Effect of viruses on host cells Flashcards
3 types of effects on host cells
cytocidal: cell death - lysis and apoptosis
non cytocidal: persistent infection
cell transformation: tumor cells
cytopathic effect or cytogenic effect
refers to damage or morphological changes to host cells during virus invasion
cell fusion (syncytium or polykaryon formation)
involves fusion of plasma membranes of four or more cells to produce an enlarged cell with 4 or more nuclei, prone to premature cell death
-results from fusion of an infected cell with neighboring infected or uninfected cells
inclusion bodies in host cell during viral infection definition
-what can they be?
abnormal structure in a cell nucleus or cytoplasm or both, such as aggregates of proteins, having characteristic staining properties and associated with certain viral infections – helps to ID viruses
-accumulation of viral components, result from degenerative changes in cell, crystalline aggregates of virions
inclusion bodies can be (5 things):
-intracytoplasmic or intranuclear, or both
-single or multiple
-large or small
-round or irregular in shape
-eosinophilic/acidophilic or basophilic
acidophilic staining
basophilic staining
acidophilic: affinity for acid dyes, such as eosin, appears PINK
basophilic: affinity for basic dyes, such as hematoxylin, appears BLUE
5 general mechanisms of virus induced cell injury and death
- inhibition of host cell nucleic acid synthesis
- inhibition of host cell RNA translation
- inhibition of host cell protein synthesis - some viruses make lysosomes release their hydrolytic enzymes, which destroy the host cell
- interference with cellular membrane function
- apoptosis
apoptosis
programmed cell death, activated by the host that is a last resort to eliminate viral factories before progeny virus production is complete
apoptotic pathways general idea
activation of host cell caspase enzymes mediate death of the cell. once activated, caspases are responsible for degradation of the cells own DNA and proteins
apoptotic pathways (2)
- intrinsic (mitochondrial) pathway: activated as a result of increased permeability of mitochondrial membranes subsequent to cell injury, such as that associated with a viral infection
- extrinsic (death receptor): extrinsic pathway is activated by engagement of specific cell membrane receptors, which are members of the TNF receptor family. binding of the cytokine TNF to its cellular receptor can trigger apoptosis
what cell is used in apoptosis
cytotoxic T lymphocytes and natural killer cells can also initiate apoptosis of virus infected target cell, utilizing performed mediators such as perforin and granzyme that activate caspases in the target cell
perforin and granzyme
perforin: makes pore in infected cell
granzyme: goes through pore to cause death of cell
AB dependent cell mediated cytotoxicity results from ??
surface membrane fusion of enveloped viruses
-viral glycoproteins are retained on the cell surface, and since these are antigenic, the cell can become a target of the immune system of the host
ADCC (4 steps)
- AB binds AG on surface of target cell
- Fc receptors on NK cell recognize bound AB
- cross linking of Fc receptors signals the NK cell to kill the target cell
- target cell dies by apoptosis
cell transformation
changing of normal cell to a cancer cell
neoplasia
descriptive term that denotes an abnormal tissue overgrowth that may be localized or disseminated. it is the process that leads to the formation of neoplasms
oncology
study of neoplasia and neoplasms
benign neoplasm
growth produced by abnormal cell proliferation that remains localized and does not invade adjacent tissue
malignant neoplasm
locally invasive and may also be spread to other parts of the body (metastasis)
oncogenic virus:
viruses that give rise to tumors
metastasis
spread of cancer cells from the part of the body where it started to other parts of the body
proto-oncogenes
encode proteins that function in normal cellular growth and division
tumor suppressor genes
-def and 2 important genes
role in keeping cell division in check, encodes proteins that regulate and inhibit uncontrolled growth
2: Rb and p53
oncogenes
mutated forms of proto-oncogenes or aberrantly expressed proto-oncogenes
Rb: retinoblastoma protein
one important tumor suppressor gene/protein that blocks E2F and keeps cell division in check, E2F facilitates cell division
p53 protein
tumor suppressor gene that prevents cells with damaged DNA from entering into cell division, tries to mediate repairing of the damaged host cell DNA. if the damaged DNA cannot be repaired, p53 mediates apoptosis of the cell with damaged DNA
tumor viruses/oncogenic virus
virus that causes cancer, usually have DNA genome or generate a DNA provirus after infection
-have viral oncogenes (genes that cause cancer) in the viral DNA, these oncogenes cause cancer in host cells and may help in virus replication process
oncogenic virus in permissive vs non permissive cell
permissive: oncogenic virus can replicate, so NO CANCER
non permissive: oncogenic virus cannot replicate so the viral DNA gets integrated into host DNA and results in CANCER
productive infection in permissive cell
virus completes replication cycle, entry and producing viral components, replication and assembly, lysis = release of virus particles = NO CANCER
transformation in non permissive cell
abortive infection - virus enters, integration of viral DNA into host genome, transformation of cells changing shape and growing = CANCER
