Lec 30-Cytokines Flashcards Preview

PH2501- pharmacology > Lec 30-Cytokines > Flashcards

Flashcards in Lec 30-Cytokines Deck (32)
Loading 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)
16
Q

Other action of TNF action in inflammation

A
  • Stimulates tissue (e.g. cartilage) degradation by increasing expression of matrix metalloproteinases
  • Stimulates expression of pro-inflammatory genes e.g. IL-1,6 and NOS
  • Promotes fibroblast proliferation
  • Promotes tissue metric deposition
  • Leads to scarring
17
Q

Linking cytokine mediators to symptoms (think of cardinal signs)

A
  • Heat- increased body temp due to IL-1 acting to increase PGE in hypothalamus
  • Redness- increased blood flow- due to cytokine promoted NO production= vasodilation
  • Swelling- increased vascular permeability due to cytokine induced PGE2 synthesis
  • Pain- cytokine induced PGE promotes nerve ending sensitisation to bradykinin
  • Loss of function- fibrous due to TNF-a activation of fibroblast proliferation
18
Q

Chemokine and chemotaxis

A
  • Chemokines are specific class of cytokine that mediate chemotaxis between cells
  • IL-8 is the only chemokine originally named an IL
  • Act on GPCR’s; co-receptor for AIDS virus (IL-5)
  • C-X-C chemokine e.g. (IL-8) act on neutrophils and are involved in acute inflammation
  • C-C chemokine e.g.(MCP-1) act on monocytes and other cells and are involved in chronic inflammation
19
Q

Anti-inflammatory cytokines

A
  • TGF-b, IL-4 and others
  • Inhibit production of chemokines
  • Inhibit responses by Th1 cells (and stimulate responses by Th2 cells) and so switch immune system from cell-mediated to immunity to antibodies
20
Q

Interferons IFN

A
  • IFN-a and IFN-b are produced from virally infected cells
  • IFN-a is used as an anti-viral agent
  • IFN-y is immunoregulatory and is used in multiple sclerosis to reduce antibody production
21
Q

Colony stimulating factors

A
  • Produced mainly by bone marrow stroll cells, endothelial cells and fibroblasts in a constitutive fashion
  • They stimulate inflammatory cell growth
  • GM-CSF. A growth factor for many progenitors and a differentiation factor acting on granulocytes, macrophages and dendritic cells-G-CSG. Stimulates neutrophils -IL e.g.3,7 can also act on CSF
  • CSF’s are used in conditions where there is depletion of WBC’s
22
Q

Steroids also lead to serious side effects

A
  • Decreased fibroblast function less collagen- poor healing -Decreased osteoblast and increase osteoclast activity= osteoporosis
  • Decreased macrophage sensitivity to cytokines- immunosuppression

+decreased leukocyte recruitment

+decreased basctericidal activity (iNOS)

+Decreased vasodilation

23
Q

Intro to steroids

A
  • 1950 Hench- RA women who became pregnant went into remission, increase glucocorticoids
  • Synthetic glucocorticoids decreases inflammation
  • Mineralo and glucorticoids synthesised in adrenal cortex in response to ACTH
  • Glucocorticoids- homeostasis of protein and CHO metabolism, anti-inflammator , immunosuppressive -Physiological role- prevent overshoot of body defence (magnitude and duration) -exert -ve feedback via pituiatary
24
Q

Endogenous glucocorticoid metabolism

A
  • 90% hydrocortisone; 10% corticosterone
  • Circulate attached to albumin or corticosteroid binding protein (CBP) but not synthetic hormones
  • Can enter directly or via a complex bound to CBP
  • Excess corticoids leads to bushings syndrome (cataract, abdominal fat, poor wound feeling, muscle wasting, HTN)
25
Q

Mechanism of GC action

A

3000-100,000 GCRs per cell in nucleus

  • GCRs and GC bind to DNA -Attach to specific sequence present in promotors of 10-100 genes (~1% of cellular genes)= GC responsive element
  • Can increase or decrease levels of protein depending on the gene -Initiator- promotes mRNA production increase in levels of protein e.g. Lipocortin
  • Inhibitor- (1) block RNA polymerase- inhibit protein expression or (2) bind to and inhibit other transcription factors e.g. AP1- repress transcription factor controlling collagen production- reduced healing
26
Q

Targets for glucocorticoids

A

UPREGULATION -Lipocortin- endogenous inhibitor of PLA2 (15-30 min)

-This means no arachidonic acid so no: TXA’s: PG; LT’s: -This pretty much cuts of inflammation at its source

DOWNREGULATION

  • COX2 but not COX-1 -IL-1 and 6
  • iNOS
  • MMP (matrix metalloprotinase)
  • Collagen
  • Adhesion molecules
27
Q

Other inflammatory mediators reduced by steroids

A
  • Complement component
  • Histamine release
  • Phagocyte activity
  • Reduced clonal expansion of T and B cells
28
Q

Clinical effects of steroids

A
  • Inhibit inflammation arsing from all types of stimuli e.g. chemical, physical and endogenous
  • Inhibit early phase- redness, heat, pain, swelling
  • Inhibit late phase- healing repair
  • Act on endothelial and inflammatory cells and their mediator
29
Q

Kinetics

A
  • Response time 6-24 hours after injection (ie. bronchodilator also required for asthma attack
  • Half life 90 minutes
30
Q

Problems associated with steroids

A
  • Large acute doses are tolerated well
  • Chronic therapeutic corticoid - suppress production of endogenous corticoids
  • Withdrawal of treatment - adrenal insufficiency- Addison’s disease- Low BP, hypoglycaemia
31
Q

Steroids also lead to serious side effects

A
  • Decreased fibroblast function- less collagen- poor healing -Decreased osteoblast and increased osteoclast activity- osteoporosis (destroy bone and not remake it)
  • Decreased macrophage sensitivity to cytokine - immunosuppression

+decreased leukocyte recruitment

+decreased bactericidal activity (iNOS)

+Decreased vasodilation

32
Q
A