HIV Structure and Genes Overview

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Questions and Answers

What does a CD4+ count of greater than 500 cells/uL indicate in the clinical categories of AIDS?

Category B2

Category B1 (correct)

Category C1

Category A1 (correct)

What is the normal range for CD4+ T cells in adults?

400–1000 cells/uL

500–1500 cells/uL

300–600 cells/uL

600–1200 cells/uL (correct)

In order to stabilize leukocytes during the diagnostic process, which method is used?

Stabilizing with paraformaldehyde (correct)

Heating with ethylene oxide

Washing with saline solution

Cooling with ice

Which clinical category corresponds to a CD4+ count of 200-499 cells/uL?

A2 Signup and view all the answers

What is the significance of the red lines in the diagram pertaining to HIV?

They represent HIV copies Signup and view all the answers

What is the primary mode of HIV transmission worldwide?

Intimate sexual contact Signup and view all the answers

Which factor increases the likelihood of HIV transmission during sexual activity?

Presence of STIs Signup and view all the answers

How is HIV transmitted through blood and body fluids?

Sharing contaminated needles Signup and view all the answers

What is the average risk of HIV transmission to health workers through percutaneous exposure?

0.3% Signup and view all the answers

What is vertical transmission of HIV?

Transmission from infected mother to infant Signup and view all the answers

What is the minimum amount of saliva mentioned to potentially transmit HIV?

9 gallons Signup and view all the answers

What role does the vpu protein play in HIV-1?

Contributes to viral release Signup and view all the answers

What is the risk percentage of HIV transmission through mucous membrane exposure for health workers?

0.09% Signup and view all the answers

What is the shape of the HIV-1 virion?

Spherical Signup and view all the answers

Which gene is responsible for enhancing the transcription of viral proteins?

TAT gene Signup and view all the answers

Which gene codes for the proteins necessary for reverse transcription?

pol gene Signup and view all the answers

What role does the vif gene play in HIV?

It makes the virus more infectious. Signup and view all the answers

What function does the REV gene serve in the HIV lifecycle?

Activates splicing and transport of mRNA Signup and view all the answers

Which of the following is not essential for viral replication but enhances the virus's capacity to survive?

nef gene Signup and view all the answers

What does the LTR sequence provide for the HIV genome?

Promoter and enhancer elements Signup and view all the answers

How does the vpr gene affect HIV replication?

It controls the rate of viral replication. Signup and view all the answers

Which cells do X4 strains of HIV primarily bind to?

CD4 T cells Signup and view all the answers

Which gene produces the envelope glycoprotein in HIV?

env gene Signup and view all the answers

What role do chemokine receptors play in HIV infection?

They facilitate the fusion process. Signup and view all the answers

What is the primary component of the HIV lipid envelope derived from?

Host cell membrane Signup and view all the answers

What is the function of the HIV enzyme reverse transcriptase?

To produce complementary DNA from viral RNA. Signup and view all the answers

Where is the HIV RNA housed within the virus?

In the capsid. Signup and view all the answers

Which chemokine receptor primarily interacts with macrophages during HIV infection?

CCR5 Signup and view all the answers

What does gp120 binding trigger in the HIV life cycle?

Conformational changes in gp41. Signup and view all the answers

What is the role of the HIV envelope in the virus's structure?

It mediates entry into host cells. Signup and view all the answers

Which type of HIV strain primarily interacts with dendritic cells?

R5 strains Signup and view all the answers

What characterizes the acute infection stage of HIV infection?

Presence of flu-like symptoms Signup and view all the answers

What is a key feature of the clinical latency stage of HIV infection?

Asymptomatic HIV infection Signup and view all the answers

At what CD4+ T cell count is a patient diagnosed with AIDS?

200 cells/mm3 or below Signup and view all the answers

Which of the following is NOT a symptom experienced during the acute infection stage?

Hives Signup and view all the answers

Which stage follows the clinical latency stage in HIV progression?

AIDS Signup and view all the answers

What occurs in the body during the AIDS stage of HIV infection?

Development of opportunistic infections Signup and view all the answers

During which stage of HIV infection is a person most likely to be asymptomatic?

