Hiv-1

Front 1

Is HIV-1 considered a close relative of HTLV-1?

Back 1

Yes. HIV likely was transferred to humans as a result of consuming infected Bush meat from infected chimpanzees.

Front 2

What are the specific target cells of the HIV virus?

Back 2

It specifically infects CD-4 proteins that are found on the surface of T cells, macrophages and dendritic cells. In fact, the human T cell leukemia virus can infect the same cells.
The HTLV virus is thought to be a much older virus than HIV.

Front 3

What is a common conduit of infection for the HTLV virus?

Back 3

These target cells can be infected during breastfeeding.
HIV is commonly transferred during sexual activity. Any breach of the epithelial barrier and submucosa is a common pathway of infection.
This local infection can last for 10 days.

Front 4

Can HIV cargo itself within dendritic cells?

Back 4

Yes.

Front 5

Like HTLV-1, the genome of HIV is protected by a protein capsid and enclosed in a cell derived envelope. True/False

Back 5

True.

Front 6

What is the SU protein?

Back 6

Protruding from the envelope is a SU protein, which binds to the CD4 protein on the cell surface. This results in a conformational change which eventually permits binding of the HIV envelope to a co-receptor molecule. This is an important characteristic for viral entry.

Front 7

What are 2 frequently used coreceptor proteins employed for binding?

Back 7

CXCR4 and CCR5. These receptors facilitate viral-cellular fusion with the cell membrane.

Front 8

Because HTLV-1 and HIV are both retroviruses, the methods they use for replication of the single stranded RNA genomes are similar. True/False

Back 8

True. Both employ cellular RNA polymerase to transcribe the integrated proviral DNA to synthesize the mRNA and new viral genomes. several accessory proteins are encoded as well.

Front 9

What is the Vpr protein?

Back 9

This is an accessory protein. It makes it possible for ther HIV virus to integrate proviral DNA into the chromosomes of some cells, such as macrophages, which are not proliferating at the time.

Front 10

In reference to the above answer, how is HTLV different from HIV regarding cellular proliferation?

Back 10

HTLV-1 is limited to infecting proliferating cells. HTLV rarely kills the cells it infects, whereas HIV usually does.

Front 11

Though HIV can infect some resting cells, very few viral particles are produced unless HIV-1 infected cells are proliferating. True/False

Back 11

True. For new viruses to be produced, integrated proviral genes must be transcribed into RNA by the cellular RNA polymerase. When cells are in the resting phase, the proteins required for transcription are produced at low maintenance levels. The proviral genome is silent.

Front 12

For HIV, the establishment of reservoirs of latently infected cells is a critical feature for infecting hosts for life. True/False

Back 12

True. A stealth infection is established. Proviral DNA is integrated into the chromosomes of infected cells. The provirus stays there. These cells are not recognized by killer T cells . Viral information is safe from attack.

Front 13

Does HTLV-1 establish a similar reservoir of infected cells?

Back 13

Yes. This safe refuge from the immune system is compled in approximately 8 days. The adaptive immune system may require more time to establish its defensive strategy.

Front 14

What is HIV transfection?

Back 14

HIV-1 can be passed efficiently from cell to cell without leaving the protected cellular environment. Antibodies can block cell to cell transfer, but only when the virus travels openly between cells.

Front 15

Ids it true that the eventual synthesis of new viruses will expose HIV infected cells, and become targets for killing by T cells?

Back 15

True.

Front 16

Does ther HIV virus possess a defense for being discovered by T cells?

Back 16

Yes. Rapid mutation is employed. During every round of infection, the reverse transcriptase enzyme must produce a DNA copy of the RNA genome. This enzyme makes an error(mutation) each time it copies a piece of viral RNA. Technically, all viruses produced in an HIV infected cell are different from the original virus that infected the cell.

Front 17

What is the consequence for the immune system when each new virus produced is different?

Back 17

A viral protein which was originally recognized by killer T cells is no longer specific or recognized, or can no longer be presented by the MHC molecule the killer T cells were instructed to originally focus on. The original T cell clone is useless against newly infected strains. Every new cell infected will be potentially different.

Front 18

What is a pDC?

