Microbiology 1

Question 1

What are the three main functions of interferon 1?

Answer 1

1. Induce antimicrobial state in infected and neighbouring cells of soluble factors
2. Promote antigen presentation and NK proliferation and activity.
3. Activate the adaptive immune response

Question 2

What is the mechanism of stimulation of action of interferon type 1?

Answer 2

Activation of PRRs
IFNbeta is secreted from epithelial cells and induces antiviral state in neighbouring cells.
Fibroblasts can secrete IFNbeta as well.
Plasmacytoid dendritic cells also can secrete a lot of IFNalpha and induce ISGs, effector T cells, increased antigen presentation and chemokine production, B cells (virus specific antibodies)

Question 3

Which type 1 interferon is secreted by all cells in the body?

Answer 3

INFbeta

Question 4

What INF receptor is present for type 1 interferons?

Answer 4

IFNAR

Question 5

What is INFbeta induction triggered by?

Answer 5

IRF-3

Question 6

What do Plasmacytoid dendritic cells secrete?

Answer 6

TNF-a and IRF-7

Question 7

What is type II interferon and what are they produced by and the receptor?

Answer 7

INF gamma
Produced by activated T cells and NK cells
IFNGR

Question 8

What is type III interferon and which receptors does it signal through?

Answer 8

Type III IFN is IFNλ

IL28 receptor, IL10beta on epithelial surfaces

Question 9

What is the difference between PAMPs and PRRs?

Answer 9

Pathogen associated molecular pathogens are foreign (e.g. nucleic acid, dsRNA extracellular).
These are recognised by Pathogen recognition receptors which are within cells and can sense whether it is being infected.

Question 10

What are the receptors that sense foreign material in the cytoplasm and the receptor in the endosome?

Answer 10

Cytoplasmic RIG-I like receptors

Endosomal Toll like receptors

Question 11

Describe the pathway of interferon induction by PRRs?

Answer 11

PRRs (Rig1 and Mda5) recognise viral mRNA
Signal to Mavs on the mitochondrial membrane
Signalling pathway and activation of tyrosine kinases Tbk1/IKKe -> phosphorylation of Irf3.
Translocation to the nucleus and bind to the promoter region of IFNbeta gene.
Transcription and translation of the gene which are then secreted to neighbouring cells

Question 12

Describe the pathway of interferon induction by TLR?

Answer 12

TLRs are located on the cell membrane
They sense RNA
Phosphorylation of Irf3 by kinases
Switch on INF-beta production

Question 13

Describe the pathway of interferon induction by plasmacytoid dendritic cells?

Answer 13

Recognise nucleic acid
Stimulation via Myd88
Phosphorylation of Irf7 by kinases
Switch on IFN-alpha production

Question 14

What is the pathway of recognition of DNA viruses?

Answer 14

cGAS enzyme in the cytoplasm senses DNA
Converts it into cGAMP
This is sensed by STING (located on ER)
STING activates Tbk1 (kinase) -> phosphorylation of Ifr3 -> make IFNbeta

Question 15

Describe interferon type 1 signalling

Answer 15

IFN-a/b binds to IFNAR receptor (INAR1 and IFNAR2 subunits form dimer when ligand bound).
Kinases Jak1 and Tyk2 phosphorylate each other and activate STAT proteins.
STAT 1 and 2 join to form a heterodimer and Irf9 joins to form trimer of ISGF3
Translocation to the nucleus and binds to promoter region on ISG called Interferon stimulated element.

Question 16

What is the importance of IFITM3?

Answer 16

(Interferon induced transmembrane protein 3)
Prevents the entry of enveloped viruses
Located in the endosome
Produced by all cells infected by viruses
Important in the protection against influenza

Question 17

How do antiviral mediators work and what are they?

Answer 17

They are GTPases with homology to dynamin
They form multimers and oligodimers
They can wrap around nucleocapsids and genomes of incoming viruses.
Mx1: important in influenza
Mx2: important in HIV

Question 18

How does protein kinase r work?

Answer 18

It phosphorylates the alpha subunit of eIF2, prevents translation.
Viruses are dependent on protein translation and therefore cannot replicate.
Stimulates IKKb -> Nfkb release which is an important in transcription factor in the antiviral response.

Question 19

What is the negative regulator of the antiviral state?

Answer 19

SOCS supressor gene of cytokine signalling suppresses the antiviral state.

Question 20

What are the different methods of viral evasion of the IFN response? (about 7)

Answer 20

Hide PAMPs
Block host cell gene expression/protein synthesis
Block IFN induction cascades by destroying or binding
Interfere with IFN signalling
Block the action of individual IFN induced antiviral enzymes
Activate SOCS
Replication strategy that is insensitive to IFN

Question 21

How does Hep C stop activation of interferon?

Answer 21

NS3/4 protease acts as an antagonist to interferon induction by cleaving MAVS.

Question 22

How does Influenza stop activation of interferon?

Answer 22

NS1 protein acts as an antagonist by binding to the Rig1-TRIM25-RNA complex. Prevents activation of signalling pathway and prevents unclear processing of newly synthesised genes.

Question 23

How does the Pox virus (type of DNA virus) stop interferon?

Answer 23

Secretes soluble cytokines (vaccinia virus 18) which mops up IFN and stops it from reaching its own receptor.

Question 24

How does Ebola virus evade interferon induction?

Answer 24

VP35 interferes with RIG ability to sense RNA -> interferon induction is blocked.
VP24 interferes with nuclear import of STAT1 complex -> interferon signalling is blocked

Question 25

What is a cytokine storm, when would it occur and it’s dangers?

Answer 25

Innate immunopathology in response to viruses.
Occurs in sepsis, severe viral infection e.g. Dengue, influenza, SARs
Virus induces high levels of IFN, with IFNa and other cytokines.
Acts to switch on IS genes but virus continues replicating.
May lead to multi-organ failure.

Question 26

What are some mediators of the cytokine storm and the clinical outcomes?

Answer 26

INFa/b, IL-6, CCL2, INF-y, TNF

Endothelial dysfunction, Inflammatory response, Pulmonary fibrosis