HUman Retroviruses: HTLV & HIV Flashcards
Retroviruses
- Enveloped, single stranded (+) RNA viruses
- Contain reverse transcriptase enzyme, which converts viral RNA into DNA that integrates into the host chromosome
- Not transmissible through air, dust or normal conditions but requires intimate contact
- Two major representatives of retroviruses
- Oncoretroviruses (HTLV-I and HTLV-II)
- Lentiviruses (HIV-1 and HIV-2)
Retroviruses - Oncoretroviruses HTLV 1 and HTLV 2
- Both HTLVs infect CD4+ T-lymphocytes
- They do not kill cells but transform the cells to produce new virus indefinitely
- Can transduce growth promoting genes called oncogenes partly responsible for malignancies
HTLV 1 causes…
Human T-lymphotropic virus type 1 (HTLV-1) causes adult T-cell leukemia and lymphoma (ATLL) mainly in Japan, Africa and Caribbean.
HTLV 2 is ssociated with…
Human T-lymphotropic virus type II (HTLV-II) is associated with hairy cell leukemia
Retroviruses - Lentiviruses
- Slow disease causing viruses •Human immunodeficiency virus; type 1 (HIV-1) and type 2 (HIV-2), the causative agents of acquired immunodeficiency syndrome (AIDS)
- Major cause of AIDS worldwide is HIV-1
- HIV infects and kills specifically CD4+ T cells
- Also infects monocytes/macrophages, dendritic cells, Langerhans cells, microglial cells, etc.
- May persist for years in a clinical latency state in the presence of viremia
- Productive infection results in full blown disease, AIDS
Structure of Retroviruses
The 3 virus specific essential enzymes
- reverse transcriptase (RT)
- protease (PR)
- integrase (IN)
are packaged in the virus particle
Retroviral Life Cycle
HIV Life Cycle - Virus Entry
CXCR4 is expressed at high levels on [] and low levels on [], whereas CCR5 is expressed at high levels on [] and low levels on [].
CXCR4 is expressed at high levels on T-cells and low levels on macrophages, whereas CCR5 is expressed at high levels on macrophages and low levels on T-cells.
HIV-1 that interacts with CD4 and CXCR4 is called [] and CD4 and CCR5 is called [] virus.
HIV-1 that interacts with CD4 and CXCR4 is called X4 (lympho-tropic) and CD4 and CCR5 is called R5 (macrophage-tropic) virus.
[] establishes infection in both macrophages and T-cells, whereas [] only in T-cells.
R5 establishes infection in both macrophages and T-cells, whereas X4 only in T-cells.
•R5 is transmitted from person-to-person and mother-to-child
The 3 Activities of reverse transcriptase enzyme:
- Viral genome (RNA) is converted cDNA by virion associated reverse transcriptase enzyme (RNA dependent DNA polymerase)
- followed by removal of RNA (RNase H) and
- synthesis of double stranded DNA (DNA dependent DNA polymerase)
•This results in a linear dsDNA molecule, which then circularizes and forms preintegration complex.