Antiviral defense II Flashcards
What cytokines do NK cells produce to limit viral replication?
TNF and IFN
What are the two mechanisms that NK cells use to kill virally infected cells?
- ADCC
- Ab bound to virus proteins
- recognition mediated FcR on the NK cell surface - kill cells that lack expression of MHC-I
What are the activating and inhibitor Rs on NK cells, what do they recognize?
activating Rs (e.g. NKG2D) recognize proteins induced by stress and viral infection (e.g. MICA and MICB)
inhibitory Rs (e.g. KIRs) recognize MHC-I
Describe how the biology of virally infected cells and tumor cells are similar
- both down regulate MHC-I
- both upregulate MICA and MICB
Describe the structure of inhibitory NK cell Rs
- extracellular domain has Ig-like domains
- cytoplasmic tail contains ITIMs
Describe KIR inhibitory signaling pathway
- MHC-I binds to KIR
- phosphoylation of KIR ITIMs by an SFK
- SHP-1 phosphotase recruited to KIR
- SHP-1 dephosphorylates NKG2D signaling proteins
What is apoptosis and why is it better than necrosis?
apoptosis = inherent cell suicide program that can be activated by NK cells and other stimuli
anti-inflammatory (insides of cells can damage other cells –> inflammation)
What are some features of apoptosis?
- cell shrinkage
- chromatin condensation
- DNA fragmentation
- mito changes
- membrane blebbing
- formation of apoptotic bodies
How are apoptotic bodies created? What cells dispose of apoptotic bodies?
apoptotic body creation:
- DNA is cleaved by nucleases and the cell’s body and nuclear contents are packaged into vimentin wrapped cages
apoptotic body disposal:
- scavenging macrophages detect PS on the surface of these packages and engulfs them for safe disposal
What kind of proteins does apoptosis require? How are these proteins activated? What do they do?
- apoptosis requires protease activation –> caspases
- caspases are activated by cleavage at aspartic acid residues (inactive prior to cleavage) –> homodimerize (active caspases composed of two small and two large subunits)
- activated caspases cleave cellular proteins –> cell death
How does granzyme B induce apoptosis?
- granzyme B cleaves Cas3 at the large domain-small domain border
- auto-catalytic Cas3 will cleave itself at the pro-domain large domain border
- cleaves BID –> induces intrinsic apoptosis pathway
Describe what a western blot would look like (probing for cas 3) in the following groups that are exposed to granzyme B and perforin: cells, cells + virus that prevents apoptosis (VV), cells + Bcl2 (prevents apoptosis)
control cells: procas 3 + cleaved cas3
cells + VV: procas 3
cells + bcl2: procas 3
Name and describe the two apoptotic pathways
- extrinisc
- activated by death R triggering (e.g. FAS) –> activates cas 8 –> activates cas 3 + cleaves BID
- talks to the intrinsic pathway - intrinsic
- activated by intracellular stress
- leads to release of cytochrom C from mito activating cas 9 –> cas 9 activates cas 3
What are the two types of caspases?
- initiator (cas 8 and9)
- activated by pro-apoptotic stimuli
- cleave and activate executioner caspases - executioner (cas 3)
- cleaves numerous substrates to dismantle the cell
How does cas 3 cause DNA fragmentation?
- ICAD inhibits CAD (a DNAse)
- active cas 3 cleaves ICAD
- CAD translocates to the nucleus and cleaves the DNA
What NK processes can viruses inhibit?
- release of granules
- interfere with apoptosis
How can HCMV evade NK and T cells?
- HCMV encoded UL18 is structurally similar to MHC-I molecules
- no homology (not derived from HLA) - downregulates MHC-I
- escape CTL detection - UL18 is expressed on the cell surface
- interacts with KIR on NK cells
- decoy MHC
How can viruses inhibit caspases?
- poxviruses and baculoviruses produce viral protein that inhibit activated caspases
- adenovirus and hCMV produce viral proteins that inhibit caspase activation
Describe how cowpox virus inhibits caspases
- encode viral CrmA
- CrmA is cleaved by cas1 and 8
- results in a covalent interaction between the cas and CrmA
- cas1 and 8 are held in a complex are unable to cleave other proteins
What protein does CrmA have homolgy to?
cellular serine proteinase inhibitors (SERPINS) which are found naturally in cells
How does baculovirus p35 work?
Same mechanism as CrmA, but can inhibit many members of the caspase family
How does CrmA inhibit NK killing via degranulation?
CrmA binds and inhibits the activity of granzyme B
What virus protein bind to inactive caspases and inhibit their activation?
- adenovirus 14.7K protein
- HCMV UL36 protein
What are three mechanisms in which the 1st caspase is cleaved in the apoptosis pathway?
- granzyme B released from NK cells or CTLs cleaves cas3 followed by an auto-catalytic event resulting in activation of cas3
- cellular stress causes changes in the mito
- activation of cell death Rs on the surface
