Interferon Flashcards
How does the immune system respond to virus?
At start of an infection you have an onslaught of viruses, first barrier is mucous membrane, mucus, skin = Intrinsic immunity.
2nd barrier would be innate immunity, no specificity, phagocytes, cytokines, NK, will suppress virus replication may not feel negative effects of response.
If virus replication is uncontrolled in first few hours, you need acquired immune response, B T cells.
What are viruses?
Masters of evolution
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What are CpG and ZAP?
Many pathogens have a different ratio of nucleotides in their genomes than we do. Too much/high load CpG is recognised foreign.
ZAP detects it while virus trying to affect your cells and transports the genome to a RNA exosome where it’s digested.
Non-specific recognition of generic difference
(CpG is just how many CG sequences there are in the genome)
What are interferons?
A soluble protein that spreads and binds to specific receptors on neighbouring cells and signals activation of de novo transcription of hundreds of Interferon stimulated genes that are fairly toxic.
Makes these cells into an antiviral state.
Produced by fibroblasts and monocytes
What are type 1 interferons?
Switch on first and earliest
Polypeptides secreted from infected cells and there are type 1 interferon receptors on all cells in the body.
What are the 3 major functions of interferon 1?
Induce antimicrobial state in infected and neighbouring cells, interferon stimulated genes
(Can signal on cell secreted by)
Modulate innate response to promote Ag presentation and NK cells (upregulation)
Activate the adaptive immune response, better antibody response
Primary role is first point.
What is the primary interferon?
Interferon beta
Any cell in your body can make it and respond to it.
What is the primary interferon secreted by macrophages and dendritic cells?
Interferon alpha
What receptor does interferon beta signal through?
IFNAR receptor which is present on all tissues
What is primary signalling molecule that switches on production of interferon beta?
IRF-3
What are plasmacytoid dendritic cells?
Specialist IFN alpha secreting cells as they express high levels of transcription factor IRF-7
What are the genetic differences between interferon beta and alpha?
One gene for beta
There are 13 to 14 interferon alphas which are all subtly different.
What is type 2 interferon?
IFN gamma
Produced by activated T cells and NK cells
Signals through a different receptor IFNGR
What is type 3 interferon?
IFN lamda
Recently described 15 years
Signals through IL28R and IL10B that are mainly present on epithelial surfaces.
Important in early events of viral infections that go through resp. tract and hepatic viruses
The receptor is present on the basolateral surface of epithelial cells in resp. and liver.
Imporved outcomes in Hep have been determined by polymorphisms in IFN lamda/receptor with both spontaneous clearance and response to anti-viral therapy.
How do we differentiate non-self and self?
PAMPs - Pathogen associated molecular pattern - usually a piece of foreign nucleic acid
No DNA in cytoplasm so this existence may indicate invasion
PRRs find DNA in wrong place and elicit a response
Cytoplasmic RIG-I like receptors RLRs
Toll like receptors TLRs
Cytoplasmic nucleotides oligomerizatoin domain receptors NLRs
Sensors that see RNA, DNA, RNA in endosomes
How does interferon induction work?
Cell just infected, virus replicating and producing single stranded RNA in cytoplasm (no CAP polyA tail). RNA is sensed by RIG-I and/or mda-5, they bind the RNA and change conformation to allow binding to a downstream molecule MAVS(mitochondrial activator of virus signalling)stuck on mitochondrial membrane.
Complex formed from PRR, signalling molecule and mitochondrial membrane leads to conformation change in MAVS which signals to downstream cascades leading to phosphorylation in IRF-3 causing dimerisation and movement into nucleus, it’s a TF and now can attach to promoter region of INF-beta to transcribe some and upregulate INF-beta
How do TLRs induce a response?
TLRs sit in endosomes, lots of RNA viruses use endosomes to uncoat and get into cells. Exposed viral RNA in an endosome can be picked up by TLR3/7/8.
Once bound to RNA ligands they signal downstream pathways, TLR3 is same as normal interferon induction.
However, TLR7/8 pathway is unique to plasmacytoid dendritic cells signal through Myd88, triggers phosphorylation of IRF7 which is constitutively expressed in plasmactyoid dendritic cells and switches on both IFN alpha and beta, burst of very strong response due to large production of IFNs.
How is DNA sensed to induce a interferon response?
Sensed by cGAS that signals through STING.
DNA viruses - herpes, pox viruses.
Need to pick up DNA in the cytoplasm of the cell.
cGAS is an enzyme which is activated by binding of dsDNA in the cytoplasm and makes a second messenger cGAMP (dinucleotide of G and A).
STING picks up the cGAMP on ER and acts as a signalling platform, switches on same phosphorylation cascade.
What is IFN beta?
Small polypeptide which is synthesised by infected cells and secreted to bind to IFNalphaR on neigbouring cells.
Autocrine and paracrine signalling.
Soluble cytokine.
Switching on hundreds of genes in neighbouring cells unlike the infected cell where one gene activated.
What are some genetic errors that can affect interferon response?
Monogenic inborn error of IRF-7
mutation in IFRNAR2 gene
mutation in IRF-3 gene - Herpes Simplex Encephalitis : Inborn errors in at least 6 genes in HSE impaired CNS intrinsic interferon alpha/beta response to HSV infection leading to uncontrolled virus replication in brain.
How important is interferon?
