FIRST HALF OF TODAY’S CLASS: THE IMMUNOGLOBULINS. A quick overview of the five immnoglobulin “ classes ”. IgG ( ( globulin ): the prototypic immunoglobulin. All three general functions (Ag binding, complement activation, stimulation of phagocytosis) occur.
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All three general functions (Ag binding, complement activation, stimulation of phagocytosis) occur.
IgG is the principal immunoglobulin of the secondary response.
IgG is the principal immunoglobulin of the adult (but not the neonate.)
IgG constitutes 80% of the circulating immunoglobulin in the adult.
The concentration of IgG in serum is high: 8-16 mg ml-1.
The architecture of IgG is simple:
two ( chains and two 8 chains or
two ( chains and two 6 chains.
a pentamer (in secreted form) attached by disulfide bonds between the C4 and C3 domains of adjacent heavy chains;
in addition, there is a single J-protein.
IgM is the first immunoglobulin to be synthesized in a primary response.
The concentration of IgM in serum is ~ 1.5 mg ml-1.
IgM is the first immunoglobulin to accumulate in the serum of neonates.
IgM has a high valency which contributes to agglutination. Also, multimeric nature contributes to effective complement activation.
mIgM is a monomer.
co-los-trum \kc-‘läs-tram \ n \ [L. beestings] (1577) :milk secreted for a few days after parturition and characterized by high protein and antibody content
Most often a dimer; sometimes a tetramer (or a trimer).
Multimers united by J-protein.
Secretion requires addition of “secretory component” produced in mucosal epithelial cells (in digestive, respiratory, genital, breast tissues and salivary and lacrimal glands).
Plasma cells secrete the Ab;
deliver IgA to epithelial cells having poly-Ig-receptor on their surface.
The poly-Ig-receptor is cleaved and the component that stays associated with IgA is the “secretory component.”
MW = 70,000 daltons; composed of 5 immunoglobulin-like domains;
binds to constant regions of heavy chains.
Movement of the receptor from one surface to another is transcytosis.
IgE is extremely rare.
IgE functions against parasites.
In the absence of para-
sites, IgE responds to allergens.
Indeed, different isotypes can share common variable regions! (Think about that.)
(More exactly, one B-cell makes one idiotype.)