Cell Recognition & the Immune system

Question 1

What is an antigen?

Answer 1

• Cell surface molecule which stimulate immune response
• Usually (glyco)protein, sometimes (glyco)lipid or polysaccharide
• Immune system recognises as “self” or “non-self” = enables identification of cells from other organisms of same species, pathogens, toxins & abnormal body cells

Question 2

How does phagocytosis destroy pathogens?

Answer 2

1. Phagocyte moves towards pathogen via chemotaxis.
2. Phagocyte engulfs pathogen via endocytosis to form a phagosome
3. Phagosome fuses with lysosome (phagolysosome)
4. Lysozymes digest pathogen
5. Phagocyte absorbs products from pathogen hydrolysis

Question 3

Explain role of antigen-presenting cells (APCs)

Answer 3

Macrophage displays antigen from pathogen on its surface (after hydrolysis in phagocytosis)

Enhances recognition by Th cells, which cannot directly interface with pathogens/ antigens in body fluid

Question 4

2 Diferences between specific and non-specific immune responses

Answer 4

Non-specific (inflammation, phagocytosis) = same for all pathogens
Specific (B & T lymphocytes) = complementary pathogen

Non-specific = immediate
Specific = time lag

Question 5

Outline process of cell-mediated response

Answer 5

1. Complementary Th lymphocytes bind to foreign antigen on APC
   2.