Micro Final - HIV
What happens when HIV enters a host cell
1. "Toe" of gp120 binds to CD4 on activated helper T-cell --> Causes shape change 2. "Heel" of gp120 then also binds to CCR5 or CXR4 "cytokine receptor" on activated helper T-cell 3. Gp41 on HIV drills down into the membrane of the host cell, fusing the viral membrane w/ the host cell's membrane
What leads to HIV latent infection?
1. A naïve helper T-cell is presented w/ an Ag' via a DC or macrophage & becomes activated 2. The now activated helper T-cell may become infected w/ HIV virus while it's making clones of itself 3. Some of the clones these activated helper T-cells (infected w/ HIV) produce are effector helper T-cells, while some are memory helper T-cells 4. Memory helper T-cells w/ HIV virus inside are considered a latent infection Memory cells are "resting cells" & don't have much activity going on inside them This makes it so HIV cannot take advantage of the host memory cell's machinery, so it doesn't really replicated
Describe the general replication cycle of HIV
1. After fusing w/ the host cell membrane, the HIV virus (w/ capsid & matrix) enters host cell 2. "Un-coding" occurs where matrix & capsid proteins are shed, exposing viral genetic material 3. Reverse transcriptase uses the sense + RNA of HIV virus to produce a complementary DNA copy ->The single-stranded DNA copy produced is then used to make a double-stranded DNA molecule 4. The viral DNA goes to the nucleus of the host cell & integrase cuts the host cell's DNA so that the HIV viral DNA may be incorporated into the host cell 5. The viral DNA uses the host cell's machinery to translate the inserted viral DNA into mRNA strands that are translated into proteins at the host cell's ribosomes 6. Viral proteins are produced (gp120, gp41, Gag protein) via RNA polymerase from transcription 7. The viral enzyme protease cleaves the immature Gag protein to produce mature capsid & matrix proteins that may be assembled 8. HIV viral parts are assembled & exit the host cell via budding, accumulating part of host cell's membrane w/ the gp120 & gp41 proteins on the envelope's surface
Name three molecules found on human cells that HIV can use as a receptor or co-receptor:
1. CD4 - this is the main receptor used by HIV - (helper T-cells) - the HIV virus uses CD4 in order to bind onto the host cell before it can enter it 2. CCR5: co-receptor 3. CXR4: co-receptor
Describe Latent infection in regards to HIV
No new, complete HIV viruses are being made ->HIV is incorporated into host cell (likely memory helper T-cell) & is not active
How does HIV acquire its envelope?
Previous host cell's membrane via budding - Budding does not kill host cell
what happens after viral proteins are produced?
Viral proteins are produced (gp120, gp41, Gag protein) o gp 120 & gp41 are extruded from the cell & reside on the host cell's membrane o Gag protein is immature, so protease cleaves it to produce mature capsid & matrix proteins that may be assembled
What happens to HIV's genetic material after it's inside the host cell?
Un-coding - Capsid & matrix shed, then HIV viral enzyme, reverse transcriptase, reads the sense + RNA to make a DNA copy of the HIV genome
Why are attenuated vaccine not good at preventing HIV?
Weakened HIV vaccines are no longer being considered because of their relatively high likelihood of reverting back to the pathogenic form of the virus. It's counter-productive to intentionally give someone a virus that causes lethal disease
Does HIV have an envelope?
Yes, (& matrix) w/ gp41 embedded in the membrane & gp120 attached to gp41, sticking out of membrane
HIV tends to infect what kind of cells?
activated CD4+ cells (helper T cells) because these cells have CD4 molecule and cytokine receptors (co-receptors IE CCR5 or CXR4)
acute phase, what's happening?
beginning of Acute phase: HIV is replicating within the host cells; host cells (CD4+ cells) die due to killing by cytotoxic T-cells end of acute phase: Viruses are being managed by the hosts immune system response and/or virus enters latent cycle; therefore numbers of CD4+ cells go up
Which one can detect HIV in the least amount of time after exposure to the virus?
