Immunity against viruses Flashcards
What is a cytolytic virus
Does not take part of the plasma membrane to form an envelope when it exits the host cells
I.e No envelope
Describe the anti-viral effects of antibodies
Action of antibody by itself
Blocks binding and entry into cells
activates intra-cellular degradation via the action of TRIM21 that marks the virus for ubiquitination (used when antibody binding is not enough to stop the virus entering the host cells)
Antibody + complement
Damage to enveloped viruses
Opsonisation for phagocytosis (addition of proteins that induce phagocytosis )
Antibody bound to infected cells causes antibody dependant cellular cytotoxicity
Describe some Invasion mechanisms
They are mechanisms used by viruses to bypass the immune system
E.g. modification of cell surface proteins (Called antigenic drift) via spontaneous mutation
Antigenic shift is the generation of a new viral strain ; occurs when there is an infection of two strains and exchange of genetic material between them occurs
Name the two ways viruses can enter host cells
Endocytosis
Fusion
Name the stages of viral replication
- Attachment via binding of viral ligand and comp receptor
- Entry via endocytosis and fusion
- Uncoating
- Macro molecular synthesis - copies of genome and proteins (+ve as RNA)
- Assembly
- Release via budding to yield enveloped virus or cell lysis
In a general immune response …..
Several mechanism act simultaneously
Describe the anti-viral action of interferons
Type 1 interferons: enhance the expression of MHC class I proteins ; better identified activate NK cells Degrade viral mRNA Inhibit protein synthesis
What are Natural killer cells ?
Large granular lymphocytes
Do not have antigen receptors on their surface
Involved in innate immunity
How do NK cells detect infected cells?
Antibody dependent cellular cytotoxicity (ADCC) : Fc receptors on surface of NK cells bind to antibodies ; antibody binds to viral antigen ; antibody acts as a bridge
Or NK mechanism : depending on which molecules are presented on the surface of the target cell killer inhibitory receptors or killer promoting receptors may be activated
Name the glycoproteins present on surface of influenza A virus
Haemagglutin and neuraminidase
Describe the mechanism of NK cell mediated cell death
They make:
perforins - make holes in cell membrane
Granzymes/Fas ligand protein on NK cell binds to Fas on target cell - activates caspases and endonucleases = apoptosis
IFN-γ = enhances HLA class I and II expression (antigen presentation)
Describe the structure of viruses
Nucleic acids :
DNA - Can be double or single stranded, circular or linear
RNA - can be ds or ss - ss can have positive or negative polarity ; linear or segmented
Protein capsid encases the nucleic acids ; can be icosahedral or helical
Surface proteins allow attachment
Lipid envelope in some viruses
No organelles
What are the two ways viruses can enter cells
Endocytosis or fusion
Describe viral replication
Only viral ss (+) RNA can be used directly to as mRNA
Viruses with ds (+/-) RNA or ss (-) RNA must have their negative strand transcribed to make mRNA first
Viruses with ds (+) DNA undergo transcription first
Viruses with ss (+) RNA undergo reverse transcription then the resulting ss DNA is replicated to make ds DNA intermediate which is then transcribed
What are the 2 ways viruses can exit cells
Budding (This forms enveloped viruses)
Cell lysis
