals.

Cytokines induce their effects in two waysCytokines induce their effects in two ways

1) they act on the same cell that produces them (autocrine 1) they act on the same cell that produces them (autocrine effect)effect)

e.g: IL-2 produced by activated T cells promotes T- cell e.g: IL-2 produced by activated T cells promotes T- cell growthgrowth

2) they affect other cells in their vicinity (paracrine effect)2) they affect other cells in their vicinity (paracrine effect)

e.g: IL-7 produced by marrow stromal cells promotes the e.g: IL-7 produced by marrow stromal cells promotes the differentiation of B- cell progenitors in the marrowdifferentiation of B- cell progenitors in the marrow

Many classic growth factors act as cytokines and Many classic growth factors act as cytokines and conversely many cytokines have growth promoting conversely many cytokines have growth promoting properties.properties.

The main sets of cytokines are The main sets of cytokines are

InterleukinsInterleukins

InterferonsInterferons

Tumour necrosis factorsTumour necrosis factors

Growth factors Growth factors

Colony stimulating factorsColony stimulating factors

Chemokines Chemokines

INTERFERONS (IFNs)INTERFERONS (IFNs)

InterferonsInterferons ( (IFNIFNs) are proteins made and released by s) are proteins made and released by helper CD4+ T lymphocytes, as well as through helper CD4+ T lymphocytes, as well as through monocytes, macrophages, and endothelial cells in monocytes, macrophages, and endothelial cells in response to the presence of pathogens — such as response to the presence of pathogens — such as viruses, bacteria or parasites — or tumor cells.viruses, bacteria or parasites — or tumor cells.

IFNs belong to the large class of glycoproteins known as IFNs belong to the large class of glycoproteins known as cytokines. Although they are named after their ability to cytokines. Although they are named after their ability to "interfere" with viral replication within host cells"interfere" with viral replication within host cells

They are produced very early in infection They are produced very early in infection and are the first line of resistance to a and are the first line of resistance to a great many virusesgreat many viruses

These are particularly important in These are particularly important in limiting the spread of certain viral limiting the spread of certain viral infections. One group of interferons infections. One group of interferons (IFNα and IFNβ) is produced by cells (IFNα and IFNβ) is produced by cells which have become virally infectedwhich have become virally infected

Types of interferonTypes of interferon

Based on the type of receptor human interferons have been Based on the type of receptor human interferons have been classified into two major types.classified into two major types.

Interferon type I: Interferon type I: All type I IFNs bind to a specific cell surface receptor All type I IFNs bind to a specific cell surface receptor

complex known as the IFN-α receptor. The type I complex known as the IFN-α receptor. The type I interferons present in humans are IFN-α, IFN-β and IFN-interferons present in humans are IFN-α, IFN-β and IFN-

ωω..Interferon type II:Interferon type II: In humans this is IFN-γIn humans this is IFN-γ

FUNCTIONSFUNCTIONS

they activate immune cells, such as natural killer cells they activate immune cells, such as natural killer cells and macrophagesand macrophages

they increase recognition of infection or tumor cells by they increase recognition of infection or tumor cells by

up-regulating antigen presentation to T lymphocytes up-regulating antigen presentation to T lymphocytes and and

they increase the ability of uninfected host cells to they increase the ability of uninfected host cells to

resist new infection by virus. Certain host symptoms, resist new infection by virus. Certain host symptoms, such as aching muscles and fever, are related to the such as aching muscles and fever, are related to the production of IFNs during infection.production of IFNs during infection.

INTERLEUKINS (ILs)INTERLEUKINS (ILs)

These are a large group of cytokines produced mainly by T These are a large group of cytokines produced mainly by T cells, although some are also produced by mononuclear cells, although some are also produced by mononuclear phagocytes (or) by tissue cells. phagocytes (or) by tissue cells.

The interleukins were first described as signals for The interleukins were first described as signals for communication between white blood cells (leuk- from communication between white blood cells (leuk- from leukocytes).leukocytes).

Currently, it is well-known that these molecules are Currently, it is well-known that these molecules are produced and used as signalling molecules in many cells produced and used as signalling molecules in many cells of the body, in addition to immune cells.of the body, in addition to immune cells.

They have a variety of functions, but most of them are They have a variety of functions, but most of them are involved in directing there cells to divide and differentiateinvolved in directing there cells to divide and differentiate

Interleukins represent a broad family of cytokines that are Interleukins represent a broad family of cytokines that are made by hematopoietic cells and act primarily on made by hematopoietic cells and act primarily on leukocytesleukocytes

There are currently 35 well-known interleukins, however, There are currently 35 well-known interleukins, however, there are many more to be found and characterized. there are many more to be found and characterized.

