5. Adaptive Immunity

Question 1

What are some features of APC’s?

Answer 1

1. Strategically located at portals of entry - skin, mucous membranes, lymphoid organs, circulation
2. Pathogen capture
3. Diversity in PRR - can recognise intracellular and extracellular pathogens

Question 2

What 3 processes must happen before an APC can present to a T cell?

Answer 2

Capture
Processing
Presentation

Question 3

Which cells are APC’s?

Answer 3

Dendrititic cells (lymph nodes)
Langerhan’s cells (Skin)
Macrophages
B cells

Question 4

How do APC’s recognise pathogens?

Answer 4

PAMPs on microbial surface bind to PRR’s on APC surface

Question 5

What response is activated if an intracellular pathogen is detected?

Answer 5

Cell-dependent immunity:

• Cytotoxic T cells
• Antibodies
• Macrophages

Question 6

What response is activated if an extracellular pathogen is detected?

Answer 6

Humoral immunity:

• Antibodies
• Complement
• Phagocytes

Question 7

What determines the APC response generated?

Answer 7

The PAMP signal detected - if intracellular PAMP then it must be viral, so cell dependent response generated

Question 8

Where are MHCI found?

Answer 8

All nucleated cells

Question 9

What HLA types are MHCI?

Answer 9

HLA-A
HLA-B
HLA-C

Question 10

Where are MHC II found?

Answer 10

APC’s (not they also express MHCI)

Question 11

What HLA types are MHC II?

Answer 11

HLA-DQ
HLA-DR
HLA-DP

Question 12

How do MHC molecules express diversity?

Answer 12

Co-dominant expression of both parental genes

Polymorphic genes- different alleles in each individual

Question 13

How does the function of MHCI and II differ?

Answer 13

MHCI - present peptides from intracellular microbes

MHCII - present peptides from extracellular microbes

Question 14

Which cells recognise MHCI?

Answer 14

CD8+ T cells

Question 15

Which cells recognise MHCII?

Answer 15

CD4+ T cells

Question 16

Outline the endogenous pathway leading to MHCI presentation?

Answer 16

Virus invades host cell
Proteosome splices viral proteins in peptide fragments which enter the ER via TAP proteins.
If there is the right MHCI, it will bind and be transported o the cell surface.

Question 17

Outline the exogenous pathway leading to MHCII presentation?

Answer 17

Pathogen is engulfed by pinocytosis into an endosome.
Endosome fuses with MHCII containing vesicle secreted by the ER.
MHCII-peptide complex is presented on the surface.

Question 18

How can MHC molecules lead to clinical problems?

Answer 18

1. Organ transplant rejection if HLA mis-match

2. Auto-immune disease

Question 19

What receptor binds to MHC molecules?

Answer 19

T cell receptor

Question 20

Why will patients lacking CD4+ T cells also lack CD8+ cytotoxic lymphocytes?

Answer 20

CD4+ release cytokines which are needed to cause activation of CD8+ T cells

Question 21

Why will patients lacking in CD4+ T cells also lack IgG?

Answer 21

Release IFN gamma which stimulates isotope switching from IgM to IgG.

Question 22

What is the benefit of the secondary immune response?

Answer 22

Faster
Stronger
Longer duration
Higher Affinity
IgG antibody more efficient

Question 23

What is the function of IgA?

Answer 23

Mucosal immunity

Breast milk

Question 24

What is the function of IgM?

Answer 24

Complement activation

Question 25

What is the function of IgG?

Answer 25

• Fc dependent phagocytosis
• Complement activation
• Neonatal immunity - placental transfer
• Toxin/virus neutralisation

Question 26

What is the function of IgE?

Answer 26

Immunity against helminths

Mast cell degranulation in allergies

Question 27

What 3 costimulatory signals are required to activate a T cell?

Answer 27

1. MHCII and TCR binding
2. CD80/86 and CD28 binding
3. Cytokines

Question 28

Which cells express CD28?

Answer 28

Naive T cells