Immune Signalling Flashcards
What is immune signalling?
conversion of external stimuli to effective immune responses
What are the medical uses of immune signalling?
- immunomodulatory biologics
- modulates TCR and BCR signals to control direction and magnitude of lymphocyte responses
Describe Muromonab-CD3
- 1st immunomodulatory biologic
- directed against CD3 - essential for T cell signal transduction
- stimulates initial T Cell proliferation followed by depletion
- depletion within hours in periphery
- prevents transplant rejection
Describe Abatacept
- directed against CTLA-4 - immune checkpoint molecule
- fusion protein - Fc portion of IgG1 and extracellular domain of CTLA-4
- binds to CD80 or CD86
- 2nd line agent for rheumatoid arthritis treatment
Describe Lokivetmab
- 1st Mab for animal use
- recombinant anti-IL-31
- triggers cell mediated immunity against pathogens
- controls atopic dermatitis - crucial for causing pruritis
- single dose ablates symptoms for 4-8 weeks
Describe Signalling Families/Pathways
- involves cell surface receptors
- not all immune specific pathways
- ‘information highways’ between cell surface and nucleus to link environmental signals to genomic responses
Give 4 signalling families/pathways
- JAK/STAT pathway - cytokines
- NGkB - inflammation
- MAPK/ERK - inflammation, cell proliferation/death
- TLR - innate immune activation, inflammation
Describe the JAK/STAT pathway
Primary signalling cascade in response to cytokines:
- JAKS associated with cell surface that lack kinase activity
- receptors oligomerise on ligand binding
- JAK phosphorylates tyrosine residues on itself and receptor cell
- STAT proteins with SH2 domains bind to residues
- JAK phosphorylates STAT residues
- STAT proteins form dimers and translocate to nucleus to initiate transcription of genes
- also initiates transcription of SOCS
- JAK/STAT signalling can integrate into other pathways
Describe STAT proteins initiating transcription of genes
- STAT proteins are transcription factors with DNA-binding domains
- currently 4 JAK and 7 STAT proteins
- different combinations bind to specific receptors
- e.g., IFNү signalling uses JAK1/JAK2 and STAT1 proteins to initiate IFN-inducible gene expression
Describe STAT proteins initiating SOCS transcription
- suppressor of cytokine signalling - negative regulator
- acts via ubiquination of JAK proteins
- targets for degradation in proteosome
Describe JAK/STAT signalling integrating into other pathways
via signalling proteins which contain SH2 domains:
- P13K/AKT/mTOR: P13K has domain
- MAPK/ERK: Grb2 has domain and initiates MAPK/ERK signalling
Describe the NF-KB pathway
protein complex controlling gene transcription: central to inflammation
- signalling involved in TLR, TNF, IL-1, TCR & BCR pathways
- in steady state - repressed by IKB (inhibitor KB) proteins
- upon ligation of upstream receptors - signal cascades
- phosphorylated IKB ubiquitinated and degraded by proteosome
- complex translocated to nucleus to initiate gene transcription including IKB - feedback loop
Describe what occurs upon ligation of upstream receptors in NF-KB pathway
- signal cascades
- results in activation of IKB Kinase
- phosphorylates serine residues on IKB
What are the 2 pathways that NF-KB is split into?
- classical
- alternate
Describe the classical NF-KB pathway
- initiated by TNF, IL-1 and TLR stimulation
- IKK regulated by NEMO - NF-KB essential modulator
- phosphorylation of IKK results in ubiquitination of NEMO and degradation by proteosome
- involves p65/50 subunits of NF-KB complex
Describe the alternate NF-KB pathway
- initiated by CD40L, BAFF, stimulation
- activation of NIKS (NF-KB inducing kinase) phosphorylates IKK
- IKK phosphorylates p100 precursor to be degraded to p52
- dimerises with RelB
Describe MAPK pathways
- highly conserved pathway in prokaryotes and mammalian cells
- 3-tier kinase pathways initiated by an activator and terminating in transcription factor
- ‘phospho-relays’ where protein kinases phosphorylate serine and tyrosine residues to potentiate intracellular signalling cascades from cell surface to nucleus
Describe ERK pathways
- Highly conserved pathway in prokaryotes and mammalian cells
- controls cell proliferation and differentiation
What are MAPK/ERK pathways activated by?
- hormones
- growth factors
- differentiation factors
- oncogenic substances
Describe MAPK/ERK pathways
- receptor linked tyrosine kinases activates GTPases
- Gr2b binds - recruits SOS - converts RasGDP to RasGTP
- activates Raf (MAPKKK)
- phosphorylates MEK1 or MEK2 (MAPKK)
- phosphorylates ERK1 (MAPK)
- ERK can phosphorylate transcription factors to form AP-1 but also activates p90-RSK
What is a TLR pathway?
- toll-like receptors - pattern recognition receptors mostly found on innate immune cells
- up to 13 TLRs depending on species:
- murine 1-13
- human 1-10
- bovine 1-10
Describe TLR pathway
- recognises wide range of molecular patterns
- mostly cell surface but TLR3, 7, 8 and 9 within intracellular vesicles
- dimerise on ligand binding to initiate signalling
- all signal through Toll/IL-01 receptor domains (TIR) on the intracellular portion to complex with and TIR containing adaptor proteins
Describe TLR-4 pathway
- TLR4 recognises lipopolysaccharide (LPS) from gram-negative bacteria in conjunction with CD14, MD2 and LPB
- TLR4 dimerises on binding with LPS
- MyD88 activates IRAK4 and IRAK1
Describe TLR4 dimerising after binding to LPS
- conformational change and recruitment of TIRAP and MyD88
- both TIR containing proteins
Describe MyD88 activating IRAK4 and IRAK1
- phosphorylates TRAF6
- complexes with TAK1 and TAB2/3
- initiates MAPK pathways - ERK, p38, JNK and NF-KB
What does the TLR-4 pathway lead to?
- cell differentiation
- cell maturation
- cytokine secretion
- receptor expression
- inflammation
Describe how Muromonab-CD3 works
- intracellular portions contain immunoreceptor tyrosine-based activation motifs (ITAM)
- phosphorylation of ITAM on CD3Ϛ chain allows binding of ZAP70
- initiates signalling cascade within T cells
- muromonab-CD3 binds to CD3 - early activation of T cells, mass cytokine release and T cell death by activation induced apoptosis pathway
Describe how Abatacept works
- downregulates immune response when bound to CD80 or CD86 - signal 2 in T cell activation
- expressed on Tregs and upregulated on conventional T cells upon activation
- inhibition mechanism controversial
How is the inhibition mechanism of abatacept controversial?
Evidence for:
- recruitment of a phosphate to disrupt TCR signalling
- depleting CD80 and CD86 from APC
- skewing immune system synapse formation in CD-Treg interaction resulting in ‘lethargic DC’ - reducing T cell priming
Describe how Lokivetmab works
- binds to IL-31 receptor A (IL-31RA) complex expressed on monocytes, epithelial cells and dorsal root ganglia
- dorsal root ganglia contributes to itching sensation (pruritis)
- IL-31RA signalling contributes to JAK/STAT, P13K/AKT, MAPK/ERK
What are the main ways of studying immune signalling?
- cellular output
- microscopy and stain cells
- western blotting
- reporter assays - confirms use of a signalling pathway
Describe cellular output for studying immune signalling
confirms interaction took place but not pathway unless inhibitors are used:
- cytokine secretion
- cell surface receptor changes
- transcription in response to stimulation
Describe microscopy and stain cells for studying immune signalling
- extract protein lysates
- stain for phosphorylated signalling molecules to confirm signal transfer
