Cytokines

Question 1

What are cytokines?

Answer 1

Diverse group of small secreted proteins (5-25KDa) and chemical messengers which modulate the behaviour of the IS

• Analogous to hormones of the IS

Question 2

Which cytokines are membrane-bound?

Answer 2

1) TNF
2) FASL

However, majority are secreted

Question 3

What are some functions of cytokines?

Answer 3

Illicit a range of activities on different targets:

• mediate inflammation
• trauma response
• cell differentiation

Question 4

How are cytokines secreted and what type of cells do they act upon?

Answer 4

Secreted y a wide range of immune and non-immune cells.
Eg - epithelial cells secrete: IL-1, 8, 6, TGFbeta, stromal cells of BM - which secrete a large no. of growth hormones which regulate haematopoeisis of the IS

Comp. to specific endo. glands for hormones.

Usually act upon immune cells (epithelial cells respond to TNF, IL22, IFN-y)

Question 5

How are cytokines sensitive?

Answer 5

E.g. IL-6 circulates in picomolar (10-12 M) concentrations and can increase up to 1,000-fold during trauma or infection.

Hormones - circulate in nanomolar (10-9 M) concentrations and usually vary by less than one order of magnitude.

Question 6

How are cytokines detected?

Answer 6

• ELISA (measures cytokines)
• ELIspot
• Flow cytometry (measures CD8+ cells and other cells)

Question 7

What does Western blotting measure?

Answer 7

Protein expression

Question 8

“Each cytokine has a unique receptor made of specific subunits”

Answer 8

True - unique receptors

False - receptors share chains and subunits

Question 9

What is ELISA?

Answer 9

Enzyme Linked ImmunoSorbent Assay

• target protein immobilised onto plate
• detection of “target” is achieved using an AB conjugated (linked) to an enzyme that produced a colour reaction
• can be done directly or via an intermediate (secondary) AB

Question 10

What are the various terms for cytokines?

Answer 10

• interferons
• interleukins
• chemokines

Question 11

How are cytokines produced?

Answer 11

De novo following stimulation - cells increase T&T follow when cytokines are needed for secretion

• can be stored too
• eg TNF-a is stored by mast cells

Question 12

How do cytokines act upon cells?

Answer 12

• autocrine and paracrine manner, and occasionally endocrine manner over long distances eg IL-6
• act upon target cells by binding specific cell surface receptors (frequently shared chains)

Question 13

Describe how cytokines act in an autocrine manner

Answer 13

Acts back on cell to regulate proliferation - eg IL-2 produced after maturing T cells following APC interaction

Question 14

Describe how cells act in a paracrine manner

Answer 14

Paracrine action: IL-4 released by Th2 cells to induce B cell class switching (changes isotope of ABs being produced + stimulates maturation of B cell down plasma/memory cell lineage)

Question 15

Describe how cytokines act in an endocrine manner

Answer 15

Eg. IL-6 and TNF-a modulate hypothalamic production of ACTH = elevated temp + regulates lipid metabolism

• so, modulates locals IRS at SOI but also hormone production by hypothalamus, reg bone morphogensis, angiogenesis, etc

Question 16

What are the 5 main groups of cytokines which are functionally classified?

Answer 16

1) immunoregulatory
- IL-2, 4, 12, 15, TNFa and TGFb

3) anti-inflammatory
4) chemotactic
5) heamatopoitic

Question 17

What are the 4 types of cytokines?

Answer 17

1) Pleiotropic
2) Redundant
3) Synergistic
4) Anatagonistic

Question 18

How does a cytokine activate its target cells?

Answer 18

A cytokine will have no effect on a cell unless it expresses a receptor for that cytokine.

Regulating the expression level of the receptor is a means of controlling the effect of the cytokine.

Question 19

What do cytokine receptors share?

Answer 19

Subunits and chains

Eg - IL-2 receptor:

• y chain critical component for a large no of cytokines/cells
• when mutated: has a wide ranging effect

Question 20

What disease can cytokines drive and what are its characteristics?

