Viral Evasion of the Host Immune Response Flashcards Preview

Y2 Micro (MCD) > Viral Evasion of the Host Immune Response > Flashcards

Flashcards in Viral Evasion of the Host Immune Response Deck (33)
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What is a key difference between internal virus proteins and surface antigens?

Internal viral proteins vary less


Describe the process of presentation of viral peptides on MHC Class I.

  • Viral peptides are chopped up by the proteasome
  • These peptides are then fed through the TAP protein into the endoplasmic reticulum
  • In the endoplasmic reticulum, it will be loaded onto an MHC class I molecule
  • It will then move to golgi apparatus
  • Finally it is moved to the cell surface where T cells can recognise the antigen


State three viruses (and the proteins involved) that evade antigen loading onto TAP.

  • EBV – EBNA1 = this cannot be chopped up by the proteasome
  • HSV – ICP47 = blocks access of the peptides to the TAP protein
  • CMV – US6 = blocks ATP binding to TAP, therefore preventing translocation


State two viruses (and the proteins involved) that modulate tapasin function and prevent MHC transport.

  • Adenovirus - E3-19K = prevents recruitment of TAP to tapasin and retains MHC in the ER
  • CMV – US3 = binds to tapasin and prevents loading of peptides onto MHC


State one virus (and the protein involved) that interferes with MHC presentation at the cell surface.

  • KSHV (Kaposi Sarcoma Herpes Virus) – kK3 = induces polyubiquitination and internalisation of MHC
    • From the internalized endosome MHC is passed to lysosomes where it is degraded.


What do NK cells recognise on the cell surface that triggers killing of cells?

Missing self – lack of MHC on the cell membrane is not healthy


How do viruses evade this mechanism of NK-mediated killing infected cells?

Viruses encode MHC analogues (e.g. CMV gp UL40) – virally encoded MHC is useless but it fools the NK cells


Which cells does HIV target?

CD4+ T cells


Which cells does Ebola kill?

Dendritic cells Macrophages T cells (by the bystander response)


In what subset of the population does HMCV (human cytomegalovirus) cause disease?



What is the problem with HCMV with regards to bone marrow transplantation?

HCMV infects 60-90% of the population If HCMV is present in donated bone marrow, it could cause problems in the immunocompromised recipient


What is antigenic drift?

Continued rapid evolution driven by antigenic pressure from the host


What is antigenic shift?

Introduction of new subtypes of the virus from an animal source NOTE: when they come from an animal source, the antigens don’t look like anything that humans have seen before


How else can viruses cause regular infections without changingtheir antigen profile?

They can have several genetically stable serotypes that co-circulate E.g. rhinovirus has more than 120 antigenically distinct serotypes


How many serotypes of influenza are there?



How many serotypes of poliovirus are there and what type of vaccine was produced for polio?

3 – trivalent vaccine NOTE: one of the serotypes has been eradicated now


What are the features of dengue haemorrhagic fever (DHF)?

Leakage of plasma from capillaries leads to: Increased haematocrit Increased red cell count Decrease in protein Tendency to severe bruising and bleeding


What is the treatment for DHF?

IV fluids


How many serotypes of dengue are there?



Explain the significance of the presence of multiple serotypes of dengue with regards to the pathogenesis of DHF.

Infection with one serotype will cause antibody production Antibody generated against this serotype will bind to but NOT neutralise infection with another dengue serotype This can lead to ANTIGEN DEPENDENT ENHANCEMENT (ADE) Denge can enter monocytes only when complexed with an antibody that binds but doesn't neutralize it Gives access to monocytes that wasn't available in the first infection of the other dengue serotype Causes cytokine storm


What can viruses do to glycoprotein antigens that hinder antibody access to the antigens?

Heavily glycosylate the antigens


What does Ebola virus have a high content of that makes them appear like apoptotic bodies?

Phosphatidyl serine lipids


What is the benefit to Ebola virus of appearing like apoptotic bodies?

They are rapidly taken up by macropinocytosis and, hence, taken away from antibody surveillance


How does the structure of Ebola affect antibody access to antigens?

Ebola has a long filamentous shape with lots of folds The folds may make the glycoproteins inaccessible to antibody


Name two factors produced by Ebola that allow it to evade detection by the innate immune system.

VP35 VP24


Why did the measles vaccine have a much larger effect on childhood mortality than expected?

Measles can infect CD150 memory lymphocytes Causes lysis of the cells Erases immunological memory So a measles virus infection can result in a 2-3 year decrease in immunological memory that leads to morbidity and mortality from otherdiseases


What is tapasin?

Protein involved in loading protein fragments brought into the ER by TAP onto the MHC molecule.


How does HPV counter the immune response?

Encodes proteins:

  • E5 - prevents MHC-I and MHC-II from reaching the cell membrane
  • E6 & E7 - block inteferon production


What is the major influenza viral antigen?



What are the features of the major influenza viral antigen?

Head region is highly variable Stalk is highly conserved