Figure 13 IgD Structure
D. IgD
1. Structure
The structure of IgD is presented in the Figure 13. IgD exists
only as a monomer.
2. Properties
a) IgD is
found in low levels in serum; its role in serum uncertain.
b) IgD is
primarily found on B cell surfaces where it functions as a
receptor for antigen. IgD on the surface of B cells has
extra amino acids at C-terminal end for anchoring to the
membrane. It also associates with the Ig-alpha and Ig-beta
chains.
c) IgD
does not bind complement.
Figure 14 IgE Structure
E. IgE
1. Structure
The structure of IgE is presented in Figure 14. IgE exists as a
monomer and has an extra domain in the constant region.
2. Properties
a) IgE is
the least common serum Ig since it binds very tightly to Fc
receptors on basophils and mast cells even before
interacting with antigen.
b)
Involved in allergic reactions - As a consequence of its
binding to basophils an mast cells, IgE is involved in
allergic reactions. Binding of the allergen to the IgE on
the cells results in the release of various pharmacological
mediators that result in allergic symptoms.
c) IgE
also plays a role in parasitic helminth diseases. Since
serum IgE levels rise in parasitic diseases, measuring IgE
levels is helpful in diagnosing parasitic infections.
Eosinophils have Fc receptors for IgE and binding of
eosinophils to IgE-coated helminths results in killing of
the parasite.
d) IgE
does not fix complement.
Figure 15 Rotating antibody
© 2000 To Clinical
Implications of Human Immunoglobulin Classes
