Cytokines Flashcards
What are cytokines?
Diverse group of small secreted proteins (5-25KDa) and chemical messengers which modulate the behaviour of the IS
- Analogous to hormones of the IS
Which cytokines are membrane-bound?
1) TNF
2) FASL
However, majority are secreted
What are some functions of cytokines?
Illicit a range of activities on different targets:
- mediate inflammation
- trauma response
- cell differentiation
How are cytokines secreted and what type of cells do they act upon?
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)
How are cytokines sensitive?
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.
How are cytokines detected?
- ELISA (measures cytokines)
- ELIspot
- Flow cytometry (measures CD8+ cells and other cells)
What does Western blotting measure?
Protein expression
“Each cytokine has a unique receptor made of specific subunits”
True - unique receptors
False - receptors share chains and subunits
What is ELISA?
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
What are the various terms for cytokines?
- interferons
- interleukins
- chemokines
How are cytokines produced?
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
How do cytokines act upon cells?
- 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)
Describe how cytokines act in an autocrine manner
Acts back on cell to regulate proliferation - eg IL-2 produced after maturing T cells following APC interaction
Describe how cells act in a paracrine manner
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)
Describe how cytokines act in an endocrine manner
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
What are the 5 main groups of cytokines which are functionally classified?
1) immunoregulatory
- IL-2, 4, 12, 15, TNFa and TGFb
3) anti-inflammatory
4) chemotactic
5) heamatopoitic
What are the 4 types of cytokines?
1) Pleiotropic
2) Redundant
3) Synergistic
4) Anatagonistic
How does a cytokine activate its target cells?
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.
What do cytokine receptors share?
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
What disease can cytokines drive and what are its characteristics?
RA: systemic autoimmune disease
- chronic inflammation of joints
- pain, loss of function, invalidity
- multifactorial: gender, age, genetics, environment
What is RA mediated by?
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
What are redundant cytokines?
When different cytokines have the same effect on their target cells
Eg - activated Th2 cell produces IL-2, 3 & 5 = B cell proliferation
What are synergistic cytokines?
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
What are antagonistic cytokines?
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
What are pleiotropic cytokines?
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
What are the cytokine families, and how are they grouped?
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
What are chemokines?
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
What are chemokines divided into?
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
What are some effects of cytokines on their target cells?
???? Second page
What are T helper cells defined by?
The cytokines they produce
Activity and differentiation is also regulated by a small number of master regulatory TFs
What is X-linked SCID?
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
What is a cytokine storm?
- 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
