Lecture 13: HIV part 1

Question 1

Write a brief overview of cellular function of the immune system;

Answer 1

Inflammation and phagocytosis
= Neutrophils
Antibody production
= B cells
Antigen specific cytotoxicity
= Cytotoxic CD8 T cells
= K lymphocytes (antibody dependant)
Non-antigen specific cytotoxicity
= Natural Killer Cells
Cytokine mediated immune regulation
= CD4 T helper cells

Question 2

What is the central role of CD4 cells?

Answer 2

CD4 helper cells have a central role in cytokine production and regulation of;

• Phagocytes
• B cells -> plasma cells + memory
• T (CD8) cells -> CD8 cytotoxic and memory cells
• Regulation of inflammation and phagocytosis

Question 3

How does HIV use CD4 cells?

Answer 3

HIV binds to the CD4 receptor of T cells and utilises CCR5 or CXCR4 to facilitate virus fusion and injection of RNA.

Cellular reverse transcriptase inserts HIV DNA into the CD4 DNA.

CD4 then expresses the HIV genes and subsequently assembles virus which bud off to infect other CD4 cells.

Question 4

How does HIV diminish CD4 cells?

Answer 4

CD8 cells sense (TCR and CD8 binding) the HIV viral proteins expressed by CD4 on their MHC class 1 receptors and kills the infected CD4 cells.

= Loss of T helper cell function = dysregulation of immune system