TUMOUR NECROSIS FACTORS (TNF)TUMOUR NECROSIS FACTORS (TNF)

Tumor necrosis factorsTumor necrosis factors (or the (or the TNF-familyTNF-family) refers to a ) refers to a

group of cytokines family that can cause cell death.group of cytokines family that can cause cell death.

TNF acts via the TNF Receptor (TNF-R) and is part of the TNF acts via the TNF Receptor (TNF-R) and is part of the extrinsic pathway for triggering apoptosis.extrinsic pathway for triggering apoptosis.

TNF interacts with tumor cells to trigger cytolysis or cell TNF interacts with tumor cells to trigger cytolysis or cell death.death.

Types:Types:

Tumor necrosis factor-alpha (TNF-α) is the most Tumor necrosis factor-alpha (TNF-α) is the most well-known member of this class, and well-known member of this class, and sometimes referred to when the term "tumor sometimes referred to when the term "tumor necrosis factor" is used.necrosis factor" is used.

Tumor necrosis factor-beta (TNF-β), also known Tumor necrosis factor-beta (TNF-β), also known as lymphotoxin is a cytokine that is induced by as lymphotoxin is a cytokine that is induced by interleukin 10interleukin 10

COLONY STIMULATING FACTORS COLONY STIMULATING FACTORS (CSFs) (CSFs)

Colony-stimulating factorsColony-stimulating factors (CSFs) are secreted (CSFs) are secreted glycoproteins which bind to receptor proteins on the glycoproteins which bind to receptor proteins on the surfaces of hemopoietic stem cells and thereby activate surfaces of hemopoietic stem cells and thereby activate intracellular signaling pathways which can cause the cells intracellular signaling pathways which can cause the cells to proliferate and differentiate into a specific kind of blood to proliferate and differentiate into a specific kind of blood cellcell

These are primarily involved in directing the division and These are primarily involved in directing the division and differentiation of bone marrow stem cells, and the differentiation of bone marrow stem cells, and the precursors of blood leucocytesprecursors of blood leucocytes

TYPES:TYPES:

CSF1 - macrophage colony-stimulating factor - macrophage colony-stimulating factor

CSF2CSF2 - Granulocyte macrophage colony- - Granulocyte macrophage colony-stimulating factors (also called GM-CSF and stimulating factors (also called GM-CSF and sargramostim)sargramostim)

CSF3 - Granulocyte colony-stimulating factors - Granulocyte colony-stimulating factors (also called G-CSF and filgrastim)(also called G-CSF and filgrastim)

GROWTH FACTROS (GF)GROWTH FACTROS (GF)

A A growth factorgrowth factor is a naturally occurring substance is a naturally occurring substance capable of stimulating cellular growth, proliferation and capable of stimulating cellular growth, proliferation and cellular differentiation.cellular differentiation.

Growth factors typically act as signaling molecules Growth factors typically act as signaling molecules between cells and they are important for regulating a between cells and they are important for regulating a variety of cellular processes.variety of cellular processes.

e.g:e.g:

Epidermal growth factor (EGF)Epidermal growth factor (EGF)

Fibroblast growth factor (FGF) Fibroblast growth factor (FGF)

Granulocyte-colony stimulating factor (G-CSF)Granulocyte-colony stimulating factor (G-CSF)

Nerve growth factor (NGF)Nerve growth factor (NGF)

CHEMOKINES:CHEMOKINES:

This large group of chemotactic cytokines direct This large group of chemotactic cytokines direct movement of cells around the body, from the movement of cells around the body, from the blood stream into tissues and to the appropriate blood stream into tissues and to the appropriate location within each tissue. location within each tissue.

Some of the chemokines also activate cells to Some of the chemokines also activate cells to carry out particular functions.carry out particular functions.

Chemokines are cytokines that share the ability Chemokines are cytokines that share the ability to stimulate leukocyte movement (chemokinesis) to stimulate leukocyte movement (chemokinesis) and directed movement (chemotaxis) and are and directed movement (chemotaxis) and are particularly important in inflammation.particularly important in inflammation.

