Interferons

Question 1

What do IFNs do?

Answer 1

Binds to specific receptors
&
signals activation of de novo transcription of hundreds of Interferon Stimulated Genes (ISGs)

Question 2

Describe Type 1 interferons

Answer 2

Polypeptides secreted from infected cells - 3 major functions:

(1) Induce antimicrobial state in infected and neighbouring cells
(2) Modulate innate response to promote Ag presentation and NK
(3) Activate the adaptive I.R

Question 3

What are the Type 1 interferons?

Answer 3

IFNalpha (IRF-7) & IFNbeta (IRF-3)

IFNb
• one gene for IFNb
• secreted FIRST by ALL cells - as have IFNAR receptors
• production is triggered by IRF-3

IFNa
• 13-14 isotypes of genes for IFNa
• plasmacytoid dendritic cells (pDC) are IFNa-secretin cells
• express IRF-7 constitutively

Question 4

Describe Type 2 interferons

Answer 4

IFNgamma!

• produced by activated T-cell & NK cells
• signals through a different receptor called IFNGR

Question 5

Describe Type 3 interferons

Answer 5

IFNlamba!

Signals through receptors IL28R and IL10beta (mainly present on epithelial surfaces)
• so normally expressed during respiratory tract infections and liver infections
• polymorphisms in IFN are associated with IMPROVED outcomes from HCV and HBV with both spontaneous clearance & response to antiviral therapy

Question 6

How do you differentiate self from non-self?

Answer 6

PAMPs (pathogen associated molecular patterns)
• often sense FOREIGN NUCLEIC ACIDS (e.g. dsRNAs)

via. PRRs (pattern recognition receptors)
• these sit inside cells & detect PAMPs

Question 7

Explain how PAMPs and PRRs function using examples

Answer 7

(1) RLRs – RIG-I-like Receptors (cytoplasmic)
• bind to Mavs (found on mitochondria) and stimulate signalling and IFN-BETA production

(2) TLRs – Toll-Like Receptors (endosomal)
• found in endosomes and makes IFN-ALPHA

(3) NLRs – NOD (Nucleotide Oligomerisation Domain) Like Receptors (cytoplasmic)

These are all PRRs (as receptors!) which detects PAMPs

Question 8

What is different about RNA viruses vs. DNA viruses

Answer 8

Single-stranded RNA is a PAMP

BUT

DNA is not:
• DNA viruses are not sensed by RLRs/ TLRs (e.g. dsDNA)

Question 9

How are DNA viruses tackled instead?

Answer 9

INSTEAD, they are sensed in nucleus by cGAS:

(1) cGAS activates 2nd messenger – cGAMP

(2) cGAMP activates STING (found on ER) –> signalling to nucleus to produce IFN-β
• as triggers SAME downstream messengers that cytoplasmic PAMP dsRNA causes

Question 10

In what manner can IFN receptors signal?

Answer 10

Paracrine manner!

This is as when activated, IFN receptors are heterodimers of
• IFNAR1 & IFNAR2

AND

are SOLUBLE CYTOKINES

Question 11

Explain IFN Type 1 Signalling

Answer 11

1. IFNAR1 and AR2 dimerise
   • & JAK1 and TYK2 cross-phosphorylate
2. STAT proteins are activated and this activates…
   (a) Antiviral response (ISRE).
   (b) Inflammatory response (GAS).
   (c) Repressors of the inflammatory pathways (GAS).

IFNs induce transcription of HUNDREDS to antiviral mediators
• hence why get a fever & feel sick

Question 12

Examples of some IFN stimulated genes?

Answer 12

PKR
• inhibits translation

Mx
•inhibits incoming viral genomes

IFITM3
• restricts virus entry through endosomes

miRNAs, ADAR, apoptosis, cell cycle arrest, etc

Question 13

IFITM3?

