interferons

Question 1

summarise the phases of the immune response against viruses

Answer 1

1st have intrinsic - skin, mucus membranes, mucus ie the physical barriers

2nd - innate immunity - non-specific suppression of virsu replication so only mildly affected or asymptomatic, can overreact = lethargy/fever

3rd - acquired immunity - B and T cell response - clear the infection

Question 2

describe CpG and intrinsic immunity *

Answer 2

virus have different nucleotides to us

if they have too much CpG (ie C followed by G) then the body recognises this as foreign

the Virus is latched onto the RNA exosome which cleaves the virus

this is how we block viruses that infect other organisms because those viruses dont hide their CpG

this is a possibility for vaccines - make viruses that express too much CpG so they dont cause infection

Question 3

what is interferon *

Answer 3

it is a generic soluble factor that is switched on in cells when cells sense that something is wrong

it communicates with other cells through INF receptor

it binds to specific receptors and signals activation of de novo transcription of 100s of interferon stimulated genes (ISGs) - these are anti-viral

Question 4

describe type 1 interferons *

Answer 4

they are switched on 1st

made in all cells

polypeptides that are secreted from infected cells

Question 5

functions of INF 1 *

Answer 5

induce antimicrobial state in infected and neighbouring cells

modulate innate response and promote Ag presentation (MHC) and recruit/effect behaviour of NK and increase chemokine production

activate the adaptive immune response - make better Ab response

switch on ISGs in infected and neighbouring cells

Question 6

describe the different types of INF 1 *

Answer 6

INFa and INFbeta

INF B is secreted by all cells, act on INFAR on all tissues

INF B production triggered by IRF3

plasmacytoid DC are specialist INF a secreting cells - express high levels of INF 7 constitutively (this is the TF for INF a)

there is 1 gene for INF B and 13/14 isotypes of INF a

Question 7

describe type 2 INF *

Answer 7

it is INF gamma

produced by activuated T cells and NK

signal through INFGR

Question 8

describe type 3 INF *

Answer 8

INF lambda

early in viral infection through resp tract and liver

receptors - IL28R and IL10Beta - mainly present on the surface of epithelial cells ie not on immune cells

Question 9

summarise the production of type 1 INF *

Answer 9

epithelium invaded by virus - there is activation of protein recognition receptors (PRRs)

cause production of INF B

if virus reaches fibroblast - causes INF B release from fibroblasts

plasmacytoid DC and macrophages are professional INF producing cells (sentinal cells) - secrete primarily INF a

Question 10

describe action of INF lambda *

Answer 10

receptor on the basolateral surface of epithelial cells

polymorphisms are associated with improved outcome from HCV and HBV - both spontaneous clearance and response to antiviral therapy - ie make you more/less suseptible to the viral infections

Question 11

how does the body identify viruses *

Answer 11

viruses have pathogen associated molecular patterns - PAMPs

these are recognised by PRRs in cytoplasm

PRRs often sense foreign nucleic acid eg DNA in cytoplasm (DNA should only be in nucleus)

PRRs include - cytoplasmic RIG-1 like receptors (RLRs) and endosomal Toll like receptors (TLRs), and cytoplasmic nucletide oligomerisation domain receptors (NLRs)

Question 12

role of different PRRs *

Answer 12

TLRs - see RNA in endosomes

RLRs - see RNA

DNA sensors - see DNA in cytoplams

Question 13

describe the pathway of INF induction by RIG-1 *

Answer 13

virus replicates and produces signle strand RNA in cytoplasm - detected as foreign because doesnt have a cap for example

this PAMP is sensed by RIG1 and mda-5 - they see different versions of wrong RNA

their conformation changes - they bind to Mavs which is on the mt membrane

complex is formed with PRR, viral RNA and Mavs = change in conformation of Mavs

Mavs signals through cascades - causes phosphorylation of irf3 or irf7 by a kinase

irf3 or 7 dimerise and enter nucleus

they are TFs and act on the promoter region of INF B = transcription of INF B = translation and secretion

