(Final) Effects of viruses on host cells Flashcards
What are the 3 categories of effects that viruses have on host cells?
Cytocidal = Cell death: apoptosis or lysis
Non-cytocidal= persistent infection: slow, latent, or chronic
Cell transformation = transformation to tumor cells
What is the cytopathic effect?
Damage or morphological changes to host cells during virus invasion
What is Syncytium?
Fusion of the plasma membranes of four or more cells to produce an enlarged cell with four or more nuclei. *these are prone to premature death
T/F: Infected host cells merge with other infected host cells during syncytium
True
Infected cells merge with non infected and or infected cells (no discrimination)
What structures help to dx and identify a viral infection via histo?
Inclusion bodies
*these are an abnormal structure in a cell nucleus or cytoplasm or both. They have characteristic staining properties with associated viral infections
What can inclusion bodies be made from?
- accumulation of viral components
- Results from degenerative changes in the cell
- Crystalline aggregates of virions
What inclusion bodies are indicative of the rabies virus?
Negri bodies
What characteristics may inclusion bodies have?
Intracytoplasmic or intranuclear or both Single or multiple Large or small Round or irregular Eosinophilic or basophilic
Eosinophilic inclusion bodies have an affinity for ______ dyes
Acid dyes such as eosin
stain pinkish
Basophilic inclusion bodies have an affinity for _______ dyes
Basic dyes such as hematoxylin
stain blue-purplish
In tissue culture, visible morphological changes/damages to monolayer cells resulting from virus infection is also known as:
- teratogenic effect
- cytopathic effect
- lethal effect
- somatopathic effect
B - Cytopathic effect
What are 6 general mechanisms of virus induced cell injury and death?
Inhibition of host cell nucleic acid synthesis
Inhibition of host cell RNA transcription (mRNA production and processing)
Inhibition of host cell protein synthesis
Induce lysosomes to release their hydrolytic enzymes (which will destroy the cell)
Interference with cellular membrane function
Stimulating apoptosis
What is apoptosis?
Programmed cell death
What is the caspase apoptosis pathway that viruses can induce?
Activation of the host-cell caspase enzymes mediate the death of the cell
Once activated, caspases are responsible for degradation of the cells own DNA and proteins
*****end result of BOTH intrinsic and extrinsic pathways
What is the intrinsic (mitochondrial) pathway of apoptosis?
The mitochondrial pathy way is activated as a result of increased permeability of mitochondiral membranes subsequent to cell injury.
What is the extrinsic (receptor) pathway of apoptosis?
Activated by engagement of the specific cell membrane receptors which are members of the TNF receptor family
What cells utilize perforin and granzyme to induce apoptosis?
Cytotoxic T lymphocytes (CD8) and natural killer cells
T/F: Naked viruses can under go membrane fusion or surface fusion
FALSE
Enveloped viruses only
What viruses undergo antibody dependent cell mediated cytotoxicity?
enveloped viruses
T/F: Apoptosis is a host defense mechanism against viral infection
TRUE
T/F: Non-cytocidal viruses do not cause immediate death of cells in which they replicate
True
These will cause damage to the cell - but they do not immediately kill the cell
Cell transformation is defined as what?
The changing of a normal cell into a cancer cell
Neoplasia is described as..?
Neoplasia is a descriptive term that denotes an abnormal tissue overgrowth that may be either localized or disseminated
What are oncogenic viruses?
Viruses that cause or give rise to tumors
What is metastasis?
The spread of cancer cells from the part of the body where it started to other parts of the body
Rb and p53 are examples of what kind of genes?
Tumor suppressor genes
What are proto-oncogenes?
Encode proteins that function in normal cellular growth and differentiation
What is the role of tumor suppressor genes?
Play a role in keeping cell division in check. Encodes proteins that regulated and inhibits uncontrolled growth
Damage to a proto-oncogene results in what?
An oncogene –> synthesis of abnormal growth factors –> abnormal cell division –> cancer
What occurs when there is a mutation in the regulatory genes of proto-oncogenes?
Excessive protein and growth factors from the proto oncogene –> out of control growth –> cancer
What is the function of Rb: Retinoblastoma protein?
It is a tumor suppressor gene that blocks E2F and keeps cell division in check. E2f facilitates cell division
What is the function of p53?
Tumor suppressor gene that prevents cells with damaged DNA from entering into cell division - will try to mediate repair. If the damaged DNA can not be repaired - it will mediate apoptosis
T/F: Oncogenic viruses generally have an RNA genome
FALSE
They generally have a DNA genome or generate a DNA provirus after infection (retrovirus)
T/F: In oncogenic DNA viruses, the oncogenes are part of the host genome
FALSE
they are part of the viral genome
T/F: When oncogenic DNA viruses infect permisive cells, they can replicate successfully, with no cancer transformation
TRUE
The virus can replicate in permissive cells – by doing so, this will kill the host cell –> no cancer
T/F: When oncogenic DNA viruses infect non permissive cells they can not replicate
TRUE
Since they can not replicate, the viral DNA will integrate into the host DNA OR in some viruses the viral DNA will remain episomal (like a plasmid) –> results in cancer
What cells must an oncogenic DNA virus infect to cause a cancerous transformation?
Non-permissive cells
This is because the virus can not replicate and kill the cell – so it can integrate into the host DNA –> cause oncogenic transformation
T/F: Oncogenic DNA viruses will cause cancerous transformation in permissive cells
FALSE
In permissive cells - the virus will replicate, causing cell lysis. This will prevent the virus from being able to integrate into the host genome in that cell
T/F: Oncogenic RNA viruses do not carry any oncogenes that cause cancer
TRUE
What are acutely transforming retroviruses?
Viruses that steal proto-oncogenes (WITHOUT the regulatory gene for the P-oncogene) from the infected host cell DNA, and then the virus converts the proto-oncogene into the cancer causing oncogene (v-onc)
How do slow/chronic transforming retroviruses cause cancer? (Oncogenic RNA viruses)
Viral RNA –> cDNA –> gets inserted into the regulatory gene of a host proto oncogene. This will stop control of the proto-oncogene –> leads to uncontrolled cell division
Where does the oncogene come from in RNA oncogenic viruses?
It comes from the host genome!
RNA oncogenic virus takes the proto oncogene from the host genome and transforms it into a cancer causing oncogene
What gene is responsible for cancer in the slow/chronic transforming retrovirus? (RNA oncovirus)
Regulatory gene of the proto-oncogene
The viral DNA is inserted into the regulatory gene of a proto-oncogene –> causes malfunction of regulation –> uncontrolled proliferation - cancer
T/F: Replication of oncogenic DNA viruses in a permissive host cell usually causes host cell transformation and cancer
FALSE
**This would be true if it said NON-permissive cell
What is a promoter gene?
DNA sequence at which DNA-dependent RNA polymerase binds to initiative transcription
What is an enhancer gene?
A transcriptional regulatory sequence located some distance from the promoter; it increases the rate of initiation of transcription
What are tumor antigens?
New antigens that appear on the surface of tumor cells that may provoke an immune response
Can the immune system identify all tumor antigens?
NO :(
What is an important tumor antigen that is expressed in association with FeLV?
FOCMA: Feline oncornavirus membrane-associated antigen