Clinical latency stage Signup and view all the answers

What is the primary consequence of the cell membrane damage due to HIV?

Cell lysis leading to host cell destruction Signup and view all the answers

Study Notes

HIV Structure

HIV-1 virion is spherical, composed of an electron-dense, cone-shaped core enclosed by a lipid envelope derived from the host cell membrane.
Genes essential to viral replication:
- TAT gene: Enhances the transcription and expression of viral proteins by binding to the TAR.
- REV gene: Post transcriptional activator for splicing and transportation of viral mRNA (production of structural proteins)
- LTR sequence: Promoter and enhancer elements
- gag gene: Codes for the group-specific antigen
- pol gene: Codes for reverse transcriptase, protease, and integrase
- env gene: Codes for the envelope glycoprotein (gp)
Genes not essential to viral replication (but enhance the capacity of the virus to survive):
- Virus infection factor (vif): Makes the virus more infectious
- Negative factor (nef): Inhibits or activates viral transcription as required, influences t cell activation, reduces CD4 expression
- vpr: Controls the rate of replication
- vpx: Specific to HIV 2, controls the rate of replication
- vpu: Specific to HIV 1, contributes to viral release, increases CD4 turnover.

HIV Transmission

Can be transmitted through:
- Intimate sexual contact:
  - 85% of transmissions are through heterosexual contact worldwide.
  - Transmission is more likely when STIs are present because of lesions in the genitals.
- Contact with blood or other body fluids:
  - Sharing of contaminated needles.
  - Average risk of transmission to healthcare workers:
    - 0.3% percutaneous exposure (needle stick).
    - 0.09% mucous membrane exposure.
- Perinatally, infected mother to infant (vertical transmission).
- Saliva is assumed to have a low risk of transmission.

HIV Binding and Fusion

gp120 (HIV) binds to CD4 T cells (T tropic/X4 strains) and other cells (M tropic/R5 strains): macrophages, monocytes, dendritic cells, Langerhans cells and microglial cells.
Fusion:
- Requires chemokine receptors:
  - CXCR4: For T-cells
  - CCR5: For macrophages
- Occurs when chemokine receptor binds to gp120 and gp41

Reverse Transcription

HIV capside: Bullet shaped core that contains HIV RNA
HIV envelope: Outer surface of HIV
HIV enzymes: Proteins that carry out steps in the HIV life cycle
HIV glycoproteins: Protein spikes on HIV envelope
HIV RNA: HIV's genetic material
Viral contents gain entry to the host membrane.
HIV RNA unravels followed by reverse transcription.
Enzyme reverse transcriptase produces complementary DNA (cDNA) from the viral RNA.

Stages of HIV Infection

Acute infection stage/primary HIV infection:
- Flu-like symptoms: fever, swollen glands, sore throat, rash, muscle and joint pains, fatigue, headache.
Clinical latency stage/chronic HIV infection: Asymptomatic HIV infection
AIDS (terminal stage):
- CD4+ cells fall below 200 cells/mm3.
- RNA copies rise.
- One or more opportunistic illnesses develop, regardless of CD4 count (AIDS defining disease).

Diagnostic Definitions of AIDS

Adults:
- Serves as a clinical diagnosis.
- Table 5. Categories of AIDS:
  - CD4+ T cells/ul | Clinical Categories
  - 500 | A1 | B1 | C1
  - 200-499 | A2 | B2 | C2
Data shows the majority of cases are in individuals aged 25-34 years old.
Minimal risk of transmission in pregnant women, but children can be infected at birth.

Serodiagnosis of HIV

Diagnostic definition:
- Signals are interpreted by the machine.
- Removing erythrocytes by lysis.
- Stabilizing leukocytes by fixation with paraformaldehyde.
- Normal: 600-1200 cells/uL

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Description

This quiz covers the essential structure of the HIV-1 virion and key genes involved in its replication. Explore the roles of the TAT, REV, LTR, gag, pol, and env genes, along with additional factors that enhance the virus's survivability. Test your knowledge on the molecular biology of HIV.