HIV

Question 1

Stages of Disease

Answer 1

1. Transmission
2. Primary
3. Chronic
4. AIDS

Question 2

Priamry HIV infection

Answer 2

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

Question 3

First detection of HIV-1

Answer 3

by RNA PCR @ 10 days

Question 4

Second detection of HIV-1

Answer 4

P24 ELISA @ 15 days

Question 5

Third Detection of HIV-1

Answer 5

Western Blot for Anti-virus antibody @ 25 days

Question 6

How does HIV cause AIDS

Answer 6

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

Question 7

HIV is the Cause of AIDS (3 proofs)

Answer 7

Koch postulates are fulfilled- 1. all people with AIDS have HIV, Lab worker exposure caused AIDS in 3 lab workers

2. Treatment with anti-HIV drugs alleviates symptoms and reduces viral load
3. SIV disease closely resembles AIDS in humans

Question 8

Structural features

Answer 8

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

Question 9

Viral genome- length and open reading frames

Answer 9

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

Question 10

HIV transmission (sexual transmission slide)

Answer 10

1. cell-free or cell-associated virus attaches to dendritic cells
2. dendritic cells feed the virus to the activated CD4 T cell
3. CD4 T cells and macrophages are infected in the draining lymph node and the gut associated lymph tissue
4. CD4 T cells in intestinal lamina are depleted and
5. virus is disseminated throughout the body

Question 11

Acute phase of infection

Answer 11

viral load is high and transient depression in CD4 cells; this is when the virus is disseminating

Question 12

chronic phase of infection

Answer 12

clinical latency when your CD4 T cells start off a little higher then slowly slowly decline

Question 13

AIDS

Answer 13

viral load increases dramatically, CD4 T cells continue to stay at low level and you get opportunistic infections and death

Question 14

what determines the rate of time to AIDS

Answer 14

viral load set point

Question 15

progressors

Answer 15

never dealt with their initial viral load; develop AIDS more quickly and have CD4 counts

Question 16

long-term non-progressors

Answer 16

intermediate; CD4 counts 350-500

Question 17

elite controllers

Answer 17

CD4 counts>500

Question 18

Retroviral lifecycle

Answer 18

1. virus attaches to CD4 + co-receptor
2. fuses with the plasma membrane
3. uncoating releases contents into the cytoplasm
4. reverse transcriptase makes dsDNA from RNA
5. dsDNA is incorporated into cell DNA in nucleus by integrases
6. cell lies dormant until it is activated, at which point it transcribes the proteins in the HIV genome
7. envelope proteins, structural proteins, and enzymatic proteins assemble at the plasma membrane
8. RNA genome becomes associated with budding virus and it buds off
9. when the protein pinches off, gag proteins get cleaved for maturation of virus

Question 19

HIV must attach to what 2 things

Answer 19

CD4 on T cells and macrophages + co receptor either CCR5 or CXCR4

Question 20

CCR5 and CXCR4 are

Answer 20

chemokine receptors that allow for chemotaxis

Question 21

what kind of receptors are CCR5 and CXCR4 and what does this mean for their structure

Answer 21

GPCR, 7 transmembrane domains

Question 22

HIV entry mechnaism

Answer 22

CD4 binding–> coreceptor binding –> virus-cell fusion

Question 23

CD4 binding

Answer 23

gp41 binds to the virus and also binds to gp120 which has a high affinity binding for CD4 which binds to the cell

Question 24

Co-receptor binding

Answer 24

gp120 opens up and exposes the co-receptor binding spot for either CCR5 or CXCR4

Question 25

Virus-cell fusion

Answer 25

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

Question 26

delta 32 ccr5

Answer 26

genetic mutation that gives people protection from HIV- 32 bp deletion in ccr5

Question 27

Number of heterozygotes/ homozygotes for mutation with protection from hiv and the effect of the mutation for both genotypes

Answer 27

15% of caucasians are heterozygotes; 1% homozygotes

heterozygotes take 2 years longer to develop AIDS and homozygotes have protection

Question 28

Role of CCR5 and CXCR4 in pathogenesis

Answer 28

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.

Question 29

reasons why ccr5 is a good drug target

Answer 29

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)

Question 30

HIV drugs have included

Answer 30

1. fusion inhibitors
2. RT inhibitors
3. integrase inhibitors
4. protease inhibitors

Question 31

What are the steps after the viral proteins are made?

Answer 31

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

Question 32

If you treat with a protease inhibitor, effect on infection/virion

Answer 32

it does not block infection however all of the virions produced are defective because they remain in the immature virion form

Question 33

APOBEC3G is a

Answer 33

cytidine deaminase that changes C to U in single stranded DNA

Question 34

what normally happens involving viruses and APOBEC3G?

Answer 34

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.

Question 35

How does vif play into the virus/apobec3g interaction?

Answer 35

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

Question 36

One Roadblock to a cure

Answer 36

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

Question 37

Obstacles to vaccine

Answer 37

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

Question 38

signs for optimism

Answer 38

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)