HIV: Retro Virus

1. HIV is a retrovirus (a virus that uses reverse transcriptase).

a. What is reverse transcriptase? It’s an enzyme that catalyzes the formation of DNA from RNA

b. How is a retrovirus different from other viruses? Retroviruses are a group of viruses, so retroviruses carry special characteristics, which are not seen in viruses. Virus contains genetic material as DNA or RNA but retrovirus contains only RNA. If the virus has DNA, it inserts DNA into the host cell, and it is integrated directly into the host genome at the lytic phase, whereas retrovirus has RNA as its genetic material and needs to convert RNA to DNA before insert it into the host genome. Viruses have transcription process, whereas retroviruses have reverse transcription process.

c. How does a retrovirus infect a cell and reproduce itself? The retrovirus comes in contact with a host cell. It attaches itself to the receptors on the surface of the host cell’s membrane. The retrovirus’s glycoproteins and the host cells receptors bind together. The outer envelope of the retrovirus fuses with the host cell membrane. This enables the viral capsid to enter the host cell.

Once the retrovirus is inside, the capsid opens and releases RNA and reverse transcriptase. Reverse transcriptase builds up a double stranded DNA molecule that has the exact information stored in the viral RNA. The viral DNA, known as a provirus, acts like the host cell’s own genes. Although, it contains instructions to replicate the virus. These new viruses make their way to the exterior of the cell. Then the process starts all over again in new host cells.

2. Review of the immune system.

a. What is a T cell? A lymphocyte that is produced or processed by the thymus gland and actively participating in the immune response.

b. What varieties of T cell exist? How are they functionally different? Cytotoxic T cell- they attack foreign cells of body cells infected by viruses. They’re involved with cell-mediated immunity Helper T cell-stimulate the activation and function of both t cells and b cells. Suppressor t cell- they inhibit the activation and function of both t cells and b cells. The interplay between suppressor and helper helps establish and control the sensitivity of the immune response.

c. What are their roles in the human body? Read above.

d. How is each T cell variety differentiated from the others (molecularly)? Class 1 MHC-CD8, cytotoxic, memory, suppressor Class 2 MHC- CD4, helper

3. Immune System and HIV

a. Which types of immune cells is/are targeted by HIV? The helper T cells are affected.

b. Why are other cells not targeted by the virus? The other cells aren’t targeted because the helper T cell won’t activate the B cell which doesn’t create antibodies to destroy the virus.

c. How should cytotoxic T cells respond to the initial phase of HIV infection (when some T helper cells are still functioning?) Explain your answer. They recognize cells that have already been infected with a virus or bacteria. Their job is to kill the infected cells before the infection spreads.

d. As time progresses, why do the cytotoxic T cells stop responding to the HIV infection? Propose an explanation. They stop responding to the infection because less TC cells are being produced and more TH cells are being infected.

e. What happens to the immune system after HIV? Why? Can this account for symptoms of AIDS? The immune systems decreases because of the increased amount of TH cells being infected and not activating the B cells.

f. How does HIV evade the immune system? The virus enters the body and finds a host cell (TH cell). The virus binds to the cell and they merge together. The virus then starts to replicate it’s RNA for the cell to reproduce more viruses. The cell releases these replicates and they go and infect more TH cells.

4. Where and how might new viral infections be stopped? What could be different about the people who seem protected against HIV that caused viral replication to stop?

Part 3 1. Design of the experiment:

a. Why were HIV and T helper cells mixed in the presence and absence of cytotoxic T cells? To see how much affect the TC cells would have on HIV.

2. For control individuals:

a. If you mix HIV and TH cells in a test tube, what would you expect to happen? I would expect HIV to infect the TH cells in the test tube because that is the cells the virus infects.

b. If you mix HIV, TH cells, and TC in a test tube, describe what you would expect to happen and why it occurs that way. I would expect the virus to infect the TH cells and then the TC cells would try to destroy the infected cells. TC cells kill infected cells of the body.

3. For protected individuals:

a. Assuming that the “Super TC cells” hypothesis is correct, then when you perform the experiment using TH cells and TC cells from protected individuals.

  1. If you mix HIV and TH cells in a test tube, what would you expect would happen? I would expect the virus to infect the helper cells.
  2. If you mix HIV, TH cells, and TC cells in a test tube, describe what you would expect to happen and explain your reasoning. I would expect the virus to infect the helper cells, but the cytotoxic cells would destroy the cell before the virus could infect the other helper cells.

b. Assuming that the “Super TH Cells” hypothesis is correct, the when you perform the experiment using the TH cells and the TH from protected individuals.

  1. If you mix HIV and TH cells in a test tube, what would you expect would happen? I would expect the virus not to infect the helper cell.
  2. If you mix HIV, TH cells, and TC cells in a test tube, describe what you would expect to happen. I would expect the same results as the first experiment. Without the virus infecting the helper cell, the cytotoxic cells wouldn’t have a cell to destroy.

4. How is this experiment able to differentiate whether the mechanism of protection against HIV is through “Super TH Cells” or “Super TC Cells” The experiment would be able to tell you if the helper cells are being infected by the virus or not.

CD4 is mutated in a helper cell so the virus can’t infect it.