11. Persistent (Chronic) Viral Infections: Retroviruses (HIV & HTLV) - Audia

Retrovirus (HIV):

Structure

• bound by what?

• what other structures on the virus? (4)

2 identical copies of the +ssRNA genome

• each bound by a host tRNA (primer)

• VAPs: gp120, gp41

• Integrase

• Reverse Transcriptase

• Protease

Retrovirus (HIV):

Which proteins encoded are most commonly detected? (3)

1. p24 (capsid - core)

2. gp120 (attachment VAP)

3. gp41 (fusion)

Retrovirus (HIV): Attachment, Fusion, Entry

• ____-restricted

  • what cells are targeted initially?

  • requirements of Retrovirus to recognize the cells (2)

• Method of Penetration?

• What cells are targeted later?

  • requirements of Retrovirus to recognize the cells? (2)

• tropically-restricted since major receptor is CD4 cells

• macrophages and dendritic cells are infected initially because they express CD4

  • retrovirus must recognize CD4 AND CCR5 by gp120

    • undergoes conformational change

• Enters by Direct Fusion

• T-cells are targeted later

  • retrovirus must recognize CD4 and CXCR4 by gp120

    • undergoes conformational change → direct fusion into cell

HIV Replication Steps (5)

1. Attachment, Fusion, Entry

2. Reverse Transcriptase → cDNA synthesis (complementary DNA)

   • makes a copy of the RNA in DNA form → degrades the RNA → makes a dsDNA molecule → DNA circularizes (LTRs on front and end merge) → integrates into host chromosome through integrase

3. Genome Integration → Transcription

   • viral proteins and new viral RNA genomes

4. Viral genome encapsidation

   • package RT, INT, PRT

     1. reverse transcriptase

     2. integrase

     3. protease - cleaves the pro-proteins into their active forms

        • final step in maturation

5. Release via Budding

HIV Pathogenesis I

• initial infection of what?

• what leads to infection of T-cells?

• virus infection can lead to formation of what?

• what happens in a 10 year time period? (untreated)

• Initial infection of Macrophages (R-5 variants, can also infect Dendritic Cells)

• Antigenic drift leads to tropism change and infection of T-cells (X-4)

• virus infection can lead to formation of syncytia (makes cell fragile and prone to lysis)

• loss of T_H function leads to decrease CD8 T cell function → AIDS

  • CD4 T cells help maintain viability of other cell types

Why is HIV so hard to treat?

always undergoes genetic drift!! so it constantly evolves and develops resistance to therapies.

HIV Disease Progression

Notable Timestamps (4)

• 1-3 weeks post-infection

• 3-6 weeks

• 10 years

• beyond 10 years

HIV Disease Progression

Characteristics of each Timestamp (4, 2+2+3+0)

1-3 weeks post-infection

• acute, flu-like symptoms

• viremia

3-6 weeks

• begin generating immune responses

• begin slow decline in CD4

10 years

• large decrease in CD4 cells

• increase viral loads

• disease progression

beyond 10 years

Treatment I

• Classes (2)

• Example of first class

• What do they target?

Nucleoside Analogue Reverse Transcriptase Inhibitors (NRTI)

• ex.) Azidothymidine (AZT) - Zidovudine/Retrovir

• targets reverse transcriptase → can’t make cDNA → can’t integrate

  • alters the active site of the enzyme synthesizing viral DNA from RNA

Non-nucleoside Reverse Transcriptase Inhibitors (NNRTI)

• targets reverse transcriptase

Treatment II

• Classes (4)

• What do they target?

Protease Inhibitors

• prevents cleavage of pro-protein into RT-integrase → prevents infection

Binding and Fusion Inhibitors

Integrase Inhibitor

Highly Active Antiretroviral Therapy (HAART)

HIV Treatment

Treatment style

Combinatorial Therapy

• give 3 different types of drugs

  • usually 2 nucleoside analogs + integrase inhibitor (example)

• treats patient and prevents the emergence of resistance

HIV Clinical Syndromes (4)

1. Lymphodenopathy and fever → AIDS-Related Complex (ARC) with presence of 2 or more of:

   • fever

   • fatigue

   • diarrhea (persistent)

   • weight loss

   • night sweats

2. Opportunistic Malignancies → human herpes virus 8-associated Kaposi, sarcoma, non-Hodgkin lymphoma, EBV- related lymphomas

3. AIDs-related Dementia

4. Opportunistic Infections:

   • Protozoan

   • Fungal

   • Mycobacterial

   • Latent viral re-activation

   • Recurrent bacteremia

HIV Transmission (6)

1. Exposure to open wound, mucous membranes

2. Intravenous drug. use

3. Tattoo needles

4. Sexual transmission

5. Perinatal transmission

6. Breast milk

Can HIV be transmitted through casual contact? (kissing, handshake, close quarters, etc..)

NOOOOOO

Test for HIV infection is performed in order to do what? (4)

1. Identify infection to initiate therapy

2. Identify carriers to limit spread

3. Follow progression of disease

4. Evaluate treatment efficacy

HIV Laboratory Diagnosis

Methods (3)

• examples of each (1, 2, 1)

Genomic-based Testing

• detecting viral genome load in blood by PCR/RT-PCR

Serology

• detection of antibodies to p24, gp41, gp120

• ELISA, Western Blot, and Agglutination tests for antibody titres

Immunological Studies

• assess CD4 and CD8 T cell levels

HIV structure characteristics (4)

1. enveloped

2. spherical

3. encloses a capsid

4. capsid contains 2 copies of +ssRNA

What is carried in the virion? (2)

1. reverse transcriptase (RNA-dependent DNA polymerase)

2. integrase enzyme

What is the initial determinant of tissue tropism?

How so?

Virus receptor

• Requires CD4

  • Co-Rc can either be:

    • CCR5 (macrophages)

    • CXCR4 (T-cell)

What can undergo genetic drift to change Co-Rc specificity and antigenicity?

gp120

What does the provirus do? (2)

integrates randomly into host chromosome and becomes a cellular gene

Simple retroviruses encode what? (3)

Complexes viruses also encode what? (5)

Simple Retroviruses:

• gag

• pol

• env

Complex Viruses:

• tat

• rev

• nef

• vif

• vpu

What protein is associated with progression to “full-blown AIDS”?

nef protein

Final morphogenesis of HIV requires what?

protease cleavage of gag and gag-pol polypeptides after envelopment!!!

Stable or unstable virus?

Transmitted primarily how?

Environmentally, unstable virus

transmitted by bodily fluids