IHO Virology EBV Case

Question 1

What is the genomic organization, envelope?, HHV #, Capsid Symmetry and Tropism of EBV?

Answer 1

dsDNA
Yes, envelope
HHV-4
Icosahedral
Tropism: Lytic cycle in epithelial cells of oropharynx. Latent infections in B cells.

Question 2

What malignancies are associated with EBV?

Answer 2

• Nasopharyngeal carcinoma
• Burkitt lymphoma
• Hodgkin disease
• Non-hodgkin lymphoma
• X-linked lymphoproliferative disease

Question 3

What do B cells do in response to EBV infection?

Answer 3

• Proliferate to fight it off.
• Only B cells w/affinity for a specific antigen will undergo clonal expansion
• B cells are primed to want to proliferate!

Question 4

How does EBV establish an infection?

Answer 4

1. First it infects epithelial cells of the oropharynx.
2. This is a lytic infection that kills the host cell and produces new infectious EBV particles.
3. When these particles infect a B cell, a different pattern of gene expression produces a latent infection.
4. Then, in the B cell infectious particles are not produced, but proliferation of infected B cells is increased.
   - -Circular EBV genome gets tethered to host genes

Question 5

What happens with B cells in a normal infection vs. an EBV infection?

Answer 5

Normal: monoclonal expansion of B cells
EBV: polyclonal expansion of B cells (all B cells proliferate!)
-Heterophile antibodies are produced that love/bind to a lot of things)

Question 6

How does EBV establish infection within the B cell?

Answer 6

1. The viral envelope proteins p350/220 bind the C3d complement receptor (a.k.a. CD21); this initiates endocytosis
2. The genome circularizes, and immediate early genes, and late genes are expressed in sequence.
3. Viral particle then buds through cellular membranes to make infectious particles

Question 7

What’s unique about the EBV genome?

Answer 7

• Circular and has multiple promoters

- Different patterns of gene expression occur during lytic and latent infection

Question 8

What three genes should you know about with EBV?

Answer 8

1. EBNA3C
2. LMP-2
3. LMP-1

Question 9

How does LMP-1 function?

Answer 9

• Acts as a constitutively active CD40.
• The signal it sends out is the same as if CD40 was binding CD40L but this is not happening
• CD40 is normally responsible for CD4+ T-cell dependent activation of B cells

Question 10

What does LMP-1 activate?

Answer 10

• NF-kB transcription factors
• Promotes transcription of NF-kB regulated genes
• It only causes downstream signal function –> NFkB activation which then promotes proliferation

Question 11

How does LMP-2 function?

Answer 11

• Functions as a constitutively active B cell receptor (even though an active BCR is not present)
• Normally, the BCR is responsible for antigen dependent B cell activation

Question 12

What does LMP-2 activate?

Answer 12

• Fos/jun (et al) transcription factors

- It promotes MAPK activation (regulator of apoptosis and proliferation)

Question 13

How does EBNA3C function?

Answer 13

It binds and activates cyclin D1 complexes, resulting in:

1. Hyper-phosphorylation of retinoblastoma protein (Rb)
2. De-repression (i.e. activation) of E2F family transcription factors
3. Expression of genes that control DNA replication
4. Cell cycle progression

Question 14

What illnesses can cause similar symptoms to EBV mono?

Answer 14

CMV, HHV-6, HHV-7

Question 15

What is the “classic triad” of symptoms associated with infectious mononucleosis (IM)?

Answer 15

1. Pharyngitis
2. Lymphadenopathy
3. Fever

Question 16

How do you diagnose mono and how does this test work?

Answer 16

• Monospot test - diagnostic for EBV IM.

- It detects heterophile antibodies produced by polyclonal expansion of B cells

Question 17

How can you detect if the patient has acute or previous infection with mono?

Answer 17

Presence of VCA-IgM in blood = acute infection

Presence of VCA-IgG in blood = previous infection

Question 18

How do you diagnose EBV with a blood smear?

Answer 18

-Atypical lymphocytes (or Downey cells)

Question 19

How does X-linked lymphoproliferative disease present?

Answer 19

(a. k.a Duncan disease)
1. Fuliminant infectious mononucleosis (FIM)
2. Median age for FIM is 3 years old; average survival after FIM is 1-2 months
3. Patients who survive FIM develop lymphoproliferative disorders and dysgammaglobulinemias

Question 20

What does X-linked mean?

Answer 20

Mothers will be carriers who give it to their sons who will have the disease.

Question 21

What is the molecular basis for X-linked lymphoproliferative disease?

Answer 21

-A mutation that results in a non-functional SAP (SLAM (aka CD150) associated protein)

Question 22

What is the significance of SAP?

Answer 22

• SAP is a protein that normally turns off the signal when an infection is beat down
• So, if you have a loss/mutation of SAP protein, you get X-linked lymphoproliferative disorder when you’re first exposed to EBV.

Question 23

What does SAP do molecularly?

Answer 23

• It binds phosphorylated tyrosine on SLAM (CD150)
• SAP acts as an adapter protein and recruits kinases to the immunological synapse
• SAP depletion results in deficiency of IL-4 production by T cells
• IL-4 normally signals CD4H2 differentiation and regulates e.g. B cell class switching

Question 24

How does SAP stop the immune response when a path open is gone?

Answer 24

• It controls apoptotic cell death of activated T cells.
• In XLP, SAP is absent, and the immune response has ‘no brakes’
• Not clear why this disorder is specific to EBV

Question 25

What is p53?

Answer 25

Tumor suppressor

• Acts like a “brake”
• If it becomes non-functional, it promotes cancer

Question 26

What is cyclin D?

Answer 26

-It acts as a proto-oncogene, if over-expressed, it promotes cell growth & proliferation of cancer