Answer 13

IFN Induced Transmembrane Protein 3

Restricts virus entry through endosomes
• by stopping them escaping SO virus broken down by acidic pH

Question 14

Mx1 & Mx2?

Answer 14

GTPases with a homology to dynamin

Forms multimers to wrap around the nucleocapsids of incoming viruses
• Mx1 - inhibits influenza
• Mx2 - inhibits HIV

Question 15

What is problematic about the IFN response however?

Answer 15

Does NOT last
• only maintained for a few hours

Ability to respond to IFN is lost gradually due to -VE regulation
• via. SCOS genes (turn IFN response OFF)

Question 16

SCOS?

Answer 16

Suppressor of Cytokine Signalling

Question 17

What is viral evasion mediated by/different strategies that can be used evade IFN response

Answer 17

o Virus hides the PAMPS – e.g. inside vesicles

o Interference with host cell gene expression (or protein synthesis)

o Block IFN induction cascades
• NS3/4 protease (HCV)

o Inhibit IFN signalling directly
• NS1 protein (influenza)

o Block action of individual IFN-induced antiviral enzymes

o Activate SOCS

o Replication strategy that is insensitive to IFN

Question 18

Example of IFN control by viruses - stopping activation?

Answer 18

o Hepatitis C
– NS3/4 proteases
• acts as antagonist to IFN
• cleave Mavs – interferes with induction of IFN

o Influenza
– NS1 protein
• acts as antagonist to IFN
• binds to RIG-I/TRIM25/RNA complex and prevents activation of signalling pathway & prevents nuclear processing of newly induced genes.

Question 19

Example of IFN control by viruses - stopping signal from getting through?

Answer 19

POX (and herpes) viruses:

 More than half of the pox virus genome is comprised of accessory genes that can modify the immune responses

 Pox viruses encode soluble cytokine receptors (vaccinia virus B18) –> being developed future immune therapies

Question 20

How does the Ebola virus cycle mechanisms help evade the I.S?

Answer 20

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

Question 21

Possible uses of IFN as new therapy development?

Answer 21

(1) Live attenuated vaccines

(2) Anti-viral treatments
• soluble cytokines

(3) IFN lambda
• influenza therapeutic drug

(4) Cancer treatment

Question 22

Explain (1) of the possible new therapy development

Answer 22

(1) 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

Question 23

Explain (2) of the possible new therapy development

Answer 23

(2) Anti-viral treatment (soluble cytokines)

IFN can be used be used as treatment (e.g. HCV)
• e.g. vaccinia B18 (Pox virus) mop up IFN so may be useful in autoimmunity
• BUT has unpleasant side-effects

Question 24

Explain (3) of the possible new therapy development

Answer 24

(3) IFN lamba
• infleunza therapeutic drug

Possibility = IFN λ:
• type 3 IFN – as only expressed on epithelial cells

 Not able to signal to immune cells because they don’t have IFN-lambda receptors
 Would switch on anti-viral state in epithelium, but wouldn’t get same side effects from immunopathology

Question 25

Explain (4) of the possible new therapy development

Answer 25

(4) Cancer treatments

o Cancer cells may be deficient in IFN (don’t show good IFN response)
• so if a cancer patient is given a novel virus, the virus can kill the cancer cells whilst the healthy cells produce IFNs to combat the virus

Question 26

Which answer is NOT true?
Viruses that can’t control the innate I.S well might….

A. be useful as oncolytic agents
B. be difficult to grow in standard cell culture systems
C. be restricted at crossing the host range barrier and unlikely to spark outbreaks in other species
D. be useful as live-attenuated vaccines
E. be highly adapted to their host species

Answer 26

E

Question 27

Which is TRUE?
Viruses that counteract activation of the innate immune system by:

A. varying their coat protein sequences
B. encoding proteins that cleave or target host immune factors for degradation
C. preventing the loading of peptides by TAP
D. inducing a cytokine storm
E. encoding MHC homologues

Answer 27

B