HIV Flashcards
Stages of Disease
- Transmission
- Primary
- Chronic
- AIDS
Priamry HIV infection
5-21 days post infection
fever, rash, sore throat
leukopenia, thrombocytopenia
Patient is antibody negative for weeks, lasts about 14 days
Patient is negative for HIV antibody
Viral loads 1 x 10^7….patient becomes antibody positive in 3-4 weeks
First detection of HIV-1
by RNA PCR @ 10 days
Second detection of HIV-1
P24 ELISA @ 15 days
Third Detection of HIV-1
Western Blot for Anti-virus antibody @ 25 days
How does HIV cause AIDS
virus kills CD4+ cells, kills helper T cells, and without the helper T cells the B cells and CTLs can’t respond to viruses
virus specifically targets the Th cells that respond to it
Generalized CD4 depletion leads to opportunistic infections
T cells can be replenished by bone marrow, but eventually the infection becomes too overwhelming and there is a CD4 cell crash
HIV is the Cause of AIDS (3 proofs)
Koch postulates are fulfilled- 1. all people with AIDS have HIV, Lab worker exposure caused AIDS in 3 lab workers
- Treatment with anti-HIV drugs alleviates symptoms and reduces viral load
- SIV disease closely resembles AIDS in humans
Structural features
Envelope = lipid bilayer with glycoproteins with gp120/gp41
Underlying envelope = matrix
in matrix= core with capsid
capsid made of- CA protein which is p24, detected in the ELISA
In the capsid = 2 RNA encoded by nucleocapsid
Also in core = integrase, protease, and reverse transcriptase, tRNA lys3 which is essential for replication of viral genome
Viral genome- length and open reading frames
10 kb long
3 open reading frames: 1- structural proteins of matrix, capsid, nucleocapsid, and p6; 2- enzymes, the proteases, integrase, and RT; 3- envelope of gp160 which will be cleaved into gp120 and gp41
HIV transmission (sexual transmission slide)
- cell-free or cell-associated virus attaches to dendritic cells
- dendritic cells feed the virus to the activated CD4 T cell
- CD4 T cells and macrophages are infected in the draining lymph node and the gut associated lymph tissue
- CD4 T cells in intestinal lamina are depleted and
- virus is disseminated throughout the body
Acute phase of infection
viral load is high and transient depression in CD4 cells; this is when the virus is disseminating
chronic phase of infection
clinical latency when your CD4 T cells start off a little higher then slowly slowly decline
AIDS
viral load increases dramatically, CD4 T cells continue to stay at low level and you get opportunistic infections and death
what determines the rate of time to AIDS
viral load set point
progressors
never dealt with their initial viral load; develop AIDS more quickly and have CD4 counts
long-term non-progressors
intermediate; CD4 counts 350-500
elite controllers
CD4 counts>500
Retroviral lifecycle
- virus attaches to CD4 + co-receptor
- fuses with the plasma membrane
- uncoating releases contents into the cytoplasm
- reverse transcriptase makes dsDNA from RNA
- dsDNA is incorporated into cell DNA in nucleus by integrases
- cell lies dormant until it is activated, at which point it transcribes the proteins in the HIV genome
- envelope proteins, structural proteins, and enzymatic proteins assemble at the plasma membrane
- RNA genome becomes associated with budding virus and it buds off
- when the protein pinches off, gag proteins get cleaved for maturation of virus
HIV must attach to what 2 things
CD4 on T cells and macrophages + co receptor either CCR5 or CXCR4
CCR5 and CXCR4 are
chemokine receptors that allow for chemotaxis
what kind of receptors are CCR5 and CXCR4 and what does this mean for their structure
GPCR, 7 transmembrane domains
HIV entry mechnaism
CD4 binding–> coreceptor binding –> virus-cell fusion
CD4 binding
gp41 binds to the virus and also binds to gp120 which has a high affinity binding for CD4 which binds to the cell
Co-receptor binding
gp120 opens up and exposes the co-receptor binding spot for either CCR5 or CXCR4
Virus-cell fusion
when the co-receptor binds, the gp41 which is spring loaded into the virus becomes unsprung and shoots into the target cell membrane, bringing the cell membrane and virus membrane close together and when they are close enough they fuse and the virus enters the cell
delta 32 ccr5
genetic mutation that gives people protection from HIV- 32 bp deletion in ccr5
Number of heterozygotes/ homozygotes for mutation with protection from hiv and the effect of the mutation for both genotypes
15% of caucasians are heterozygotes; 1% homozygotes
heterozygotes take 2 years longer to develop AIDS and homozygotes have protection
Role of CCR5 and CXCR4 in pathogenesis
HIV-1 is transmitted by viruses that use CCR5 so initially, all of the viruses have CCR5. Later in infection, co-receptor switching, due to a mutation in v3 loop of gp120 that alters the coreceptor binding site, allows the receptors to switch to CXCR4. CXCR4 allows the virus to infect more cells because it is expressed on the majority of Th cells.
reasons why ccr5 is a good drug target
its a host protein- less fear of immunorejection
its on the cell surface
a small molecule binding to ccr5 and interfering with its function as a chemokine receptor shouldnt be harmful
it is required for early on viral replication
only problem is that viruses can switch to cxcr4
(Maraviroc was a drug given to patients for this purpose)
HIV drugs have included
- fusion inhibitors
- RT inhibitors
- integrase inhibitors
- protease inhibitors
What are the steps after the viral proteins are made?
they gather at the plasma membrane, you have GAG dimerization, assembly, release, and maturation that is the result of proteases cleaving the tails of the virus
If you treat with a protease inhibitor, effect on infection/virion
it does not block infection however all of the virions produced are defective because they remain in the immature virion form
APOBEC3G is a
cytidine deaminase that changes C to U in single stranded DNA
what normally happens involving viruses and APOBEC3G?
normally as the virus buds off in a cell, apobec3g gets incorporated. when the molecule goes to the next cell, and it fuses and releases its components. The virion does reverse transcription and apobec3g makes all of the C’s into U’s. The cell recognizes that U is not a part of DNA, recognizes this as aberrant DNA, and either degrades it or hypermutates it.
How does vif play into the virus/apobec3g interaction?
vif is encoded by a central region of the viral genome and it shunts apobec3g to the proteasome before it has a chance to be incorporated into the viral particle
One Roadblock to a cure
latent cells- they are not affected by treatment at all and one way to fix this would be to come up with a way to get the T cells to produce the virus and get killed rather than becoming latent
Obstacles to vaccine
Virus is variable- immunization to one clade one protect from the rest
Only site for antibody binding is gp120/gp41 and its highly variable from person to person (because RT is error prone and this allows the virus to escape the neutralizing antibodies that would be made); carbohydrates block the antibody site of gp120 and gp41 and the coreceptor binding site only becomes exposed after binding to CD4
Virus encodes immune evasion proteins like Nef
signs for optimism
gene therapy- with zinc finger nucleases that cut dsDNA at particular parts (can cut up ccr5); potent neutralizing antibodies and engineered immunity (ways to deliver the antibodies)
