virus pathogenesis Flashcards
what are the mechanisms of cellular injury?
- altered shape
- detachment from the substrate
- lysis
- membrane fusion
- membrane permeability
- apoptosis
explain how HIV is a pathogen
HIV causes cell fusion. infection of CD4 cells with some isolates of HIV cause cell-cell fusion and production of syncitia. this process is promoted by the glycoprotein envelope of the virus
how does epstein-barr virus affect cells?
infects B cells and leads to immortalisation and proliferation
what type of virus is HIV?
lentivirus, group VI.
explain HIV pathogenesis
HIV infects CD4 T-lymphocytes. most retroviruses dont kill the host cell, the genome persists for a long time as a cellular gene. antigenic variation of HIV prevents recognition by the immune system
how is AIDS defined?
the presence of HIV infection, plus either: a CD4 count of less than 200 cells/ml blood. or development of opportunistic infection that occurs when immune system compromised
how does subacute sclerosing panencephalitis occur?
infection with measles -> systemic infection. instead of virus being cleared, replication persists at a low level, disease caused by immune system attempting to remove virus from brain
how does dengue cause disease?
primary degue yields antibodies, but there are four serotypes, and antibodies against one does not offer cross-protection. antibodies also enhance the infection of peripheral blood mononuclear cells. dengue shock syndrome occurs due to immune mediated damage of virus infected cells. cell damage causes capillary permeability to increase
what is transformation?
a change in the morphological, biochemical, or growth parameters of a cell. these cells have an altered phenotype
what is meant by loss of anchorage dependence?
normal adherent cells such as fibroblasts or epithelial cells require a surface to adhere to
why is colony formation in semi-solid media indicative of transformation?
most normal cells will not grow in media that is partially solid due to presence of agarose
what is true about the genome replication of all transforming viruses?
they all have a DNA step in their lifecycle
what is oncogenesis?
a multistep phenomenon in which normal cells are transformed into cancer cells
which viruses cause cancers?
- EBV
- Hep B
- Hep C
- HPV
- human T-lymphotrophic virus 1
- Kaposi’s sarcoma virus
- Merkel cell polyomavirus
what are oncogenes? what are proto-oncogenes?
oncogenes are mutated forms of proto-oncogenes- cellular genes whose normal function is to promote normal growth and division of cells
what are tumour suppressor genes?
genes which normally inhibit the cell cycle
what are the categories of oncogenes?
- extracellular growth factors
- receptor tyrosine kinases
- membrane associated nonreceptor tyrosine kinases
- GPCRs
- membrane associated G proteins
- serine/threonine kinases
- nuclear DNA binding/transcription factors
what is the difference between transducing, cis-activating and trans-activating transforming viruses?
transducing viruses have the greatest efficiency and speed of tumour formation, these encode a viral copy of the oncogene, and activated c-onc.
cis-activating viruses activate c-onc but dont encode their own copy. trans-activating viruses activate cellular genes by trans-activating virus proteins, least efficiency and speed of tumour formation
how do v-oncs and c-oncs differ?
v-oncs usually contain minor alterations to structure and function of produced oncoprotein
how can viruses result in tumour formation via an unadulterated oncogene?
they can cause abnormal expression of this oncogene, and disrupt the cell cycle
why is the T-antigen from SV40 important for genome control?
interacts with p53 and prb tumour suppressor genes, they do this by binding to p53 and allowing DNA replication
give some examples of DNA transforming viruses
adenovirus, human papillomavirus, herpesviruses
what is shutoff?
the dramatic cessation of most host cell macromolecular synthesis
which phage toxins can cause disease in humans?
stx1 and stx2 toxin genes in lyosgenic prophages found in E.coli
give 2 examples of EGF oncogenes
c-sis: encodes platelet derived growth factor B chain
Int-2: encodes fibroblast related growth factor
give 2 examples of RTK oncogenes
c-fms: encodes colony stimulating factor 1 receptor
c-kit: encodes mast cell growth factor receptor
what are the different types of retroviruses that are capable of transforming cells?
- transducing (actively transpforming)
- cis-activating (chronic transforming)
- trans-activating
