Antigen presentation by MHC class II

Question 1

MHC class II present peptides to:

Answer 1

CD4+ molecules

Question 2

Main roles of MHC class II antigen presentation

Answer 2

T helper cells
Production of cytokines

Question 3

Main 4 subsets of Th cells

Answer 3

Th1 -> produce IL-2, INF-gamma
Th2 -> produce IL-4, IL-5
Th17 -> produce IL-17
Tregs -> produce TGF-beta, IL-10

Question 4

Function of Th1 response

Answer 4

enhances cellular immunity

Question 5

Function of Th2 response

Answer 5

enhances humoral response

Question 6

MHC class II/peptide complexes recognised by CD4+ T cells

Answer 6

CD4 molecule on helper t cell recognises class II heavy chain
T cell receptor recognises MHC class II

Question 7

Key points of MHC class II antigen processing pathway

Answer 7

Source of antigen
Capture of antigen
Proteolysis (degradation) of antigen
Role of accessory proteins
Antigen presenting cells

Question 8

macropinocytosis

Answer 8

almost like drinking up cellular fluid; captures smaller particles than phagocytosis

Question 9

Endocytic route of antigen capture

Answer 9

receptor-mediated endocytosis
phagocytosis
macropinocytosis

Question 10

Peptide generation in endocytic vesicles

Answer 10

Controlled breakdown of antigen into peptides
Antigen moves through acidic endosomal compartments -> initiates protein unfolding

Question 11

Enzyme that catalyses disulphide bond at low pH in protein unfolding for class II processing

Answer 11

GILT-IFNg inducible lysosomal reductase

Question 12

Lysosomal and endosome proteases (there are 4)

Answer 12

Cathepsins
Endopeptidases
Exopeptidases
Asparaginyl endopeptidase (AEP)

Question 13

MHC class II antigen presentation can be blocked by:

Answer 13

Chloroquine/NH4Cl - prevents acidification
Protease inhibitors

Question 14

CLIP

Answer 14

Class II associated invariant peptide

Question 15

Invariant chain (Ii) function

Answer 15

In the ER the MHC class II molecule is complexed with a polypeptide called the invariant chain. This prevents peptides from binding and it chaperones class II to endosomal/lysosomal compartments

Question 16

Invariant chain degradation

Answer 16

Degraded into fragments by proteases - one of these fragments is CLIP, which binds in the MHC class II peptide groove

Question 17

What are professional antigen presenting cells (APCs)?

Answer 17

Heterogenous population of leukocytes
Specialised to have class II MHC molecules

Question 18

Three main examples of professional APCs

Answer 18

Dendritic cells
Macrophages
B cells

Question 19

Dendritic cells

Answer 19

Immature in peripheral organs; migration to the follicles of secondary lymphoid organs becoming matures
MHC and other co-stimulatory molecules on surface
Key role: activate naive t cell responses

Question 20

Conventional DCs

Answer 20

Capture pathogens
V efficient at achieving t cell response

Question 21

Plasmacytoid DCs

Answer 21

primarily monitor for viral infections and produce cytokines

Question 22

Interactions of APCs with T cells

Answer 22

More than just the TCR and MHC complex
First contact (adhesion)
MHC/TCR interaction
Co-stimulation (activation or inhibition)
Activation - release of cytokines/granzyme/perforin

Question 23

Immunological synapse

Answer 23

between t cell and target cell; secretory domain