The eleventh lecture in a series for the module Cells and Immunity. This lecture covers antibodies, their antigens, neutralisation and more. A great way to start your understanding of the module or to miss a lecture or two.
L11 – Antibodies
Lecture:
5 classes of isotypes (heavy chain dependent)
o α IgA = can be just a monomer but most are dimeric via disulfide bonds that link
both monomers by the J chain
In secretary substances (eg saliva) has secretory component
Residue of Poly-Ig receptor that passes dimeric molecule through
the mucosa to the lumen.
With exocytosis from the epithelial cells to the lumen the Poly-Ig is
enzymatically cleaved to leave the secretary components on the
dimeric IgA
Monomeric and dimeric (most dimeric as mucosal secretions)
6-day serum half life
3mg/ml
Found in breast milk
o δ IgD =
Found on surface of B cells
In very low serum concentrations
o ε IgE = has extra CH domain (4) with ε polypeptide structure
3-day half life
Very low concentration (bound to mast cells/basophils w/high affinity
(immobilised))
o γ IgG = with γ chains
3 week half-life (more stable)
10-20mg/ml
70% total Ig in bloodstream
Crosses cap walls to reach ECF (160kDa)
Major Ig Class in sec response and in breast milk
o μ IgM = can be an antigen receptor as a monomer on B cells but mostly pentamer
structure (4 CH chains and a J chain)
5-day half life
Confined to vascular system (bc 900kDa)
1-2mg/ml
Major class in primary immune response
o Can all express the same receptor but bind to different molecules
Immunoglobulin class switching
o Changes light chain variables (κ or λ)
Differences (qualitative and quantitative)
o They change dependent upon the primary vs he secondary response
o IgG rapidly increases to dominate in the secondary response and IgM dominates
primary response
o IgA rapidly increases in the secondary response and trace amounts of IgE
o Signals cause the classes to change in quantity
IL-4 cytokines stimulate IgG1 and IgE
IL-5 cytokines stimulate IgA
Biological roles of antibodies:
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