Lec 30-Cytokines Flashcards
1
Q
Introduction
A
- Cytokines are immunomodualtors that act at specific receptors on target cells
- Hormone-like polypeptide molecules: IL, chemokine, TNF-a, interferons, colony stimulating factors (CSFs)
- Cytokines circulate at lower levels than hormones (10-12M and active between 10-10M -10-15M and may increase by x106 during inflammation
- Cytokines can modify cell activity through acting at several types of surface receptors -Most effects are due to changes in gene expression
2
Q
What do cytokines do
A
- Growth factors
- Differentiation factors-
- Secretion of autocoids, production of antibodies and other proteins
- Chemotaxis (for cell-cell interactions
- Cytokines exhibit redundancy and are pleiotropic (many different action)
- Cytokines e.g. TNF can activate cells that produce it (Autocrine) or other cells (paracrine)
3
Q
Receptors tyrosine kinases
A
- Receptors consist of 2 identical single-pass transmembrane protein
- Receptors have kinase binding domains at intracellular cytoplasmic ends
- Tyrosine kinases are recruited to a receptor following agonists binding
- Cause activation of intracellular signalling cascades
- One such receptor-associated tyrosine kinase in janus kinase (JAK), many of whose effects are mediated by STAT (Signal transducer and Activator of Transcription)- proteins
4
Q
JAK-STAT- SIGNALLING BY RECEPTOR ASSOCIATED WITH TYROSINE KINASE
A
- when the cytokine binds to cytokine receptor the JAK is activated, meaning its kinase activity occurs and it phosphorylates the receptors
- This attracts normally inactive protein STAT’s causing the stat to bind to the receptor
- When this occurs the JAK will the place an phosphate onto the STAT
- Once STAT is phosphorylated they release from the receptor and form dimers with another STAT molecule- this is the active form
- These enter the nucleus to act as transcription factors to allowing protein synthesis to occur
5
Q
How is JAK-STAT different to other tyrosine kinases
A
- The JAK-STAT pathways are much shorter and simpler than the pathways triggered by RTK’s and so the response of cells to these ligands tends to be much more rapid
- NB this pathways is also used by IL’s, CSF’s and interferons
6
Q
TNF (tumor necrosis factor) signalling
A
- TNF is mitogenic (causes mitosis) in normal cells but induces cell death in cancer cells
- Excess TNF activity inflammation by enhancing expression of pro-inflammatory genes
- The TNF-induced survival pathway is mediated by the transcription factor NF-kB
- Activation of NF-kB occurs via phosphorylation of IkB which dissociated and is degraded
- Active NF-kB moves into the nucleus where it alters genes and expression
7
Q
TNF-a signalling (to kill cells
A
- TNF-a receptor is a trimer and binds to another protein called DISC
- This causes mitochondrial perturbation and punches holes in the mitochondrial membrane
- Causes the release of effector caspase’s -Causing apoptosis
8
Q
TNF signalling-a in normal cells to promote survival
A
- TNF-a binds to TNFRI (receptor) and activates NF-kB
- This protein is normal inactive by being complexed with IkB (-ve regulator)
- IkB is then phosphorylated by TNFRI and falls off NFkB
- IkB is then sent to proteasome’s to be degraded
- NF-kB is then able to enter the nucleus where it can interact with the kB unit on the gene and switch on transcription
9
Q
TNF-a (the other signalling pathway)
A
- DISC is activated ]
- This activate MAP3K
- This activated JNK
- Can bind to the gene
10
Q
Induction of inflammation IL2, IL4 -we can either produce T cells or B cells (the 2 different pathways)- This is T cell
A
- Antigen is presented to T CD4+ (T cell that can develop in multiple ways)
- If IL2 predominates then this will stimulate T cells to turn into Th0 -Then Th1
- Th1 then increases release of interferon gamma (INFy) and more IL2
- This process activates macrophages, NK cells -IFN will suppress the production of Th2
- Leads to a prolonged inflammatory response (this process is associated with inflammation)
11
Q
Induction of inflammation; B cell pathway
A
- Antigen is presented to T CD4+
- If IL4 predominates
- Th0 is produced
- Then Th2 is produced
- B cells are then stimulated to develop into anti-body producing plasma cells
- IL4 and TGF-b suppress Th1 cells
- This process is associated with anti-inflammatory
12
Q
Induction of inflammation: inhibition of the pathways
A
- INFy (created in the T cell pathway) will inhibit the B cell pathway
- IL4 and TGFb will inhibit T cell pathway
13
Q
TNF; IL-1; IL-6
A
- Main pro-inflammatory cytokines
- Involved in effector phase of immune/inflammatory response -Produced by macrophages and other cells
14
Q
IL-6; IL-1; TNF increase expression of COX2
A
- Cox-2 activity is increased in inflammation
- Leads to enhanced production of PGE2
- In hypothalamus leads to a rise in body temperature
- In endothelial cells leads to increase in vascular permeability
15
Q
Effects of TNF, IL-1 and IL-6 (think of areas of the body)
A
- Acts on hypothalamus to induce fever
- Act on liver to induce production of acute-phase proteins (e.g. serum amyloid protein, CRP, complement, mannose binding protein)
- Act on vascular endothelial cells and macrophages to induce secretion of colony stimulating factor (CSF) that subsequently act on bone marrow to increase WBC
- Act on vascular endothelial cells to increase both vascular permeability (Leukocyte migration) and expression of cell adhesion molecules (for rolling and firm adhesion of leukocytes)