Back 18

Plasmacytoid dendritic cell. These cells have pattern recognition receptors(TLR7) which can alert the immune system if the cell is infected by a retrovirus.

Front 19

How does the TLR7 respond upon infection?

Back 19

The TLR7 sends a signal to the nucleus of the pDC and the genes for interferone alpha and beta are activated, and interferon is produced.

Front 20

What happens when interferon binds to receptors?

Back 20

When the alpha and beta forms bind to receptors on cell surfaces, it induces the expression of interferon stimulated genes(ISGs). These genes have antiviral functions.

Front 21

What is APOBEC3G?

Back 21

This is a gene that encodes a protein which is antiretroviral in nature. This protein acts as a powerful mutagen. It introduces many mutations into the HIV-1 proviral genome during the process of reverse transcription. Remember, that the HIV-1 polymerase is already quite error prone. The function of the APOBEC3G is to render the resultant mutant viruses non functional.

Front 22

Can the HIV-1 virus defend itself against the APOBEC3G gene?

Back 22

Yes. The HIV-1 genome encodes an accessory protein, termed Vif, which targets the APOBEC3G protein for degradation in infected cells. The result is neutralization of the host defense.

Front 23

Can the HIV virus turn host defenses against itself.

Back 23

Yes. Non infectious viral particles outnumber infectious ones about 1,000 to 1, and most HIV infections are started when a single virus can penetrate the mucosal barrier. Though few resting cells can be infected, they actually produce few new viruses. When HIV-1 targets helper T cells that are in the process of dividing, these cells can easily be turned into virus factories. The HIV-1 virus wants to intentionally alert the immune system to its presence, so in fact, its target cells become activated.

Front 24

Regarding the above explanation, how does the HIV-1 virus alert the immune system?

Back 24

This is done by infecting the plasmacytoid dendritic cells. The interferon they produce not only alerts cells of a viral infection, it also activates helper T cells and other immune system defenders. Many immune cells are now activated, and are primary targets for infection.

Front 25

Are there many immune cells found in the submucosa?

Back 25

No. most of HIV-1 target cells are found in lymph nodes and similar secondary lymphoid organs.

Front 26

Is there another type of dendritic cell found in the submucosa?

Back 26

Yes. It is the conventional dendritic cell(cDC).

Front 27

What is the function of the cDC?

Back 27

Its function is to travel to a nearby lymph node to warn the immune system cells which reside there, that there has been a viral attack.
However, HIV-1 virus particles can infect cDCs at the site of the initial infection, and can also bind to the surface of these cells.

Front 28

When cDCs go to a lymph node to warn of a viral attack, can HIV virus particles stay latent in these cells?

Back 28

Yes. In lymph nodes there are lots of CD4 cells. cDCs function to activate these cells, many will soon be proliferating. They will be perfect targets for HIV-1 viral infection.

Front 29

The HIV-1 virus can destroy about 80% of the helper t cells in the lymph nodes which drain the intestine during the first 3 weeks of an HIV-1 infection. True/false

Back 29

True.

Front 30

When HTLV-1 infected cells with integrated proviruses are activated, the usual outcome is a continued stealth posture. True/False

Back 30

True. The proviral genome is quietly passed down to the daughter cells, and little or no virus is produced.
When cells latently infected with HIV-1 proliferate, it is more usual that viral RNA transcription is stimulated, and within 12 hours, new virus particles begin to bud from the infected cell.

Front 31

In relation to HTLV-1 in which bodily fluids contain large numbers of infected cells , but little infectious virus, how does HIV-1 differ?

Back 31

The bodily fluids of an individual infected with HIV-1 contain both infected cells and infectious virus.

Front 32

Children infected with HIV-1 at birth almost never survive long enough to spread the virus by sexual contact, or by breastfeeding. True/False

Back 32

True. Mother to child transmission of HIV-1 is a a type of dead end transmission for the virus.
each day, over a billion new viruses are born, and many new CD4 T cells are produced, only to be infected by new viruses. True

Front 33

Each day, over a billion new viruses are born, and many new CD4 T cells are produced, only to be infected by new viruses. True/False

Back 33

True.