Role of each immune molecule

Q6: Define the role of each immune molecule/cell:

• Role of MHC I:
  
• Found on all nucleated cells.
• Displays viral peptides to cytotoxic T cells (Tc cells) so infected cells can be destroyed.
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• Role of MHC II:
  
• Found on antigen-presenting cells (like B cells, dendritic cells, macrophages).
• Presents antigens to helper T cells (TH cells) to start the adaptive immune response.
• 
  
• Role of TH (Helper T) Cells:
  
• Help activate B cells (to make antibodies) and Tc cells.
• Release cytokines to coordinate the immune response.
• These are the main cells HIV infects and destroys.
• 
  
• Role of TC (Cytotoxic T) Cells:
  
• Destroy virus-infected cells using perforin and granzymes.
• Recognize infected cells using MHC I + viral antigen.
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Q7: What could be leading to the decrease in CD4 cell numbers?

Answer:

• Direct infection by HIV (virus kills CD4 cells).
• Immune-mediated killing (Tc cells destroy infected CD4 cells).
• Chronic activation/exhaustion of CD4 cells leads to cell death.
• Syncytia formation (infected cells fuse and die).
• Apoptosis (cell suicide triggered by HIV or immune stress).

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Q8: Why do AIDS patients die from other infections, not HIV itself?

Answer:

• AIDS patients have very low CD4+ T cell counts, which weakens their entire immune system.
• They can’t fight off other pathogens (like bacteria, viruses, fungi).
• As a result, they die from opportunistic infections like TB, pneumonia, or fungal infections, not HIV itself.