Retroviruses Flashcards
What are the general characteristics of all retroviruses?
Enveloped, 2 complete copies of +ssRNA, encode RNA-dependent DNA polymerase, replication via a DNA intermediate
What retroviruses can immortalize and transform cells leading to lymphomas?
Human T-Cell Lymphotropic Virus - HTLV-1 & HTLV-2
How is HTLV spread?
IV drug use, sexual contact, breast milk, transfusions
What HTLV is most common in the United States? How is it spread?
HTLV-2, spread via IV drug use
What cells are targeted for infection by HTLV-1 & HTLV-2?
HTLV-1 targets CD4+ T Cells
HTLV-2 targets CD8+ T Cells
How does HTLV-1 manifest clinically?
T-cell leukemia/lymphoma - lymphadenopathy, skin lesions, bone lesions, hepatosplenomegaly, death
Tropical spastic paraparesis - spinal cord atrophy, leg weakness, gait disturbances, incontinence
How does HTLV-2 manifest clincally?
Generally asymptomatic. In rare situations, may cause tropical spastic paraparesis-like syndrom
How does HTLV-1 cause a transformation infection?
The tax protein activates cellular and viral RNA synthesis in CD4 T cells. This activates synthesis of IL-2 and its receptor, which promotes rapid T cell growth and may lead to transformation.
What regulatory proteins are ended by HTLV-1? What are their functions?
Tax gene - transcriptional activator
Rex gene - mRNA processing and export
What are the two strains of HIV? How do their origins differ?
HIV-1 derived from chimpanzees
HIV-2 derived from sooty mangabey
What are the subgroups of HIV-1?
M, N, O, P.
M responsible for AIDS epidemic
N, P emerged more recently
What strain of HIV is responsible for the majority of AIDS cases?
HIV-1
HIV-1, subgroup M is seen in the United States. What clade predominates in the country?
Clade B
HIV-2 is most prevalent in West Africa. What clades are responsible for human-human transmission?
Clades A & B
What virion gene in HIV codes for group-specific antigen proteins, such as p24?
gag
What virion gene in HIV codes for the reverse transcriptase and other enzymes?
pol
What virion gene in HIV codes for envelope glycoproteins?
env
What HIV gene regulates viral transcription?
tat
What is the function of the HIV rev gene?
Promotes export of viral RNA from the nucleus
What major core protein is used for diagnosis of HIV-1?
p24
What glycoproteins make up the HIV envelope? How are they derived?
gp41 & gp120 - translated as gp160 and cleaved by proteases to form separate proteins
What is the function of Long Terminal Repeats (LTR) in the HIV genome?
Contains promoters & sequences for the binding of transcription factors
True/False. Resting T cells are not productively infected by HIV.
True. Resting T cells contain incomplete viral cDNA or proviral DNA that is not integrated into the host chromosome. This is referred to as pre-integration latency.
Generally describe how HIV replicates in a host.
The virus binds to and enters the host cell via fusion. The genomic RNA is transcribed into cDNA using an RNA-dependent DNA polymerase. The cDNA enters the nucleus and integrates into host chromosomes. From here, viral genes are transcribed and translated and new particles are produced. New viral particles bud through the cell membrane to acquire their envelope and undergo maturation.
