lecture 4

Question 1

what is an antigen

Answer 1

Anything which has the potential to be recognised by the immune system
Can be foreign: pathogens, transplants, chemicals etc
Auto-antigens: immune system normally tolerant however sometimes recognised -autoimmune disorders

Question 2

evolution of adaptive immunity

Answer 2

phagocytes evolved to keep remnants of pathogens and display to other immune cells e.g T cells (adaptive)

Question 3

why do cells take up antigens

Antigen presenting cells

Answer 3

1. Clearance of pathogens (innate response)

2. Presentation to T cells (adaptive response)

Question 4

what are MHCs

Answer 4

Major histocompatibility complexes

scaffolds for peptides present on most cells

Question 5

2 classes of MHCs

Answer 5

MHC-1: presents endogenous intracellular antigen expressed on all nucleated cells
MHC2: presents exogenous extracellular antigens e.g peptides from bacteria, parasites.

Question 6

how are peptides from antigen proteins held

Answer 6

in peptide binding cleft

protein in MHC complex

Question 7

Peptides generated from protein antigens

Answer 7

displayed on MHC molecules

surveyed by antigen-specific T cells (receptors)

Question 8

T cells

Answer 8

have receptors looking at peptide to determine if dangerous and will initiate response accordingly

Question 9

MHC-1 antigen processing steps

Answer 9

1. endogenous antigenic proteins are degraded to peptides in cytoplasm
2. peptides transported to rough ER await empty MHC-1
3. Peptide loading of MHC-1 takes place in ER and then expressed on cell’s membrane via regulatory exocytosis

Question 10

MHC-2 antigen processing steps

Answer 10

1. phagocytosis of exogenous antigen
2. pathogen is broken down by phagolysosome
3. exogenous antigenic proteins are degraded to peptides in phagolysosome
4. peptide loaded onto MHC-2 takes place in phagolysosome and then transported to cell membrane
   (MHC-2 complexes are produced in the rough ER but are brought to the phagolysosome)