Page 969 - Veterinary Immunology, 10th Edition

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FIG. 29.9 A simplified view of mast cell signal transduction. The
process is triggered by cross-linking two bound IgE molecules with
antigen. The combined signal eventually leads to degranulation
(granule exocytosis), leukotriene and prostaglandin synthesis, and
cytokine production.

Cross-linking of two FcεRI by an antigen also activates
phospholipase A. This acts on membrane phospholipids to produce
arachidonic acid. Other enzymes then convert the arachidonic acid
to leukotrienes and prostaglandins (see Fig. 3.7). Finally, the protein

kinases promote transcription of genes coding for many different
cytokines as well as for cyclooxygenases and lipoxygenase.
The degranulation of mast cells is the central event in the
development of allergic (type I hypersensitivity) reactions.

Mast cell granules contain a complex mixture of potent
proinflammatory molecules (Chapter 3). Some granules in mouse
mast cells contain serotonin or cathepsin D, whereas others contain
histamine and TNF-α. Different stimuli determine which granule

subsets are exocytosed and thus which mediators are released. It is
possible that different clinical forms of allergy may be determined
by the granule subset released. Likewise, appropriate treatment of
allergies may differ according to the mixture of inflammatory

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