L24 - viral evasion of the Innate/interfon response

Question 1

what is the innate immune response accompanied by

Answer 1

inflammatory reponse

= induced by unnatural cell damage
= necrosis instead of apoptosis

ascociated with viral infections

Question 2

what does the innate reponse recognise

Answer 2

PAMPs
pathogen acociated molecular properties

• unusaul polymeras on viral particles
• cell surface componets
• dsRNA

Question 3

how many types of interferon are there

Answer 3

3

Question 4

Type 1 interferons

Answer 4

IFN-⍺ = viral infection - dsRNA

IFN-b = viral infection - dsRNA

both produced by all cells but mainly dendritic

target all nucleated cells

Question 5

Type 2 interferons

Answer 5

IFN-y = antigens,mitogens = IL-2 and IL-12

produced by T and Nk cells = activate/cause proliferation of cells

act on all nculeated cells

Question 6

type 3 interferons

Answer 6

IFN-λ
= viral infection - dsRNA

produced by most cells but mainly dendritic

act on epithelial cells

Question 7

whiuch type of inteferon is most important for viral infection

Answer 7

type 1

IFN-a and IFN-b

Question 8

3 key steps in intereron system

Answer 8

1. sensing
2. signalling
3. antiviral state

Question 9

stages of interferon system simply

Answer 9

1. sensing:
   TLRs bind to PAMPs and induce Nf-kb
2. Signalling:
   inteferons produced and released from cell then bind to adjacent cells
3. antiviral state:
   activates Intereron-induced-genes

Question 10

RIG-I like receptors vs TLRs

Answer 10

RLRs are found within the cytoplasm

TLRs are found on surfaces - cell surface membrane _ endosome surface

Question 11

what detects PAMPs to induce Nf-kb

Answer 11

TLRs and RLRs

Question 12

describe the intracellular signalling pathway following TLR activation

Answer 12

activated receptors due to phosphorylation on tyrosine residues

Myd88 recruited to receptor

eventual production of Nf-kb,IRF3 and IRF7

= interfon regulatory factors

Question 13

name the 3 signaling molecules produced at the end of downstreaem signalling from TLRs/RLRs in viral infection mand results

Answer 13

Nf-kb:
pro-inflammatory cytokine production

IRF3 + IRF7:
Type 1 IFN produced

Question 14

name the 4 most important TLRs for viral infections

Answer 14

TLR3
TLR7
TLR8
TLR9

Question 15

name a TLR that is on the inside of a endosome and what it binds to

Answer 15

TLR3

dsRNA

Question 16

how does IRF3 enter the nucleus following TLR activation

Answer 16

phosphorylatted and forms a dimer

= Type 1 IFN produced

Question 17

How do RLRs cause signalling

Answer 17

cytoplasmic receptors

1. RLR binds to dsRNA in the cytoplasm

= comformational change

2. recruits MAVs protein via ‘CARD’ domains to mitochondria

= mitochondrial antiviral signalling protein

3. actiavtion of MAVS causes downstream signalling

= production of IRF3, Nf-kb

Question 18

describe cGAS role in stimulating pruction of iinteferon transcription factors

Answer 18

cGAS (cyclic GMP-AMP synthetase)

1. cGAs binds to viraln DNA in cytoplasm
2. produces cGAMP by linking an ATP + GTP
   3.cGGAMP binds to STING

= stimulator of inteferon genes

4. activated STINg moves to golgi activating the kinase = TBK1
5. TBK1 produces IRF3 + Nf-kb

Question 19

biphasic vs monophasic production of interferons

Answer 19

most cells is biphasic:
IFN-b is made which CAUSES IFN-a to be made

1. IRF3 produced at the end of donstream signalling produces IRF7 from IFN-b gene
2. IRF7 activates IFN-a

dendritic cells:
IRF7 is already present in inactive state = ‘primed’

= much faster and amplified production of IFNs

Question 20

how many sibunits make up a IFN-receptor

Answer 20

2

= tyrosine kinase receptors - ITAMs

Question 21

describe the downstream signalling when type 1 IFNs bind to receptors

Answer 21

1. IFNs bind to their recptors causing phosphorylation of ITAMs
2. STAT 1 + 2 dimerise and are phosphylated

= Signal Transduction and Activators of Transcription proteins

3. inteferon stimulated gene factors (ISGFs) induced
4. stimulate ISGs (inteferon stimulated genes)

= antiviral state

Question 22

3 levels of the antiviral state

Answer 22

1. mechanusms to prevent viral replication
2. mechansism to killhost cell if infected
3. mechaims to kill unifected cells in the area of infection

Question 23

what ways can ISGs affect virals replicative life cycle

Answer 23

prevent entering

prevent unbcoating of viruses

block transcription

Question 24

3 classical antiviral mechanisms

Answer 24

1. dsRNA-dependant PKR pathway (protein kinase)
2. The 2-5A system
3. Mx pathway

Question 25

describe the antiviral mechansism PKR - proteinb kinase

Answer 25

1. PKR is an inactive protein kiase that recognises dsRNA
2. binding causes autophosphorylation and dimerisation of 2x PKRs
3. active dimer PKR phosphorylates elF2

= elongation factor in traqnslation

4. elF2 binds irreversibly to elF2B

= protein sysnthesis halted in cell

Question 26

describe the antiviral 2-5 A mechansism

Answer 26

1. RNase L is a nuclease
2. IFN induction causes mass production BUT remians inactive
3. 2’-5’ Oligo(A) synthetase (OAS) produces adenylic acid when activated by dsRNA
4. nucleotides activates RNase L

= cleaves viral RNA

Question 27

describe the antiviral mechanism MxA

Answer 27

unlike PKR and RNase L

= Mx proteins are directed against specific viruses

2 different forms of Mx proteins that klive in cytoplasm - MxA + MxB

= interfere with different parts of lifecycle

Question 28

name a way parmyxous virus has evolved to prevent ‘sensing’ stage of antiviral response

Answer 28

V protein blocks interecation of RLR with MAVS

= no downstream signalling

Question 29

describe how the influenxaza virus has evolved to prevent ‘antiviral state’ part of the antiviral response

Answer 29

protein binds to PKR and prevents phosphorylation of elF2

Question 30

why are intefrons not used more in drugs

Answer 30

has affects on healthy uninfeccted cells
- blcoks cell division
- alters transcription

= localasied ‘fire break’ to infection