CYTOKINE RECEPTORSCYTOKINE RECEPTORS

Cytokine receptors fall into four familiesCytokine receptors fall into four families

1) Type I receptors1) Type I receptors

2) Type II receptors2) Type II receptors

3) Type III receptors3) Type III receptors

4) Type IV receptors4) Type IV receptors

TYPE I RECEPTORS:TYPE I RECEPTORS:

The largest family of cytokine receptors is Type I The largest family of cytokine receptors is Type I receptor superfamily. It is characterized by an receptor superfamily. It is characterized by an extracellular region of structural homology extracellular region of structural homology approximately 200 amino acids long.approximately 200 amino acids long.

Receptors for cytokines such as IL-2, IL-3, IL-4, 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 IL-5, IL-6, IL-7, IL-9, IL-12, G-CSF and GM-CSF belong to this family.belong to this family.

TYPE II RECEPTORS:TYPE II RECEPTORS: The Type II family of related cytokine receptors The Type II family of related cytokine receptors

can be considered part of the immunoglobulin can be considered part of the immunoglobulin superfamily and contains receptors for all IFN superfamily and contains receptors for all IFN types as well as IL-10 and M-CSFtypes as well as IL-10 and M-CSF

TYPE III RECEPTORS:TYPE III RECEPTORS: TNF family cytokines bind to Type III cytokine TNF family cytokines bind to Type III cytokine

receptors which all have multiple cysteine-rich receptors which all have multiple cysteine-rich repeats of about 40 amino acids in the repeats of about 40 amino acids in the extracellular domainextracellular domain..

TYPE IV:TYPE IV:

Receptors for IL-1α and β are representative of Receptors for IL-1α and β are representative of the Type IV cytokine receptor family.the Type IV cytokine receptor family.

Regardless of these subtypes, cytokine Regardless of these subtypes, cytokine receptors have several common characteristics. receptors have several common characteristics. They usually consist of two or more subunits, and They usually consist of two or more subunits, and receptors for different cytokines may even share receptors for different cytokines may even share common subunits.common subunits.

MECHANISMS OF CELL ACTIVATIONMECHANISMS OF CELL ACTIVATION

The binding of a cytokine to its appropriate receptor sets The binding of a cytokine to its appropriate receptor sets off a cascade that leads to induction or inhibition of off a cascade that leads to induction or inhibition of transcription of a number of cytokine regulated genes.transcription of a number of cytokine regulated genes.

This occurs via a chain of protein-protein recognition This occurs via a chain of protein-protein recognition events leading to binding of diverse trancription factors to events leading to binding of diverse trancription factors to DNA .DNA .

Cytokines initiate intracellular signals through ligand-Cytokines initiate intracellular signals through ligand-induced aggregation of receptor components.induced aggregation of receptor components.

Cytokine binding can cause hetero or homo-dimerization Cytokine binding can cause hetero or homo-dimerization of receptors or trimerization depend on particular family.of receptors or trimerization depend on particular family.

Rheumatoid ArthritisRheumatoid Arthritis RA is a chronic systemic inflammatory disorder that may RA is a chronic systemic inflammatory disorder that may

affect many tissues and organs but principally attacks the affect many tissues and organs but principally attacks the joints.joints.

An auto immune reaction in which T cells play the pivotal An auto immune reaction in which T cells play the pivotal role is widely held to be responsible for the chronic role is widely held to be responsible for the chronic destructive nature of RA.destructive nature of RA.

Once an inflammatory synovitis has been initiated by an Once an inflammatory synovitis has been initiated by an exogenous agent.exogenous agent.

T- cells, mainly CD4+ memory cells appear within the T- cells, mainly CD4+ memory cells appear within the affected joints early early in the development of RAaffected joints early early in the development of RA

Soon the endothelial cells of synovial capillaries are activated Soon the endothelial cells of synovial capillaries are activated with the expression of ICAM-1with the expression of ICAM-1

Leading to further attachment and transmigration of other Leading to further attachment and transmigration of other inflammatory cellsinflammatory cells

This sequence is further enhanced by release of IL-1, TNF-This sequence is further enhanced by release of IL-1, TNF-αα and IFN-and IFN-γγ

Activated CD4+ cells simultaneously activate monocytes, Activated CD4+ cells simultaneously activate monocytes, macrophages and promote the release of monokines and macrophages and promote the release of monokines and activated B cells with antibody production in affected jointsactivated B cells with antibody production in affected joints

TNFTNF- - αα and have induces resorption of cartilage and and have induces resorption of cartilage and bone bystimulating release of collagenases from synovial bone bystimulating release of collagenases from synovial cells.cells.

