Page 960 - Veterinary Immunology, 10th Edition

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FIG. 29.2 The role of IL-4 in induction of IgE responses. IL-4 is
produced by Th2 cells. Once released, it promotes the development
of more Th2 cells, which are major sources of this cytokine and
promote IgE responses. The degranulation of mast cells also
releases IL-4, which further promotes this reaction. NK cells may
serve as an initial source of IL-4. The response to IL-4 is inhibited
by IFN-γ and IL-12.

Immunoglobulin E Receptors

Animals have two IgE receptors: high-affinity FcεRI and low-
affinity FcεRII (CD23). FcεRI occurs in two forms. One form is
expressed on mast cells, basophils, neutrophils, and eosinophils. It

consists of four peptide chains, one α, one β, and two γ chains
(αβγγ) (Fig. 29.3). The α chain binds IgE, the β chain stabilizes the
complex, and the γ chains serve as signal transducers. (This same γ

chain is also a signal transducer in FcγRI, FcγRIII, and γ/δ TCR.)

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