CMB1003/L23 Humoral Specific Immunity II Flashcards
What are the 2 types of light chains on antibodies?
Kappa or lambda
What are the domains of the heavy chain on antibodies? (2)
C(H)1-3
V(H)
What are the domains of the light chain on antibodies? (2)
C(L)
V(L)
What is the domain of the glycosylated H chains on antibodies?
C(H)2
Define the term ‘domain’.
Compactly folded globular units within proteins, often with evolutionary significance
The domains found in Ig are also found in which other molecules involved in immunity? (3)
T cell receptor
MHC molecules
Various cell adhesion molecules
Signalling molecules
Describe the structure of C(L) and V(L) domains. (4)
Compact immunoglobulin domains
100-110 amino acids
2 sheets of B strands
Intra-chain disulphide bond
What are hypervariable (HV)/ complementary-determining regions (CDR)? (3)
3 loops of HV on each H and L chain
6 CDR form the antigen binding sites
Framework (other loops and strands) less variable
What do the C domains control?
Effector function of Ig
What are the 5 heavy chain isotypes of antibodies?
Mu/ IgM
Delta/ IgD
Gamma/ IgG
Epsilon/ IgE
Alpha/ IgA
What is the functional difference between kappa and lambda light chains?
None
What are the macro structures of the 5 isotypes?
IgG, IgD, IgE simple
IgA forms a dimer
IgM forms a pentamer
Describe the structure of IgM. (3)
Mew chains
5 domains
No hinge
(Mew2L2)5 covalently bound to J chain
What is the valency of IgM?
10
Describe the affinity of IgM. (2)
First response
Relatively low affinity as pre-affinity maturation
What is the function of IgM? (4)
Monomer present on B cell surface (BCR) during B cell development
Activates complement
Agglutination
Protects from common pathogens
Describe the structure of IgD. (4)
Present on B cell surface during B cell development
Delta2L2
Delta chain
4 domains
Long hinge
What is the function of IgD?
Largely unknown
Describe the structure of IgG. (4)
Gamma2L2
Gamma chains
4 domains
Most prevalent class in serum
Production increased in secondary responses
Describe the differences in the sub-classes of IgG.
Differ in hinge regions
What is the function of IgG? (4)
Large increase in secondary response
Complement activation
Opsonisation
ADCC
Crosses placenta
Describe the structure of IgA. (4)
Alpha2L2
Alpha chains
4 domains
Hinge
Monomer in serum
Dimer in secretions bound to J chain and secretory component
What is the difference in the subclasses of IgA?
IgA1 - predominant serum
IgA2 - found in secretions
What is the function of IgA? (4)
Most abundant Ig around mucosal membrane
Inhibition of microbial adherence
Neutralise toxins and pathogens
Prevent commensal bacteria from entering bloodstream
Intestinal protection of neonate
Describe how IgA accesses the gut lumen. (3)
Dimeric IgA is transported into gut lumen through epithelial cells as base of crypts
Dimeric IgA binds to layer of mucus overlying gut epithelium
IgA in gut neutralises pathogens and their toxins
Describe the structure of IgE. (3)
Epsilon2L2
Epsilon chain
5 domains
Lowest concentration of Ig in serum
Describe the action of IgE. (2)
Binds with high affinity to FcR on mast cells & basophils
Releases vasoactive/inflammatory mediators
What is the function of IgE? (3)
ADCC
Protection against helminth and protozoa infection
Induces eosinophils and basophils to release histamine and proteases
Role in allergy and asthma
Describe the role of IgE in allergy. (2)
Resting mast cell has granules that contain histamine and other inflammatory mediators
Multivalent antigen cross-links bound IgE antibody, causing release of granule contents
Describe the series of events following IgE binding to Fc receptors on mast cells and basophils. (3)
Increased histamine release
Increased TNFa
Increased vasodilation
How does epinephrine (EpiPen) stop anaphylaxis? (2)
Increased vasoconstriction
Increased blood glucose levels
Where is IgG and IgM predominantly found?
In blood
Where is IgG and IgA predominantly found?
Extracellular fluid
Where in the body is devoid of Ig?
Brain
Where is IgA predominantly found?
Secretions (mucosal membrane) and breast milk
Which form of Ig does the foetus receive from the mother?
IgG
Which Ig is associated with mast cells just below epithelial surfaces?
IgE
Describe how B cells are able to produce different Ig isotypes. (3)
During development, IgM & IgD is produced
As immune response progresses, B cells isotype switch appropriately
Isotype switching involves irreversible DNA recombination