Page 974 - Veterinary Immunology, 10th Edition

Mast cells Enhances degranulation Suppresses degranulation
VetBooks.ir Blood vessels Constricts Dilates
Smooth muscle Contracts
Relaxes

Regulation of the Response to Mast Cell

Mediators

The α- and β-adrenoceptors are found not only on mast cells but
also on secretory and smooth muscle cells throughout the body. α-
stimulators cause vasoconstriction and may be of use treating

severe allergic reactions, in reducing edema, and raising blood
pressure. β-stimulators mediate smooth muscle relaxation and may
therefore reduce the severity of smooth muscle contraction. Pure α-
and β-stimulators are of only limited use in the treatment of allergic

diseases because each alone is insufficient to counteract all the
effects of mast cell–derived factors. Epinephrine (or adrenalin), on
the other hand, has both α- and β-adrenergic activity. In addition to
causing vasoconstriction in skin and viscera, its β effects cause

smooth muscle to relax. This combination of effects is well suited to
combat the vasodilation and smooth muscle contraction produced
in type I hypersensitivity reactions. Ideally, epinephrine should be
available whenever potential allergens are administered to animals.

Mast Cells in Infections

Mast cells play important roles in both antimicrobial and
antiparasite immunity. They can respond within seconds or
minutes to microbial invasion. They possess a large array of PRRs

as well as being able to recognize antigen indirectly through their
Fc receptors. Lipopolysaccharide stimulation of mast cell TLR4 can
induce cytokine production in the absence of degranulation.

Increased vascular permeability due to mast cell–derived mediators
promotes inflammation. They also release preformed antimicrobial
peptides such as the cathelicidins. Mast cell tryptase and chymases
have antibacterial and anti-parasite activity while neutrophils are
attracted by mast cell–derived leukotrienes.

Late-Phase Reaction

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