Looking for the presence for HIV nucleic acids (about 12 days)
Describe 5 different ways that current HIV treatments work
1. Drugs that make it more difficult for HIV to bind to the CCR5 co-receptor on host cells 2. Drugs that make it more difficult for the envelope of HIV to fuse w/ the host cell membrane 3. Drugs that inhibit reverse transcriptase so that a DNA copy of the HIV RNA cannot be produced. These drugs typically work by being nucleoside analogs 4. Drugs that make it more difficult for the DNA copy of the HIV genome to become integrated into the DNA of the host (these drugs are called "integrase inhibitors") 5. Drugs that make it more difficult for the HIV Gag protein to be cleaved. This prevents the production of HIV capsid proteins & matrix proteins. These drugs are called "protease inhibitors".
two general challenges that make it difficult to develop an HIV vaccine that completely protects against infection?
1. HIV has a relatively high rate of mutation -> it uses RNA polymerase which is prone to make a lot of mistakes i.Therefore, the virus you see in the future may not be the virus that your current vaccine protects against 2. Neutralizing epitopes on HIV are blocked -> antibodies normally bind to the epitope portions of HIV or any other pathogens to prevent them from infecting the host cell. However, HIV's neutralizing epitopes are blocked by carbohydrate molecules on them which antibodies can't stick to
3 ways that the presence of HIV is detected in a person's body.
1. Look to see if person has antibodies against HIV present -> about 25 days after infection can a positive result be detected -> fairly inexpensive 2. Look for presence of HIV nucleic acids (via PCR) -> about 12 days after infection can a positive result be detected -> expensive 3. Look for presence of HIV antigens (IE capsid proteins) -> about 16 days after infection can a positive result be detected -> fairly inexpensive
How does the ELISA work to detect the presence of HIV?
1. The well of an ELISA plate is coated w/ a coating antigen (e.g. capsid protein from HIV) 2. A serum sample (taken from person being tested) is placed into the well 3. The well is washed to remove any antibodies in the serum that do not recognize/bind to HIV capsid protein 4. Secondary antibody (w/ attached enzyme) is added to the well. This Ab' binds to the Fc portion of any Ab' that have bound to the coating Ag' 5. The well is washed to remove any secondary Ab' that hasn't bound to the well 6. The enzyme (the one attached to the secondary antibody) has its substrate added to the well. The enzyme binds to the substrate, causing it to undergo a chemical reaction that produces a color. This color can then be viewed by the person running the test; it indicates the person being tested is likely infected w/ HIV. If the person is not infected w/ HIV, then the substrate would never bind to the enzyme (because the enzyme, & the antibody it's attached to, would get washed away by one of the wash steps).
What triggers HIV latent infections to become active infections?
1. When the host memory T-cell w/ the HIV virus inside of it becomes activated again, this activates the HIV virus to make new viruses inside host cell Memory helper T-cell is presented w/ Ag' they're specific for = become activated *Ag' is not necessarily HIV virus—it's whatever Ag' led to it becoming activated in the first place
During typical (untreated) HIV infection, how long does it take to reach AIDS phase?
6/7 - 10 years
Basic Structure of HIV picture
A envelope/lipid membrane B gp 120 C gp41 D matrix E capsid F reverse transcriptase G integrase H protease Genetic information - RNA sense +
Gp41
Allows viral envelope (membrane) to fuse w/ host cell membrane
Gp120
Allows virus to bind to host cell
What role do antibodies play in the immune response to HIV infection:
Antibodies may prevent some viruses from infecting our cells because it's part of our natural immune response -> the antibodies stick to the virus because the B-cell has come across the antigen already -> which produced the antibodies that stick to the virus
Describe at least one treatment that seems to have cured someone of HIV (i.e. resulted in no detectable levels of HIV in the body):
Bone marrow transplant to make it so that the person with HIV produces WBC (Helper T-cells) without CCR5, so that HIV cannot bind. If it cannot bind, then it cannot enter the cell and infect it side affects: shorter lifespan and more likely to die from influenza
What kills the host cell in an HIV infection?
Budding does not kill host cell *Actually is our own immune system's response to the HIV virus that kills our cells
cytokine receptors on helper T-cells?