Question 14

what does Mavs stand for

Answer 14

mitochondrial activator of viral signalling

Question 15

describe INF production via TLRs *

Answer 15

happens in DC

TLR sit in endosomes (viruses use endosomes to uncoat and enter cells)

when RNA binds to TLR3 - trigger IRF3 downstream pathway

when RNA binds to TRL7 or 8 = phosphorylation of Myd88 = phosphorylation of TF IRF7 which is constituently produced in plasmacytoid DC = production of INF a and B

Question 16

describe how DNA in cytoplasm causes INF production (

Answer 16

cGAS is an enzyme that is activated when bound in cytoplasm by dsDNA - stimulates enzyme to make second messenger cGAMP

cGAMP is picked up by STING on membrane of ER = signalling platform - switch on phosphorylation cascade = phosphorylation of IRF3 = IRF3 pathway = INF B production

Question 17

describe INF action on receptors *

Answer 17

soluble cytokine - polypeptide

acts autocrine and paracrine

bind to INFAR on neighbouring cells

cause de novo stimulation of ISGs (300/400 genes - requires a lot of energy)

these genes are anti-viral and toxic to host cells

Question 18

examples of problems with INF pathways

Answer 18

monogenic inborn error of IRF7 gene because of heterozygous mutation - in pDC mean INF a not switched on properly = unable to control virus

autosomal recessive INFAR2 gene - dont ahve INF receptor - cant make ISGs

heterozygoud mutation in IRF-3 - not responding to make immune response

Question 19

effect of interferon pathway defect *

Answer 19

unable to mount INF response - cant protect yourself against viral infections that are normally not harmful

Question 20

describe herpes simplex encephalitis *

Answer 20

most common cause of sporadic encephalitis in western world

affect previously healthy individuals on primary infection with HSV-1, most common in childhood

there are inborn errors in at least 6 genes including TLR3, UNC93B1, TRIF, TRAF3, TBK1, IRF3 - impair CNS intrinsic INF a and B response to HSV = uncontrolled virus replication in brain

Question 21

describe the cascade of how INF stimulates ISGs *

Answer 21

the INFAR is a heterodimer made of INFAR1 and INFAR2

cascade involving Jak and STAT

phosphorylation and dimerisation of STAT

STAT enters nucleus - sits on promotor of ISGs

genes are transcribed = new protein production

Question 22

summarise actions of ISGs *

Answer 22

PKR (protein kinase R) - inhibits translation - means ribosomes dont work, so cant maintain cell either but viruses need host translation machinery to replicate because they dont have their own ribosomes

2’5’OAS - activates RNAse L that destroys ssRNA - including mRNA the virus was going to use to replicate

Mx - inhibits viral genomes - latches on and binds to virus, stopping it enter

ADAR induces errors in viral replication

serpine - activates proteases

viperin inhibits viral budding

Question 23

describe the action of IFITM3 *

Answer 23

it is an ISG

viruses fuse with the endosome membrane to enter the cells -

IFITM3 stops endosome from fusing meaning virus is locked in the endosome and cant enter the nucleus

people without IFITM3 get more severe flu - more people in Japan and China have this mutation = more suseptible

Question 24

describe the action of Mx1 and Mx2 *

Answer 24

ISGs

they control entry - they latch onto the virus as they try to escape the endosome

GTPase homology to dyamin

Mx form multimers that wrap around the nucleocapsids of incoming viruses

Mx1 inhibits influenza, Mx2 inhibits HIV

Question 25

what is the effect of the virus replicating quickly \*

Answer 25

can enter the cells before there is a full INF response eventually INF will dampen down the viral replication

Question 26

describe how the INF response is limited \*

Answer 26

only maintained for hours then ability for INF is lost because of -ve regulation SOCS (suppressirs if cytokine signalling) genes turn off the response - these genes are swithced on by INF

