55
JULY/AUGUST 2017
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TVPJOURNAL.COM
CONTINUING
EDUCATION
Mast cell
activation and
granule release
GI Tract:
Increased fluid
secretion
Increased peristalsis
Expulsion of the
GI tract contents
(vomiting and
diarrhea)
Congestion and
blockage of airway
(wheezing, coughing,
phlegm)
Swelling and mucus
secretion
Increased fluid in
tissues causing
increased lymph
flow, fluid shifts to
the interstitium
Airway:
Decreased diameter
Increased mucus
secretion
Blood Vessels:
Increased blood flow
Increased
permeability
more antigen exposure and do not result in the release of
histamine as a mediator. Furthermore, IgE-independent
reactions do not require initial allergen exposure.
2,3
Anaphylactoid Reaction:
Nonimmunologic Anaphylaxis
Nonimmunologic reactions may occur via degranulation
of mast cells and basophils without immunoglobulins.
They may be triggered by external influences, such
as physical factors, drugs, and external toxins.
2,3
CHEMICAL MEDIATORS
Mediators stored in mast cells and basophils (ie,
histamine, heparin, proteases such as tryptase and
chymase, and cytokines) are released during degranulation
( Figure 1 ), which causes an increased production of
phospholipase A and thus arachidonic acid and its
metabolites. Downstream activation of this cascade leads
to an increase in newly synthesized mediators, such
as prostaglandins, leukotrienes, and plasma activating
factor. These newly synthesized mediators induce an
inflammatory response. The release of inflammatory
and vasoactive mediators leads to shock.
10,12
Histamine
Once an antigen has bound to the primed IgE
receptors, histamine is released. Histamine is the
principal mediator stored in granules of mast cells and
basophils. It is released quickly during anaphylaxis and
can be found in elevated concentrations in circulating
plasma less than 1 minute after allergen interaction.
3
FIGURE 1. Effect of mast cell degranulation.
11
GI, gastrointestinal.