Answer 20

RA: systemic autoimmune disease

• chronic inflammation of joints
• pain, loss of function, invalidity
• multifactorial: gender, age, genetics, environment

Question 21

What is RA mediated by?

Answer 21

T cells, B cells, DC, macs, neutrophils and fibroblasts

Cytokines: TNFa, IL-1b, IL-6 and IL-7

Blocking of TNFa - can dramatically reduce inflammation and even reverse some of the cartilage damage (anti-TNF damage)

• possibly occurs due to misregulation of cytokines

Question 22

What are redundant cytokines?

Answer 22

When different cytokines have the same effect on their target cells

Eg - activated Th2 cell produces IL-2, 3 & 5 = B cell proliferation

Question 23

What are synergistic cytokines?

Answer 23

When different cytokines augment (massively up-reg expansion) the response of each on its own

Eg - activated Th1 cell produces IFNy and mac produces TNF = both increase expression of MHC I on many cell types

Question 24

What are antagonistic cytokines?

Answer 24

When different cytokines have opposite effects on the target cell

Eg - Th2 produces IL-4 (drives class switching to IgE) and IFNy (blocks this action)

• feedback loops

Question 25

What are pleiotropic cytokines?

Answer 25

When one cytokine can have different (completely unrelated) effects in different target cells IL-6 = extreme example, acts in an endocrine manner ``` IL-4 = affects B cell class switching of IgE to IgM Also inhibits macs + induced Th2 differentiation ```

Question 26

What are the cytokine families, and how are they grouped?

Answer 26

FUNCTIONALLY: 1) interleukins (IL): 4 alpha helix bundles eg IL-1,2,3..36. Also include EPO and thrombopoeitin 2) tumour necrosis factors (TNF): primarily TM, surface proteins. TNF-a, beta but also CD40L, FASL, CD30L 3) growth factors (GF): cytokines that direct proliferation (+ diff) eg TGF-b, VEGF STRUCTURALLY: 1) interferons (IFN): structurally diverse and grouped into type I: IFN-a,b,(k,d,e), and type II: IFNy. Tend to “interfere” with viral replication 2) colony stimulating factors (CSF): secreted glycoproteins that act upon haematopoeitic cells to regulate proliferation and differentiation, G-CSF, M-CSF, GM-CSF 3) chemokines (CK): group of cytokines that direct cell movement (chemoattractants). 4 subfamilies classified by the arrangement of their cysteine bonds into the CC, CXC, CX3C groups

Question 27

What are chemokines?

Answer 27

Mediate chemotaxis (not the only cytokines that do this) But their primary function. Contain 2/4 cysteine residues in a conserved structural location, which form disulphides bonds. Yeah

Question 28

What are chemokines divided into?

Answer 28

4 groups depending on the number of cysteines and their spacing. 1) C chemokine 2) CC chemokine - no space, directly next to each other 3) CXC chemokine - AA spacer 4) CX3C chemokine

Question 29

What are some effects of cytokines on their target cells?

Answer 29

???? Second page

Question 30

What are T helper cells defined by?

Answer 30

The cytokines they produce Activity and differentiation is also regulated by a small number of master regulatory TFs

Question 31

What is X-linked SCID?

Answer 31

X-linked severe combined immunodeficiency - X-linked recessive trait - mutated IL2-Ry chain - IL-2Ry shared between receptors for IL-2,4,7,9,15 and 21 - isolation in a “bubble” was an early prophylactic treatment - bubble = incapable of mounting a response to bacterial/fungal/viral infections - BM transplant - standard treatment

Question 32

What is a cytokine storm?

Answer 32

- IR is controlled by feedback mechanisms - fail = too many cells recruits and systemic IR results, releasing >150 mediators - high fever, swelling and redness, extreme fatigue and nausea (heightening normal inflammation) - causes unknown, results form infectious and non-infections diseases including (GVHD), acute respiratory distress syndrome (ARDS), sepsis, Ebola, avian influenza, SARS