Absolutely essential
Need it to deal with simple viruses we would otherwise be at large risk to.
What happens after IFNs have been secreted?
Secreted by infected cell
Float around on outside cells until it lands on heterodimer IFNAR 1/2.
Another signalling cascade that involves JAK and STAT. Phosphorylation of STAT and dimerisation allowing entry of STAT into nucleus where it sits on promoter of hundreds of different genes, transcribed and translation of mRNA in cytoplasm, spectrum of 2-300 proteins.
Give some examples of proteins produced by neighbouring cells.
Protein Kinase R - inhibits translation
2’5’Oligoadenylate synthase - activates RNAase L that destroys ssRNA
Mx - inhibits incoming viral genomes
ADAR - induces errors in viral replication
Serpine - Activates proteases
Viperin - inhibits viral budding
virus is dependent on YOUR machinery
transient shut down of protein synthesis may save the cell.
Local response
What are 3 things that STAT activates?
a. Antiviral response (ISRE).
b. Inflammatory response (GAS).
c. Repressors of the inflammatory pathways (GAS).
What is IFITM3?
Restrictrs virus entry through endosomes, fuses with endosome membrane, prevents endosome changing. Stops virus escaping so broken down by acidic pH
E.g. influenza can’t do it
People lacking IFITM3 have more severe influenza
It’s an interferon stimulated gene
What are Mx1 and 2?
Mx1 and Mx2 – GTPases with a homology to dynamin:
Forms multimers to wrap around nucleocapsids of viruses.
Mx1 – inhibits influenza.
Mx2 – inhibits HIV.
All reliant on initial interferon response
How is damage limited during antiviral state?
IFN response only maintained for several hours.
Ability to respond to IFN lost due to negative regulation
SOCS (suppressor of cytokine signalling) genes turn off response
Antiviral state is a harmful necessary response.
What are different strategies that viruses use to evade IFN response
Hide PAMP
Interfere globally with host cell gene expression/protein synthesis
Block IFN induction cascade by destroying or binding
Inhibit IFN signalling
Block action of individual IFN induced antiviral enzymes
Activate SOCS
Replication that is insensitive to IFN
Give some examples of interferon control by viruses
Hep C: NS3/4 protease acts as an antagonist to interferon induction by cleaving MAVS.
Influenza virus: NS1 protein acts as an antagonist to interferon induction by binding RIG-I/TRIM25/RNA complex and preventing activation of signalling pathway, prevents nuclear processing of newly induced genes by entering the nucleus and bind to TF to prevent transcription.
How do Pox viruses prevent signal getting through?
DNA viruses have lots of space to deal with IFN and immune response.
They are called accessory genes - they don’t need these for replication just to combat our IS.
More than half of Pox genome is compromised of accessory genes that modify immune response.
An example: Pox encodes a soluble cytokine receptor binding to any interferon produced by infected cells.
Being developed for future autoimmue therapies e.g. RA where you have to many cytokines in order to mop it up
What are general mechanisms of ebola to evade immune system?
Endoces proteins that stop it being seen/sensed reducing interferon production.
In neighbouring cells VP24 stops signalling in neighbouring cells
Ebola – evades the IFN response by VP35, VP24 and VP30:
VP35 – blocks RIG-I Like complexes and RNAi expression.
VP30 – blocks RNAi expression.
VP24 – directly blocks IFN signalling.
Only has a small genome 7 genes 3 of which are dedicated to evasion L00000L
Why do we get symptoms?
Consequence of innate immunity
Combination of damage of infected cells by virus and damage/infected and bystander cells by immune responses
How does interferon interference skew immune response?
Immune response modulated for virus own replication and transmission.
Inadvertent pathology can result.
Proportions are all wrong too much IL-6 fever/lethargy
100 times more IFN needed for IL6 induction compared to Mx.
What is a cytokine storm?
Cytokine storm – virus replication than induces high IFN accompanied by a massive surge in TNF-alpha and others.
o Differences in the clinical outcome may vary with age and health and can reflect vigour of innate immune system.
E.G. Dengue haemorrhagic fever, Ebola and severe influenza.
Cytokines involved – TNF, IFN(a/b), IFN(gamma), IL-1, IL-6, CCL2.
Result in endothelial dysfunction, inflammatory responses and pulmonary fibrosis.
The interferons and other factors are not successfully mediating the viral replication.
Can IFN be used as an anti-viral treatment?
Associated with unpleasant side effects, feel worse than normal.
Can IFN lambda be used as an influenza therapeutic?
IFN - influenza therapeutic drug:
IFN only stimulates an anti-viral state and
NOT an immune response and immunopathology.
Only stimulates response at epithelial surface to protect it.
How can viruses be used as a new generation of live attenuated viruses?
Viruses deficient in control of IFN are attenuated in IFN competent cells.
The high IFN levels they induce can also recruit useful immune cells, IFN acting as an adjuvant.
E.g. removal of NS1
Live attenuated vaccines:
Creation – viruses deficient in control of IFN are attenuated in IFN competent cells.
Cells naturally or engineered to be deficient in IFN response can be used to grow these attenuated virus strains.
Use – high IFN levels they induce can recruit useful immune cells with IFN acting as an adjuvant.
What is relationship between IFN system and cancer?
Cancer cells don’t make good IFN response. Replicate and kill cancer cells but not healthy cells. Opportunity to genetically engineer cancer oncolytic viruses.
