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29 Cards in this Set

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What is an important early defense mechanism against viruses that peaks within 1-3 days of viral infection
NK cell response. They have broad specificity and will lyse a wide variety of virally-infected cells; they are not antigen specific and do not exhibit immunological memory
How do NK cells kill
They are characterized by their ability to recognize and kill virally infected as well as transformed cells. They express a broad array of activating receptors whose ligands are expressed on transformed and viral infected cells as well as in normal cells
How do NK cells avoid killing normal cells
They express inhibitory receptors that are engaged by ligands expressed on normal cells and are downregulated or absent in viral infected and transformed cells
NK cells specialize in eradicating what type of cell
Low MHC cells, which are for the most part abnormal. Also some viruses down-regulate MHC expression in host cells
dsRNA causes infected cells to do what
Produce type I interferons
Which cells produce interferon-alpha
B cells, monocytes and macrophages
Which cells produce Interferon-Beta
Fibroblasts and many other cells
Early in viral infection, what binds to specific receptors on neighboring cells and induces an antiviral state
Interferons alpha and Beta. An antiviral state means the cells are primed to respond if they themselves become infected and encounter dsRNA (viral replication intermediates)
What does 2'-5' oligo (A) synthetase do when induced by interferons
Leads to degradation of host and viral mRNAs
What does Pkr (dsRNA-activated protein kinase) do when induced by interferon
Phosphorylates and thereby inactivates the eIF2 translation initiation factor
In addition to inhibiting viral protein synthesis, what else do interferons do
Increase lytic potential of NK cells
Increase MHC class I expression
What three cell types are involved in adaptive immunity against viruses
Antigen presenting cells (dendritic cells and macrophages), T cells, and B cells
In cell-mediated immunity, what cytokine causes proliferation and differentiation of CTL precursors into CTL effector cells?
What is it produced by?
IL-2, produced by T helper cells
What two processes are necessary for activation of viral-specific CTLs
Viral particles presented on MHC class I molecules (endogenous pathway)
IL-2 from T helper cells
What cytokine, which is released by activated CTL and Helper T cells, has direct antiviral activity by enhancing macrophages, CTLs and NK cells, and increasing MHC expression
Interferon-gamma
CTLs are activated to do what two things
Lyse virally infected cells, and release interferon-gamma
What pathway involves processing of viral particles by APCs, which allows presentation of viral peptides in association with MHC Class II antigens to T helper cells
The exogenous pathway
What five things are required for generation of anti-viral antibodies
1: Activation of viral-specific T helper cells
2: Cytokine production to activate T and B cells
3: Binding of virus particles to B cells and expression of their MHC II
4: Proliferation and activation of B cells after interaction with activated Helper T cells
5: Secretion of Abs
What is the limitation of antibodies in the immune response to viruses
They tend to recognize "whole" proteins, and viruses may never express surface proteins or only at late stages
Why are T cells more effective than antibodies in the immune response to antibodies
They can recognize portions of almost any viral protein when expressed in the context of MHC, even those made at very early stages
What are the three strategies viruses use to evade antibodies
1: Mutation of viral gene sequences by Antigenic Drift
2: Wholesale replacement of viral proteins by Antigenic Shift
3: Down-regulation of viral protein expression
Why are neurons a popular site of viral persistence
They express little or no class I MHC
What is the T2 protein of poxvirus
A TNF receptor analogue, which will mop up TNF and prevent it from killing virally-infected cells
What are the four main types of vaccine
Killed, live-attenuated, subunit, passive
What type of vaccine has inactivated viral nucleic acid but has not lost the immunogenicity of the viral proteins
Killed-virus vaccines.
What are the disadvantages of killed-virus vaccines
Requires boosters (low antigenicity)
Incomplete inactivation of vaccine virus
Induction of low IgA and CMI
Potential for disease
What type of vaccine has a variant virus that replicates and produces the same antigens as virulent viruses, but no longer causes disease
Live attenuated-virus vaccines. They are often achieved by serial passage in unnatural hosts or tissue cultures, which selects for mutations resulting in decreased virulence
What type of vaccine has a component of the virus (a protein) known to be a protective antigen, that is made and used as the immunogen in the vaccine
Subunit
What type of vaccine has immunoglobulin preparations containing specific antibodies to the virus in question, as prophylatic or post-exposure treatments
Passive immunization