Topic 36 - HIV/Retrovirus

What is unique about retroviral genomes?

Diploid (2 RNA copies), RNA made by host RNA polymerase II, uses tRNA as primer, (+) RNA does NOT act as mRNA immediately.

Why is retroviral RNA NOT used as mRNA?

Must first be converted to DNA.

What is the genome type of HIV?

(+) ssRNA, diploid.

What is the structure of the HIV virion?

Enveloped, cone-shaped capsid.

What enzymes are packaged in the HIV virion?

Reverse transcriptase, integrase, protease.

Why is the HIV envelope hard to target?

Heavily glycosylated → hides from antibodies.

What is a provirus?

Integrated viral DNA.

Is integration of viral DNA into the host genome required?

YES (essential step).

What does reverse transcriptase do?

Converts RNA to DNA.

What does integrase do?

Inserts DNA into the host genome.

What does protease do?

Cuts polyproteins.

What primes reverse transcription?

tRNA.

What primes the (+) DNA strand during reverse transcription?

Poly-purine tract (PPT).

What is the main HIV receptor?

CD4.

What co-receptors does HIV use?

CCR5, CXCR4.

Which co-receptor is used early in HIV infection?

CCR5.

Which co-receptor is associated with progression to AIDS?

CXCR4.

Which cells express CD4?

Helper T cells, macrophages, dendritic cells.

Why can't HIV be eliminated?

Integration into host genome, high mutation rate, infects CD4+ T cells, glycosylated envelope, immune evasion genes, latent/persistent reservoirs.

Why are drugs ineffective long-term against HIV?

Virus mutates rapidly.

What cells does HIV destroy?

CD4+ T cells.

What defines AIDS?

CD4+ count < 200 cells.

Why do patients die from AIDS?

Opportunistic infections.

How is HIV transmitted?

Sexual contact, blood (needles, transfusion), mother to child, breastfeeding.

What increases the risk of HIV transmission?

Other STDs.

How can HIV be prevented?

Safe sex, avoid needle sharing, screening blood, treat pregnant mothers.

What is PrEP?

Preventive antiviral treatment.

Is there a cure for HIV?

NO.

What is HAART?

Combination drug therapy.

Why use combination therapy for HIV treatment?

Prevents resistance.

Why is HIV hard to vaccinate against?

High mutation rate, many strains (quasispecies), glycosylated envelope, poor understanding of immunity.

What type of infection does HIV cause?

Chronic persistent infection.

Where does HIV persist?

Memory T cells.

What makes retroviruses unique?

RNA → DNA → integration.

What enzyme is most important in retroviruses?

Reverse transcriptase.

What primes DNA synthesis in retroviruses?

tRNA.

What is the biggest reason HIV persists?

Integration into genome.

What cells are destroyed by HIV?

CD4+ T cells.