Lecture22: HIV and AIDs

Question 1

HIV ___ is responsible for causing AIDS in much of West Aftica but HIV___ causes AIDS throughout the rest of the world

Answer 1

• West Africa: HIV-2
• Rest of world: HIV-1
• (note the differences)
  
  • 40% genetically different
    
    • HIV-1 is more progressive and more infections
  • Different origins
    
    • HIV-1:
      
      • single subspecies of the chimpanzee (Pan troglodytes troglodytes)
    • HIV-2:
      
      • Sooty mangabey (Cercocebus atys)

Question 2

• What are the four groups of HIV-1?
• What is the most important group?

Answer 2

• Groups: M,N,O,and P (note that within each group is 9 subtypes (A,B,C, etc.))
  
  • M is the most important group (the Major group)

Question 3

Structure of HIV virus

Answer 3

• Retrovirus containing 2 positive strands of ssRNA
• Has reverse trancriptase and integrase
• Glycoproteins gp120 and gp41 on the outer membrane are involved in adsorption and penetration
• Capsid protein p24 (this can be found in blood as an indicator of HIV progression)
• p17: is a matrix protein that forms the iner surface of the viral membrane and orchestrates viral assembly ​
  *

Question 4

Are the envelop glycoproteins of HIV-1 and HIV-2 cross- reactive

Answer 4

No they are distinct and thus not immunologically cross-reactive

Question 5

• HIV Genomic Organization
  
  • What are the major structural genes of HIV

Answer 5

Question 6

Binding and entry of HIV

Answer 6

• CD4 is high affinity receptor for gp120
• Co-receptor
  
  • consists of the cell surface receptors that bind chemokines, CXCR4 or CCR5
• ​Surface expression of CXCR4, CCR5 on CD4 T cells, DCs and Macrophages defines the cellular targets for HIV

Question 7

what are the major cellular reservoirs of HIV in the host

Answer 7

• Latently-infected (integrated) memory T cells
  
  • half life of months/year
• Infected macrophages
  
  • have half life of months/year

Question 8

Clinical Disease progression of HIV/AIDS

Answer 8

Question 9

CD4+/CD8+ cell ratio in healthy individual is ___ while in an HIV infected individual it is

Answer 9

• 2:1
• 1:1

Question 10

Normal CD4 T cell count is

Answer 10

600-1200 cells/mL

Question 11

Mechanisms of CD4+ cell depletion

Answer 11

• It can be caused by:
  
  • Direct infection of HIV
  • Chronic immune activation causes apoptosis of CD4+ T cells
  • AICD (activation induced cell death) killing of CD4+ T cells carrying gp120 viral protein
  • CTL activity against normal CD4+ T cells
  • Bone marrow toxicity–> inhibition of lymphocyte regeneration

Question 12

Why antibody responses not effective against HIV

Answer 12

• Results from Low Fidelity of reverse transcriptase
  
  • leads to production of mutant virions with distinct antigenic make up
    
    • this means that the Abs can’t keep up with the changing virions

Question 13

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Question 15

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Question 17

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Question 19

Question 20

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Question 22

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Question 23

Question 24

Question 25

Question 26