Page 971 - Veterinary Immunology, 10th Edition

VetBooks.ir Mast Cell–Derived Mediators

Mast cell granules are loaded with amines such as histamine,
serotonin, and dopamine; lipids such as prostaglandins and
leukotrienes; lysosomal enzymes including tryptases, chymases,

and cathepsins; cytokines such as TNF-α, IL-4, -5, -6, -15; and some
chemokines (Fig. 29.11). Mast cells can capture and store IL-17 by
endocytosis. It is then released in allergic reactions. Mast cells also
produce chitinases. Chitin is characteristically found in insects,

fungi, and helminths, and the production of chitinases supports the
suggestion that allergic reactions may have evolved to combat these
invaders. Chitin itself is a key allergen in some helminth infections.
Mast cells also release small heparin-containing granules that are

especially rich in TNF-α. These particles are carried in afferent
lymph to draining lymph nodes, where they can trigger changes in
cell behavior. The presence of heparin also stabilizes TNF-α so that
it persists after delivery.

FIG. 29.11 The soluble mediators released from degranulating
mast cells. These fall into three categories: molecules released from
exocytosed granules, lipids (eicosanoids) synthesized within
minutes, and proteins synthesized over several hours.

Interleukin-33

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