Viruses Flashcards
How are viruses classified?
- specificity of infection
- genome
- structures
Outline the innate immune response
- non-specific
- Produces soluble factors
- Phagocytic cells
- Immediate and early
Outline adaptive immunity
- Takes 1-2 weeks
- highly antigen specific
- memory based
- Activation of B+T cells
Outline the features of influenza type A virus
- SSRNA virus
- Envelope virus carrying glycoproteins
- Infects birds and mammals
What are the 2 main vaccine targets on influenza type A virus?
- Hemagglutinin
- Neuraminidase
What is antigenic drift?
Minor antigenic changes in glycoproteins on the surface of a virus
What is antigenic shift?
The abrupt and major changes in glycoprotein
What causes antigenic drift in influenza A?
- Has an RNA genome
- Replication of RNA has high mutation rate
- No proofreading
Why does the flu vaccine not work every year?
- The annual flu vaccine is based on predicting the HA and NA antigens
- Mutations in HA and NA surface proteins which occur may be different to the ones predicted
How does Antigenic shift occur?
- Genetic reassortment of HA and NA genes occurs in an intermediate host
- This leads to recomination or reassortment of viral strains
- This often occurs when a flu strain jumps species
Outline the features of HIV-1 retrovirus
- RNA envelope virus
- Replication requires reverse transcriptase
- Infects immune cells
What type of cells does HIV infect?
CD4+ helper T cells
What are the features of Reverse transcriptase?
- Replicates the viral RNA genome into DNA
- Not normally expressed in human cells
- Lacks 3’-5’ proofreading so high error rate
What are impacts of reverse transcriptase not having prrofreading?
- Mutations accumulate
- Mutations which affect reverse transcriptase itself occur
- Affects the therapeutic outcome
How can viral replication be inhibited with nucleoside analogues?
- DNA synthesis joins 3’OH of growing DNA chain to 5’ phosphate group of the incoming dNTP
- If the 3’OH is blocked (by analogues) then DNA chain growth will terminate
Give the name of a treatment for HIV?
AZT
How does AZT work to treat HIV?
- Acts as a nucleoside analogue
- Lacks 3’ OH so causes chain termination
How can AZT target HIV infected cells specifically?
Reverse transcriptase is 100x better at incorporating AZT into DNA than DNA polymerase
What sort of virus is herpes simplex?
Double stranded DNA virus
Give the name of a treatment for herpes simplex virus
Acyclovir
How does acyclovir have specificity?
- For the drug to be activated it must have a phosphate group attached within the cell by thymidine kinase
- The viral thymidine kinase is much better than host TK at phosphorylating
Which enzyme is used to phosphorylating acyclovir?
Thymidine kinase
How does acyclovir treat herpes?
Causes replication chain termination due to a lack of 3’OH
What is an oncogenic virus?
A gene suspected of causing cancer in organisms
What is a long terminal repeat?
A sequence present at the ends of viral genome which provides promoter activity and drives gene expression
What are the 3 ways viruses can cause cancer?
- Virus inserts oncogene into host genome
- Insertion of virus brings a strong promoter to activate a cellular proto-oncogene
- Insertion of a virus (which lacks an oncogene) distrupts and inactivates a tumour suppressor gene
What is a proto-oncogene?
A normal cellular gene capable of causing cancer when dysregulated
