Exam II: Lecture 7 Flashcards
What is the most basic counterdefense mechanism used by viruses?
To shut down the host cell systems rapidly after infection and take over the host machinery for their own use
Why is shutting down host machinery and taking it over so effective (2)?
- Prevents the expression of antiviral genes
2. Dedicates the cell to making more virus particles
What 9 strategies do viruses use to evade host defenses?
- Shut down of host macromolecule synthesis
- Interference with MHC I antigen presentation
- Interference with MHC II antigen presentation
- Interference with cytokine function
- Inhibition of apoptosis
- Inhibition of antiviral gene expression
- Prevention the activation of the antiviral state
- Mutate antigens
- Hide
How come RNA viruses such as polio can cleave the host mRNA cap, stopping host translation, but still replicate its RNA?
RNA virus translation is cap-independent
Poliovirus also interferes with a Na/K pump in the cell - what does it interfere with and what is the consequence?
It causes an increase in Na concentration and decrease in K concentration
Blocks translation of mRNA
How does MHC interference help the virus?
It make the cell invisible to CTLS
How can viruses inhibit MHC presentation? (5)
- Retard the processing in the golgi
- Create proteins that bind to MHC and prevent transport to cell surface
- Inhibit transcription of MHC / TAP genes
- Induce premature degredation of MHC by the proteasome
- Mimic B2 microglobulin > changes MHC structure
How does inhibition of cytokine function help the virus?
Cytokines are essential for activation and coordination of immune response
How can viruses inhibit cytokine function?
- Prevent localization to the membrane
- Prevents translation block induced by IFN
- Blocks PKR = turns on translation
- Homologue, antagonized Th response
- Blocks co-activaor required for transcription of IFN = block antiviral state
How does inhibition of apoptosis help the virus?
Allows the virus time to replicate
How can viruses inhibit apoptosis? (5)
- Produce serpins = inhibit proteases
- TNF receptor homologue
- Block Fas movement to cell surface
- Homologues of Bcl-2
- Protiens that prevent activation of p53
How does evation of the antiviral state help the virus?
The virus does not allow the cell the have a “head start”
How can viruses inhibit PKR activation (main antiviral state protien)?
- Block PKR activation
- Inhibit acivation of IFN-stimulated genes (ISES)
- Block PKR by bidning to dsRNA
- Homolouge substrate for PKR
What are some other mechanisms the viruses uses to escape the immune response discussed in class?
- Prevent activation of complement
- Go latent
- Infect cells of the immune system > immune suppression
- Antigenic drift = prevents immune system form recognizing viral proteins
- Interfere with NK activation
How did viruses evolve homologues?
Probably aquired from the host
