Page 959 - Veterinary Immunology, 10th Edition

VetBooks.ir Immunoglobulin E

IgE is an immunoglobulin of conventional four-chain structure and
about 200 kDa (see Fig. 16.7). It is found in serum in exquisitely

small quantities (9 to 700 µg/mL in dogs), and its serum half-life is
only 2 days. Most IgE is firmly bound to Fcε receptors on tissue
mast cells, where it has a half-life of 11 to 12 days. Some connective
tissue mast cells situated close to blood vessels can extend
cytoplasmic processes between the endothelial cells and into the

vascular lumen to “fish” for IgE that binds to their receptors.
Some IgG subclasses may also bind to mast cell FcR and mediate
type I hypersensitivity reactions. For example, IgG4 is associated

with some cases of canine atopic dermatitis. However, the affinity
of these subclasses for Fc receptors is much lower than that of IgE,
and they are of much less clinical significance.

Immunoglobulin E Production

Atopic individuals are predisposed to mount type 2 immune
responses. Their Th2 cells produce IL-4, IL-5, and IL-13. These,
together with co-stimulation by CD40, trigger B cell IgE synthesis.
IL-4 is also produced in significant amounts by degranulating mast

cells. This mast cell–derived IL-4 may alter the helper cell balance
and enhance yet more Th2 cell production and IL-4 release (Fig.
29.2).

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