Immunoglobulin Structure Flashcards
What is the main function of each Ig isotype? (MAGDE)
IgM = primary response IgA = mucosal immunity IgG = secondary response; can cross placental barrier IgD = on B cell surface IgE = allergic hypersensitivity
Describe the core structure of an antibody.
2 Heavy chains - variable region and constant region; indicates isotype
2 Light chains - variable region and constant region
variable regions determine antigen specificity
What does the antigen-binding site of the variable regions bind to?
epitope - 6-8 AAs on an antigen
Which Ig isotypes have more than one subtype?
IgA = 2 IgG = 4
How many kinds of light chains are there?
kappa
lambda
On which terminal of the heavy and light chains is the variable region found?
N terminal
What functions do the constant regions carry out?
- determines if it can cross the placenta
- determines binding to Fc receptors on monocytes, mast cells, and macrophages
- determines binding to complement
What are CDRs?
complementarity-determining regions
- 3 regions of hypervariability in AA sequence
- stick out as loops off the variable region’s antigen binding site
- determines specificity to antigen
What is the Fab fragment? Fc?
Fab = antigen binding fragment; made up of VH and VL, constant region of the light chain, and one domain of the constant heavy chain region
Fc = crystallizable; made up of the heavy chain base; used to create antibodies against Ig
How would you detect presence of IgM in a solution?
use anti-mu antibodies that would bind to the IgM heavy chain (mu)
Describe the structure(s) of IgM.
- transmembrane = monomeric; found on B cells; part of B-Cell Receptor
- serum = pentameric; joined by J chain
Which antibodies can be involved in complement?
IgM IgG (depending on subclass)
Rank the antibodies by their serum concentration.
IgG IgA IgM IgD IgE
Describe the structure of IgG.
monomeric
Which antibody can cross the placenta?
IgG via FcRn receptor
Describe the structure of IgD.
monomeric and transmembrane
found on B cells, part of BCR
Describe the structure of IgE
monomeric
secreted
Describe the activation of IgE during allergic hypersensitivity.
- Fc-epsilon receptors are found on the surface of mast cells, basophils, etc.
- IgE binds to the receptors
- allergen binds to 2 neighboring IgE molecules, causing the cross-linking of heavy chains
- signal cascade leads to degranulation
Describe the structure(s) of IgA.
secretory/mucosal IgA = dimeric, held together by J chain
serum IgA = monomeric
Which is the most produced antibody?
IgA
80% of immunoglobulin production is IgA
constantly being made
Describe neutralization.
antibody binds to antigen
prevents adherence to host cells
prevents entrance
Describe opsonization
antibody binds to antigen
Fc Ig binds to Fc receptors on phagocytes
facilitates phagocytosis of invader
Describe complement activation
antibody binds to antigen
antibody binds to complement receptor on phagocytes
facilitates enhancement of opsonization
leads to lysis of invader
Describe serum levels of antibodies around the time of birth.
- passively transferred maternal IgG lasts about 3 months after birth (due to half-life)
- IgM is the first to be produced by newborns and reaches adult levels after 9 months
- IgG is the second to be produced by newborns and reaches adult levels after 4 years
- IgA is the last to be produced by newborns and reaches adult levels after 10 years
What are polyclonal antibodies?
antibodies are produced by different B cells and against different epitopes of the same antigen
- found in the serum of immunized individuals
What is a clinical use of polyclonal antibodies?
IVIG
- infusion of Ig into an individual
What are monoclonal antibodies?
antibodies produced by a single B cell with the same epitope binding site
What is a clinical use of monoclonal antibodies?
- against a specific tumor
