Retrovirus-AuCoin Flashcards
What kind of virus is HTLV (human T-lymphotropic virus)?
an oncovirus and a retroviridae
How do you get spread of HTLV?
via spread by infected lymphocytes (CD4+ T cells)
Where is the HTLV virus present in the fluids?
semen, blood and breast milk
How long is the incubation period for adult T-cell leukemia (ATL)?
20-50 years
What is the clinical presentation of HTLV and ATL?
increased skin lesions, leukemia cells, hepatosplenomegaly and hypercalcemia (increased PTHRP)
How do you diagnose HTVL?
ELISA for antibody (serology)
Is there a vaccine or specific therapy for HTLV?
No vaccine or specific therapy
How does HIV work?
gp120 on HIV binds CD4 receptor on T cells, monocytes, and dendritic cells.
How is HIV transmitted?
by sexual contact, blood, IV drug use and vertically
What are common in HIV?
opportunistsic microbial infections
What is the acute phase of HIV?
“flu-like symptoms” followed by clinical latency period of weight loss, night sweats, fatigue, and lymphadenopathy
How long does it take for HIV to progress to AID?
10 years
What is the definition of AIDS?
CD4+ T cell count of 200 cells/ul (normal 800-1200 cells/ ul)
How do you diagnose HIV?
serology and RT PCR to quantitate viral load
What is the therapy for HIV/AIDS?
HAART (high active anti-retroviral therapy)
Is there a vaccine for HIV/AIDS?
no vaccine
What is the structure of retroviruses?
enveloped, (+) strand RNA viruses
What do retroviruses encode?
an RNA-dependent DNA polymerase (reverse transcriptase [RT]
How does the retrovirus replicate?
- Retroviruses encode an RNA-dependent DNA polymerase
- Replicates through a DNA intermediate
- DNA copy of the viral genome is then integrated into the host chromosome to become a cellular gene- provirus
What was the first retrovirus to be isolated it produced solid tumors in chickens?
Rous sarcoma virus
Other cancer causing retroviruses are classified as (blank) or (blank)
RNA tumor viruses or oncornaviruses
How do RNA tumor viruses or oncornaviruses work?
these viruses alter cellular growth by expressing analogues of cellular growth controlling genes (oncogenes) (v-src)
What was the first retrovirus found to be associated with human disease? Where did they get it from?
HTLV-1
T-cell leukemia
How are retroviruses classified?
by disease they cause
by tissue tropism and host range
by virion morphology
by genetic complexity
The (blank) include only the retroviruses that can immortalize or transform target tissue
oncoviruses (HTLV)
The (blank) are associated with neurologic and immunosuppresive diseases.
lentiviruses (HIV)
What are the three subfamilies of retroviruses?
oncovirinae (HTLV1,2,5)
Lentivirinae (HTLV 1, 2)
Spumavirinae
What is the first isolated human retrovirus, however not associated with a disease?
spumavirinae
What is the struture of retroviruses?
spherical, enveloped, RNA viruses of 80-120nm
Envelope contains viral glycoproteins and is acquired by the plasma membrane
The envelope surrounds a capsid that contains two identical copies of the (+) strand RNA genome
How big is the RNA genome?
9 kilobases
The virion also contains what enzymes?
10-50 copies of the reverse transcriptase and integrase enzymes and two cellular transfer RNA (tRNAs)
The tRNAs found inside a virion are base-paired to each copy of the genome to be used as a (blank) for the reverse transcriptase.
primer
All retroviruses include three major genes that encode polyproteins. What are they?
Gag-> group specific antigen
Pol-> polymerase (reverse transcriptase, protease, integrase)
Env-> envelope (glycoproteins- gp120 and gp41 for HIV)
What are found at each end of the retrovirus genome?
long terminal repeat sequences (LTR) that contain promoters and enhancers to bind cellular transcription factors.
Complex retroviruses, HTLV and HIV encode several (blank) that require more complex transcriptional processing (splicing).
virulence-enhancing proteins
The viral glycoproteins are produced by (blank) of the polyprotein encoded by env gene
proteolytic cleavage
Gp160 of HIV is cleaved into (blank) and (blank)
gp41 and gp120
What do gp41 and gp120 form?
the trimer spikes (lollipop) that are visible on the virion surface
What does gp120 bind to? What does this do?
cell surface receptors
determines the tissue tropism of the virus, it is recognized by neutralizing antibodies
gp120 is extensively (blank) and its antigenicity and receptors speficity can (blank) during the course of a chronic HIV infection. These factors impede immune clearance of the virus
glycosylated
drift
(bank) promotes cell fusion
gp41
How does HIV replicate?
replication begins with gp120 (trimer) binding to the T cell CD4 receptor and a second G protein coupled chemokine receptor (co-receptor) called CCR5 (expresse on macrophages, and other T cells)
During chronic HIV infection, what happens to the env gene?
it mutates and gp120 can bind to CXCR4 (chemokine receptor which is expressed primarily on T cells)
What happens when HIV binds the co-receptor CCR5?
brings the viral envelope and the cell plasma membrane close and allows the gp41 to promote membrane fusion
In HIV replication what does the (+) sense genome do?
it is released into the cytoplasm and RT (using the tRNA as a primer) synthesizes a complementary (-) strand DNA (cDNA)
In HIV replication, what else does RT act as?
as a ribonuclease H and degrades the (+) RNA of the hybrid and then synthesizes the (+) strand of DNA to form the cDNA
RT is very (blank) prone. What is the mutation rate? WHat does this allow for?
error
1 error per 2000 bases
the evolution of new strains which may alter pathogenicity and promote immune evasion/selection
What happens to the viral cDNA created by HIV?
it is delivered to the nucleus and is integrated into host chromosome by the integrase enzyme
What do you called viral integrate DNA?
provirus
How do you get viral genome to integrate into the the host DNA?
with long terminal repeats (LTR)