Interferons

• Cytokine family important for innate immunity against viruses

• Three classes of IFNs according to the receptor used

• Type I IFNs essential for antiviral response

IFN, IFN… IFNIFN

IFN-stimulated genes - ISGs

e.g. PRRse.g. ISG15, MxGTPases, OAS-directed RNaseL pathway, PKR

Antiviral Effect

Direct Indirect

• Detection of viral molecules• Modulation of signalling pathways and transcription factors• Increased IFN production

Protection from virus spread

• Induction of apoptosis• Regulation of post-transcriptional events (like RNA degradation)• Regulation of post-translational modifications

ISG15

• Homologue to Ubiquitin

• 158 putative target proteins identified so far (JAK1, STAT1, PRRs, MxA, PKR, RNAseL, …)

important role of ISGylation in the IFN-mediated antiviral response through modification of components of the host immune response or viruses

Mx GTPases

• Expression strictly regulated by type I and type III IFNs

• Accumulate as oligomers in cytoplasm close to intracellular membranes

• MxA monomers are released to bind, trap and degrade viral components like nucleocapsids

• constitutively expressed OAS synthesizes 2’,5’-oligoade-nylates after polymerization triggered by viral dsRNA

• Binding of 2’,5’-oligomers to the ankyrin repeats of RNasL leads to its homodimerization

• Activated RNaseL cleaves viral RNAs

• Type I IFNs upregulate OAS expression

OAS/RNaseL pathway

OAS: 2‘,5‘-oligoadenylate synthetase

PKR

• Constitutively expressed (as inactive kinase) at low levels but induced by type I and type III IFNs

• Direct activation by viral RNAs or other ligands followed by dimerization and autophosphorylation

• Phosphorylation of EIF2 blocks recycling of GDP

protein translation inhibited

Apoptosis of the cell

EIF2: eukaryotic translation initiation factor

Additional immune functions

• ISGylation: UBE1L is found to be a tumour suppressor (deleted in almost all small-lung cancers) possible mechanism how type I IFNs regulate proliferation

• A polymorphism in OAS1 is associated with type I diabetes

• PKR promotes degradation of IkB -> activating NFkB

• PKR implicated in IgE class switching in B cells -> viral infection might induce IgE-mediated disorders like allergy or asthma

Future directionsFurther details of the mechanisms of each

effector still have to be elucidated:

• Precise function of Mx proteins remains uncertain GTPase activity?

• Contribution of alternative PKR substrates to immune response is poorly explored

• Roles of PKR in regulation of inflammatory response• Precise roles of different OAS proteins• cataloguing of SNPs (single nucleotide polymorphisms)

in human and animals correlation to susceptibility to viruses provide insight into gene function

• roles of these proteins in mediating adaptive immune response potential to manipulate immunity, enhance resistance to pathogens and disease or diminish autoimmune responses

Summary

• Type I IFNs are essential for antiviral response -> ISGs• Important role of ISGylation (ISG15) in the IFN-mediated

antiviral response through modification of components of the host immune response or viruses

• Mx GTPase binds, traps and degrades viral components like nucleocapsids

• RNaseL cleaves viral RNA with the help of an OAS signal

• PKR inhibits protein translation and promotes apoptosis• OAS and PKR also act as PRRs due to constitutive low

level expression

Viral replication is blocked

Thank you for your attention!