Up regulates expression of adhesion molecules Up regulates expression of adhesion molecules (ICAM-1) which inhibits synthesis of proteoglycans in (ICAM-1) which inhibits synthesis of proteoglycans in cartilagecartilage

Stimulates fibroblasts via platelet derived growth factor.Stimulates fibroblasts via platelet derived growth factor.

MULTIPLE MYELOMAMULTIPLE MYELOMA

Multiple myeloma is a plasma cell cancer that originatesMultiple myeloma is a plasma cell cancer that originates

in the bone marrow and is characterized by involvement of in the bone marrow and is characterized by involvement of

the skeleton at multiple sites.the skeleton at multiple sites.

The proliferation and differentiation of myeloma cells The proliferation and differentiation of myeloma cells seem to be dependent on several cytokines most notably seem to be dependent on several cytokines most notably ‘IL-6’‘IL-6’

Serum levels of this cytokine are increased in patients Serum levels of this cytokine are increased in patients with active disease.with active disease.

IL-6 seems to be produced by tumorous plasma cells IL-6 seems to be produced by tumorous plasma cells themselves as well as by fibroblasts and macrophages in themselves as well as by fibroblasts and macrophages in the surrounding stroma.the surrounding stroma.

In addition to causing the growth of myeloma cells, In addition to causing the growth of myeloma cells, cytokines also mediate bone destruction by acting as cytokines also mediate bone destruction by acting as osteoclast activating factors.osteoclast activating factors.

(TNF-(TNF-ββ, IL-1, IL-6 and M-CSF), IL-1, IL-6 and M-CSF)

CYTOKINE THERAPYCYTOKINE THERAPY

Non specific stimulation or inhibition of particular Non specific stimulation or inhibition of particular

components of the immune system may sometimes be of components of the immune system may sometimes be of

benefit.benefit.

The best results have been obtained with cytokines and The best results have been obtained with cytokines and among these interferon-among these interferon-αα (IFN- (IFN- αα) is the most widely used ) is the most widely used mainly for it’s antiviral properties.mainly for it’s antiviral properties.

The most striking clinical effect of a cytokine has been that The most striking clinical effect of a cytokine has been that of G-CSF in restoring bone marrow function after anti of G-CSF in restoring bone marrow function after anti cancer therapy.cancer therapy.

Interferon beta-1a and interferon beta-1b are used to treat Interferon beta-1a and interferon beta-1b are used to treat and control multiple sclerosis, an autoimmune disorder.and control multiple sclerosis, an autoimmune disorder.

Interferon therapy is used (in combination with Interferon therapy is used (in combination with chemotherapy and radiation) as a treatment for many chemotherapy and radiation) as a treatment for many cancers. This treatment is most effective for treating cancers. This treatment is most effective for treating hematological malignancy; leukemia and lymphomas hematological malignancy; leukemia and lymphomas including hairy cell leukemia, chronic myeloid leukemia, including hairy cell leukemia, chronic myeloid leukemia, nodular lymphoma, cutaneous T-cell lymphoma.nodular lymphoma, cutaneous T-cell lymphoma.

Both hepatitis B and hepatitis C are treated with IFN-α, Both hepatitis B and hepatitis C are treated with IFN-α, often in combination with other antiviral drugsoften in combination with other antiviral drugs

Administered intranasally in very low doses, interferon is Administered intranasally in very low doses, interferon is extensively used in Eastern Europe and Russia as a extensively used in Eastern Europe and Russia as a method to prevent and treat viral respiratory diseases method to prevent and treat viral respiratory diseases such as cold and flu.such as cold and flu.

IFN therapy causes immunosuppression, in particular IFN therapy causes immunosuppression, in particular through neutropenia and can result in some infections through neutropenia and can result in some infections manifesting in unusual ways.manifesting in unusual ways.

The discovery that the β chemokines RANTES, MIP The discovery that the β chemokines RANTES, MIP (macrophage inflammatory proteins) suppress HIV-1.(macrophage inflammatory proteins) suppress HIV-1.

CYTOKINE INHIBITORSCYTOKINE INHIBITORS

Cytokine inhibitors can be used for severe Cytokine inhibitors can be used for severe or chronic inflammatory conditions.or chronic inflammatory conditions.

Various ways of inhibiting TNF and IL-1 Various ways of inhibiting TNF and IL-1 have proved valuable in rheumatoid have proved valuable in rheumatoid arthritis and more controversially in septic arthritis and more controversially in septic shock and severe malaria.shock and severe malaria.

e.g:e.g:

Cyclosporin A; Pentamidine.Cyclosporin A; Pentamidine.