Immune evasion by microbes Flashcards
What is the ultimate goal of the immune response to a viral infection?
Eliminate both the virus and the host cells harbouring or replicating the virus
What may failure to resolve infection lead to?
Persistent/ Chronic infection or Death
How do antibodies respond to viral infections?
Blocks viral attachment proteins
Destabilises viral structure
What do antibodies do specifically to respond to viral infections?
- Opsonises virus for phagocytosis
- Promotes killing of target cell by the complement cascade and antibody-dependent cellular cytotoxicity
- Resolves lytic viral infections.
- Blocks viremic spread to target tissue
- IgM is an indicator of recent or current infection
- IgG is a more effective antiviral than IgM
- Secretory IgA is important for protecting mucosal surfaces
How do human rhinoviruses escape antibody recognition?
Exist as hundreds of antigenically distinct serotypes
How does HIV escape antibody recognition?
Exists as multiple clades or quasi-species
How do Hep B and Ebola escape antibody recognition?
Encode secreted surface antigens that mop up antibody
Stopping it reaching virus particles or infected cells
How does Dengue virus escape antibody recognition?
Exists as 4 serotypes
Previous infection with one serotype followed by infection with a different serotype can lead to antibody dependent enhancement of disease
As virus enters immune cells via antibody and the Fc-Receptor
This triggers Dengue Haemorrhagic Fever
How do influenza viruses escape antibody recognition?
Mutate and evolve to change year on year a.k.a antigenic drift
Influenza viruses can acquire new antigens by reassortment with animal viruses a.k.a antigen shift
Can lead to pandemics
How does antibody evasion cause problems for vaccination?
Too many rhinovirus serotypes make finding a cold vaccine difficult
A new influenza vaccine is required each year to reflect the circulating virus types
What are interferons?
Small proteins play a role in immune protection against viruses
Where do interferons come from?
Induced by molecules made by viruses
Secreted from the infected cell and binds to interferon receptors
What do interferons do?
Initiates the antiviral state in the infected cells and in surrounding cells.
What is the antiviral state?
Transcription of hundreds of genes that block viral replication
What are the different types of interferons?
Type I
Type II
Type III
What are the type I interferons?
IFN-alpha
IFN-beta
What’s the deal with type I interferons?
IFN-beta secreted by all cells
IFNR-alpha receptor is present on all tissues
Plasmacytoid dendritic cells are specialist IFN-alpha secreting cells
There is one gene for IFN-beta
13/14 isotopes IFN-alpha
What is type II interferon?
IFN-gamma
What’s the deal with type II interferons?
Produced by activated T-cells and NK cells
Signals through a different receptor: IFN-gammaR
What is type III interferon?
IFN-lamda
What’s the deal with type III interferons?
Signals through IFN-lamda receptors that are present on epithelial surfaces
Summarise the actions of interferons?
Binds to cell surface reception
Induces production of anti-viral enzymes
How are NK cell activated in response to a viral infection?
Activated by IFN-alpha and Interleukin-12
These activate macrophages with IFN-gamma
What do NK cells do in response to a viral infection?
Target and kill virus-infected cells
When they find cells displaying fewer than normal MHC molecules they release toxic substances
These kill virally infected cells
