Antibody structure & function Flashcards
What can the heavy chain consist of?
Alpha, delta, epsilon, gamma, mu
What can the light chain consist of?
Lambda, and K
How did they assign biological function to structure?
Proteolytic cleavage
Pepsin digestion of Ig
F(ab’)2 and Fc fragments
Papain digestion of Ig
2 x Fab and Fc
Mercaptoethanol reduction
H chains and L chains
What do the VL and VH domains contain?
3 hypervariable (CDR) regions
Which chain determines what kind of antibody you have?
Heavy chain
What defines the specificity of antibodies?
VH and VL regions
How is the antigen binding site created?
CDRs pf H and L chains combine
Types of antigen epitopes
Multivalent antigen with different epitopes, multivalent antigen with repeated epitope, linear epitope or discontinuous epitope
Polyclonal
Antibodies secreted by different B cell lineages e.g. serum antibodies
How are monoclonal antibodies derived?
From a single plasma cell
What can monoclonal antibodies be used for?
Treating disease
What are the 4 types of therapeutic monoclonal antibody?
Mouse, chimeric, humanised, human
What are the IgG subclasses?
IgG1, IgG2, IgG3, IgG4
How do the IgG subclasses differ?
Arrangement of disulphide bonds linking the heavy chains
Which IgG subclass is most susceptible to proteolytic cleavage but has greater capacity to bind C1q and activate complement
IgG3
What antibodies are good at activating and fixing complement
IgM and IgG3
What is the first complement
C1q (consists of 18 peptide chains)
What antibodies are bad at activating and fixing complement?
IgD, IgG4, IgE
What does IgM contain that is required for polymerisation?
J chain
How many antigen binding sites does IgM contain?
10
What is IgA important for?
External secretions (mucosal surfaces e.g. gut, lungs)
What is the structure of IgA?
Dimeric with J chain and secretory component (composed with Ig-like domain) to link 2 chains together
What is the secretory component needed for?
Stability
What is required for Ig transport across epithelia?
Poly-Ig receptor
What is the major antibody class synthesised at mucosal sites
IgA
Where is IgE found
Bound to receptors on mast cells
What is a mast cell?
Cell filled with basophil granules (found in connective tissue) - releases histamine and other substances during inflammatory and allergic reactions.
Why is IgE important in allergic reactions?
Cross-linking by antigen (allergen) causes release of allergic mediators
What is an allergen?
Antigen that stimulates IgE
What do Fc receptors do?
Allow cells to be activated by antibody bound to antigens/ pathogens
What is the high affinity receptor for IgG1 and IgG3
Fc(gamma)RI - consisys of alpha and gamma chain
What part of the antibody does Fc(gamma)RI bind?
The lower hinge and constant heavy2 of IgG3
What is the role of Fc receptors on phagocytes?
Trigger the uptake and destruction of antibody-coated pathogens
How can you distinguish an inhibitory Fc receptor?
ITIM domain on cytoplasmic side
What does the B cell receptor consist of?
Membrane bound Ig with Igalpha and Igbeta chains
After how many days is there a primary antibody response?
14
