Week 6 - Immunodiagnosis Flashcards
What is the definition of an Antibody?
= protein produced by B cells and plasma cells that is able to bind specifically with an antigen
What is the definition of an Antigen?
= a molecule that is able to elicit a specific immune response immune response when introduced into a person
What is the definition of an Epitope?
= specific regions recognised by antibody or T cell receptor
What are the five different isotypes produced by B cells?
IgM, IgD, IgG, IgE, IgA
What are characteristics of IgM?
- highly inflammatory antibody
- low affinity (doesn’t bind to target antigen with great specificity)
- High avidity (many antigen binding sites)
What is the main function of IgM?
= Superb activator of complement leading to:
- opsonisation
- inflammation
- lysis
What is the main functions of IgG?
- Major serum Ab
- Activates complement leading to:
- opsonisation
- inflammation
- lysis
What are characteristics of IgG?
- High affinity
What are characteristics of IgA?
= major Ab of mucosal immune system
- can be high affinity -> good at neutralising gut and resp pathogens
- does not activate complement
What are the functions of IgA?
Two types -> Serum IgA & Mucosal IgA
- Serum IgA1 = pro-inflammatory and can activate innate immune cells
- Mucosal IgA2 = non-inflammatory
What are the characteristics and functions of IgE?
= specialised for helminth infestation
- causes allergies
- most found on surface of mast cells, eosinophils & basophils
What are the characteristics and functions of IgD?
= receptor for naive B cells
- Function = obscure
What is the major Ab found in primary vs secondary infections?
- IgM produced in Primary infection
- In secondary infection, IgG predominates more
How is Antibody measured?
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)
How are monoclonal antibodies made?
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
What are the different types of humanised monoclonal antibodies?
-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
What is the first mechanism in which a monoclonal antibody works?
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
What is Rituximab specific for?
specific for a B cell surface molecule CD20
What is the second mechanism in which a monoclonal antibody works?
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
How does the 2 Signal Model for T cell activation work?
- 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
What is PD-1?
= 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
What is the difference between PD-L1 and PD-L2
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
What is CTLA-4?
= 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
What can tumours do to stop T cells?
express PD-L1 and inhibit T cells by interacting with PD-1 on activated T cells and therefore inhibiting them