CCR5 & CXCR4. IE co-receptors
Which one detects HIV in the most amount of time after exposure to the virus?
Looking to see if person has antibodies against HIV (about 26 days)
Capsid & matrix
Maintains viral structure & protects genetic material
What type(s) of cell can HIV infect?
CD4+ cells = Activated helper T-cells. ->Can typically only infect activated helper T-cells because these T-cells have more cytokine receptors, which are the co-receptors for HIV to gain entry into cell
What's the role of cytotoxic T-cells in slowing HIV infection?
Cytotoxic T-cells kill CD4+ cells that are infected with actively replicating HIV, which slows down the progression of the virus.
What role do T-cells play in the immune response to HIV infection:
Cytotoxic T-cells need to be activated by activated (effector) helper T-cells that are not infected by the virus
Protease
Enzyme on viral RNA that chops up proteins for purpose of making mature, fully functional HIV proteins
Integrase
Enzyme on viral RNA that helps integrase viral DNA copy of the RNA genome & integrates it into the DNA of host cell (cuts DNA of host cell to insert viral DNA)
Reverse transcriptase
Enzyme on viral RNA that reads viral RNA to produce DNA copy (in host cell)
ELISA
Enzyme-linked immunoabsorbent assay
HIV infection
HIV virus has entered body & is replicating; signs & symptoms of disease are not necessarily present
which strand of HIV is more virulent?
HIV-1
which strand of HIV infects more people around the world?
HIV-1 -> Group M (main)
Describe Clinical latency in regards to HIV
New, complete HIV viruses are being produced, but at a rate that our immune system is able to handle, so our immune system eliminates most of the viruses being produced during clinical latency
asymptomatic phase, what's happening?
IE Clinical latency Viruses are being managed by the hosts immune system response and/or virus enters latent cycle; numbers of CD4+ cells drop due to killing by cytotoxic T-cells •HIV viruses kept in check (for most part) by activated cytotoxic T-cells & plasma cells. This is why the # of viruses increases—but very slowly.
AIDS
Last stage of HIV disease -> CD4+ levels drop below 200/microliter of blood (normal levels are 1,000/microliter of blood) ->Signs & symptoms of immunodeficiency appear—severe immune system breakdown
What kind of genetic material does HIV have?
Segmented sense + RNA
HIV disease
Signs & symptoms of viral disease are present
What are general structure of the virus includes?
gp 120 gp41 envelope capsid matrix reverse transcriptase integrase protease Genetic information - RNA sense +
What are "neutralizing epitopes"?
is an antibody that is able to "neutralize" the effects of a virus
Gag (AKA Group antigen)
it is a combination of multiple HIV proteins. It needs to be cleaved after translation via protease to produce mature capsid & matrix proteins that will surround & protect the HIV genetic info when new HIV viruses are made
Un-coding
matrix & capsid proteins are shed, exposing viral genetic material
HIV tends to cause latent infections in what kind of cells?
memory CD4+ cells (Helper T cells) • Memory T-cells (AKA resting T-cells) don't really have much enzyme activity, they are just resting and not doing anything until they are activated so, the HIV virus just "rests" with it
Why are inactivated vaccines not good at preventing HIV?
o Killed HIV vaccines are no longer being considered because they do not induce a strong enough immune response that would protect someone against HIV infection. - Can't get into our own cells because it's dead form of pathogen = no MHCI -> never activates cytotoxic T-cells -> no memory cytotoxic T-cells (which are needed!) - Antibodies produced in body from this vaccine may be effective against 1 HIV strain but due to high mutation rate, Ab' produced by body may not be able to recognize HIV someone is infected w/ - Ab' also cannot bind to the carbohydrates on the gp120 of the HIV virus
During AIDS phase, what's happening ?
• CD4+ (e.g. helper T-cells) decreases to the point where cytotoxic T-cells (& B-cells) cannot be sufficiently activated & decline drastically—once the CD4+ count in the blood goes below 200/microliter of blood, the body is unable to maintain defense against the spread of HIV throughout the body & within WBCs • HIV count rises drastically, as it is no longer inhibited by the body's immune defenses
