MHC & Antigen presentation

Question 1

T cells recognise antigen…

Answer 1

by detecting peptides of foreign proteins bound to MHC molecules on the cell surface of APCs

Question 2

MHC is not a single gene

Answer 2

its a multigene locus (HLA in humans)

Question 3

Class I molecules (K,D or L)

Answer 3

alpha-chain and beta2 microglobulin chain

Question 4

Class II molecules (IA or IE)

Answer 4

alpha and beta chains both encoded at the MHC locus

Question 5

Class I presents…

Answer 5

endogeneous antigen to CD8+ cytotoxic T cells

Question 6

Class II presents…

Answer 6

exogeneous antigen to CD4+ T helper cells

Question 7

Endogeneous antigens (class I presented)

Answer 7

• produced within the cell host
• trafficking (MHC class I collect peptides)
• MHC class I display fragments on cell surface
• peptides bound to MHC Class I recognised by CD8+ cytotoxic T cells which kill virally infected cell

Question 8

Exogneneous peptides (presented by MHC class II)

Answer 8

MHC class II display proteins engulfed by APCs 
-recognised by CD4+ helper T Cells whoch activate B cells / macrophages

Question 9

What prevents endogeneous peptide loading of MHC Class II in Endoplasmic reticulum

Answer 9

Binding of endogeneous peptides to newly synthesised and folded MHC Class II is blocked by binding of a molecule known as the “invariant chain” (Ii)

Question 10

Tolerance

Answer 10

-protects against autoimmunity, food antigens or harmless commensals

Question 11

T cell activation

Question 12

Costimulation

Answer 12

• involves bidirectional signalling between cell surface receptor pairs
• such as between CD80/86 (expressed by APC) and CD28 (expressed by T cell)

Question 13

IL-12 (cytokine produced by the APC)

Answer 13

required for differentiation of the effector T cells