Effects Of Viruses On Host Cells

Question 1

Describe the summary of effects of viruses on host cells.

Answer 1

Question 2

Describe the visual effects of virus induced cell damage.

Answer 2

1. cytopathic effect or cytopathogenic effect (CPE)
   >damage or morphological changes to host cell during virus invasion
2. Cell fusion (syncytium or polykaryon formation)
   >fusion of PM of 4+ cells to make an enlarged cell w 4+ nuclei (prone to premature cell death)
   >results from fusion of infected cell w neighboring infected or uninfected cells
3. Inclusion bodies in host cell during viral infection
   >abnormal structure in cell nucleus or cytoplasm (or both) like aggregates of proteins w staining properties & associated w viral inf
   >help ID certain viral inf

Question 3

Describe examples & properties of inclusion bodies.

Answer 3

EX:
1. Accumulation of viral components
2. Result from degen change in cell
3. Crystalline aggregate of virions
PROPERTIES:
1. Intracytoplasmic or intranuclear (both)
2. Single or multi
3. Lg or sm
4. Round or irregular in shape
5. Eosinophilic/acidophilic or basophilic

Question 4

Describe acidophilic staining VS basophilic staining.

Answer 4

1. Acidophilic
   -recog/affinity for acid dyes like eosin
   -pink
2. Basophilic
   -recog/affinity for basic dyes like hematoxylin
   -purple/blue

Question 5

Describe the general mechanisms of virus induced cell injury & death.

Answer 5

1. Inhibition of host cell nucleic acid synthesis
2. Inhibition of host cell RNA transcription (mRNA production & processing)
3. Inhibition of host cell protein synthesis
4. Some viruses cause lysosomes to release their hydrolytic enzymes which then destroy the host cell
5. Interference w cell membrane function
6. Apoptosis

Question 6

Describe apoptosis.

Answer 6

-programmed cell death
-cell death that the host activates as a last resort to elim viral factors before progeny virus prod complete
-diff from lysis where viral replication is complete, host cell destroyed & new virions released

Question 7

Describe apoptotic pathways.

Answer 7

-activation of host cell caspase enzymes mediate death of cell -> caspases degrade cell DNA & proteins
-cytotoxic T lymphocytes & NK cells can initiate apoptosis of virus infected target cell using mediators like perforin & granzyme that activate caspase directly in target cell

Question 8

Describe the two different types of apoptotic pathways.

Answer 8

1. Intrinsic (mitochondrial) pathway
   -activated as result of inc permeability of mitochondrial membranes due to cell injury like a viral inf
2. Extrinsic (death receptor) pathway
   -activated by engagement of specific cell membrane receptors (members of TNF receptor fam like FAS)
   -binding of cytokine TNF to cell receptor triggers apoptosis

Question 9

Describe antibody mediated cytotoxicity.

Answer 9

-results from surface membrane fusion of enveloped viruses
-viral glycoprotein retained on cell surface (antigenic) -> cell becomes target of IS of host

Question 10

Describe the terms for virus induced cell transformation.

Answer 10

1. Cell transformation
   -changing from normal to cancer cell
2. Neoplasia
   -descriptive term to denote an abnormal tissue overgrowth that may be localized or disseminated
   -process leads to formation of neoplasm (carcinogenesis)
3. Oncology
   -study of neoplasia & neoplasms
4. Benign neoplasm
   -growth made by abnormal cell prolif that remains localized & doesnt invade adj tissue
5. Malignant neoplasm (cancer)
   -locally invasive & spread to other parts of the body (metastasis)
6. Oncogenic virus
   -virus that cause/give rise to tumors
7. Metastasis
   -spread of cancer cells from part of body where it starts to other parts of the body
8. Oncogenes
   -mutated forms of proto-oncogenes or aberrantly expressed proto-oncogenes

Question 11

Describe regulating the cell cycle.

Answer 11

1. Rb: retinoblastoma protein
   -imp tumor suppressor gene/protein that blocks E2F & keeps cell division in check
   -E2F facilitates cell division
2. P53 protein
   -imp tumor suppressor gene/protein that prevents cell w damaged DNA from entering cell division
   -mediate repairs of damaged host cell DNA
   >if it cannot be repaired -> apoptosis

Question 12

Describe tumor viruses/oncogenic viruses.

Answer 12

-virus that cause cancer
-oncogenic virus have DNA genome or gen DNA provirus after infection (retrovirus)

Question 13

Describe oncogenic DNA viruses.

Answer 13

-have viral oncogenes (genes that cause cancer) in viral DNA
-oncogenes cause cancer in host cell & help in virus replication process
OUTCOMES
1. when oncogenic DNA virus infect permissive cells -> replicate successfully = no cancer
2. when oncogenic DNA virus infect non permissive cells -> cant replicate -> viral DNA integrate into host DNA or in some virus the viral DNA remain in episomal (plasmid like) = cancer

Question 14

Describe the 2 ways DNA tumor viruses interact with cells.

Answer 14

1. Productive infection in permissive cell
   -virus completes its replication -> cell lysis or no cancer
2. Non productive infection in non permissive cell
   -virus transforms the cell w/o completing its replication cycle -> cancer
   -viral genome or a truncated version of its integrated into cell DNA
   -complete genome persists as autonomously replicating plasmid (episome)

Question 15

Describe oncogenic RNA viruses - acutely transforming retrovirus.

Answer 15

-virus that steals proto oncogene from the infected host cell DNA -> virus converts the proto oncogene into oncogene (v-onc, cancer causing gene)

Question 16

Describe oncogenic RNA viruses - slow/chronic transforming retrovirus.

Answer 16

-virus genome gets inserted into regulatory (enhancer region) gene of host cell DNA -> regulatory gene cant function properly -> no control on proto oncogene of host DNA -> excessive cell division / cancer

Question 17

Describe tumor antigens.

Answer 17

-new antigens appear on surface of tumor cells that may provoke an IR