Page 961 - Veterinary Immunology, 10th Edition
P. 961
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The affinity of FcεRI for IgE is very high (10 M), so they bind
VetBooks.ir almost irreversibly and thus ensure that mast cells are constantly
coated with IgE.
FIG. 29.3 The structure of FcεRI. This tetrameric form of the IgE
receptor containing two γ chains is found on mast cells and
basophils.
The other form of FcεRI contains only three chains: one α chain
and two γ chains (αγγ). It is expressed on antigen-presenting
dendritic cells and monocytes. When an antigen-IgE complex binds
to this receptor, it is ingested and treated as exogenous antigen. The
expression of FcεRI on antigen-presenting cells is enhanced by IL-4
from Th2 cells. Thus a positive feedback loop (the allergy loop)
develops (Fig. 29.4). The antigen processing cells present antigen
more effectively to Th2 cells. The Th2 cells then secrete IL-4 and
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