Viral immune evasion Flashcards
What is the goal of the immune system?
- After bypassing host tissue barriers, infectious microorganisms must also evade host innate and adaptive immunity to successfully proliferate and be transmitted to the next host.
- The ultimate goal of the immune response to a viral infection is to eliminate both the virus and the host cells harbouring or replicating the virus
- Failure to resolve the infection may lead to persistent or chronic infection or death.
- Knowledge of how viruses evade the immune response is key to understanding the mechanisms of virus pathogenesis, which may lead to novel therapeutic approaches and aids in the development of effective vaccines.
How does an antibody neutralise extracellular virus?
o It blocks viral attachment proteins (e.g., glycoproteins, capsid proteins)
o It destabilises viral structure
What does an antibody do?
- Antibody opsonizes virus for phagocytosis.
- Antibody promotes killing of target cell by the complement cascade and antibody-dependent cellular cytotoxicity.
- Antibody resolves lytic viral infections.
- Antibody blocks viremic spread to target tissue
What is IgM an indicator of?
Of recent or current infection
What is more effect IgM and IgG?
IgG is a more effective antiviral than IgM
What is secretory IgA important for?
protecting mucosal surfaces
What does resolution of infection need?
-Requires elimination of free virus (antibody agglutination) and the virus-producing cell (viral or immune cell–mediated lysis)
Why is the common cold bad?
Human rhinoviruses that cause the common cold exist as hundreds of antigenically distinct serotypes
How does HIV exist?
HIV exists as multiple clades or quasi-species
What does hepatitis B and Ebola virus do?
Hepatitis B virus (HBV) and Ebola virus encode secreted surface antigens that mop up antibody, stopping it reaching virus particles or infected cells
What does Dengue Virus do?
- Dengue Virus exists as 4 serotypes
1. 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
2. This triggers Dengue Haemorrhagic Fever
Who does antigenic drift?
Influenza viruses mutate and evolve to change year on year
What else will influenza virus do?
- Influenza viruses can also acquire completely new antigens by reassortment with animal viruses
- This is called antigen shift and can lead to pandemics
How do these viruses make vaccination difficult?
- 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 do viral infected cells produce and release?
small proteins called interferons, which play a role in immune protection against viruses
What is an interferon?
- Interferon (IFN) is induced by molecules made by viruses that are sensed by the cell as foreign or in the wrong cellular location.
- For example, double-stranded RNA, RNA that lacks a 5’ cap, or DNA in the cytoplasm
What happens when interferon is secreted?
- Interferon is secreted from the infected cell and binds to interferon receptors
- IFN initiates the antiviral state in the infected cells and in surrounding cells.
What is the antiviral states?
-The Antiviral state involves transcription of hundreds of genes that block viral replication, for example 2’5’ oligoadenylate synthetase and protein kinase R.