HIV-1 Flashcards
What is AIDs in relation to HIV?
HIV is a viral infection which, if left untreated, can lead to AIDS, which is the immunodeficient phase of the disease.
Which type of T lymphocyte is severely destroyed in HIV, and why?
CD4 T helper cells.
This is because HIV binds to the CD4 molecule of these T helper cells to replicate, eventually leading to a decline in the balance of T lymphocytes amounts.
What reactions occur during HIV?
- T cell suppression
2. Intense immune activation
Where are T cells mostly concentrated within the body, which is also where HIV reservoirs form?
Lymph tissues and the GIT.
What are the events stem from HIV?
- A fall in circulating CD4 T helper cells
- Vulnerability to opportunistic infections
- Infecting other CD expressing cells
When can a productive infection of CD4 T helper cells be detected?
Within 2 days of viral challenge.
How do other cells, other than CD4 T helper cells, get infected by HIV?
Cells travelling to the lymph nodes also become infected (since HIV first infects CD4 T helper cells in the lymph nodes), so this leads to a major loss of antigen dependent responses.
How does CD4 T helper cell levels decline overtime in HIV?
During the 1st HIV infection, there is a reduction in peripheral CD4 T helper cells (which can be detected), but these levels can fluctuate after the primary infection is resolved.
CD4 T helper cells hence decline over many years.
What occurs during the latent (asymptomatic) phase of HIV?
Specific homeostasis mechanisms control the imbalance between T helper cells and other lymphocytes.
- Think of it like a pie; this is the T lymphocyte compartment, where the homeostasis of T cells must be maintained.
What makes up most of the T cell compartment of homeostasis?
- CD4 T helper cells
2. CD8 cytotoxic T cell
What happens if T cells are lost?
New or naive T cells can differentiate from bone marrow pre-cursors, or from existing pools of memory T cells.
How is T cell homeostasis preserved in HIV?
Loss of CD4 T helper cell is balanced with an increase of CD8 cytotoxic T cells.
This is shortly lived until AIDs occurs.
Eventually sources of T cells become exhausted trying to balance this, so T lymphocyte levels eventually fall.
What are some examples of other HIV targets?
Chemokine receptors, found in other WBCs to enter the host cell.
Monocytes, macrophages, and dendritic cells can also be infected.
Different variants use different receptors to infect more T helper cells.
What parts of the body can act as reservoirs for replication of HIV?
- Liver
- Spleen
- Bone marrow
- Lymph nodes
- GI
What can CD4 T helper depletion in the gut lead to?
Increased permeability of the intestinal lining, which can translocate bacteria leading to more immune activation.
Why can HIV never be eradicated from the body?
Because memory cells are long-lived & don’t die, so when infected with HIV it can never go away.
How is HIV reactivated in the body after a latent period?
When the infected cells reappear from their reservoirs.
What is the normal process of CD4 T helper cell activation?
Antigens stimulate naive CD4 T helper cells which proliferate into effector T cells to destroy the pathogen.
As the pathogen becomes weaker, T cells can either undergo apoptosis, or remain dormant until the same antigen appears.
What can occur when HIV affects naive T cells?
HIV can integrate into the DNA of the host cell, and lock itself into memory cells.
If the same antigen appears, then HIV becomes reactivated again.
What are the 3 possible outcomes if memory T cells become latently infected?
- They can reactivate & die
- They can release HIV
- They can transmit HIV to another host cell
Why are CD8 cytotoxic T cells unusually vigorous in HIV?
Because it needs to help with the imbalance of CD4 T helper cells.
How long after initial exposure of HIV to reservoirs form in the body?
Within 5 days.
How can HIV block symptoms of the immune system?
HIV integrates its genes into chromosomes which usually modulate the killing of the host cell.
In this way, the immune system response is blocked.
How do self-cells in the body become ‘invisible’ in the presence of HIV?
HIV decreases the expression of MHC I (which is a self-recognising protein), so self-cells become invisible.
What can constant HIV mutations lead to?
- Emergence of new HIV variants in the already infected person
- Resist drug therapy
- Resisting immune attack
Why are the lymph nodes considered a ‘sanctuary’ for harbouring HIV?
Because limited anti-viral drug can penetrate into the lymph nodes, and there is also limited host clearance mechanisms there.
What occurs in a very high HIV load, high HIV load, and low HIV load?
Very high: CD4 T helper/CD8 cytotoxic T cells are exhausted and decreased
High: Low CD4 T helper cells
Low: Stable amounts of CD4 T helper cells and CD8 cytotoxic T cells.
What patient factor can be shown when monitoring the viral load of HIV in an individual?
Viral load can show the patients adherence to the drug
How does antiretroviral therapy (ART) help in suppressing HIV replication?
ART prevents new cells from becoming infected, but do not eliminate the infection once it has already integrated into the host cell.
What is the aim of HAART intensification in HIV?
To achieve a complete suppression of residual virus (completely removing the reservoirs).
It is also known as a ‘cocktail’ of drugs
How do immunosuppressants aid in eradicating HIV?
They decrease the activation of CD4 T helper cells, and reduce their susceptibility to viral infection + replication.
How can the reactivation of latent reservoirs aid in the eradication of HIV?
Viral load stops ‘hiding’, which can then be killed in combination with HAART + other drugs.
Why is HIV still an issue in poorer countries?
Because tests are expensive, slow and hard to access.
Why are HIV patients asymptomatic to tuberculosis?
Because tuberculosis infects WBC’s, and since HIV patients have a low WBC count, they wont experience the symptoms of TB.
