Week 6 - Immunodiagnosis

Question 1

What is the definition of an Antibody?

Answer 1

= protein produced by B cells and plasma cells that is able to bind specifically with an antigen

Question 2

What is the definition of an Antigen?

Answer 2

= a molecule that is able to elicit a specific immune response immune response when introduced into a person

Question 3

What is the definition of an Epitope?

Answer 3

= specific regions recognised by antibody or T cell receptor

Question 4

What are the five different isotypes produced by B cells?

Answer 4

IgM, IgD, IgG, IgE, IgA

Question 5

What are characteristics of IgM?

Answer 5

• highly inflammatory antibody
• low affinity (doesn’t bind to target antigen with great specificity)
• High avidity (many antigen binding sites)

Question 6

What is the main function of IgM?

Answer 6

= Superb activator of complement leading to:
- opsonisation
- inflammation
- lysis

Question 7

What is the main functions of IgG?

Answer 7

• Major serum Ab
• Activates complement leading to:
• opsonisation
• inflammation
• lysis

Question 8

What are characteristics of IgG?

Answer 8

• High affinity

Question 9

What are characteristics of IgA?

Answer 9

= major Ab of mucosal immune system
- can be high affinity -> good at neutralising gut and resp pathogens
- does not activate complement

Question 10

What are the functions of IgA?

Answer 10

Two types -> Serum IgA & Mucosal IgA
- Serum IgA1 = pro-inflammatory and can activate innate immune cells
- Mucosal IgA2 = non-inflammatory

Question 11

What are the characteristics and functions of IgE?

Answer 11

= specialised for helminth infestation
- causes allergies
- most found on surface of mast cells, eosinophils & basophils

Question 12

What are the characteristics and functions of IgD?

Answer 12

= receptor for naive B cells
- Function = obscure

Question 13

What is the major Ab found in primary vs secondary infections?

Answer 13

• IgM produced in Primary infection
• In secondary infection, IgG predominates more

Question 14

How is Antibody measured?

Answer 14

Precipitation-based assays:
- soluble antigen and soluble Ab interact in correct proportions to form an insoluble precipitate
Agglutination-based Assays:
- formation of cross-linked antigen-antibody lattices in which antibody is on cell surface, bacteria or insoluble particle
Labeled Antibodies:
- Radioactive (RIA), Enzymes (ELISA, IHC), Fluorochromes (IF, FACS)

Question 15

How are monoclonal antibodies made?

Answer 15

animal is immunised
B cells harvested from the animal
B cell is fused with tumour cell
Hybridoma is produced and secretes antibody of single specificity

Question 16

What are the different types of humanised monoclonal antibodies?

Answer 16

-omab:
- Fully a mouse antibody
e.g Muromomab
-ximab:
- Human constant region domains but mouse variable domains
e.g Rituximab
-zumab:
- Complementery determining regions of mice but everything else is human
e.g Natalizumab
-umab:
- Fully human
Denosumab

Question 17

What is the first mechanism in which a monoclonal antibody works?

Answer 17

Mab against cell surface molecules can deplete target cells by ADCC or complement

NK cells have Fc receptors for IgG -> they can kill cells recognised by infused mAb

Cells can also be killed by complement activation

Question 18

What is Rituximab specific for?

Answer 18

specific for a B cell surface molecule CD20

Question 19

What is the second mechanism in which a monoclonal antibody works?

Answer 19

Mab can modulate the function of their target molecule

Mabs can bind to their target and antagonise (block) molecular function

Mabs can also bind to their target and agonise

Question 20

How does the 2 Signal Model for T cell activation work?

Answer 20

• Signal 1 is transduced through TCR/CD3 complex -> after cognate recog of peptide MHC
• Signal 2 is transduced through CD28 (expressed on T cells)
• The ligands for CD28 and CD80 and CD86 (expressed only on APCs
• CD28 is a go signal for T cells

Question 21

What is PD-1?

Answer 21

= a negative regulator of T cells
- expressed on surface of activated T cells
- PD-1 transduces a negative signal
- PD-1 is a checkpoint to prevent the chronic activation of T cells

Question 22

What is the difference between PD-L1 and PD-L2

Answer 22

PD-L1 is broadly expressed -> T cells, B cells, Macrophages, NK cells, Endothelial cells, Small Intestine, etc
PD-L2 however has a similar expression to CD80 and CD86

Question 23

What is CTLA-4?

Answer 23

= Negative regulator of T cells
- is a ligand for both CD80 and CD86
- expressed only on surface of activated T cells
- transduces and inhib signal

Question 24

What can tumours do to stop T cells?

Answer 24

express PD-L1 and inhibit T cells by interacting with PD-1 on activated T cells and therefore inhibiting them