Immunity Flashcards
What factors make up the triad model of disease?
host
environment
viral pathogen
How can the immune response to virus infections can be broken down into?
Nonspecific, innate immunity plays a role shortly after infection and is directed against any virus
Specific, adaptive immunity requires days to weeks before they are induced or effective in clearing specific viruses
- Slower but more powerful
What is the first line of defense against viral infections?
Apoptosis-programmed cell death (PCD)
Which gene helps regulate cell apoptosis?
p53
Which viruses target p53 to counteract apoptosis?
Adenovirus, HPV, and Hep B
What are the key components of the innate immune response?
- Cytokines
- Local sentinel cells
- Natural killer (NK) cells
What effect can IFN-a/b have?
IFN a/b: induce antiviral state
cells that are infected produce and release these cytokines
- these cytokines alert neighboring cells that a virus is
here (get ready, ramp up defenses)
- Like paul revere: the british are coming
What kinds of symptoms do interferons (cytokines) produce in host?
IFN production causes flu-like symptoms in infected host
When an IFN binds to a cell receptor, it triggers the expression of gene products that do what?
Block different stages of viral life cycle:
INHIBIT:
1) viral penetration and uncoating
2) viral mRNA and protein synthesis
BLOCK:
3) virus genome replication
4) assembly/release of new virions
How is an antiviral state established?
IFN produced and released from virus-infected cells ->
IFN binds to target cells ->
Signal transduction ->
Increased transcription of antiviral genes ->
Establishment of antiviral state
How were interferons discovered?
Isaacs and Lindenmann experiment:
- found some kind of interfering substance being
generated inside of cells against viruses
Step 1: get eggs ready and put egg cells into 2 different test tubes
Step 2: treat 1 tube w/ saline solution, added inactivated (killed) influenza virus into tube 2
Step 3: Allow tubes to incubate then infect both tubes w/ live flu virus, allow to incubate
Step 4: Measured both tubes to see how many new influenza virons were present
- Found less infectious particles in tube 2 (the one w/
inactivated virus added)
Some kind of interfering substance must be inhibiting the virus in tube tube, called these substances “interferons”
What are the stages of signalling from cytokines (or any chemical messenger)?
Primary Signal
Transduction (protein kinase phosphorylation)
Response
What antiviral proteins are expressed in response to IFN signaling?
- PKR activated by dsRNA
- block protein synthesis
- 2’5’-oligo(A) synthetase is expressed and activates RNase L
- degrades mRNA (no protein synthesis so no viral
replication) - contributes to apoptosis
- degrades mRNA (no protein synthesis so no viral
How does PKR activation prevent viral replication? What is an example of a virus that can get around IFN response in cells?
IFN activates Protein Kinase R (PKR)
-PKR phosphorylates eIF-2a which inhibits protein synthesis = blocking viral replication
HSV-1
- makes protein ICP34.5
- ICP34.5 directs host cell enzyme Protein Phosphatase 1a
to cleave the phosphate from eIF-2a that was inhibiting
protein synthesis
- Protein synthesis proceeds and viral replication can
occur
How do POX viruses get around IFN response?
POX viruses can make soluble proteins that are released from cells and bind IFN receptors on the cell’s surface (competitive inhibition)
What are local sentinel cells?
Macrophages and dendridic cells
- Both professional APCs
- can present w/ both MHC I and II
WHat are the roles of dendritic cells in antiviral response?
- Directly inhibit virus replication through the production of IFN and other cytokines
- Trigger the adaptive T-cell mediated immunity to the virus by presenting viral antigens to TH cells.
WHat are natural killer cells?
Participate in both innate and adaptive immune responses
NK cells are activated by IFNs and other cytokines and respond within minutes/hours
NK cells release perforins, granzymes and chemokines to kill virus-infected cells
How are NK cells regulated?
NK cells constantly patrolling for infected cells
NK cells Have inhibitory and activating receptors
- MHC molecules on host cell will bind receptor on NK
- MHC + Inhibitory receptor = NK stands down
infected cells will down regulate MHC expression
- No MHC+inhibitory receptor binding = activating receptor binding = NK cell signalled to release perforin/granzymes to kill infected cell
Infected cells downregulate MHC I expression = good target for NK cells to kill b/c activating receptor binds
What are the arms of adaptive immunity?
Two Arms of Adaptive Immunity:
1) Cell mediated Response
- T Cells
2) Humoral Response
- B Cells and antibodies they produce
What Cells are involved in adaptive immunity?
1) T Cells
a) Cytotoxic T Cells (TCTL)
- induce apoptosis of cells that are infected w/ virus
b) Helper T Cells (TH)
- Help other cells w/ cytokine communication
- Need antigens to be processed and presented by
APC’s (macrophages & dendritic cells)
- activate B cells
- Help Tc
2) B Cells
a) Plasma Bodies
- produce Antibodies
- can recognize foreign antigen w/o any help
- antigen doesn’t have to be processed and
presented like T cells need
What are the properties of adaptive immunity?
Slower to develop
Very Specific
Memory
What is the difference between adaptive and innate immunity?
Nonspecific immunity plays a role shortly after infection and is directed against any pathogen
Specific immunity requires days to weeks before they are induced or effective in clearing specific viruses
What are B Lymphocytes?
B lymphocytes are generated and mature in the bone marrow
- contain surface antibody receptors w/ high specificity for
specific antigen
- each B cell contains Ab’s for only one type of antigen
When they encounter an antigen they divide/differentiate into plasma bodies which produce HUGE quantities of soluble Ab’s
- After virus cleared some B cells form memory B cells
What are T Lymphocytes?
T lymphocytes mature in the thymus gland
- Have Tcr (T cell receptor) which binds antigens
presented by APCs
T Helper cells contain co receptor CD4
- TCR recognize antigen present via MHC II
Cytotoxic T cells contain co receptor CD8
- TC activated when it’s TCR recognize antigen presented
via MHC I
What role does the lymph system play in adaptive immunity?
Lymph supplies lymphocytes to the bloodstream
Lymphocytes congregate in the lymph nodes and exit through the outgoing lymph vessels
Most cells of body contain which type of MHC?
MHC I
most cells of body don’t have MHC II
How are B and T lymphocytes responsible for Specificity?
T Cell
each T cell recognizes a specificantigen associated with an MHC I (CD8 T-cell) or MHC-II (CD4 T-cell) receptor
B Cell
each antibody recognizes a unique antigen
How are B and T lymphocytes responsible for Memory?
Once stimulated by antigen, a memory pool of T and B cells are established
How are B and T lymphocytes responsible for Self-Nonself recognition?
During development, T and B cells are selected that can recognize foreign (non-self) antigens but not self proteins -prevent autoimmunity