Question 27

how can viruses evade the IFN response \*

Answer 27

avoid detection by hiding PAMPs eg by replicating in membrane bound compartments where PRRs cant access interfere globally with host cell gene expression and/or block protein synthesis blocking IFN induction cascades by destroying or binding - eg destroy IRF3 inhibit IFN signalling eg inhibit STAT block action of INF induced antiviral enzymes activate SOCS replication strategy that is insensitive to IFN = too fast for the INF response

Question 28

describe how hep c blocks the INF response \*

Answer 28

has NS3/4 protease that is used to cleave own polypeptides this protease can cleave Mavs - signalling platform isnt made - therefore act as antagonist to IFN induction

Question 29

describe how influenza avoids IFN \*

Answer 29

has NS1 protein that acts as antagonist to IFN induction by binding to RIG-1/TRIM25/RNA complex - stop detection of RNA by RIG-1 prevents activation of signalling pathway and prevents nuclear processing of newly induced genes NS1 blocks TF in nucleus - mean cant make IFN B or ISGs

Question 30

describe how Pox viruses overcome IFN \*

Answer 30

Pox and herpes viruses are large DNA viruses \>1/2 pox genome is comprised of accessory genes that modify immune response - not needed for replication of virus but by blocking the immune response they make the virus more effective Pox viruses encode sol cytokine receptors - like soluble INFAR - mop up INF so it cant act on cell

Question 31

describe how Pox's way to overcome IFN might be able to be used therapeutically \*

Answer 31

mop up the extra cytokines that are present during inflammation

Question 32

describe how ebola evades the immune system \*

Answer 32

produces VP35 that stops it being sensed by the cell = reduced IFN production VP35 also stops switch on of ISGs

Question 33

what are the consequences of innate immunity \*

Answer 33

there is damage to host cells by both the virus and cytokines/chemokines produced by the immune response

Question 34

describe how viruses action on immune response can cause pathology \*

Answer 34

the modulate the immune reponse = overproduction of cytokines the effect of IFN can be immunopathologic depending on how much IFN is made - 100x more IFN is required for IL-6 than Mx can cause cytokine storm - the high IFN is accompanied by TNF-a and other cytokines the difference in clinical outcome might reflect the vigor of the immune response - which might vary with age

Question 35

viruses that skew the immune system \*

Answer 35

dengue haemorrhagic fever influenza infections ebola

Question 36

describe the cytokine storm \*

Answer 36

IFNs aren't controlling virus = production of more IFNs and IL6, IL6, TNF= cause damage to more organs than the virus would have done in the 1st place cause endothelium to be leaky, stimulate inappropriate inflammatory response and cause pulmonary fibrosis

Question 37

what can be seen histologically in a cytokine storm \*

Answer 37

too many immune cells in alveoli fibrosis as cell tries to regenerate

Question 38

describe IFN as an antiviral treatment \*

Answer 38

for HCV, pegylated IFN often used with ribavrin - no have more specific anti-virals so not used has unpleasant SE - switch on inflammation = flu like SE

Question 39

describe with type 3 IFN could be used therapeutically \*

Answer 39

IFN lambda only involves epithelial cells - so protective to them doesnt act on immune cells - so doesnt cause the same level of inflammation/chemokines/cytokines as type 1 IFN

Question 40

describe how we can use viruses that cant control IFN as attenuated vaccines \*

Answer 40

eg influenza that doesnt have NS1 = the viruses are attenuated in IFN competent cells - ie will be cleared quickly the high levels of IFN that will be produced can recruit useful immune cells - IFN acting as an adjuvant however - cant grow these viruses in normal cells because they will be overcome by IFN - so need to grow on cells that have been genetically engineered not to produce IFN

Question 41

describe oncolytic viruses \*

Answer 41

cancer cells dont make good IFN response - therefore viruses that lack ability to control IFN can kill the cancer cells but would be unable to kill healthy cells that produce IFN the cancer cell is unable to do IFN actions and stop the actions of the virus eg stopping cell division and growth, inducing cell death, alerting the immune system, and stopping angiogenesis